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by Henry Alleyne Nicholson
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Title: The Ancient Life History of the Earth
A Comprehensive Outline Of The Principles And Leading Facts Of
Palæontological Science
Author: Henry Alleyne Nicholson
Release Date: December 6, 2004 [EBook #14279]
Language: English
*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF THE EARTH ***
Produced by Robert J. Hall
THE ANCIENT LIFE-HISTORY OF THE EARTH
A COMPREHENSIVE OUTLINE OF THE PRINCIPLES AND LEADING FACTS OF
PALÆONTOLOGICAL SCIENCE
BY H. ALLEYNE NICHOLSON
M.D., D.SC., M.A., PH. D. (GÖTT), F.R.S.E, F.L.S.
PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF ST ANDREWS
PREFACE.
The study of Palæontology, or the science which is concerned
with the living beings which flourished upon the globe during
past periods of its history, may be pursued by two parallel but
essentially distinct paths. By the one method of inquiry, we may
study the anatomical characters and structure of the innumerable
extinct forms of life which lie buried in the rocks simply as
so many organisms, with but a slight and secondary reference
to the _time_ at which they lived. By the other method, fossil
animals are regarded principally as so many landmarks in the
ancient records of the world, and are studied _historically_
and as regards their relations to the chronological succession
of the strata in which they are entombed. In so doing, it is of
course impossible to wholly ignore their structural characters,
and their relationships with animals now living upon the earth;
but these points are held to occupy a subordinate place, and to
require nothing more than a comparatively general attention.
In a former work, the Author has endeavoured to furnish a summary
of the more important facts of Palæontology regarded in its strictly
scientific aspect, as a mere department of the great science of
Biology. The present work, on the other hand, is an attempt to
treat Palæontology more especially from its historical side, and
in its more intimate relations with Geology. In accordance with
this object, the introductory portion of the work is devoted to a
consideration of the general principles of Palæontology, and the
bearings of this science upon various geological problems--such
as the mode of formation of the sedimentary rocks, the reactions
of living beings upon the crust of the earth, and the sequence
in time of the fossiliferous formations. The second portion of
the work deals exclusively with Historical Palæontology, each
formation being considered separately, as regards its lithological
nature and subdivisions, its relations to other formations, its
geographical distribution, its mode of origin, and its characteristic
life-forms.
In the consideration of the characteristic fossils of each successive
period, a general account is given of their more important zoological
characters and their relations to living forms; but the technical
language of Zoology has been avoided, and the aid of illustrations
has been freely called into use. It may therefore be hoped that
the work may be found to be available for the purposes of both the
Geological and the Zoological student; since it is essentially an
outline of Historical Palæontology, and the student of either of
the above-mentioned sciences must perforce possess some knowledge
of the last. Whilst primarily intended for students, it may be
added that the method of treatment adopted has been so far
untechnical as not to render the work useless to the general
reader who may desire to acquire some knowledge of a subject of
such vast and universal interest.
In carrying out the object which he has held before him, the
Author can hardly expect, from the nature of the materials with
which he has had to deal, that he has kept himself absolutely
clear of errors, both of omission and commission. The subject,
however, is one to which he has devoted the labour of many years,
both in studying the researches of others and in personal
investigations of his own; and he can only trust that such errors
as may exist will be found to belong chiefly to the former class,
and to be neither serious nor numerous. It need only be added
that the work is necessarily very limited in its scope, and that
the necessity of not assuming a thorough previous acquaintance
with Natural History in the reader has inexorably restricted its
range still further. The Author does not, therefore, profess to
have given more than a merely general outline of the subject; and
those who desire to obtain a more minute and detailed knowledge
of Palæontology, must have recourse to other and more elaborate
treatises.
UNITED COLLEGE, ST ANDREWS.
October 2, 1876.
CONTENTS.
PART I.
PRINCIPLES OF PALÆONTOLOGY.
INTRODUCTION.
The general objects or geological science--The older theories of
catastrophistic and intermittent action--The more modern doctrines
of continuous and uniform action--Bearing of these doctrines
respectively on the origin or the existing terrestrial
order--Elements or truth in Catastrophism--General truth of the
doctrine of Continuity--Geological time.
CHAPTER I.
Definition of Palæontology--Nature of Fossils--Different processes
of fossilisation.
CHAPTER II.
Aqueous and igneous rocks--General characters of the sedimentary
rocks--Mode or formation of the sedimentary rocks--Definition
of the term "formation"--Chief divisions of the aqueous
rocks--Mechanically-formed rocks, their characters and mode of
origin--Chemically and organically formed rocks--Calcareous
rocks--Chalk, its microscopic structure and mode of
formation--Limestone, varieties, structure, and origin--Phosphate
of lime--Concretions--Sulphate of lime--Silica and siliceous
deposits of various kinds--Greensands--Red clays--Carbon and
carbonaceous deposits.
CHAPTER III.
Chronological succession of the fossiliferous rocks--Tests or age
of strata--Value of Palæontological evidence in stratigraphical
Geology--General sequence of the great formations.
CHAPTER IV.
The breaks in the palæontological and geological record--Use of
the term "contemporaneous" as applied to groups of strata--General
sequence of strata and of life-forms interfered with by more or
less extensive gaps--Unconformability--Phenomena implied by
this--Causes of the imperfection of the palæontological record.
CHAPTER V.
Conclusions to be drawn from fossils--Age of rocks--Mode of origin
of any fossiliferous bed--Fluviatile, lacustrine, and marine
deposits--Conclusions as to climate--Proofs of elevation and
subsidence of portions of the earth's crust derived from fossils.
CHAPTER VI.
The biological relations of fossils--Extinction of
life-forms--Geological range of different species--Persistent types
of life--Modern origin of existing animals and plants--Reference
of fossil forms to the existing primary divisions of the animal
kingdom--Departure of the older types of life from those now in
existence--Resemblance of the fossils of a given formation to
those of the formation next above and next below--Introduction
of new life-forms.
PART II.
HISTORICAL PALÆONTOLOGY.
CHAPTER VII.
The Laurentian and Huronian periods--General nature, divisions,
and geographical distribution of the Laurentian deposits--Lower
and Upper Laurentian--Reasons for believing that the Laurentian
rocks are not azoic based upon their containing limestones, beds of
oxide of iron, and graphite--The characters, chemical composition,
and minute structure of _Eozoön Canadense_--Comparison of _Eozoön_
with existing Foraminifera--_Archoeosphoerinoe_--Huronian
formation--Nature and distribution of Huronian deposits--Organic
remains of the Huronian--Literature.
CHAPTER VIII.
The Cambrian period--General succession of Cambrian deposits in
Wales--Lower Cambrian and Upper Cambrian--Cambrian deposits of
the continent of Europe and North American--Life of the Cambrian
period--Fucoids--Eophyton--Oldhamia--Sponges--Echinoderms--Annelides
--Crustaceans--Structure of Trilobites--Brachiopods--Pteropods,
Gasteropods, and Bivalves--Cephalopods--Literature.
CHAPTER IX.
The Lower Silurian period--The Silurian rocks generally--Limits
of Lower and Upper Silurian--General succession, subdivisions,
and characters of the Lower Silurian rocks of Wales--General
succession, subdivisions, and characters of the Lower Silurian
rocks of the North American continent--Life of the
period--Fucoids--Protozoa--Graptolites--Structure of
Graptolites--Corals--General structure of Corals--Crinoids--
Cystideans--General characters of Cystideans--Annelides--
Crustaceans--Polyzoa--Brachiopods--Bivalve and Univalve
Molluscs--Chambered Cephalopods--General characters of the
Cephalopoda--Conodonts.
CHAPTER X.
The Upper Silurian period--General succession of the Upper Silurian
deposits of Wales--Upper Silurian deposits of North America--Life
of the Upper Silurian--Plants--Protozoa--Graptolites--Corals--
Crinoids--General structure of Crinoids--Star-fishes--Annelides--
Crustaceans--Eurypterids--Polyzoa--Brachiopods--Structure of
Brachiopods--Bivalves and Univalves--Pteropods--Cephalopods--
Fishes--Silurian literature.
CHAPTER XI.
The Devonian period--Relations between the Old Red Sandstone
and the marine Devonian deposits--The Old Red Sandstone of
Scotland--The Devonian strata of Devonshire--Sequence and
subdivisions of the Devonian deposits of North America--Life
of the period--Plants--Protozoa--Corals-Crinoids--Pentremites--
Annelides--Crustaceans--Insects--Polyzoa--Brachiopods--Bivalves--
Univalves--Pteropods--Cephalopods--Fishes--General divisions of
the Fishes--Palæontological evidence as to the independent
existence of the Devonian system as a distinct
formation--Literature.
CHAPTER XII.
The Carboniferous period--Relations of Carboniferous rocks to
Devonian--The Carboniferous Limestone or Sub-Carboniferous
series--The Millstone-grit and the Coal-measures--Life of the
period--Structure and mode of formation of Coal--Plants of the
Coal.
CHAPTER XIII.
Animal life of the Carboniferous period--Protozoa--Corals--
Crinoids--Pentremites--Structure of Pentremites--Echinoids--
Structure of Echinoidea--Annelides--Crustacea--Insects--
Arachnids--Myriapods--Polyzoa--Brachiopods--Bivalves and
Univalves--Cephalopods--Fishes--Labyrinthodont Amphibians--
Literature.
CHAPTER XIV.
The Permian period--General succession, characters, and mode
of formation of the Permian deposits--Life of the period--
Plants--Protozoa--Corals--Echinoderms--Annelides--Crustaceans--
Polyzoa--Brachiopods--Bivalves-Univalves--Pteropods--
Cephalopods--Fishes--Amphibians--Reptiles--Literature.
CHAPTER XV.
The Triassic period--General characters and subdivisions of the
Trias of the Continent of Europe and Britain--Trias of North
America--Life of the period--Plants--Echinoderms--Crustaceans--
Polyzoa--Brachiopods--Bivalves--Univalves--Cephalopods--
Intermixture of Palæozoic with Mesozoic types of Molluscs--
Fishes--Amphibians--Reptiles--Supposed footprints of Birds--
Mammals--Literature.
CHAPTER XVI.
The Jurassic period--General sequence and subdivisions of the
Jurassic deposits in Britain--Jurassic rocks of North America--Life
of the period--Plants--Corals--Echinoderms--Crustaceans--Insects--
Brachiopods--Bivalves--Univalves-Pteropods--Tetrabranchiate
Cephalopods--Dibranchiate Cephalopods--Fishes--Reptiles--Birds--
Mammals--Literature.
CHAPTER XVII.
The Cretaceous period--General succession and subdivisions of
the Cretaceous rocks in Britain--Cretaceous rocks of North
America--Life of the period--Plants--Protozoa--Corals--Echinoderms--
Crustaceans--Polyzoa--Brachiopods--Bivalves--Univalves--
Tetrabranchiate and Dibranchiate Cephalopods--Fishes--Reptiles--
Birds--Literature.
CHAPTER XVIII.
The Eocene period--Relations between the Kainozoic and Mesozoic
rocks in Europe and in North America--Classification of the Tertiary
deposits--The sequence and subdivisions of the Eocene rocks of
Britain and France--Eocene strata of the United States--Life of the
period--Plants--Foraminifera--Corals--Echinoderms--Mollusca--Fishes--
Reptiles--Birds--Mammals.
CHAPTER XIX.
The Miocene period--Miocene strata of Britain--Of France--Of
Belgium--Of Austria--Of Switzerland--Of Germany--Of Greece--Of
India--Of North America--Of the Arctic regions--Life of the
period--Vegetation of the Miocene period--Foraminifera--Corals--
Echinoderms--Articulates--Mollusca--Fishes-Amphibians--Reptiles--
Mammals.
CHAPTER XX.
The Pliocene period--Pliocene deposits of Britain--Of Europe--Of
North America--Life of the period--Climate of the period as indicated
by the Invertebrate animals--The Pliocene Mammalia--Literature
relating to the Tertiary deposits and their fossils.
CHAPTER XXI.
The Post-Pliocene period--Division of the Quaternary deposits into
Post-Pliocene and Recent--Relations of the Post-Pliocene deposits
of the northern hemisphere to the "Glacial period"--Pre-Glacial
deposits--Glacial deposits--Arctic Mollusca in Glacial
beds--Post-Glacial deposits--Nature and mode of formation of
high-level and low-level gravels--Nature and mode of formation
of cavern-deposits--Kent's Cavern-Post--Pliocene deposits of
the southern hemisphere.
CHAPTER XXII.
Life of the Post-Pliocene period--Effect of the coming on and
departure of the Glacial period upon the animals inhabiting the
northern hemisphere--Birds of the Post-Pliocene--Mammalia of the
Post-Pliocene--Climate of the Post-Glacial period as deduced from
the Post-Glacial Mammals--Occurrence of the bones and implements
of Man in Post-Pliocene deposits in association with the remains
of extinct Mammalia--Literature relating to the Post-Pliocene
period.
CHAPTER XXIII.
The succession of life upon the globe--Gradual and successive
introduction of life-forms--What is meant by "lower" and "higher"
groups of animals and plants--Succession in time of the great
groups of animals in the main corresponding with their zoological
order--Identical phenomena in the vegetable kingdom--Persistent
types of life--High organisation of many early forms--Bearings
of Palæontology on the general doctrine of Evolution.
APPENDIX.--Tabular view of the chief Divisions of the Animal Kingdom.
GLOSSARY.
INDEX.
LIST OF ILLUSTRATIONS
FIG.
1. Cast of _Trigonia longa_.
2. Microscopic section of the wood of a fossil Conifer.
3. Microscopic section of the wood of the Larch.
4. Section of Carboniferous strata, Kinghorn, Fife.
5. Diagram illustrating the formation of stratified deposits.
6. Microscopic section of a calcareous breccia.
7. Microscopic section of White Chalk.
8. Organisms in Atlantic Ooze.
9. Crinoidal marble.
10. Piece of Nummulitic limestone, Pyramids.
11. Microscopic section of Foraminiferal
limestone--Carboniferous, America.
12. Microscopic section of Lower Silurian limestone.
13. Microscopic section of oolitic limestone, Jurassic.
14. Microscopic section of oolitic limestone, Carboniferous.
15. Organisms in Barbadoes earth.
16. Organisms in Richmond earth.
17. Ideal section of the crust of the earth.
18. Unconformable junction of Chalk and Eocene rocks.
19. Erect trunk of a _Sigillaria_.
20. Diagrammatic section of the Laurentian rocks.
21. Microscopic section of Laurentian limestone.
22. Fragment of a mass of _Eozoön Canadense_.
23. Diagram illustrating the structure of _Eozoön_.
24. Microscopic section of _Eozoön Canadense_.
25. _Nonionina_ and _Gromia_.
26. Group of shells of living _Foraminifera_.
27. Diagrammatic section of Cambrian strata.
28. _Eophyton Linneanum_.
29. _Oldhamia antiqua_.
30. _Scolithus Canadensis_.
31. Group of Cambrian Trilobites.
32. Group of characteristic Cambrian fossils.
33. Fragment of _Dictyonema sociale_.
34. Generalised section of the Lower Silurian rocks
of Wales.
35. Generalised section of the Lower Silurian rocks
of North America.
36. _Licrophycus Ottawaensis_.
37. _Astylospongia proemorsa_.
38. _Stromatopora rugosa_.
39. _Dichograptus octobrachiatus_.
40. _Didymograptus divaricatus_.
41. _Diplograptus pristis_.
42. _Phyllograptus typus_.
43. _Zaphrentis Stokesi_.
44. _Strombodes pentagonus_.
45. _Columnaria alveolata_.
46. Group of Cystideans.
47. Group of Lower Silurian Crustaceans.
48. _Ptilodictya falciformis_.
49. _Ptilodictya Schafferi_.
50. Group of Lower Silurian Brachiopods.
51. Group of Lower Silurian Brachiopods.
52. _Murchisonia gracilis_.
53. _Bellerophon argo_.
54. _Maclurea crenulata_.
55. _Orthoceras crebriseptum_.
56. Restoration of _Orthoceras_.
57. Generalised section of the Upper Silurian rocks.
58. _Monograptus priodon_.
59. _Halysites catenularia_ and _H. agglomerata_.
60. Group of Upper Silurian Star-fishes.
61. _Protaster Sedgwickii_.
62. Group of Upper Silurian Crinoids.
63. _Planolites vulgaris_.
64. Group of Upper Silurian Trilobites.
65. _Pterygotus Anglicus_.
66. Group of Upper Silurian _Polyzoa_.
67. _Spirifera hysterica_.
68. Group of Upper Silurian Brachiopods.
69. Group of Upper Silurian Brachiopods.
70. _Pentamerus Knightii_.
71. _Cardiola interrupta, C. fibrosa_, and _Pterinoea
subfalcata_.
72. Group of Upper Silurian Univalves.
73. _Tentaculites ornatus_.
74. _Pteraspis Banksii_.
75. _Onchus tenuistriatus_ and _Thelodus_.
76. Generalised section of the Devonian rocks of North America.
77. _Psilophyton princeps_.
78. _Prototaxites Logani_.
79. _Stromatopora tuberculata_.
80. _Cystiphyllum vesiculosum_.
81. _Zaphrentis cornicula_.
82. _Heliophyllum exiguum_.
83. _Crepidophyllum Archiaci_.
84. _Favosites Gothlandica_.
85. _Favosites hemisphoerica_.
86. _Spirorbis omphalodes_ and _S. Arkonensis_.
87. _Spirorbis laxus_ and _S. Spinulifera_.
88. Group of Devonian Trilobites.
89. Wing of _Platephemera antiqua_.
90. _Clathropora intertexta_.
91. _Ceriopora Hamiltonensis_.
92. _Fenestella magnifica_.
93. _Retepora Phillipsi_.
94. _Fenestella cribrosa_.
95. _Spirifera sculptilis_.
96. _Spirifera mucronata_.
97. _Atrypa reticularis_.
98. _Strophomena rhomboidalis_.
99. _Platyceras dumosum_.
100. _Conularia ornata_.
101. _Clymenia Sedgwickii_.
102. Group of Fishes from the Devonian rocks of North America.
103. _Cephalaspis Lyellii_.
104. _Pterichthys cornutus_.
105. _Polypterus_ and _Osteolepis_.
106. _Holoptychius nobilissimus_.
107. Generalised section of the Carboniferous rocks of the
North of England.
108. _Odontopteris Schlotheimii_.
109. _Calamites cannoeformis_.
110. _Lepidodendron Sternbergii_.
111. _Sigillaria Groeseri_.
112. _Stigmaria ficoides_.
113. _Trigonocarpum ovatum_.
114. Microscopic section of Foraminiferal
limestone--Carboniferous, North America.
115. _Fusulina cylindrica_.
116. Group of Carboniferous Corals.
117. _Platycrinus tricontadactylus_.
118. _Pentremites pyriformis_ and _P. conoideus_.
119. _Archoeocidaris ellipticus_.
120. _Spirorbis Carbonarius_.
121. _Prestwichia rotundata_.
122. Group of Carboniferous Crustaceans.
123. _Cyclophthalmus senior_.
124. _Xylobius Sigillarioe_.
125. _Haplophlebium Barnesi_.
126. Group of Carboniferous _Polyzoa_.
127. Group of Carboniferous _Brachiopoda_.
128. _Pupa vetusta_.
129. _Goniatites Fossoe_.
130. _Amblypterus macropterus_.
131. _Cochliodus contortus_.
132. _Anthracosaurus Russelli_.
133. Generalised section of the Permian rocks.
134. _Walchia piniformis_.
135. Group of Permian _Brachiopods_.
136. _Arca antiqua_.
137. _Platysomus gibbosus_.
138. _Protorosaurus Speneri_.
139. Generalised section of the Triassic rocks.
140. _Zamia spiralis_.
141. Triassic Conifers and Cycads.
142. _Encrinus liliiformis_.
143. _Aspidura loricata_.
144. Group of Triassic Bivalves.
145. _Ceratites nodosus_.
146. Tooth of _Ceratodus serratus_ and _C. Altus_.
147. _Ceratodus Fosteri_.
148. Footprints of _Cheirotherium_.
149. Section of tooth of _Labyrinthodont_.
150. Skull of _Mastodonsaurus_.
151. Skull of _Rhynchosaurus_.
152. _Belodon_, _Nothosaurus_, _Paloeosaurus_, &c.
153. _Placodus gigas_.
154. Skulls of _Dicynodon_ and _Oudenodon_.
155. Supposed footprint of Bird, from the Trias of Connecticut.
156. Lower jaw of _Dromatherium sylvestre_.
157. Molar tooth of _Microlestes antiquus_.
158. _Myrmecobius fasciatus_.
159. Generalised section of the Jurassic rocks.
160. _Mantellia megalophylla_.
161. _Thecosmilia annularis_.
162. _Pentacrinus fasciculosus_.
163. _Hemicidaris crenularis_.
164. _Eryon arctiformis_.
165. Group of Jurassic Brachiopods.
166. _Ostrea Marshii_.
167. _Gryphoea incurva_
168. _Diceras arietina_.
169. _Nerinoea Goodhallii_.
170. _Ammonites Humphresianus_.
171. _Ammonites bifrons_.
172. _Beloteuthis subcostata_.
173. Belemnite restored; diagram of Belemnite; _Belemnites
canaliculata_.
174. _Tetragonolepis_.
175. _Acrodus nobilis_.
176. _Ichthyosaurus communis_.
177. _Plesiosaurus dolichodeirus_.
178. _Pterodactylus crassirostris_.
179. _Ramphorhynchus Bucklandi_, restored.
180. Skull of _Megalosaurus_.
181. _Archoeopteryx macrura_.
182. _Archoeopteryx, restored_.
183. Jaw of _Amphitherium Prevostii_.
184. Jaws of Oolitic Mammals.
185. Generalised section of the Cretaceous rocks.
186. Cretaceous Angiosperms.
187. _Rotalia Boueana_.
188. _Siphonia ficus_.
189. _Ventriculites simplex_.
190. _Synhelia Sharpeana_.
191. _Galerites albogalerus_.
192. _Discoidea cylindrica_.
193. _Escharina Oceani_.
194. _Terebratella Astieriana_.
195. _Crania Ignabergensis_.
196. _Ostrea Couloni_.
197. _Spondylus spinosus_.
198. _Inoceramus sulcatus_.
199. _Hippurites Toucasiana_.
200. _Voluta elongata_.
201. _Nautilus Danicus_.
202. _Ancyloceras Matheronianus_.
203. _Turrilites catenatus_
204. Forms of Cretaceous _Ammonitidoe_.
205. _Belemnitella mucronata_.
206. Tooth of _Hybodus_.
207. Fin-spine of _Hybodus_.
208. _Beryx Lewesiensis_ and _Osmeroides Mantelli_.
209. Teeth of _Iguanodon_.
210. Skull of _Mosasaurus Camperi_.
211. _Chelone Benstedi_.
212. Jaws and vertebræ of _Odontornithes_.
213. Fruit of _Nipadites_.
214. _Nummulina loevigata_.
215. _Turbinolia sulcata_.
216. _Cardita planicosta_.
217. _Typhis tubifer_.
218. _Cyproea elegans_.
219. _Cerithium hexagonum_.
220. _Limnoea pyramidalis_.
221. _Physa columnaris_.
222. _Cyclostoma Arnoudii_.
223. _Rhombus minimus_.
224. _Otodus obliquus_.
225. _Myliobatis Edwardsii_.
226. Upper jaw of Alligator.
227. Skull of _Odontopteryx toliapicus_.
228. _Zeuglodon cetoides_.
229. _Paloeotherium magnum_, restored.
230. Feet of _Equidoe_.
231. _Anoplothelium commune_.
232. Skull of _Dinoceras mirabilis_.
233. _Vespertilio Parisiensis_.
234. Miocene Palms.
235. _Platanus aceroides_.
236. _Cinnamomum polymorphum_.
237. _Textularia Meyeriana_.
238. _Scutella subrotunda_.
239. _Hyalea Orbignyana_.
240. Tooth of _Oxyrhina_.
241. Tooth of _Carcharodon_.
242. _Andrias Scheuchzeri_.
243. Skull of _Brontotherium ingens_.
244, _Hippopotamus Sivalensis_.
245. Skull of _Sivatherium_.
246. Skull of _Deinotherium_.
247. Tooth of _Elephas planfrons_ and of _Mastodon
Sivalensis_.
248. Jaw of _Pliopithecus_.
249. _Rhinoceros Etruscus_ and _R. megarhinus_.
250. Molar tooth of _Mastodon Arvernensis_.
251. Molar tooth of _Etephas meridionalis_.
252. Molar tooth of _Elephas antiquus_.
253. Skull and tooth of _Machairodus cultridens_.
254. _Pecten Islandicus_.
255. Diagram of high-level and low-level gravels.
256. Diagrammatic section of Cave.
257. _Dinornis elephantopus_.
258. Skull of _Diprotodon_.
259. Skull of _Thylacoleo_.
260. Skeleton of _Megatherium_.
261. Skeleton of _Mylodon_.
262. _Glyptodon clavipes_.
263. Skull of _Rhinoceros tichorhinus_.
264. Skeleton of _Cervus megaceros_.
265. Skull of _Bos primigenius_.
266. Skeleton of Mammoth.
267. Molar tooth of Mammoth.
268. Skull of _Ursus speloeus_.
269. Skull of _Hyoena speloea_.
270. Lower jaw of _Trogontherium Cuvieri_.
PART I.
PRINCIPLES OF PALÆONTOLOGY.
INTRODUCTION.
THE LAWS OF GEOLOGICAL ACTION.
Under the general title of "Geology" are usually included at
least two distinct branches of inquiry, allied to one another in
the closest manner, and yet so distinct as to be largely capable
of separate study. _Geology_,[1] in its strict sense, is the
science which is concerned with the investigation of the materials
which compose the earth, the methods in which those materials
have been arranged, and the causes and modes of origin of these
arrangements. In this limited aspect, Geology is nothing more than
the Physical Geography of the past, just as Physical Geography
is the Geology of to-day; and though it has to call in the aid
of Physics, Astronomy, Mineralogy, Chemistry, and other allies
more remote, it is in itself a perfectly distinct and individual
study. One has, however, only to cross the threshold of Geology
to discover that the field and scope of the science cannot be
thus rigidly limited to purely physical problems. The study of
the physical development of the earth throughout past ages brings
us at once in contact with the forms of animal and vegetable
life which peopled its surface in bygone epochs, and it is found
impossible adequately to comprehend the former, unless we possess
some knowledge of the latter. However great its physical advances
may be, Geology remains imperfect till it is wedded with
Palæontology,[2] a study which essentially belongs to the vast
complex of the Biological Sciences, but at the same time has its
strictly geological side. Dealing, as it does, wholly with the
consideration of such living beings as do not belong exclusively
to the present order of things, Palæontology is, in reality, a
branch of Natural History, and may be regarded as substantially
the Zoology and Botany of the past. It is the ancient life-history
of the earth, as revealed to us by the labours of palæontologists,
with which we have mainly to do here; but before entering upon
this, there are some general questions, affecting Geology and
Palæontology alike, which may be very briefly discussed.
[Footnote 1: Gr. _ge_, the earth; _logos_, a discourse.]
[Footnote 2: Gr. _palaios_, ancient; _onta_, beings; _logos_,
discourse.]
The working geologist, dealing in the main with purely physical
problems, has for his object to determine the material structure
of the earth, and to investigate, as far as may be, the long chain
of causes of which that structure is the ultimate result. No wider
or more extended field of inquiry could be found; but philosophical
geology is not content with this. At all the confines of his
science, the transcendental geologist finds himself confronted
with some of the most stupendous problems which have ever engaged
the restless intellect of humanity. The origin and primæval
constitution of the terrestrial globe, the laws of geologic action
through long ages of vicissitude and development, the origin of
life, the nature and source of the myriad complexities of living
beings, the advent of man, possibly even the future history of
the earth, are amongst the questions with which the geologist
has to grapple in his higher capacity.
These are problems which have occupied the attention of philosophers
in every age of the world, and in periods long antecedent to
the existence of a science of geology. The mere existence of
cosmogonies in the religion of almost every nation, both ancient
and modern, is a sufficient proof of the eager desire of the
human mind to know something of the origin of the earth on which
we tread. Every human being who has gazed on the vast panorama
of the universe, though it may have been but with the eyes of
a child, has felt the longing to solve, however imperfectly,
"the riddle of the painful earth," and has, consciously or
unconsciously, elaborated some sort of a theory as to the why and
wherefore of what he sees. Apart from the profound and perhaps
inscrutable problems which lie at the bottom of human existence,
men have in all ages invented theories to explain the common
phenomena of the material universe; and most of these theories,
however varied in their details, turn out on examination to have a
common root, and to be based on the same elements. Modern geology
has its own theories on the same subject, and it will be well to
glance for a moment at the principles underlying the old and
the new views.
It has been maintained, as a metaphysical hypothesis, that there
exists in the mind of man an inherent principle, in virtue of
which he believes and expects that what has been, will be; and
that the course of nature will be a continuous and uninterrupted
one. So far, however, from any such belief existing as a necessary
consequence of the constitution of the human mind, the real fact
seems to be that the contrary belief has been almost universally
prevalent. In all old religions, and in the philosophical systems
of almost all ancient nations, the order of the universe has
been regarded as distinctly unstable, mutable, and temporary.
A beginning and an end have always been assumed, and the course
of terrestrial events between these two indefinite points has
been regarded as liable to constant interruption by revolutions
and catastrophes of different kinds, in many cases emanating from
supernatural sources. Few of the more ancient theological creeds,
and still fewer of the ancient philosophies, attained body and
shape without containing, in some form or another, the belief
in the existence of periodical convulsions, and of alternating
cycles of destruction and repair.
That geology, in its early infancy, should have become imbued
with the spirit of this belief, is no more than might have been
expected; and hence arose the at one time powerful and
generally-accepted doctrine of "Catastrophism." That the succession
of phenomena upon the globe, whereby the earth's crust had assumed
the configuration and composition which we find it to possess,
had been a discontinuous and broken succession, was the almost
inevitable conclusion of the older geologists. Everywhere in
their study of the rocks they met with apparently impassable
gaps, and breaches of continuity that could not be bridged over.
Everywhere they found themselves conducted abruptly from one system
of deposits to others totally different in mineral character or
in stratigraphical position. Everywhere they discovered that
well-marked and easily recognisable groups of animals and plants
were succeeded, without the intermediation of any obvious lapse
of time, by other assemblages of organic beings of a different
character. Everywhere they found evidence that the earth's crust
had undergone changes of such magnitude as to render it seemingly
irrational to suppose that they could have been produced by any
process now in existence. If we add to the above the prevalent
belief of the time as to the comparative brevity of the period
which had elapsed since the birth of the globe, we can readily
understand the general acceptance of some form of catastrophism
amongst the earlier geologists.
As regards its general sense and substance, the doctrine of
catastrophism held that the history of the earth, since first
it emerged from the primitive chaos, had been one of periods
of repose, alternating with catastrophes and cataclysms of a
more or less violent character. The periods of tranquillity were
supposed to have been long and protracted; and during each of them
it was thought that one of the great geological "formations" was
deposited. In each of these periods, therefore, the condition of
the earth was supposed to be much the same as it is now--sediment
was quietly accumulated at the bottom of the sea, and animals and
plants flourished uninterruptedly in successive generations.
Each period of tranquillity, however, was believed to have been,
sooner or later, put an end to by a sudden and awful convulsion
of nature, ushering in a brief and paroxysmal period, in which
the great physical forces were unchained and permitted to spring
into a portentous activity. The forces of subterranean fire,
with their concomitant phenomena of earthquake and volcano, were
chiefly relied upon as the efficient causes of these periods of
spasm and revolution. Enormous elevations of portions of the
earth's crust were thus believed to be produced, accompanied by
corresponding and equally gigantic depressions of other portions.
In this way new ranges of mountains were produced, and previously
existing ranges levelled with the ground, seas were converted into
dry land, and continents buried beneath the ocean--catastrophe
following catastrophe, till the earth was rendered uninhabitable,
and its races of animals and plants were extinguished, never to
reappear in the same form. Finally, it was believed that this
feverish activity ultimately died out, and that the ancient peace
once more came to reign upon the earth. As the abnormal throes
and convulsions began to be relieved, the dry land and sea once
more resumed their relations of stability, the conditions of
life were once more established, and new races of animals and
plants sprang into existence, to last until the supervention
of another fever-fit.
Such is the past history of the globe, as sketched for us, in
alternating scenes of fruitful peace and revolutionary destruction,
by the earlier geologists. As before said, we cannot wonder at the
former general acceptance of Catastrophistic doctrines. Even in
the light of our present widely-increased knowledge, the series
of geological monuments remains a broken and imperfect one; nor
can we ever hope to fill up completely the numerous gaps with
which the geological record is defaced. Catastrophism was the
natural method of accounting for these gaps, and, as we shall see,
it possesses a basis of truth. At present, however, catastrophism
may be said to be nearly extinct, and its place is taken by the
modern doctrine of "Continuity" or "Uniformity"--a doctrine with
which the name of Lyell must ever remain imperishably associated.
The fundamental thesis of the doctrine of Uniformity is, that,
in spite of all apparent violations of continuity, the sequence
of geological phenomena has in reality been a regular and
uninterrupted one; and that the vast changes which can be shown
to have passed over the earth in former periods have been the
result of the slow and ceaseless working of the ordinary physical
forces--acting with no greater intensity than they do now, but
acting through enormously prolonged periods. The essential element
in the theory of Continuity is to be found in the allotment of
indefinite time for the accomplishment of the known series of
geological changes. It is obviously the case, namely, that there
are two possible explanations of all phenomena which lie so far
concealed in "the dark backward and abysm of time," that we can
have no direct knowledge of the manner in which they were produced.
We may, on the one hand, suppose them to be the result of some
very powerful cause, acting through a short period of time. That
is Catastrophism. Or, we may suppose them to be caused by a much
weaker force operating through a proportionately prolonged period.
This is the view of the Uniformitarians. It is a question of
_energy_ versus _time_ and it is _time_ which is the true element
of the case. An earthquake may remove a mountain in the course
of a few seconds; but the dropping of the gentle rain will do
the same, if we extend its operations over a millennium. And
this is true of all agencies which are now at work, or ever have
been at work, upon our planet. The Catastrophists, believing
that the globe is but, as it were, the birth of yesterday, were
driven of necessity to the conclusion that its history had been
checkered by the intermittent action of paroxysmal and almost
inconceivably potent forces. The Uniformitarians, on the other
hand, maintaining the "adequacy of existing causes," and denying
that the known physical forces ever acted in past time with greater
intensity than they do at present, are, equally of necessity,
driven to the conclusion that the world is truly in its "hoary
eld," and that its present state is really the result of the
tranquil and regulated action of known forces through unnumbered
and innumerable centuries.
The most important point for us, in the present connection, is
the bearing of these opposing doctrines upon the question, as
to the origin of the existing terrestrial order. On any doctrine
of uniformity that order has been evolved slowly, and, according
to law, from a pre-existing order. Any doctrine of catastrophism,
on the other hand, carries with it, by implication, the belief
that the present order of things was brought about suddenly and
irrespective of any pre-existent order; and it is important to
hold clear ideas as to which of these beliefs is the true one. In
the first place, we may postulate that the world had a beginning,
and, equally, that the existing terrestrial order had a beginning.
However far back we may go, geology does not, and cannot, reach the
actual beginning of the world; and we are, therefore, left simply
to our own speculations on this point. With regard, however, to
the existing terrestrial order, a great deal can be discovered,
and to do so is one of the principal tasks of geological science.
The first steps in the production of that order lie buried in
the profound and unsearchable depths of a past so prolonged as
to present itself to our finite minds as almost in eternity.
The last steps are in the prophetic future, and can be but dimly
guessed at. Between the remote past and the distant future, we
have, however, a long period which is fairly open to inspection;
and in saying a "long" period, it is to be borne in mind that
this term is used in its _geological_ sense. Within this period,
enormously long as it is when measured by human standards, we
can trace with reasonable certainty the progressive march of
events, and can determine the laws of geological action, by which
the present order of things has been brought about.
The natural belief on this subject doubtless is, that the world,
such as we now see it, possessed its present form and configuration
from the beginning. Nothing can be more natural than the belief
that the present continents and oceans have always been where
they are now; that we have always had the same mountains and
plains; that our rivers have always had their present courses,
and our lakes their present positions; that our climate has always
been the same; and that our animals and plants have always been
identical with those now familiar to us. Nothing could be more
natural than such a belief, and nothing could be further removed
from the actual truth. On the contrary, a very slight acquaintance
with geology shows us, in the words of Sir John Herschel, that
"the actual configuration of our continents and islands, the
coast-lines of our maps, the direction and elevation of our
mountain-chains, the courses of our rivers, and the soundings
of our oceans, are not things primordially arranged in the
construction of our globe, but results of successive and complex
actions on a former state of things; _that_, again, of similar
actions on another still more remote; and so on, till the original
and really permanent state is pushed altogether out of sight
and beyond the reach even of imagination; while on the other
hand, a similar, and, as far as we can see, interminable vista
is opened out for the future, by which the habitability of our
planet is secured amid the total abolition on it of the present
theatres of terrestrial life."
Geology, then, teaches us that the physical features which now
distinguish the earth's surface have been produced as the ultimate
result of an almost endless succession of precedent changes.
Palæontology teaches us, though not yet in such assured accents,
the same lesson. Our present animals and plants have not been
produced, in their innumerable forms, each as we now know it,
as the sudden, collective, and simultaneous birth of a renovated
world. On the contrary, we have the clearest evidence that some
of our existing animals and plants made their appearance upon the
earth at a much earlier period than others. In the confederation
of animated nature some races can boast of an immemorial antiquity,
whilst others are comparative _parvenus_. We have also the clearest
evidence that the animals and plants which now inhabit the globe
have been preceded, over and over again, by other different
assemblages of animals and plants, which have flourished in
successive periods of the earth's history, have reached their
culmination, and then have given way to a fresh series of living
beings. We have, finally, the clearest evidence that these successive
groups of animals and plants (faunæ and floræ) are to a greater
or less extent directly connected with one another. Each group
is, to a greater or less extent, the lineal descendant of the
group which immediately preceded it in point of time, and is
more or less fully concerned with giving origin to the group
which immediately follows it. That this law of "evolution" has
prevailed to a great extent is quite certain; but it does not
meet all the exigencies of the case, and it is probable that
its action has been supplemented by some still unknown law of
a different character.
We shall have to consider the question of geological "continuity"
again. In the meanwhile, it is sufficient to state that this
doctrine is now almost universally accepted as the basis of all
inquiries, both in the domain of geology and that of palæontology.
The advocates of continuity possess one immense advantage over
those who believe in violent and revolutionary convulsions, that
they call into play only agencies of which we have actual knowledge.
We _know_ that certain forces are now at work, producing certain
modifications in the present condition of the globe; and we _know_
that these forces are capable of producing the vastest of the
changes which geology brings under our consideration, provided
we assign a time proportionately vast for their operation. On
the other hand, the advocates of catastrophism, to make good
their views, are compelled to invoke forces and actions, both
destructive and restorative, of which we have, and can have, no
direct knowledge. They endow the whirlwind and the earthquake,
the central fire and the rain from heaven, with powers as mighty
as ever imagined in fable, and they build up the fragments of a
repeatedly shattered world by the intervention of an intermittently
active creative power.
It should not be forgotten, however, that from one point of view
there is a truth in catastrophism which is sometimes overlooked
by the advocates of continuity and uniformity. Catastrophism
has, as its essential feature, the proposition that the known
and existing forces of the earth at one time acted with much
greater intensity and violence than they do at present, and they
carry down the period of this excessive action to the commencement
of the present terrestrial order. The Uniformitarians, in effect,
deny this proposition, at any rate as regards any period of the
earth's history of which we have actual cognisance. If, however,
the "nebular hypothesis" of the origin of the universe be well
founded--as is generally admitted--then, beyond question, the
earth is a gradually cooling body, which has at one time been
very much hotter than it is at present. There has been a time,
therefore, in which the igneous forces of the earth, to which we
owe the phenomena of earthquakes and volcanoes, must have been
far more intensely active than we can conceive of from anything
that we can see at the present day. By the same hypothesis, the
sun is a cooling body, and must at one time have possessed a
much higher temperature than it has at present. But increased
heat of the sun would seriously alter the existing conditions
affecting the evaporation and precipitation of moisture on our
earth; and hence the aqueous forces may also have acted at one
time more powerfully than they do now. The fundamental principle
of catastrophism is, therefore, not wholly vicious; and we have
reason to think that there must have been periods--very remote,
it is true, and perhaps unrecorded in the history of the earth--in
which the known physical forces may have acted with an intensity
much greater than direct observation would lead us to imagine.
And this may be believed, altogether irrespective of those great
secular changes by which hot or cold epochs are produced, and
which can hardly be called "catastrophistic," as they are produced
gradually, and are liable to recur at definite intervals.
Admitting, then, that there _is_ a truth at the bottom of the once
current doctrines of catastrophism, still it remains certain that
the history of the earth has been one of _law_ in all past time,
as it is now. Nor need we shrink back affrighted at the vastness
of the conception--the vaster for its very vagueness--that we
are thus compelled to form as to the duration of _geological
time_. As we grope our way backward through the dark labyrinth
of the ages, epoch succeeds to epoch, and period to period, each
looming more gigantic in its outlines and more shadowy in its
features, as it rises, dimly revealed, from the mist and vapour
of an older and ever-older past. It is useless to add century
to century or millennium to millennium. When we pass a certain
boundary-line, which, after all, is reached very soon, figures
cease to convey to our finite faculties any real notion of the
periods with which we have to deal. The astronomer can employ
material illustrations to give form and substance to our conceptions
of celestial space; but such a resource is unavailable to the
geologist. The few thousand years of which we have historical
evidence sink into absolute insignificance beside the unnumbered
æons which unroll themselves one by one as we penetrate the dim
recesses of the past, and decipher with feeble vision the ponderous
volumes in which the record of the earth is written. Vainly does
the strained intellect seek to overtake an ever-receding
commencement, and toil to gain some adequate grasp of an apparently
endless succession. A beginning there must have been, though we
can never hope to fix its point. Even speculation droops her
wings in the attenuated atmosphere of a past so remote, and the
light of imagination is quenched in the darkness of a history so
ancient. In _time_, as in _space_, the confines of the universe
must ever remain concealed from us, and of the end we know no
more than of the beginning. Inconceivable as is to us the lapse
of "geological time," it is no more than "a mere moment of the
past, a mere infinitesimal portion of eternity." Well may "the
human heart, that weeps and trembles," say, with Richter's pilgrim
through celestial space, "I will go no farther; for the spirit of
man acheth with this infinity. Insufferable is the glory of God.
Let me lie down in the grave, and hide me from the persecution
of the Infinite, for end, I see, there is none."
CHAPTER I.
THE SCOPE AND MATERIALS OF PALÆONTOLOGY.
The study of the rock-masses which constitute the crust of the
earth, if carried out in the methodical and scientific manner of
the geologist, at once brings us, as has been before remarked, in
contact with the remains or traces of living beings which formerly
dwelt upon the globe. Such remains are found, in greater or less
abundance, in the great majority of rocks; and they are not only of
great interest in themselves, but they have proved of the greatest
importance as throwing light upon various difficult problems in
geology, in natural history, in botany, and in philosophy. Their
study constitutes the science of palæontology; and though it is
possible to proceed to a certain length in geology and zoology
without much palæontological knowledge, it is hardly possible to
attain to a satisfactory general acquaintance with either of
these subjects without having mastered the leading facts of the
first. Similarly, it is not possible to study palæontology without
some acquaintance with both geology and natural history.
Palæontology, then, is the science which treats of the living
beings, whether animal or vegetable, which have inhabited the earth
during past periods of its history. Its object is to elucidate,
as far as may be, the structure, mode of existence, and habits
of all such ancient forms of life; to determine their position
in the scale of organised beings; to lay down the geographical
limits within which they flourished; and to fix the period of
their advent and disappearance. It is the ancient life-history
of the earth; and were its record complete, it would furnish
us with a detailed knowledge of the form and relations of all
the animals and plants which have at any period flourished upon
the land-surfaces of the globe or inhabited its waters; it would
enable us to determine precisely their succession in time; and
it would place in our hands an unfailing key to the problems of
evolution. Unfortunately, from causes which will be subsequently
discussed, the palæontological record is extremely imperfect,
and our knowledge is interrupted by gaps, which not only bear
a large proportion to our solid information, but which in many
cases are of such a nature that we can never hope to fill them
up.
Fossils.--The remains of animals or vegetables which we now find
entombed in the solid rock, and which constitute the working
material of the palæontologist, are termed "fossils,"[3] or
"petrifactions." In most cases, as can be readily understood,
fossils are the actual hard parts of animals and plants which
were in existence when the rock in which they are now found was
being deposited. Most fossils, therefore, are of the nature of
the shells of shell-fish, the skeletons of coral-zoophytes, the
bones of vertebrate animals, or the wood, bark, or leaves of
plants. All such bodies are more or less of a hard consistence
to begin with, and are capable of resisting decay for a longer
or shorter time--hence the frequency with which they occur in
the fossil condition. Strictly speaking, however, by the term
"fossil" must be understood "any body, _or the traces of the
existence of any body_, whether animal or vegetable, which has
been buried in the earth by natural causes" (Lyell). We shall
find, in fact, that many of the objects which we have to study
as "fossils" have never themselves actually formed parts of any
animal or vegetable, though they are due to the former existence
of such organisms, and indicate what was the nature of these.
Thus the footprints left by birds, or reptiles, or quadrupeds
upon sand or mud, are just as much proofs of the former existence
of these animals as would be bones, feathers, or scales, though
in themselves they are inorganic. Under the head of fossils,
therefore, come the footprints of air-breathing vertebrate animals;
the tracks, trails, and burrows of sea-worms, crustaceans, or
molluscs; the impressions left on the sand by stranded jelly-fishes;
the burrows in stone or wood of certain shell-fish; the "moulds"
or "casts" of shells, corals, and other organic remains; and
various other bodies of a more or less similar nature.
[Footnote 3: Lat. _fossus_, dug up.]
Fossilisation.-- The term "fossilisation" is applied to all those
processes through which the remains of organised beings may pass
in being converted into fossils. These processes are numerous
and varied; but there are three principal modes of fossilisation
which alone need be considered here. In the first instance, the
fossil is to all intents and purposes an actual portion of the
original organised being--such as a bone, a shell, or a piece
of wood. In some rare instances, as in the case of the body of
the Mammoth discovered embedded in ice at the mouth of the Lena
in Siberia, the fossil may be preserved almost precisely in its
original condition, and even with its soft parts uninjured. More
commonly, certain changes have taken place in the fossil, the
principal being the more or less total removal of the organic
matter originally present. Thus bones become light and porous
by the removal of their gelatine, so as to cleave to the tongue
on being applied to that organ; whilst shells become fragile, and
lose their primitive colours. In other cases, though practically
the real body it represents, all the cavities of the fossil,
down to its minutest recesses, may have become infiltrated with
mineral matter. It need hardly be added, that it is in the more
modern rocks that we find the fossils, as a rule, least changed
from their former condition; but the original structure is often
more or less completely retained in some of the fossils from
even the most ancient formations.
In the second place, we very frequently meet with fossils in the
state of "casts" or moulds of the original organic body. What
occurs in this case will be readily understood if we imagine any
common bivalve shell, as an Oyster, or Mussel, or Cockle, embedded
in clay or mud. If the clay were sufficiently soft and fluid, the
first thing would be that it would gain access to the interior
of the shell, and would completely fill up the space between the
valves. The pressure, also, of the surrounding matter would insure
that the clay would everywhere adhere closely to the exterior of
the shell. If now we suppose the clay to be in any way hardened
so as to be converted into stone, and if we were to break up the
stone, we should obviously have the following state of parts.
The clay which filled the shell would form an accurate cast of
the _interior_ of the shell, and the clay outside would give us
an exact impression or cast of the _exterior_ of the shell (fig.
1). We should have, then, two casts, an interior and an exterior,
and the two would be very different to one another, since the
inside of a shell is very unlike the outside. In the case, in
fact, of many univalve shells, the interior cast or "mould" is
so unlike the exterior cast, or unlike the shell itself, that
it may be difficult to determine the true origin of the former.
[Illustration: Fig. 1.--_Trigonia longa_, showing casts to of
the exterior and interior of the shell.--Cretaceous (Neocomian).]
It only remains to add that there is sometimes a further
complication. If the rock be very porous and permeable by water,
it may happen that the original shell is entirely dissolved away,
leaving the interior cast loose, like the kernel of a nut, within
the case formed by the exterior cast. Or it may happen that
subsequent to the attainment of this state of things, the space
thus left vacant between the interior and exterior cast--the space,
that is, formerly occupied by the shell itself--may be filled up
by some foreign mineral deposited there by the infiltration of
water. In this last case the splitting open of the rock would
reveal an interior cast, an exterior cast, and finally a body
which would have the exact form of the original shell, but which
would be really a much later formation, and which would not exhibit
under the microscope the minute structure of shell.
[Illustration: Fig. 2.--Microscopic section of the silicified
wood of a Conifer (_Sequoia_) cut in the long direction of the
fibres. Post-tertiary? Colorado. (Original.)]
[Illustration: Footnote: Fig. 3.--Microscopic section of the wood
of the common Larch (_Abies larix_), cut in the long direction of
the fibres. In both the fresh and the fossil wood (fig. 2) are
seen the discs characteristic of coniferous wood. (Original.)]
In the third class of cases we have fossils which present with
the greatest accuracy the external form, and even sometimes the
internal minute structure, of the original organic body, but
which, nevertheless, are not themselves truly organic, but have
been formed by a "replacement" of the particles of the primitive
organism by some mineral substance. The most elegant example
of this is afforded by fossil wood which has been "silicified"
or converted into flint (_silex_). In such cases we have fossil
wood which presents the rings of growth and fibrous structure of
recent wood, and which under the microscope exhibits the minutest
vessels which characterise ligneous tissue, together with the even
more minute markings of the vessels (fig. 2). The whole, however,
instead of being composed of the original carbonaceous matter of
the wood, is now converted into flint. The only explanation that
can be given of this by no means rare phenomenon, is that the
wood must have undergone a slow process of decay in water charged
with silica or flint in solution. As each successive particle of
wood was removed by decay, its place was taken by a particle of
flint deposited from the surrounding water, till ultimately the
entire wood was silicified. The process, therefore, resembles
what would take place if we were to pull down a house built of
brick by successive bricks, replacing each brick as removed by
a piece of stone of precisely the same size and form. The result
of this would be that the house would retain its primitive size,
shape, and outline, but it would finally have been converted
from a house of brick into a house of stone. Many other fossils
besides wood--such as shells, corals, sponges, &c.--are often
found silicified; and this may be regarded as the commonest form
of fossilisation by replacement. In other cases, however, though
the principle of the process is the same, the replacing substance
may be iron pyrites, oxide of iron, sulphur, malachite, magnesite,
talc, &c.; but it is rarely that the replacement with these minerals
is so perfect as to preserve the more delicate details of internal
structure.
CHAPTER II.
THE FOSSILIFEROUS ROCKS.
Fossils are found in rocks, though not universally or promiscuously;
and it is therefore necessary that the palæontologist should
possess some acquaintance with, at any rate, those rocks which
yield organic remains, and which are therefore said to be
"_fossiliferous_." In geological language, all the materials
which enter into the composition of the solid crust of the earth,
be their texture what it may--from the most impalpable mud to
the hardest granite--are termed "rocks;" and for our present
purpose we may divide these into two great groups. In the first
division are the _Igneous Rocks_--such as the lavas and ashes of
volcanoes--which are formed within the body of the earth itself,
and which owe their structure and origin to the action of heat.
The Igneous Rocks are formed primarily below the surface of the
earth, which they only reach as the result of volcanic action;
they are generally destitute of distinct "stratification," or
arrangement in successive layers; and they do not contain fossils,
except in the comparatively rare instances where volcanic ashes
have enveloped animals or plants which were living in the sea
or on the land in the immediate vicinity of the volcanic focus.
The second great division of rocks is that of the _Fossiliferous,
Aqueous_, or _Sedimentary_ Rocks. These are formed at the surface
of the earth, and, as implied by one of their names, are invariably
deposited in water. They are produced by vital or chemical action,
or are formed from the "sediment" produced by the disintegration
and reconstruction of previously existing rocks, without previous
solution; they mostly contain fossils; and they are arranged
in distinct layers or "strata." The so-called "aerial" rocks
which, like beds of blown sand, have been formed by the action
of the atmosphere, may also contain fossils; but they are not
of such importance as to require special notice here.
For all practical purposes, we may consider that the Aqueous
Rocks are the natural cemetery of the animals and plants of bygone
ages; and it is therefore essential that the palæontological
student should be acquainted with some of the principal facts as
to their physical characters, their minute structure and mode of
origin, their chief varieties, and their historical succession.
The Sedimentary or Fossiliferous Rocks form the greater portion of
that part of the earth's crust which is open to our examination, and
are distinguished by the fact that they are regularly "stratified" or
arranged in distinct and definite layers or "strata." These layers
may consist of a single material, as in a block of sandstone, or
they may consist of different materials. When examined on a large
scale, they are always found to consist of alternations of layers
of different mineral composition. We may examine any given area,
and find in it nothing but one kind of rock--sandstone, perhaps,
or limestone. In all cases, however, if we extend our examination
sufficiently far, we shall ultimately come upon different rocks;
and, as a general rule, the thickness of any particular set of
beds is comparatively small, so that different kinds of rock
alternate with one another in comparatively small spaces.
[Illustration: Fig. 4.--Sketch of Carboniferous strata at Kinghorn,
in Fife, showing stratified beds (limestone and shales) surmounted
by an unstratified mass of trap. (Original.)]
As regards the origin of the Sedimentary Rocks, they are for
the most part "derivative" rocks, being derived from the wear
and tear of pre-existent rocks. Sometimes, however, they owe
their origin to chemical or vital action, when they would more
properly be spoken of simply as Aqueous Rocks. As to their mode
of deposition, we are enabled to infer that the materials which
compose them have formerly been spread out by the action of water,
from what we see going on every day at the mouths of our great
rivers, and on a smaller scale wherever there is running water.
Every stream, where it runs into a lake or into the sea, carries
with it a burden of mud, sand, and rounded pebbles, derived from
the waste of the rocks which form its bed and banks. When these
materials cease to be impelled by the force of the moving water,
they sink to the bottom, the heaviest pebbles, of course, sinking
first, the smaller pebbles and sand next, and the finest mud
last. Ultimately, therefore, as might have been inferred upon
theoretical grounds, and as is proved by practical experience,
every lake becomes a receptacle for a series of stratified rocks
produced by the streams flowing into it. These deposits may vary
in different parts of the lake, according as one stream brought
down one kind of material and another stream contributed another
material; but in all cases the materials will bear ample evidence
that they were produced, sorted, and deposited by running water.
The finer beds of clay or sand will all be arranged in thicker or
thinner layers or laminæ; and if there are any beds of pebbles
these will all be rounded or smooth, just like the water-worn
pebbles of any brook-course. In all probability, also, we should
find in some of the beds the remains of fresh-water shells or
plants or other organisms which inhabited the lake at the time
these beds were being deposited.
In the same way large rivers--such as the Ganges or
Mississippi--deposit all the materials which they bring down
at their mouths, forming in this way their "deltas." Whenever
such a delta is cut through, either by man or by some channel of
the river altering its course, we find that it is composed of a
succession of horizontal layers or strata of sand or mud, varying
in mineral composition, in structure, or in grain, according to
the nature of the materials brought down by the river at different
periods. Such deltas, also, will contain the remains of animals
which inhabit the river, with fragments of the plants which grew
on its banks, or bones of the animals which lived in its basin.
Nor is this action confined, of course, to large rivers only,
though naturally most conspicuous in the greatest bodies of water.
On the contrary, all streams, of whatever size, are engaged in
the work of wearing down the dry land, and of transporting the
materials thus derived from higher to lower levels, never resting
in this work till they reach the sea.
[Illustration: Fig. 5.--Diagram to illustrate the formation of
sedimentary deposits at the point where a river debouches into
the sea.]
Lastly, the sea itself--irrespective of the materials delivered
into it by rivers--is constantly preparing fresh stratified deposits
by its own action. Upon every coast-line the sea is constantly
eating back into the land and reducing its component rocks to
form the shingle and sand which we see upon every shore. The
materials thus produced are not, however, lost, but are ultimately
deposited elsewhere in the form of new stratified accumulations,
in which are buried the remains of animals inhabiting the sea
at the time.
Whenever, then, we find anywhere in the interior of the land
any series of beds having these characters--composed, that is,
of distinct layers, the particles of which, both large and small,
show distinct traces of the wearing action of water--whenever and
wherever we find such rocks, we are justified in assuming that
they have been deposited by water in the manner above mentioned.
Either they were laid down in some former lake by the combined
action of the streams which flowed into it; or they were deposited
at the mouth of some ancient river, forming its delta; or they
were laid down at the bottom of the ocean. In the first two cases,
any fossils which the beds might contain would be the remains
of fresh-water or terrestrial organisms. In the last case, the
majority, at any rate, of the fossils would be the remains of
marine animals.
The term "formation" is employed by geologists to express "any
group of rocks which have some character in common, whether of
origin, age, or composition" (Lyell); so that we may speak of
stratified and unstratified formations, aqueous or igneous
formations, fresh-water or marine formations, and so on.
CHIEF DIVISIONS OF THE AQUEOUS ROCKS.
The Aqueous Rocks may be divided into two great sections, the
Mechanically-formed and the Chemically-formed, including under
the last head all rocks which owe their origin to vital action,
as well as those produced by ordinary chemical agencies.
[Illustration: Fig. 6.--Microscopic section of a calcareous breccia
in the Lower Silurian (Coniston Limestone) of Shap Wells,
Westmoreland. The fragments are all of small size, and consist of
angular pieces of transparent quartz, volcanic ashes, and limestone
embedded in a matrix of crystalline limestone. (Original.)]
A. MECHANICALLY-FORMED ROCKS.--These are all those Aqueous Rocks
of which we can obtain proofs that their particles have been
mechanically transported to their present situation. Thus, if
we examine a piece of _conglomerate_ or puddingstone, we find
it to be composed of a number of rounded pebbles embedded in an
enveloping matrix or paste, which is usually of a sandy nature,
but may be composed of carbonate of lime (when the rock is said to
be a "calcareous conglomerate"). The pebbles in all conglomerates
are worn and rounded by the action of water in motion, and thus
show that they have been subjected to much mechanical attrition,
whilst they have been mechanically transported for a greater
or less distance from the rock of which they originally formed
part. The analogue of the old conglomerates at the present day
is to be found in the great beds of shingle and gravel which
are formed by the action of the sea on every coast-line, and
which are composed of water-worn and well-rounded pebbles of
different sizes. A _breccia_ is a mechanically-formed rock, very
similar to a conglomerate, and consisting of larger or smaller
fragments of rock embedded in a common matrix. The fragments,
however, are in this case all more or less angular, and are not
worn or rounded. The fragments in breccias may be of large size,
or they may be comparatively small (fig. 6); and the matrix may
be composed of sand (arenaceous) or of carbonate of lime
(calcareous). In the case of an ordinary sandstone, again, we
have a rock which may be regarded as simply a very fine-grained
conglomerate or breccia, being composed of small grains of sand
(silica), sometimes rounded, sometimes more or less angular,
cemented together by some such substance as oxide of iron, silicate
of iron, or carbonate of lime. A sandstone, therefore, like a
conglomerate is a mechanically-formed rock, its component grams
being equally the result of mechanical attrition and having equally
been transported from a distance; and the same is true of the
ordinary sand of the sea-shore, which is nothing more than an
unconsolidated sandstone. Other so-called sands and sandstones,
though equally mechanical in their origin, are truly calcareous in
their nature, and are more or less entirely composed of carbonate
of lime. Of this kind are the shell-sand so common on our coasts,
and the coral-sand which is so largely formed in the neighbourhood
of coral-reefs. In these cases the rock is composed of fragments
of the skeletons of shellfish, and numerous other marine animals,
together, in many instances, with the remains of certain sea-weeds
(_Corallines_, _Nullipores_, &c,) which are endowed with the
power of secreting carbonate of lime from the sea-water. Lastly,
in certain rocks still finer in their texture than sandstones,
such as the various mud-rocks and shales, we can still recognise
a mechanical source and origin. If slices of any of these rocks
sufficiently thin to be transparent are examined under the
microscope, it will be found that they are composed of minute
grains of different sizes, which are all more or less worn and
rounded, and which clearly show, therefore, that they have been
subjected to mechanical attrition.
All the above-mentioned rocks, then, are _mechanically-formed_
rocks; and they are often spoken of as "Derivative Rocks," in
consequence of the fact that their particles can be shown to
have been mechanically _derived_ from other pre-existent rocks.
It follows from this that every bed of any mechanically-formed
rock is the measure and equivalent of a corresponding amount of
destruction of some older rock. It is not necessary to enter
here into a minute account of the subdivisions of these rocks, but
it may be mentioned that they may be divided into two principal
groups, according to their chemical composition. In the one group
we have the so-called _Arenaceous_ (Lat. _arena_, sand) or
_Siliceous_ Rocks, which are essentially composed of larger or
smaller grains of flint or silica. In this group are comprised
ordinary sand, the varieties of sandstone and grit, and most
conglomerates and breccias. We shall, however, afterwards see
that some siliceous rocks are of organic origin. In the second
group are the so-called _Argillaceous_ (Lat. _argilla_, clay)
Rocks, which contain a larger or smaller amount of clay or hydrated
silicate of alumina in their composition. Under this head come
clays, shales, marls, marl-slate, clay-slates, and most flags
and flagstones.
B. CHEMICALLY-FORMED ROCKS.--In this section are comprised all
those Aqueous or Sedimentary Rocks which have been formed by
chemical agencies. As many of these chemical agencies, however,
are exerted through the medium of living beings, whether animals
or plants, we get into this section a number of what may be called
"_organically-formed rocks_." These are of the greatest possible
importance to the palæontologist, as being to a greater or less
extent composed of the actual remains of animals or vegetables,
and it will therefore be necessary to consider their character
and structure in some detail.
By far the most important of the chemically-formed rocks are
the so-called _Calcareous Rocks_ (Lat. _calx_, lime), comprising
all those which contain a large proportion of carbonate of lime,
or are wholly composed of this substance. Carbonate of lime is
soluble in water holding a certain amount of carbonic acid gas
in solution; and it is, therefore, found in larger or smaller
quantity dissolved in all natural waters, both fresh and salt,
since these waters are always to some extent charged with the
above-mentioned solvent gas. A great number of aquatic animals,
however, together with some aquatic plants, are endowed with
the power of separating the lime thus held in solution in the
water, and of reducing it again to its solid condition. In this
way shell-fish, crustaceans, sea-urchins, corals, and an immense
number of other animals, are enabled to construct their skeletons;
whilst some plants form hard structures within their tissues
in a precisely similar manner. We do meet with some calcareous
deposits, such as the "stalactites" and "stalagmites" of caves,
the "calcareous tufa" and "travertine" of some hot springs, and
the spongy calcareous deposits of so-called "petrifying springs,"
which are purely chemical in their origin, and owe nothing to the
operation of living beings. Such deposits are formed simply by
the precipitation of carbonate of lime from water, in consequence
of the evaporation from the water of the carbonic acid gas which
formerly held the lime in solution; but, though sometimes forming
masses of considerable thickness and of geological importance,
they do not concern us here. Almost all the limestones which
occur in the series of the stratified rocks are, primarily at any
rate, of _organic_ origin, and have been, directly or indirectly,
produced by the action of certain lime-making animals or plants,
or both combined. The presumption as to all the calcareous rocks,
which cannot be clearly shown to have been otherwise produced,
is that they are thus organically formed; and in many cases this
presumption can be readily reduced to a certainty. There are
many varieties of the calcareous rocks, but the following are
those which are of the greatest importance:--
_Chalk_ is a calcareous rock of a generally soft and pulverulent
texture, and with an earthy fracture. It varies in its purity,
being sometimes almost wholly composed of carbonate of lime,
and at other times more or less intermixed with foreign matter.
Though usually soft and readily reducible to powder, chalk is
occasionally, as in the north of Ireland, tolerably hard and
compact; but it never assumes the crystalline aspect and stony
density of limestone, except it be in immediate contact with
some mass of igneous rock. By means of the microscope, the true
nature and mode of formation of chalk can be determined with
the greatest ease. In the case of the harder varieties, the
examination can be conducted by means of slices ground down to
a thinness sufficient to render them transparent; but in the
softer kinds the rock must be disintegrated under water, and the
_débris_ examined microscopically. When investigated by either
of these methods, chalk is found to be a genuine organic rock,
being composed of the shells or hard parts of innumerable marine
animals of different kinds, some entire, some fragmentary, cemented
together by a matrix of very finely granular carbonate of lime.
Foremost amongst the animal remains which so largely compose
chalk are the shells of the minute creatures which will be
subsequently spoken of under the name of _Foraminifera_ (fig.
7), and which, in spite of their microscopic dimensions, play a
more important part in the process of lime-making than perhaps
any other of the larger inhabitants of the ocean.
[Illustration: Fig. 7.--Section of Gravesend Chalk, examined
by transmitted light and highly magnified. Besides the entire
shells of _Globigerina_, _Rotalia_, and _Textularia_, numerous
detached chambers of _Globigerina_ are seen. (Original.)]
As chalk is found in beds of hundreds of feet in thickness,
and of great purity, there was long felt much difficulty
in satisfactorily accounting for its mode of formation and origin.
By the researches of Carpenter, Wyville Thomson,
Huxley, Wallich, and others, it has, however, been shown
that there is now forming, in the profound depths of our
great oceans, a deposit which is in all essential respects
identical with chalk, and which is
generally known as the "Atlantic ooze," from its having been
first discovered in that sea. This ooze is found at great
depths (5000 to over 15,000 feet) in both the Atlantic and
Pacific, covering enormously large areas of the sea-bottom,
and it presents itself as a whitish-brown, sticky, impalpable mud,
very like greyish chalk when dried. Chemical examination
shows that the ooze is composed almost wholly of carbonate of
lime, and microscopical examination proves it to be of organic
origin, and to be made up of the remains of living beings.
The principal forms of these belong to the _Foraminifera_, and
the commonest of these are the irregularly-chambered shells of
_Globigerina_, absolutely indistinguishable from the
_Globigerinoe_ which are so largely present in the chalk (fig. 8).
Along with these occur fragments of the skeletons of other larger
creatures, and a certain proportion of the flinty cases of minute
animal and vegetable organisms (_Polycystina_ and _Diatoms_).
Though many of the minute animals, the hard parts of which form
the ooze, undoubtedly live at or near the surface of the sea,
others, probably, really live near the bottom; and the ooze
itself forms a congenial home for numerous sponges, sea-lilies,
and other marine animals which flourish at great
depths in the sea. There is thus established an intimate
and most interesting parallelism between the chalk and
the ooze of modern oceans. Both are formed essentially in
the same way, and the latter only requires consolidation to
become actually converted into chalk. Both are fundamentally
organic deposits, apparently requiring a great depth of water
for their accumulation, and mainly composed of the remains of
_Foraminifera_, together with the entire or broken skeletons
of other marine animals of greater dimensions. It is to be
remembered, however, that the ooze, though strictly
representative of the chalk, cannot be said in any proper sense
to be actually _identical_ with the formation so called by
geologists. A great lapse of time separates the two, and though
composed of the remains of representative classes or groups of
animals, it is only in the case of the lowly-organised
_Globigerinoe_, and of some other organisms of little higher
grade, that we find absolutely the same kinds or species of
animals in both.
[Illustration: Fig. 8.--Organisms in the Atlantic Ooze, chiefly
_Foraminifera_ (_Globigerina_ and _Textularia_), with _Polycystina_
and sponge-spicules; highly magnified. (Original.)]
[Illustration: Fig. 9.--Slab of Crinoidal marble, from the
Carboniferous limestone of Dent, in Yorkshire, of the natural
size. The polished surface intersects the columns of the Crinoids
at different angles, and thus gives rise to varying appearances.
(Original.)]
_Limestone_, like chalk, is composed of carbonate of lime, sometimes
almost pure, but more commonly with a greater or less intermixture
of some foreign material, such as alumina or silica. The varieties
of limestone are almost innumerable, but the great majority can
be clearly proved to agree with chalk in being essentially of
organic origin, and in being more or less largely composed of the
remains of living beings. In many instances the organic remains
which compose limestone are so large as to be readily visible to
the naked eye, and the rock is at once seen to be nothing more
than an agglomeration of the skeletons, generally fragmentary, of
certain marine animals, cemented together by a matrix of carbonate
of lime. This is the case, for example, with the so-called "Crinoidal
Limestones" and "Encrinital Marbles" with which the geologist
is so familiar, especially as occurring in great beds amongst
the older formations of the earth's crust. These are seen, on
weathered or broken surfaces, or still better in polished slabs
(fig. 9), to be composed more or less exclusively of the broken
stems and detached plates of sea-lilies (_Crinoids_). Similarly,
other limestones are composed almost entirely of the skeletons of
corals; and such old coralline limestones can readily be paralleled
by formations which we can find in actual course of production
at the present day. We only need to transport ourselves to the
islands of the Pacific, to the West Indies, or to the Indian
Ocean, to find great masses of lime formed similarly by living
corals, and well known to everyone under the name of "coral-reefs."
Such reefs are often of vast extent, both superficially and in
vertical thickness, and they fully equal in this respect any of
the coralline limestones of bygone ages. Again, we find other
limestones--such as the celebrated "Nummulitic Limestone" (fig. 10),
which sometimes attains a thickness of some thousands of feet--which
are almost entirely made up of the shells of _Foraminifera_. In
the case of the "Nummulitic Limestone," just mentioned, these
shells are of large size, varying from the size of a split pea
up to that of a florin. There are, however, as we shall see,
many other limestones, which are likewise largely made up of
_Foraminifera_, but in which the shells are very much more minute,
and would hardly be seen at all without the microscope.
[Illustration: Fig. 10.--Piece of Nummulitic Limestone from the
Great Pyramid. Of the natural size. (Original.)]
We may, in fact, consider that the great agents in the production
of limestones in past ages have been animals belonging to the
_Crinoids_, the _Corals_, and the _Foraminifera_. At the present
day, the Crinoids have been nearly extinguished, and the few known
survivors seem to have retired to great depths in the ocean; but
the two latter still actively carry on the work of lime-making,
the former being very largely helped in their operations by certain
lime-producing marine plants (_Nullipores_ and _Corallines_). We
have to remember, however, that though the limestones, both ancient
and modern, that we have just spoken of, are truly organic, they
are not necessarily formed out of the remains of animals which
actually lived on the precise spot where we now find the limestone
itself. We may find a crinoidal limestone, which we can show to
have been actually formed by the successive growth of generations
of sea-lilies _in place_; but we shall find many others in which
the rock is made up of innumerable fragments of the skeletons
of these creatures, which have been clearly worn and rubbed by
the sea-waves, and which have been mechanically transported to
their present site. In the same way, a limestone may be shown
to have been an actual coral-reef, by the fact that we find in
it great masses of coral, growing in their natural position,
and exhibiting plain proofs that they were simply quietly buried
by the calcareous sediment as they grew; but other limestones
may contain only numerous rolled and water-worn fragments of
corals. This is precisely paralleled by what we can observe in
our existing coral-reefs. Parts of the modern coral-islands and
coral-reefs are really made up of corals, dead or alive, which
actually grew on the spot where we now find them; but other parts
are composed of a limestone-rock ("coral-rock"), or of a loose
sand ("coral-sand"), which is organic in the sense that it is
composed of lime formed by living beings, but which, in truth,
is composed of fragments of the skeletons of these living beings,
mechanically transported and heaped together by the sea. To take
another example nearer home, we may find great accumulations of
calcareous matter formed _in place_, by the growth of shell-fish,
such as oysters or mussels; but we can also find equally great
accumulations on many of our shores in the form of "shell-sand,"
which is equally composed of the shells of molluscs, but which is
formed by the trituration of these shells by the mechanical power
of the sea-waves. We thus see that though all these limestones are
primarily organic, they not uncommonly become "mechanically-formed"
rocks in a secondary sense, the materials of which they are composed
being formed by living beings, but having been mechanically
transported to the place where we now find them.
[Illustration: Fig. 11.--Section of Carboniferous Limestone from
Spergen Hill, Indiana, U.S., showing numerous large-sized
_Foraminifera_ (_Endothyra_) and a few oolitic grains; magnified.
(Original.)]
[Illustration: Fig 12.--Section of Coniston Limestone (Lower
Silurian) from Keisler, Westmoreland; magnified. The matrix is
very coarsely crystalline, and the included organic remains are
chiefly stems of Crinoids. (Original.)]
Many limestones, as we have seen, are composed of large and
conspicuous organic remains, such as strike the eye at once.
Many others, however, which at first sight appear compact, more
or less crystalline, and nearly devoid of traces of life, are
found, when properly examined, to be also composed of the remains
of various organisms. All the commoner limestones, in fact, from
the Lower Silurian period onwards, can be easily proved to be
thus _organic_ rocks, if we investigate weathered or polished
surfaces with a lens, or, still better, if we cut thin slices
of the rock and grind these down till they are transparent. When
thus examined, the rock is usually found to be composed of
innumerable entire or fragmentary fossils, cemented together
by a granular or crystalline matrix of carbonate of lime (figs.
11 and 12). When the matrix is granular, the rock is precisely
similar to chalk, except that it is harder and less earthy in
texture, whilst the fossils are only occasionally referable to
the _Foraminifera_. In other cases, the matrix is more or less
crystalline, and when this crystallisation has been carried to
a great extent, the original organic nature of the rock may be
greatly or completely obscured thereby. Thus, in limestones which
have been greatly altered or "metamorphosed" by the combined
action of heat and pressure, all traces of organic remains become
annihilated, and the rock becomes completely crystalline throughout.
This, for example, is the case with the ordinary white "statuary
marble," slices of which exhibit under the microscope nothing but
an aggregate of beautifully transparent crystals of carbonate
of lime, without the smallest traces of fossils. There are also
other cases, where the limestone is not necessarily highly
crystalline, and where no metamorphic action in the strict sense
has taken place, in which, nevertheless, the microscope fails
to reveal any evidence that the rock is organic. Such cases are
somewhat obscure, and doubtless depend on different causes in
different instances; but they do not affect the important
generalisation that limestones are fundamentally the product
of the operation of living beings. This fact remains certain;
and when we consider the vast superficial extent occupied by
calcareous deposits, and the enormous collective thickness of
these, the mind cannot fail to be impressed with the immensity of
the period demanded for the formation of these by the agency of
such humble and often microscopic creatures as Corals, Sea-lilies,
Foraminifers, and Shell-fish.
Amongst the numerous varieties of limestone, a few are of such
interest as to deserve a brief notice. _Magnesian limestone_
or _dolomite_, differs from ordinary limestone in containing
a certain proportion of carbonate of magnesia along with the
carbonate of lime. The typical dolomites contain a large proportion
of carbonate of magnesia, and are highly crystalline. The ordinary
magnesian limestones (such as those of Durham in the Permian
series, and the Guelph Limestones of North America in the Silurian
series) are generally of a yellowish, buff, or brown colour,
with a crystalline or pearly aspect, effervescing with acid much
less freely than ordinary limestone, exhibiting numerous cavities
from which fossils have been dissolved out, and often assuming
the most varied and singular forms in consequence of what is
called "concretionary action." Examination with the microscope
shows that these limestones are composed of an aggregate of minute
but perfectly distinct crystals, but that minute organisms of
different kinds, or fragments of larger fossils, are often present
as well. Other magnesian limestones, again, exhibit no striking
external peculiarities by which the presence of magnesia would be
readily recognised, and though the base of the rock is crystalline,
they are replete with the remains of organised beings. Thus many
of the magnesian limestones of the Carboniferous series of the
North of England are very like ordinary limestone to look at,
though effervescing less freely with acids, and the microscope
proves them to be charged with the remains of _Foraminifera_
and other minute organisms.
_Marbles_ are of various kinds, all limestones which are sufficiently
hard and compact to take a high polish going by this name. Statuary
marble, and most of the celebrated foreign marbles, are "metamorphic"
rocks, of a highly crystalline nature, and having all traces
of their primitive organic structure obliterated. Many other
marbles, however, differ from ordinary limestone simply in the
matter of density. Thus, many marbles (such as Derbyshire marble)
are simply "crinoidal limestones" (fig. 9); whilst various other
British marbles exhibit innumerable organic remains under the
microscope. Black marbles owe their colour to the presence of
very minute particles of carbonaceous matter, in some cases at
any rate; and they may either be metamorphic, or they may be
charged with minute fossils such as _Foraminifera_ (_e.g._, the
black limestones of Ireland, and the black marble of Dent, in
Yorkshire).
[Illustration: Fig. 13.--Slice of oolitic limestone from the
Jurassic series (Coral Rag) of Weymouth; magnified. (Original.)]
"_Oolitic_" _limestones_, or "_oolites_," as they are often called,
are of interest both to the palæontologist and geologist. The
peculiar structure to which they owe their name is that the rock
is more or less entirely composed of spheroidal or oval grains,
which vary in size from the head of a small pin or less up to
the size of a pea, and which may be in almost immediate contact
with one another, or may be cemented together by a more or less
abundant calcareous matrix. When the grains are pretty nearly
spherical and are in tolerably close contact, the rock looks very
like the roe of a fish, and the name of "oolite" or "egg-stone"
is in allusion to this. When the grains are of the size of peas
or upwards, the rock is often called a "pisolite" (Lat. _pisum_,
a pea). Limestones having this peculiar structure are especially
abundant in the Jurassic formation, which is often called the
"Oolitic series" for this reason; but essentially similar limestones
occur not uncommonly in the Silurian, Devonian, and Carboniferous
formations, and, indeed, in almost all rock-groups in which
limestones are largely developed. Whatever may be the age of
the formation in which they occur, and whatever may be the size
of their component "eggs," the structure of oolitic limestones
is fundamentally the same. All the ordinary oolitic limestones,
namely, consist of little spherical or ovoid "concretions," as
they are termed, cemented together by a larger or smaller amount
of crystalline carbonate of lime, together, in many instances,
with numerous organic remains of different kinds (fig. 13). When
examined in polished slabs, or in thin sections prepared for the
microscope, each of these little concretions is seen to consist
of numerous concentric coats of carbonate of lime, which sometimes
simply surround an imaginary centre, but which, more commonly,
have been successively deposited round some foreign body, such as
a little crystal of quartz, a cluster of sand-grains, or a minute
shell. In other cases, as in some of the beds of the Carboniferous
limestone in the North of England, where the limestone is highly
"arenaceous," there is a modification of the oolitic structure.
Microscopic sections of these sandy limestones (fig. 14) show
numerous generally angular or oval grains of silica or flint,
each of which is commonly surrounded by a thin coating of carbonate
of lime, or sometimes by several such coats, the whole being
cemented together along with the shells of _Foraminifera_ and
other minute fossils by a matrix of crystalline calcite. As compared
with typical oolites, the concretions in these limestones are
usually much more irregular in shape, often lengthened out and
almost cylindrical, at other times angular, the central nucleus
being of large size, and the surrounding envelope of lime being
very thin, and often exhibiting no concentric structure. In both
these and the ordinary oolites, the structure is fundamentally
the same. Both have been formed in a sea, probably of no great
depth, the waters of which were charged with carbonate of lime
in solution, whilst the bottom was formed of sand intermixed with
minute shells and fragments of the skeletons of larger marine
animals. The excess of lime in the sea-water was precipitated
round the sand-grams, or round the smaller shells, as so many
nuclei, and this precipitation must often have taken place time
after time, so as to give rise to the concentric structure so
characteristic of oolitic concretions. Finally, the oolitic grains
thus produced were cemented together by a further precipitation
of crystalline carbonate of lime from the waters of the ocean.
[Illustration: Fig. 14.--Slice of arenaceous and oolitic limestone
from the Carboniferous series of Shap, Westmoreland; magnified.
The section also exhibit _Foraminifera_ and other minute fossils.
(Original.)]
_Phosphate of Lime_ is another lime-salt, which is of interest to
the palæontologist. It does not occur largely in the stratified
series, but it is found in considerable beds [4] in the Laurentian
formation, and less abundantly in some later rock-groups, whilst
it occurs abundantly in the form of nodules in parts of the
Cretaceous (Upper Greensand) and Tertiary deposits. Phosphate
of lime forms the larger proportion of the earthy matters of the
bones of Vertebrate animals, and also occurs in less amount in the
skeletons of certain of the Invertebrates (_e.g._, _Crustacea_). It
is, indeed, perhaps more distinctively than carbonate of lime, an
organic compound; and though the formation of many known deposits
of phosphate of lime cannot be positively shown to be connected
with the previous operation of living beings, there is room for
doubt whether this salt is not in reality always primarily a
product of vital action. The phosphatic nodules of the Upper
Greensand are erroneously called "coprolites," from the belief
originally entertained that they were the droppings or fossilised
excrements of extinct animals; and though this is not the case,
there can be little doubt but that the phosphate of lime which
they contain is in this instance of organic origin.[5] It appears,
in fact, that decaying animal matter has a singular power of
determining the precipitation around it of mineral salts dissolved
in water. Thus, when any animal bodies are undergoing decay at the
bottom of the sea, they have a tendency to cause the precipitation
from the surrounding water of any mineral matters which may be
dissolved in it; and the organic body thus becomes a centre round
which the mineral matters in question are deposited in the form
of a "concretion" or "nodule." The phosphatic nodules in question
were formed in a sea in which phosphate of lime, derived from the
destruction of animal skeletons, was held largely in solution;
and a precipitation of it took place round any body, such as a
decaying animal substance, which happened to be lying on the
sea-bottom, and which offered itself as a favourable nucleus. In
the same way we may explain the formation of the calcareous nodules,
known as "septaria" or "cement stones," which occur so commonly in
the London Clay and Kimmeridge Clay, and in which the principal
ingredient is carbonate of lime. A similar origin is to be ascribed
to the nodules of clay iron-stone (impure carbonate of iron) which
occur so abundantly in the shales of the Carboniferous series and
in other argillaceous deposits; and a parallel modern example
is to be found in the nodules of manganese, which were found
by Sir Wyville Thomson, in the Challenger, to be so numerously
scattered over the floor of the Pacific at great depths. In
accordance with this mode of origin, it is exceedingly common
to find in the centre of all these nodules, both old and new,
some organic body, such as a bone, a shell, or a tooth, which
acted as the original nucleus of precipitation, and was thus
preserved in a shroud of mineral matter. Many nodules, it is
true, show no such nucleus; but it has been affirmed that all of
them can be shown, by appropriate microscopical investigation,
to have been formed round an original organic body to begin with
(Hawkins Johnson).
[Footnote 4: Apart from the occurrence or phosphate of lime in
actual beds in the stratified rocks, as in the Laurentian and
Silurian series, this salt may also occur disseminated through
the rock, when it can only be detected by chemical analysis. It
is interesting to note that Dr Hicks has recently proved the
occurrence of phosphate of lime in this disseminated form in
rocks as old as the Cambrian, and that in quantity quite equal to
what is generally found to be present in the later fossiliferous
rocks. This affords a chemical proof that animal life flourished
abundantly in the Cambrian seas.]
[Footnote 5: It has been maintained, indeed, that the phosphatic
nodules so largely worked for agricultural purposes, are in
themselves actual organic bodies or true fossils. In a few cases
this admits of demonstration, as it can be shown that the nodule
is simply an organism (such as a sponge) infiltrated with phosphate
of lime (Sollas); but there are many other cases in which no actual
structure has yet been shown to exist, and as to the true origin
of which it would be hazardous to offer a positive opinion.]
The last lime-salt which need be mentioned is _gypsum_, or _sulphate
of lime_. This substance, apart from other modes of occurrence, is
not uncommonly found interstratified with the ordinary sedimentary
rocks, in the form of more or less irregular beds; and in these
cases it has a palæontological importance, as occasionally yielding
well-preserved fossils. Whilst its exact mode of origin is uncertain,
it cannot be regarded as in itself an organic rock, though clearly
the product of chemical action. To look at, it is usually a whitish
or yellowish-white rock, as coarsely crystalline as loaf-sugar,
or more so; and the microscope shows it to be composed entirely
of crystals of sulphate of lime.
We have seen that the _calcareous_ or lime-containing rocks are
the most important of the group of organic deposits; whilst the
_siliceous_ or flint-containing rocks may be regarded as the
most important, most typical, and most generally distributed
of the mechanically-formed rocks. We have, however, now briefly
to consider certain deposits which are more or less completely
formed of flint; but which, nevertheless, are essentially organic
in their origin.
Flint or silex, hard and intractable as it is, is nevertheless
capable of solution in water to a certain extent, and even of
assuming, under certain circumstances, a gelatinous or viscous
condition. Hence, some hot-springs are impregnated with silica
to a considerable extent; it is present in small quantity in
sea-water; and there is reason to believe that a minute proportion
must very generally be present in all bodies of fresh water as
well. It is from this silica dissolved in the water that many
animals and some plants are enabled to construct for themselves
flinty skeletons; and we find that these animals and plants are and
have been sufficiently numerous to give rise to very considerable
deposits of siliceous matter by the mere accumulation of their
skeletons. Amongst the animals which require special mention in
this connection are the microscopic organisms which are known to
the naturalist as _Polycystina_. These little creatures are of the
lowest possible grade of organisation, very closely related to the
animals which we have previously spoken of as _Foraminifera_, but
differing in the fact that they secrete a shell or skeleton composed
of flint instead of lime. The _Polycystina_ occur abundantly in
our present seas; and their shells are present in some numbers
in the ooze which is found at great depths in the Atlantic and
Pacific oceans, being easily recognised by their exquisite shape,
their glassy transparency, the general presence of longer or
shorter spines, and the sieve-like perforations in the walls.
Both in Barbadoes and in the Nicobar islands occur geological
formations which are composed of the flinty skeletons of these
microscopic animals; the deposit in the former locality attaining
a great thickness, and having been long known to workers with
the microscope under the name of "Barbadoes earth" (fig. 15).
[Illustration: Fig. 15.--Shells of _Polycystina_ from "Barbadoes
earth;" greatly magnified. (Original.)]
[Illustration: Fig. 16.--Cases of Diatoms in the Richmond "Infusorial
earth;" highly magnified. (Original.)]
In addition to flint-producing animals, we have also the great
group of fresh-water and marine microscopic plants known as
_Diatoms_, which likewise secrete a siliceous skeleton, often of
great beauty. The skeletons of Diatoms are found abundantly at the
present day in lake-deposits, guano, the silt of estuaries, and in
the mud which covers many parts of the sea-bottom; they have been
detected in strata of great age; and in spite of their microscopic
dimensions, they have not uncommonly accumulated to form deposits
of great thickness, and of considerable superficial extent. Thus
the celebrated deposit of "tripoli" ("Polir-schiefer") of Bohemia,
largely worked as polishing-powder, is composed wholly, or almost
wholly, of the flinty cases of Diatoms, of which it is calculated
that no less than forty-one thousand millions go to make up a
single cubic inch of the stone. Another celebrated deposit is
the so-called "Infusorial earth" of Richmond in Virginia, where
there is a stratum in places thirty feet thick, composed almost
entirely of the microscopic shells of Diatoms.
Nodules or layers of _flint_, or the impure variety of flint
known as _chert_, are found in limestones of almost all ages
from the Silurian upwards; but they are especially abundant in
the chalk. When these flints are examined in thin and transparent
slices under the microscope, or in polished sections, they are
found to contain an abundance of minute organic bodies--such as
_Foraminifera_, sponge-spicules, &c.--embedded in a siliceous
basis. In many instances the flint contains larger organisms--such
as a Sponge or a Sea-urchin. As the flint has completely surrounded
and infiltrated the fossils which it contains, it is obvious
that it must have been deposited from sea-water in a gelatinous
condition, and subsequently have hardened. That silica is capable
of assuming this viscous and soluble condition is known; and
the formation of flint may therefore be regarded as due to the
separation of silica from the sea-water and its deposition round
some organic body in a state of chemical change or decay, just as
nodules of phosphate of lime or carbonate of iron are produced.
The existence of numerous organic bodies in flint has long been
known; but it should be added that a recent observer (Mr Hawkins
Johnson) asserts that the existence of an organic structure can
be demonstrated by suitable methods of treatment, even in the
actual matrix or basis of the flint.[6]
[Footnote 6: It has been asserted that the flints of the chalk
are merely fossil sponges. No explanation of the origin of flint,
however, can be satisfactory, unless it embraces the origin of
chert in almost all great limestones from the Silurian upwards,
as well as the common phenomenon of the silicification of organic
bodies (such as corals and shells) which are known with certainty
to have been originally calcareous.]
In addition to deposits formed of flint itself, there are other
siliceous deposits formed by certain _silicates_, and also of
organic origin. It has been shown, namely--by observations carried
out in our present seas--that the shells of _Foraminifera_ are
liable to become completely infiltrated by silicates (such as
"glauconite," or silicate of iron and potash). Should the actual
calcareous shell become dissolved away subsequent to this
infiltration--as is also liable to occur--then, in place of the
shells of the _Foraminifera_, we get a corresponding number of
green sandy grains of glauconite, each grain being the _cast_
of a single shell. It has thus been shown that the green sand
found covering the sea-bottom in certain localities (as found by
the Challenger expedition along the line of the Agulhas current)
is really organic, and is composed of casts of the shells of
_Foraminifera_. Long before these observations had been made,
it had been shown by Professor Ehrenberg that the green sands of
various geological formations are composed mainly of the internal
casts of the shells of _Foraminifera_, and we have thus another
and a very interesting example how rock-deposits of considerable
extent and of geological importance can be built up by the operation
of the minutest living beings.
As regards _argillaceous_ deposits, containing _alumina_ or _clay_
as their essential ingredient, it cannot be said that any of
these have been actually shown to be of organic origin. A recent
observation by Sir Wyville Thomson would, however, render it not
improbable that some of the great argillaceous accumulations of
past geological periods may be really organic. This distinguished
observer, during the cruise of the Challenger, showed that the
calcareous ooze which has been already spoken of as covering
large areas of the floor of the Atlantic and Pacific at great
depths, and which consists almost wholly of the shells of
_Foraminifera_, gave place at still greater depths to a red ooze
consisting of impalpable clayey mud, coloured by oxide of iron,
and devoid of traces of organic bodies. As the existence of this
widely-diffused red ooze, in mid-ocean, and at such great depths,
cannot be explained on the supposition that it is a sediment
brought down into the sea by rivers, Sir Wyville Thomson came to
the conclusion that it was probably formed by the action of the
sea-water upon the shells of _Foraminifera_. These shells, though
mainly consisting of lime, also contain a certain proportion of
alumina, the former being soluble in the carbonic acid dissolved
in the sea-water, whilst the latter is insoluble. There would
further appear to be grounds for believing that the solvent power
of the sea-water over lime is considerably increased at great
depths. If, therefore, we suppose the shells of _Foraminifera_
to be in course of deposition over the floor of the Pacific, at
certain depths they would remain unchanged, and would accumulate
to form a calcareous ooze; but at greater depths they would be
acted upon by the water, their lime would be dissolved out, their
form would disappear, and we should simply have left the small
amount of alumina which they previously contained. In process
of time this alumina would accumulate to form a bed of clay; and
as this clay had been directly derived from the decomposition
of the shells of animals, it would be fairly entitled to be
considered an organic deposit. Though not finally established,
the hypothesis of Sir Wyville Thomson on this subject is of the
greatest interest to the palæontologist, as possibly serving to
explain the occurrence, especially in the older formations, of
great deposits of argillaceous matter which are entirely destitute
of traces of life.
It only remains, in this connection, to shortly consider the
rock-deposits in which _carbon_ is found to be present in greater
or less quantity. In the great majority of cases where rocks
are found to contain carbon or carbonaceous matter, it can be
stated with certainty that this substance is of organic origin,
though it is not necessarily derived from vegetables. Carbon
derived from the decomposition of animal bodies is not uncommon;
though it never occurs in such quantity from this source as it
may do when it is derived from plants. Thus, many limestones are
more or less highly bituminous; the celebrated siliceous flags
or so-called "bituminous schists" of Caithness are impregnated
with oily matter apparently derived from the decomposition of the
numerous fishes embedded in them; Silurian shales containing
Graptolites, but destitute of plants, are not uncommonly
"anthracitic," and contain a small percentage of carbon derived
from the decay of these zoophytes; whilst the petroleum so largely
worked in North America has not improbably an animal origin.
That the fatty compounds present in animal bodies should more or
less extensively impregnate fossiliferous rock-masses, is only
what might be expected; but the great bulk of the carbon which
exists stored up in the earth's crust is derived from plants;
and the form in which it principally presents itself is that of
coal. We shall have to speak again, and at greater length, of
coal, and it is sufficient to say here that all the true coals,
anthracites, and lignites, are of organic origin, and consist
principally of the remains of plants in a more or less altered
condition. The bituminous shales which are found so commonly
associated with beds of coal also derive their carbon primarily
from plants; and the same is certainly, or probably, the case
with similar shales which are known to occur in formations younger
than the Carboniferous. Lastly, carbon may occur as a conspicuous
constituent of rock-masses in the form of _graphite_ or _black-lead_.
In this form, it occurs in the shape of detached scales, of veins
or strings, or sometimes of regular layers;[7] and there can be
little doubt that in many instances it has an organic origin,
though this is not capable of direct proof. When present, at any
rate, in quantity, and in the form of layers associated with
stratified rocks, as is often the case in the Laurentian formation,
there can be little hesitation in regarding it as of vegetable
origin, and as an altered coal.
[Footnote 7: In the Huronian formation at Steel River, on the
north shore of Lake Superior, there exists a bed of carbonaceous
matter which is regularly interstratified with the surrounding
rocks, and has a thickness of from 30 to 40 feet. This bed is
shown by chemical analysis to contain about 50 per cent of carbon,
partly in the form of graphite, partly in the form of anthracite;
and there can be little doubt but that it is really a stratum
of "metamorphic" coal.]
CHAPTER III.
CHRONOLOGICAL SUCCESSION OF THE FOSSILIFEROUS ROCKS.
The physical geologist, who deals with rocks simply as rocks,
and who does not necessarily trouble himself about what fossils
they may contain, finds that the stratified deposits which form
so large a portion of the visible part of the earth's crust are
not promiscuously heaped together, but that they have a certain
definite arrangement. In each country that he examines, he finds
that certain groups of strata lie above certain other groups;
and in comparing different countries with one another, he finds
that, in the main, the same groups of rocks are always found in the
same relative position to each other. It is possible, therefore,
for the physical geologist to arrange the known stratified rocks
into a successive series of groups, or "formations," having a
certain definite order. The establishment of this physical order
amongst the rocks introduces, however, at once the element of
_time_, and the physical succession of the strata can be converted
directly into a historical or _chronological_ succession. This
is obvious, when we reflect that any bed or set of beds of
sedimentary origin is clearly and necessarily younger than all
the strata upon which it rests, and older than all those by which
it is surmounted.
It is possible, then, by an appeal to the rocks alone, to determine
in each country the general physical succession of the strata,
and this "stratigraphical" arrangement, when once determined,
gives us the _relative_ ages of the successive groups. The task,
however, of the physical geologist in this matter is immensely
lightened when he calls in palæontology to his aid, and studies
the evidence of the fossils embedded in the rocks. Not only is
it thus much easier to determine the order of succession of the
strata in any given region, but it becomes now for the first time
possible to compare, with certainty and precision, the order of
succession in one region with that which exists in other regions
far distant. The value of fossils as tests of the relative ages
of the sedimentary rocks depends on the fact that they are not
indefinitely or promiscuously scattered through the crust of the
earth,--as it is conceivable that they might be. On the contrary,
the first and most firmly established law of Palæontology is, that
_particular kinds of fossils are confined to particular rocks_,
and _particular groups of fossils are confined to particular
groups of rocks_. Fossils, then, are distinctive of the rocks in
which they are found--much more distinctive, in fact, than the
mere mineral character of the rock can be, for _that_ commonly
changes as a formation is traced from one region to another,
whilst the fossils remain unaltered. It would therefore be quite
possible for the palæontologist, by an appeal to the fossils
alone, to arrange the series of sedimentary deposits into a pile
of strata having a certain definite order. Not only would this
be possible, but it would be found--if sufficient knowledge had
been brought to bear on both sides--that the palæontological
arrangement of the strata would coincide in its details with the
stratigraphical or physical arrangement.
Happily for science, there is no such division between the
palæontologist and the physical geologist as here supposed; but
by the combined researches of the two, it has been found possible
to divide the entire series of stratified deposits into a number
of definite _rock-groups_ or _formations_, which have a recognised
order of succession, and each of which is characterised by possessing
an assemblage of organic remains which do not occur in association
in any other formation. Such an _assemblage of fossils_,
characteristic of any given formation, represents the _life_ of
the particular _period_ in which the formation was deposited.
In this way the past history of the earth becomes divided into a
series of successive _life-periods_, each of which corresponds
with the deposition of a particular _formation_ or group of strata.
Whilst particular _assemblages_ of organic forms characterise
particular _groups_ of rocks, it may be further said that, in
a general way, each subdivision of each formation has its own
peculiar fossils, by which it may be recognised by a skilled
worker in Palæontology. Whenever, for instance, we meet with
examples of the fossils which are known as _Graptolites_, we may
be sure that we are dealing with _Silurian_ rocks (leaving out
of sight one or two forms doubtfully referred to this family).
We may, however, go much farther than this with perfect safety. If
the Graptolites belong to certain genera, we may be quite certain
that we are dealing with _Lower_ Silurian rocks. Furthermore, if
certain special forms are present, we may be even able to say to
what exact subdivision of the Lower Silurian series they belong.
As regards particular fossils, however, or even particular classes
of fossils, conclusions of this nature require to be accompanied
by a tacit but well-understood reservation. So far as our present
observation goes, none of the undoubted Graptolites have ever been
discovered in rocks later than those known upon other grounds
to be Silurian; but it is possible that they might at any time be
detected in younger deposits. Similarly, the species and genera
which we now regard as characteristic of the Lower Silurian, may
at some future time be found to have survived into the Upper
Silurian period. We should not forget, therefore, in determining
the age of strata by palæontological evidence, that we are always
reasoning upon generalisations which are the result of experience
alone, and which are liable to be vitiated by further and additional
discoveries.
When the palæontological evidence as to the age of any given
set of strata is corroborated by the physical evidence, our
conclusions may be regarded as almost certain; but there are
certain limitations and fallacies in the palæontological method
of inquiry which deserve a passing mention. In the first place,
fossils are not always present in the stratified rocks; many
aqueous rocks are unfossiliferous, through a thickness of hundreds
or even thousands of feet of little-altered sediments; and even
amongst beds which do contain fossils, we often meet with strata
of many feet or yards in thickness which are wholly destitute
of any traces of fossils. There are, therefore, to begin with,
many cases in which there is no palæontological evidence extant
or available as to the age of a given group of strata. In the
second place, palæontological observers in different parts of
the world are liable to give different names to the same fossil,
and in all parts of the world they are occasionally liable to
group together different fossils under the same title. Both these
sources of fallacy require to be guarded against in reasoning as
to the age of strata from their fossil remains. Thirdly, the mere
fact of fossils being found in beds which are known by physical
evidence to be of different ages, has commonly led palæontologists
to describe them as different species. Thus, the same fossil,
occurring in successive groups of strata, and with the merely
trivial and varietal differences due to the gradual change in its
environment, has been repeatedly described as a distinct species,
with a distinct name, in every bed in which it was found. We know,
however, that many fossils range vertically through many groups
of strata, and there are some which even pass through several
formations. The mere fact of a difference of physical position
ought never to be taken into account at all in considering and
determining the true affinities of a fossil. Fourthly, the results
of experience, instead of being an assistance, are sometimes
liable to operate as a source of error. When once, namely, a
generalisation has been established that certain fossils occur
in strata of a certain age, palæontologists are apt to infer
that _all_ beds containing similar fossils must be of the same
age. There is a presumption, of course, that this inference would
be correct; but it is not a conclusion resting upon absolute
necessity, and there might be physical evidence to disprove it.
Fifthly, the physical geologist may lead the palæontologist astray
by asserting that the physical evidence as to the age and position
of a given group of beds is clear and unequivocal, when such
evidence may be, in reality, very slight and doubtful. In this
way, the observer may be readily led into wrong conclusions as
to the nature of the organic remains--often obscure and
fragmentary--which it is his business to examine, or he may be
led erroneously to think that previous generalisations as to
the age of certain kinds of fossils are premature and incorrect.
Lastly, there are cases in which, owing to the limited exposure
of the beds, to their being merely of local development, or to
other causes, the physical evidence as to the age of a given
group of strata may be entirely uncertain and unreliable, and
in which, therefore, the observer has to rely wholly upon the
fossils which he may meet with.
In spite of the above limitations and fallacies, there can be
no doubt as to the enormous value of palæontology in enabling us
to work out the historical succession of the sedimentary rocks.
It may even be said that in any case where there should appear
to be a clear and decisive discordance between the physical and
the palæontological evidence as to the age of a given series
of beds, it is the former that is to be distrusted rather than
the latter. The records of geological science contain not a few
cases in which apparently clear physical evidence of superposition
has been demonstrated to have been wrongly interpreted; but the
evidence of palæontology, when in any way sufficient, has rarely
been upset by subsequent investigations. Should we find strata
containing plants of the Coal-measures apparently resting upon
other strata with Ammonites and Belemnites, we may be sure that
the physical evidence is delusive; and though the above is an
extreme case, the presumption in all such instances is rather that
the physical succession has been misunderstood or misconstrued,
than that there has been a subversion of the recognised succession
of life-forms.
We have seen, then, that as the collective result of observations
made upon the superposition of rocks in different localities,
from their mineral characters, and from their included fossils,
geologists have been able to divide the entire stratified series into
a number of different divisions or formations, each characterised
by a _general_ uniformity of mineral composition, and by a special
and peculiar _assemblage_ of organic forms. Each of these primary
groups is in turn divided into a series of smaller divisions,
characterised and distinguished in the same way. It is not pretended
for a moment that all these primary rock-groups can anywhere be seen
surmounting one another regularly.[8] There is no region upon the
earth where all the stratified formations can be seen together;
and, even when most of them occur in the same country, they can
nowhere be seen all succeeding each other in their regular and
uninterrupted succession. The reason of this is obvious. There
are many places--to take a single example--where one may see the
the Silurian rocks, the Devonian, and the Carboniferous rocks
succeeding one another regularly, and in their proper order. This
is because the particular region where this occurs was always
submerged beneath the sea while these formations were being
deposited. There are, however, many more localities in which
one would find the Carboniferous rocks resting unconformably upon
the Silurians without the intervention of any strata which could
be referred to the Devonian period. This might arise from one of
two causes: 1. The Silurians might have been elevated above the
sea immediately after their deposition, so as to form dry land
during the whole of the Devonian period, in which case, of course,
no strata of the latter age could possibly be deposited in that
area. 2. The Devonian might have been deposited upon the Silurian,
and then the whole might have been elevated above the sea, and
subjected to an amount of denudation sufficient to remove the
Devonian strata entirely. In this case, when the land was again
submerged, the Carboniferous rocks, or any younger formation,
might be deposited directly upon Silurian strata. From one or
other of these causes, then, or from subsequent disturbances
and denudations, it happens that we can rarely find many of the
primary formations following one another consecutively and in
their regular order.
[Footnote 8: As we have every reason to believe that dry land
and sea have existed, at any rate from the commencement of the
Laurentian period to the present day, it is quite obvious that
no one of the great formations can ever, under any circumstances,
have extended over the entire globe. In other words, no one of
the formations can ever have had a greater geographical extent
than that of the seas of the period in which the formation was
deposited. Nor is there any reason for thinking that the proportion
of dry land to ocean has ever been materially different to what
it is at present, however greatly the areas of sea and land may
have changed as regards their place. It follows from the above,
that there is no sufficient basis for the view that the crust of
the earth is composed of a succession of concentric layers, like
the coats of an onion, each layer representing one formation.]
In no case, however, do we ever find the Devonian resting upon
the Carboniferous, or the Silurian rocks reposing on the Devonian.
We have therefore, by a comparison of many different areas, an
established order of succession of the stratified formations, as
shown in the subjoined ideal section of the crust of the earth
(fig. 17).
The main subdivisions of the stratified rocks are known by the
following names:--
1. Laurentian.
2. Cambrian (with Huronian ?).
3. Silurian.
4. Devonian or Old Red Sandstone.
5. Carboniferous.
6. Permian \_ New Red Sandstone.
7. Triassic /
8. Jurassic or Oolitic.
9. Cretaceous.
10. Eocene.
11. Miocene.
12. Pliocene.
13. Post-tertiary.
[Illustration: Fig. 17. IDEAL SECTION OF THE CRUST OF THE EARTH.]
Of these primary rock divisions, the Laurentian, Cambrian, Silurian,
Devonian, Carboniferous, and Permian are collectively grouped
together under the name of the Primary or _Paloeozoic_ rocks (Gr.
_palaios_, ancient; _zoe_, life). Not only do they constitute the
oldest stratified accumulations, but from the extreme divergence
between their animals and plants and those now in existence, they may
appropriately be considered as belonging to an "Old-Life" period of
the world's history. The Triassic, Jurassic, and Cretaceous systems
are grouped together as the _Secondary_ or _Mesozoic_ formations
(Gr. _mesos_, intermediate; _zoe_, life); the organic remains of
this "Middle-Life" period being, on the whole, intermediate in
their characters between those of the palæozoic epoch and those
of more modern strata. Lastly, the Eocene, Miocene, and Pliocene
formations are grouped together as the _Tertiary_ or _Kainozoic_
rocks (Gr. _kainos_, new; _zoe_, life); because they constitute
a "New-Life" period, in which the organic remains approximate in
character to those now existing upon the globe. The so-called
_Post-Tertiary_ deposits are placed with the Kainozoic, or may
be considered as forming a separate _Quaternary_ system.
CHAPTER IV.
THE BREAKS IN THE GEOLOGICAL AND PALÆONTOLOGICAL RECORD.
The term "contemporaneous" is usually applied by geologists to
groups of strata in different regions which contain the same
fossils, or an assemblage of fossils in which many identical
forms are present. That is to say, beds which contain identical,
or nearly identical, fossils, however widely separated they may
be from one another in point of actual distance, are ordinarily
believed to have been deposited during the same period of the
earth's history. This belief, indeed, constitutes the keystone
of the entire system of determining the age of strata by their
fossil contents; and if we take the word "contemporaneous" in a
general and strictly geological sense, this belief can be accepted
as proved beyond denial. We must, however, guard ourselves against
too literal an interpretation of the word "contemporaneous,"
and we must bear in mind the enormously-prolonged periods of
time with which the geologist has to deal. When we say that two
groups of strata in different regions are "contemporaneous," we
simply mean that they were formed during the same geological
period, and perhaps at different stages of that period, and we
do not mean to imply that they were formed at precisely the same
instant of time.
A moment's consideration will show us that it is only in the former
sense that we can properly speak of strata being "contemporaneous;"
and that, in point of fact, beds containing the same fossils, if
occurring in widely distant areas, can hardly be "contemporaneous"
in any literal sense; but that the very identity of their fossils
is proof that they were deposited one after the other. If we find
strata containing identical fossils within the limits of a single
geographical region--say in Europe--then there is a reasonable
probability that these beds are strictly contemporaneous, in the
sense that they were deposited at the same time. There is a
reasonable probability of this, because there is no improbability
involved in the idea of an ocean occupying the whole area of
Europe, and peopled throughout by many of the same species of
marine animals. At the present day, for example, many identical
species of animals are found living on the western coasts of
Britain and the eastern coasts of North America, and beds now
in course of deposition off the shores of Ireland and the seaboard
of the state of New York would necessarily contain many of the
same fossils. Such beds would be both literally and geologically
contemporaneous; but the case is different if the distance between
the areas where the strata occur be greatly increased. We find,
for example, beds containing identical fossils (the Quebec or
Skiddaw beds) in Sweden, in the north of England, in Canada,
and in Australia. Now, if all these beds were contemporaneous,
in the literal sense of the term, we should have to suppose that
the ocean at one time extended uninterruptedly between all these
points, and was peopled throughout the vast area thus indicated
by many of the same animals. Nothing, however, that we see at
the present day would justify us in imagining an ocean of such
enormous extent, and at the same time so uniform in its depth,
temperature, and other conditions of marine life, as to allow the
same animals to flourish in it from end to end; and the example
chosen is only one of a long and ever-recurring series. It is
therefore much more reasonable to explain this, and all similar
cases, as owing to the _migration_ of the fauna, in whole or in
part, from one marine area to another. Thus, we may suppose an
ocean to cover what is now the European area, and to be peopled
by certain species of animals. Beds of sediment--clay, sands,
and limestones--will be deposited over the sea-bottom, and will
entomb the remains of the animals as fossils. After this has
lasted for a certain length of time, the European area may undergo
elevation, or may become otherwise unsuitable for the perpetuation
of its fauna; the result of which would be that some or all of the
marine animals of the area would migrate to some more suitable
region. Sediments would then be accumulated in the new area to
which they had betaken themselves, and they would then appear,
for the second time, as fossils in a set of beds widely separated
from Europe. The second set of beds would, however, obviously
not be strictly or literally contemporaneous with the first, but
would be separated from them by the period of time required for
the migration of the animals from the one area into the other.
It is only in a wide and comprehensive sense that such strata
can be said to be contemporaneous.
It is impossible to enter further into this subject here; but it
may be taken as certain that beds in widely remote geographical
areas can only come to contain the same fossils by reason of a
migration having taken place of the animals of the one area to
the other. That such migrations can and do take place is quite
certain, and this is a much more reasonable explanation of the
observed facts than the hypothesis that in former periods the
conditions of life were much more uniform than they are at present,
and that, consequently, the same organisms were able to range over
the entire globe at the same time. It need only be added, that
taking the evidence of the present as explaining the phenomena
of the past--the only safe method of reasoning in geological
matters--we have abundant proof that deposits which _are_ actually
contemporaneous, in the strict sense of the term, _do not contain
the same fossils, if far removed from one another in point of
distance_. Thus, deposits of various kinds are now in process of
formation in our existing seas, as, for example, in the Arctic
Ocean, the Atlantic, and the Pacific, and many of these deposits
are known to us by actual examination and observation with the
sounding-lead and dredge. But it is hardly necessary to add that
the animal remains contained in these deposits--the fossils of some
future period--instead of being identical, are widely different
from one another in their characters.
We have seen, then, that the entire stratified series is capable of
subdivision into a number of definite rock-groups or "formations,"
each possessing a peculiar and characteristic assemblage of fossils,
representing the "life" of the "period" in which the formation
was deposited. We have still to inquire shortly how it came to
pass that two successive formations _should_ thus be broadly
distinguished by their life-forms, and why they should not rather
possess at any rate a majority of identical fossils. It was
originally supposed that this could be explained by the hypothesis
that the close of each formation was accompanied by a general
destruction of all the living beings of the period, and that
the commencement of each new formation was signalised by the
creation of a number of brand-new organisms, destined to figure
as the characteristic fossils of the same. This theory, however,
ignores the fact that each formation--as to which we have any
sufficient evidence--contains a few, at least, of the life-forms
which existed in the preceding period; and it invokes forces
and processes of which we know nothing, and for the supposed
action of which we cannot account. The problem is an undeniably
difficult one, and it will not be possible here to give more than
a mere outline of the modern views upon the subject. Without
entering into the at present inscrutable question as to the manner
in which new life-forms are introduced upon the earth, it may be
stated that almost all modern geologists hold that the living
beings of any given formation are in the main modified forms of
others which have preceded them. It is not believed that any
general or universal destruction of life took place at the
termination of each geological period, or that a general introduction
of new forms took place at the commencement of a new period.
It is, on the contrary, believed that the animals and plants
of any given period are for the most part (or exclusively) the
lineal but modified descendants of the animals and plants of
the immediately preceding period, and that some of them, at any
rate, are continued into the next succeeding period, either
unchanged, or so far altered as to appear as new species. To
discuss these views in detail would lead us altogether too far,
but there is one very obvious consideration which may advantageously
receive some attention. It is obvious, namely, that the great
discordance which is found to subsist between the animal life of
any given formation and that of the next succeeding formation,
and which no one denies, would be a fatal blow to the views just
alluded to, unless admitting of some satisfactory explanation.
Nor is this discordance one purely of life-forms, for there is
often a physical break in the successions of strata as well.
Let us therefore briefly consider how far these interruptions
and breaks in the geological and palæontological record can be
accounted for, and still allow us to believe in some theory of
continuity as opposed to the doctrine of intermittent and occasional
action.
In the first place, it is perfectly clear that if we admit the
conception above mentioned of a continuity of life from the
Laurentian period to the present day, we could never _prove_ our
view to be correct, unless we could produce in evidence fossil
examples of _all_ the kinds of animals and plants that have lived
and died during that period. In order to do this, we should require,
to begin with, to have access to an absolutely unbroken and perfect
succession of all the deposits which have ever been laid down
since the beginning. If, however, we ask the physical geologist
if he is in possession of any such uninterrupted series, he will
at once answer in the negative. So far from the geological series
being a perfect one, it is interrupted by numerous gaps of unknown
length, many of which we can never expect to fill up. Nor are
the proofs of this far to seek. Apart from the facts that we
have hitherto examined only a limited portion of the dry land,
that nearly two-thirds of the entire area of the globe is
inaccessible to geological investigation in consequence of its
being covered by the sea, that many deposits can be shown to
have been more or less completely destroyed subsequent to their
deposition, and that there may be many areas in which living
beings exist where no rock is in process of formation, we have
the broad fact that rock-deposition only goes on to any extent
in water, and that the earth must have always consisted partly of
dry land and partly of water--at any rate, so far as any period
of which we have geological knowledge is concerned. There _must_,
therefore, always have existed, at some part or another of the
earth's surface, areas where no deposition of rock was going on,
and the proof of this is to be found in the well-known phenomenon
of "_unconformability_." Whenever, namely, deposition of sediment
is continuously going on within the limits of a single ocean, the
beds which are laid down succeed one another in uninterrupted
and regular sequence. Such beds are said to be "conformable," and
there are many rock-groups known where one may pass through fifteen
or twenty thousand feet of strata without a break--indicating
that the beds had been deposited in an area which remained
continuously covered by the sea. On the other hand, we commonly
find that there is no such regular succession when we pass from
one great formation to another, but that, on the contrary, the
younger formation rests "unconformably," as it is called, either
upon the formation immediately preceding it in point of time,
or upon some still older one. The essential physical feature of
this unconformability is that the beds of the younger formation
rest upon a worn and eroded surface formed by the beds of the
older series (fig. 18); and a moment's consideration will show
us what this indicates. It indicates, beyond the possibility of
misconception, that there was an interval between the deposition
of the older series and that of the newer series of strata; and
that during this interval the older beds were raised above the
sea-level, so as to form dry land, and were subsequently depressed
again beneath the waters, to receive upon their worn and wasted
upper surface the sediments of the later group. During the interval
thus indicated, the deposition of rock must of necessity have
been proceeding more or less actively in other areas. Every
unconformity, therefore, indicates that at the spot where it
occurs, a more or less extensive series of beds must be actually
missing; and though we may sometimes be able to point to these
missing strata in other areas, there yet remains a number of
unconformities for which we cannot at present supply the deficiency
even in a partial manner.
[Illustration: Fig. 18.--Section showing strata of Tertiary age
(a) resting upon a worn and eroded surface of White Chalk (b),
the stratification of which is marked by lines of flint.]
It follows from the above that the series of stratified deposits
is to a greater or less extent irremediably imperfect; and in
this imperfection we have one great cause why we can never obtain
a perfect series of all the animals and plants that have lived
upon the globe. Wherever one of these great physical gaps occurs,
we find, as we might expect, a corresponding break in the series
of life-forms. In other words, whenever we find two formations
to be unconformable, we shall always find at the same time that
there is a great difference in their fossils, and that many of
the fossils of the older formation do not survive into the newer,
whilst many of those in the newer are not known to occur in the
older. The cause of this is, obviously, that the lapse of time,
indicated by the unconformability, has been sufficiently great
to allow of the dying out or modification of many of the older
forms of life, and the introduction of new ones by immigration.
Apart, however, altogether, from these great physical breaks
and their corresponding breaks in life, there are other reasons
why we can never become more than partially acquainted with the
former denizens of the globe. Foremost amongst these is the fact
that an enormous number of animals possess no hard parts of the
nature of a skeleton, and are therefore incapable, under any
ordinary circumstances, of leaving behind them any traces of
their existence. It is true that there are cases in which animals
in themselves completely soft-bodied are nevertheless able to leave
marks by which their former presence can be detected: Thus every
geologist is familiar with the winding and twisting "trails" formed
on the surface of the strata by sea-worms; and the impressions
left by the stranded carcases of Jelly-fishes on the fine-grained
lithographic slates of Solenhofen supply us with an example of how
a creature which is little more than "organised sea-water" may
still make an abiding mark upon the sands of time. As a general
rule, however, animals which have no skeletons are incapable of
being preserved as fossils, and hence there must always have
been a vast number of different kinds of marine animals of which
we have absolutely no record whatever. Again, almost all the
fossiliferous rocks have been laid down in water; and it is a
necessary result of this that the great majority of fossils are
the remains of aquatic animals. The remains of air-breathing
animals, whether of the inhabitants of the land or of the air
itself, are comparatively rare as fossils, and the record of
the past existence of these is much more imperfect than is the
case with animals living in water. Moreover, the fossiliferous
deposits are not only almost exclusively aqueous formations, but
the great majority are marine, and only a comparatively small
number have been formed by lakes and rivers. It follows from the
foregoing that the palæontological record is fullest and most
complete so far as sea-animals are concerned, though even here we
find enormous gaps, owing to the absence of hard structures in
many great groups; of animals inhabiting fresh waters our knowledge
is rendered still further incomplete by the small proportion
that fluviatile and lacustrine deposits bear to marine; whilst
we have only a fragmentary acquaintance with the air-breathing
animals which inhabited the earth during past ages.
Lastly, the imperfection of the palæontological record, due to
the causes above enumerated, is greatly aggravated, especially
as regards the earlier portion of the earth's history, by the
fact that many rocks which contained fossils when deposited have
since been rendered barren of organic remains. The principal cause
of this common phenomenon is what is known as "metamorphism"--that
is, the subjection of the rock to a sufficient amount of heat to
cause a rearrangement of its particles. When at all of a pronounced
character, the result of metamorphic action is invariably the
obliteration of any fossils which might have been originally
present in the rock. Metamorphism may affect rocks of any age,
though naturally more prevalent in the older rocks, and to this
cause must be set down an irreparable loss of much fossil evidence.
The most striking example which is to be found of this is the
great Laurentian series, which comprises some 30,000 feet of
highly-metamorphosed sediments, but which, with one not wholly
undisputed exception, has as yet yielded no remains of living
beings, though there is strong evidence of the former existence
in it of fossils.
Upon the whole, then, we cannot doubt that the earth's crust, so
far as yet deciphered by us, presents us with but a very imperfect
record of the past. Whether the known and admitted imperfections
of the geological and palæontological records are sufficiently
serious to account satisfactorily for the deficiency of direct
evidence recognisable in some modern hypotheses, may be a matter
of individual opinion. There can, however, be little doubt that
they are sufficiently extensive to throw the balance of evidence
decisively in favour of some theory of _continuity_, as opposed
to any theory of intermittent and occasional action. The apparent
breaks which divide the great series of the stratified rocks
into a number of isolated formations, are not marks of mighty
and general convulsions of nature, but are simply indications
of the imperfection of our knowledge. Never, in all probability,
shall we be able to point to a complete series of deposits, or a
complete succession of life linking one great geological period
to another. Nevertheless, we may well feel sure that such deposits
and such an unbroken succession must have existed at one time.
We are compelled to believe that nowhere in the long series of
the fossiliferous rocks has there been a total break, but that
there must have been a complete continuity of life, and a more
or less complete continuity of sedimentation, from the Laurentian
period to the present day. One generation hands on the lamp of
life to the next, and each system of rocks is the direct offspring
of those which preceded it in time. Though there has not been
continuity in any given area, still the geological chain could
never have been snapped at one point, and taken up again at a
totally different one. Thus we arrive at the conviction that
_continuity_ is the fundamental law of geology, as it is of the
other sciences, and that the lines of demarcation between the
great formations are but gaps in our own knowledge.
CHAPTER V.
CONCLUSIONS TO BE DRAWN FROM FOSSILS.
We have already seen that geologists have been led by the study
of fossils to the all-important generalisation that the vast
series of the Fossiliferous or Sedimentary Rocks may be divided
into a number of definite groups or "formations," each of which is
characterised by its organic remains. It may simply be repeated here
that these formations are not properly and strictly characterised
by the occurrence in them of any one particular fossil. It may be
that a formation contains some particular fossil or fossils not
occurring out of that formation, and that in this way an observer
may identify a given group with tolerable certainty. It very often
happens, indeed, that some particular stratum, or sub-group of a
series, contains peculiar fossils, by which its existence may
be determined in various localities. As before remarked, however,
the great formations are characterised properly by the association
of certain fossils, by the predominance of certain families or
orders, or by an _assemblage_ of fossil remains representing
the "life" of the period in which the formation was deposited.
Fossils, then, enable us to determine the _age_ of the deposits
in which they occur. Fossils further enable us to come to very
important conclusions as to the mode in which the fossiliferous
bed was deposited, and thus as to the condition of the particular
district or region occupied by the fossiliferous bed at the time
of the formation of the latter. If, in the first place, the bed
contain the remains of animals such as now inhabit rivers, we
know that it is "fluviatile" in its origin, and that it must at
one time have either formed an actual riverbed, or been deposited
by the overflowing of an ancient stream. Secondly, if the bed
contain the remains of shellfish, minute crustaceans, or fish,
such as now inhabit lakes, we know that it is "lacustrine," and
was deposited beneath the waters of a former lake. Thirdly, if
the bed contain the remains of animals such as now people the
ocean, we know that it is "marine" in its origin, and that it
is a fragment of an old sea-bottom.
We can, however, often determine the conditions under which a bed
was deposited with greater accuracy than this. If, for example, the
fossils are of kinds resembling the marine animals now inhabiting
shallow waters, if they are accompanied by the detached relics
of terrestrial organisms, or if they are partially rolled and
broken, we may conclude that the fossiliferous deposit was laid
down in a shallow sea, in the immediate vicinity of a coast-line,
or as an actual shore-deposit. If, again, the remains are those
of animals such as now live in the deeper parts of the ocean,
and there is a very sparing intermixture of extraneous fossils
(such as the bones of birds or quadrupeds, or the remains of
plants), we may presume that the deposit is one of deep water.
In other cases, we may find, scattered through the rock, and
still in their natural position, the valves of shells such as
we know at the present day as living buried in the sand or mud
of the sea-shore or of estuaries. In other cases, the bed may
obviously have been an ancient coral-reef, or an accumulation of
social shells, like Oysters. Lastly, if we find the deposit to
contain the remains of marine shells, but that these are dwarfed
of their fair proportions and distorted in figure, we may conclude
that it was laid down in a brackish sea, such as the Baltic, in
which the proper saltness was wanting, owing to its receiving
an excessive supply of fresh water.
In the preceding, we have been dealing simply with the remains
of aquatic animals, and we have seen that certain conclusions
can be accurately reached by an examination of these. As regards
the determination of the conditions of deposition from the remains
of aerial and terrestrial animals, or from plants, there is not
such an absolute certainty. The remains of land-animals would,
of course, occur in "sub-aerial" deposits--that is, in beds,
like blown sand, accumulated upon the land. Most of the remains
of land-animals, however, are found in deposits which have been
laid down in water, and they owe their present position to the
fact that their former owners were drowned in rivers or lakes,
or carried out to sea by streams. Birds, Flying Reptiles, and
Flying Mammals might also similarly find their way into aqueous
deposits; but it is to be remembered that many birds and mammals
habitually spend a great part of their time in the water, and
that these might therefore be naturally expected to present
themselves as fossils in Sedimentary Rocks. Plants, again, even
when undoubtedly such as must have grown on land, do not prove
that the bed in which they occur was formed on land. Many of the
remains of plants known to us are extraneous to the bed in which
they are now found, having reached their present site by falling
into lakes or rivers, or being carried out to sea by floods or
gales of wind. There are, however, many cases in which plants
have undoubtedly grown on the very spot where we now find them.
Thus it is now generally admitted that the great coal-fields
of the Carboniferous age are the result of the growth _in situ_
of the plants which compose coal, and that these grew on vast
marshy or partially submerged tracts of level alluvial land. We
have, however, distinct evidence of old land-surfaces, both in
the Coal-measures and in other cases (as, for instance, in the
well-known "dirt-bed" of the Purbeck series). When, for example,
we find the erect stumps of trees standing at right angles to
the surrounding strata, we know that the surface through which
these send their roots was at one time the surface of the dry
land, or, in other words, was an ancient soil (fig. 19).
[Illustration: Fig. 19.--Erect Tree containing Reptilian remains.
Coal-measures, Nova Scotia. (After Dawson.)
In many cases fossils enable us to come to important conclusions
as to the climate of the period in which they lived but only a
few instances of this can be here adduced. As fossils in the
majority of instances are the remains of marine animals, it is
mostly the temperature of the sea which can alone be determined
in this way; and it is important to remember that, owing to the
existence of heated currents, the marine climate of a given area
does not necessarily imply a correspondingly warm climate in
the neighbouring land. Land-climates can only be determined by
the remains of land-animals or land-plants, and these are
comparatively rare as fossils. It is also important to remember
that all conclusions on this head are really based upon the present
distribution of animal and vegetable life on the globe, and are
therefore liable to be vitiated by the following considerations:--
a. Most fossils are extinct, and it is not certain that the
habits and requirements of any extinct animal were exactly similar
to those of its nearest living relative.
b. When we get very far back in time, we meet with groups of
organisms so unlike anything we know at the present day as to
render all conjectures as to climate founded upon their supposed
habits more or less uncertain and unsafe.
c. In the case of marine animals, we are as yet very far from
knowing the exact limits of distribution of many species within
our present seas; so that conclusions drawn from living forms
as to extinct species are apt to prove incorrect. For instance,
it has recently been shown that many shells formerly believed to
be confined to the Arctic Seas have, by reason of the extension
of Polar currents, a wide range to the south; and this has thrown
doubt upon the conclusions drawn from fossil shells as to the
Arctic conditions under which certain beds were supposed to have
been deposited.
d. The distribution of animals at the present day is certainly
dependent upon other conditions beside climate alone; and the causes
which now limit the range of given animals are certainly such as
belong to the existing order of things. But the establishment of
the present order of things does not date back in many cases to
the introduction of the present species of animals. Even in the
case, therefore, of existing species of animals, it can often
be shown that the past distribution of the species was different
formerly to what it is now, not necessarily because the climate
has changed, but because of the alteration of other conditions
essential to the life of the species or conducing to its extension.
Still, we are in many cases able to draw completely reliable
conclusions as to the climate of a given geological period, by
an examination of the fossils belonging to that period. Among
the more striking examples of how the past climate of a region
may be deduced from the study of the organic remains contained in
its rocks, the following may be mentioned: It has been shown that
in Eocene times, or at the commencement of the Tertiary period,
the climate of what is now Western Europe was of a tropical or
sub-tropical character. Thus the Eocene beds are found to contain
the remains of shells such as now inhabit tropical seas, as, for
example, Cowries and Volutes; and with these are the fruits of
palms, and the remains of other tropical plants. It has been
shown, again, that in Miocene times, or about the middle of the
Tertiary period, Central Europe was peopled with a luxuriant
flora resembling that of the warmer parts of the United States,
and leading to the conclusion that the mean annual temperature
must have been at least 30° hotter than it is at present. It has
been shown that, at the same time, Greenland, now buried beneath
a vast ice-shroud, was warm enough to support a large number of
trees, shrubs, and other plants, such as inhabit temperate regions
of the globe. Lastly, it has been shown upon physical as well as
palæontological evidence, that the greater part of the North
Temperate Zone, at a comparatively recent geological period, has
been visited with all the rigours of an Arctic climate, resembling
that of Greenland at the present day. This is indicated by the
occurrence of Arctic shells in the superficial deposits of this
period, whilst the Musk-ox and the Reindeer roamed far south of
their present limits.
Lastly, it was from the study of fossils that geologists learnt
originally to comprehend a fact which may be regarded as of cardinal
importance in all modern geological theories and
speculations--namely, that the crust of the earth is liable to
local elevations and subsidences. For long after the remains of
shells and other marine animals were for the first time observed
in the solid rocks forming the dry land, and at great heights
above the sea-level, attempts were made to explain this almost
unintelligible phenomenon upon the hypothesis that the fossils
in question were not really the objects they represented, but
were in truth mere _lusus naturoe_, due to some "plastic virtue
latent in the earth." The common-sense of scientific men, however,
soon rejected this idea, and it was agreed by universal consent
that these bodies really were remains of animals which formerly
lived in the sea. When once this was admitted, the further steps
were comparatively easy, and at the present day no geological
doctrine stands on a firmer basis than that which teaches us
that our present continents and islands, fixed and immovable as
they appear, have been repeatedly sunk beneath the ocean.
CHAPTER VI.
THE BIOLOGICAL RELATIONS OF FOSSILS.
Not only have fossils, as we have seen, a most important bearing
upon the sciences of Geology and Physical Geography, but they
have relations of the most complicated and weighty character with
the numerous problems connected with the study of living beings,
or in other words, with the science of Biology. To such an extent
is this the case, that no adequate comprehension of Zoology and
Botany, in their modern form, is so much as possible without
some acquaintance with the types of animals and plants which have
passed away. There are also numerous speculative questions in
the domain of vital science, which, if soluble at all, can only
hope to find their key in researches carried out on extinct
organisms. To discuss fully the biological relations of fossils
would, therefore, afford matter for a separate treatise; and all
that can be done here is to indicate very cursorily the principal
points to which the attention of the palæontological student
ought to be directed.
In the first place, the great majority of fossil animals and
plants are "extinct"--that is to say, they belong to species
which are no longer in existence at the present day. So far,
however, from there being any truth in the old view that there
were periodic destructions of all the living beings in existence
upon the earth, followed by a corresponding number of new creations
of animals and plants, the actual facts of the case show that
the extinction of old forms and the introduction of new forms
have been processes constantly going on throughout the whole
of geological time. Every species seems to come into being at
a certain definite point of time, and to finally disappear at
another definite point; though there are few instances indeed,
if there are any, in which our present knowledge would permit
us safely to fix with precision the times of entrance and exit.
There are, moreover, marked differences in the actual time during
which different species remained in existence, and therefore
corresponding differences in their "vertical range," or, in other
words, in the actual amount and thickness of strata through which
they present themselves as fossils. Some species are found to
range through two or even three formations, and a few have an
even more extended life. More commonly the species which begin
in the commencement of a great formation die out at or before its
close, whilst those which are introduced for the first time near
the middle or end of the formation may either become extinct, or
may pass on into the next succeeding formation. As a general rule,
it is the animals which have the lowest and simplest organisation
that have the longest range in time, and the additional possession
of microscopic or minute dimensions seems also to favour longevity.
Thus some of the _Foraminifera_ appear to have survived, with
little or no perceptible alteration, from the Silurian period
to the present day; whereas large and highly-organised animals,
though long-lived as _individuals_, rarely seem to live long
_specifically_, and have, therefore, usually a restricted vertical
range. Exceptions to this, however, are occasionally to be found
in some "persistent types," which extend through a succession
of geological periods with very little modification. Thus the
existing Lampshells of the genus _Lingula_ are little changed
from the _Linguloe_ which swarmed in the Lower Silurian seas; and
the existing Pearly Nautilus is the last descendant of a clan
nearly as ancient. On the other hand, some forms are singularly
restricted in their limits, and seem to have enjoyed a comparatively
brief lease of life. An example of this is to be found in many of
the _Ammonites_--close allies of the Nautilus--which are often
confined strictly to certain zones of strata, in some cases of
very insignificant thickness.
Of the _causes_ of extinction amongst fossil animals and plants,
we know little or nothing. All we can say is, that the attributes
which constitute a _species_ do not seem to be intrinsically
endowed with permanence, any more than the attributes which
constitute an _individual_, though the former may endure whilst
many successive generations of the latter have disappeared. Each
species appears to have its own life-period, its commencement,
its culmination, and its gradual decay; and the life-periods
of different species may be of very different duration.
From what has been said above, it may be gathered that our existing
species of animals and plants are, for the most part, quite of modern
origin, using the term "modern" in its geological acceptation.
Measured by human standards, the majority of existing animals
(which are capable of being preserved as fossils) are known to
have a high antiquity; and some of them can boast of a pedigree
which even the geologist may regard with respect. Not a few of
our shellfish are known to have commenced their existence at
some point of the Tertiary period; one Lampshell (_Terebratulina
caput-serpentis_) is believed to have survived since the Chalk; and
some of the _Foraminifera_ date, at any rate, from the Carboniferous
period. We learn from this the additional fact that our existing
animals and plants do not constitute an assemblage of organic
forms which were introduced into the world collectively and
simultaneously, but that they commenced their existence at very
different periods, some being extremely old, whilst others may be
regarded as comparatively recent animals. And this introduction of
the existing fauna and flora was a slow and _gradual_ process, as
shown admirably by the study of the fossil shells of the Tertiary
period. Thus, in the earlier Tertiary period, we find about 95
per cent of the known fossil shells to be species that are no
longer in existence, the remaining 5 per cent being forms which are
known to live in our present seas. In the middle of the Tertiary
period we find many more recent and still existing species of
shells, and the extinct types are much fewer in number; and this
gradual introduction of forms now living goes on steadily, till,
at the close of the Tertiary period, the proportions with which
we started may be reversed, as many as 90 or 95 per cent of the
fossil shells being forms still alive, while not more than 5 per
cent may have disappeared.
All known animals at the present day may be divided into some
five or six primary divisions, which are known technically as
"_sub-kingdoms_." Each of these sub-kingdoms [9] may be regarded
as representing a certain type or plan of structure, and all
the animals comprised in each are merely modified forms of this
common type. Not only are all known living animals thus reducible
to some five or six fundamental plans of structure, but amongst
the vast series of fossil forms no one has yet been found--however
unlike any existing animal--to possess peculiarities which would
entitle it to be placed in a new sub-kingdom. All fossil animals,
therefore, are capable of being referred to one or other of the
primary divisions of the animal kingdom. Many fossil groups have
no closely-related group now in existence; but in no case do
we meet with any grand structural type which has not survived
to the present day.
[Footnote 9: In the Appendix a brief definition is given of the
sub-kingdoms, and the chief divisions of each are enumerated.]
The old types of life differ in many respects from those now
upon the earth; and the further back we pass in time, the more
marked does this divergence become. Thus, if we were to compare
the animals which lived in the Silurian seas with those inhabiting
our present oceans, we should in most instances find differences
so great as almost to place us in another world. This divergence
is the most marked in the Palæozoic forms of life, less so in
those of the Mesozoic period, and less still in the Tertiary
period. Each successive formation has therefore presented us
with animals becoming gradually more and more like those now in
existence; and though there is an immense and striking difference
between the Silurian animals and those of to-day, this difference
is greatly reduced if we compare the Silurian fauna with the
Devonian; _that_ again with the Carboniferous; and so on till
we reach the present.
It follows from the above that the animals of any given formation
are more like those of the next formation below, and of the next
formation above, than they are to any others; and this fact of
itself is an almost inexplicable one, unless we believe that
the animals of any given formation are, in part at any rate, the
lineal descendants of the animals of the preceding formation,
and the progenitors, also in part at least, of the animals of the
succeeding formation. In fact, the palæontologist is so commonly
confronted with the phenomenon of closely-allied forms of animal
life succeeding one another in point of time, that he is compelled
to believe that such forms have been developed from some common
ancestral type by some process of "_evolution_." On the other
hand, there are many phenomena, such as the apparently sudden
introduction of new forms throughout all past time, and the common
occurrence of wholly isolated types, which cannot be explained
in this way. Whilst it seems certain, therefore, that many of
the phenomena of the succession of animal life in past periods
can only be explained by some law of evolution, it seems at the
same time certain that there has always been some other deeper
and higher law at work, on the nature of which it would be futile
to speculate at present.
Not only do we find that the animals of each successive formation
become gradually more and more like those now existing upon the
globe, as we pass from the older rocks into the newer, but we also
find that there has been a gradual progression and development
in the _types_ of animal life which characterise the geological
ages. If we take the earliest-known and oldest examples of any
given group of animals, it can sometimes be shown that these
primitive forms, though in themselves highly organised, possessed
certain characters such as are now only seen in the _young_ of
their existing representatives. In technical language, the early
forms of life in some instances possess "_embryonic_" characters,
though this does not prevent them often attaining a size much
more gigantic than their nearest living relatives. Moreover, the
ancient forms of life are often what is called "comprehensive
types"--that is to say, they possess characters in combination
such as we nowadays only find separately developed in different,
groups of animals. Now, this permanent retention of embryonic
characters and this "comprehensiveness" of structural type are
signs of what a zoologist considers to be a comparatively low
grade of organisation; and the prevalence of these features in
the earlier forms of animals is a very striking phenomenon, though
they are none the less perfectly organised so far as their own
type is concerned. As we pass upwards in the geological scale,
we find that these features gradually disappear, higher and ever
higher forms are introduced, and "specialisation" of type takes
the place of the former comprehensiveness. We shall have occasion
to notice many of the facts on which these views are based at
a later period, and in connection with actual examples. In the
meanwhile, it is sufficient to state, as a widely-accepted
generalisation of palæontology, that there has been in the past
a general progression of organic types, and that the appearance
of the lower forms of life has in the main preceded that of the
higher forms in point of time.
PART II
HISTORICAL PALÆONTOLOGY
CHAPTER VII.
THE LAURENTIAN AND HURONIAN PERIODS.
The _Laurentian Rocks_ constitute the base of the entire stratified
series, and are, therefore, the oldest sediments of which we have
as yet any knowledge. They are more largely and more typically
developed in North America, and especially in Canada, than in
any known part of the world, and they derive their title from
the range of hills which the old French geographers named the
"Laurentides." These hills are composed of Laurentian Rocks, and
form the watershed between the valley of the St Lawrence river
on the one hand, and the great plains which stretch northwards
to Hudson Bay on the other hand. The main area of these ancient
deposits forms a great belt of rugged and undulating country,
which extends from Labrador westwards to Lake Superior, and then
bends northwards towards the Arctic Sea. Throughout this extensive
area the Laurentian Rocks for the most part present themselves
in the form of low, rounded, ice-worn hills, which, if generally
wanting in actual sublimity, have a certain geological grandeur
from the fact that they "have endured the battles and the storms
of time longer than any other mountains" (Dawson). In some places,
however, the Laurentian Rocks produce scenery of the most magnificent
character, as in the great gorge cut through them by the river
Saguenay, where they rise at times into vertical precipices 1500
feet in height. In the famous group of the Adirondack mountains,
also, in the state of New York, they form elevations no less than
6000 feet above the level of the sea. As a general rule, the
character of the Laurentian region is that of a rugged, rocky,
rolling country, often densely timbered, but rarely well fitted
for agriculture, and chiefly attractive to the hunter and the
miner.
As regards its mineral characters, the Laurentian series is composed
throughout of metamorphic and highly crystalline rocks, which
are in a high degree crumpled, folded, and faulted. By the late
Sir William Logan the entire series was divided into two great
groups, the _Lower Laurentian_ and the _Upper Laurentian_, of
which the latter rests unconformably upon the truncated edges
of the former, and is in turn unconformably overlaid by strata
of Huronian and Cambrian age (fig. 20).
[Illustration: Fig. 20.--Diagrammatic section of the Laurentian
Rocks in Lower Canada. a Lower Laurentian; b Upper Laurentian,
resting unconformably upon the lower series; c Cambrian strata
(Potsdam Sandstone), resting unconformably on the Upper Laurentian.]
The _Lower Laurentian_ series attains the enormous thickness of
over 20,000 feet, and is composed mainly of great beds of gneiss,
altered sandstones (quartzites), mica-schist, hornblende-schist,
magnetic iron-ore, and hæmatite, together with masses of limestone.
The limestones are especially interesting, and have an extraordinary
development--three principal beds being known, of which one is
not less than 1500 feet thick; the collective thickness of the
whole being about 3500 feet.
The _Upper Laurentian_ series, as before said, reposes unconformably
upon the Lower Laurentian, and attains a thickness of at least
10,000 feet. Like the preceding, it is wholly metamorphic, and
is composed partly of masses of gneiss and quartzite; but it
is especially distinguished by the possession of great beds of
felspathic rock, consisting principally of "Labrador felspar."
Though typically developed in the great Canadian area already
spoken of, the Laurentian Rocks occur in other localities, both
in America and in the Old World. In Britain, the so-called
"fundamental gneiss" of the Hebrides and of Sutherlandshire is
probably of Lower Laurentian age, and the "hypersthene rocks"
of the Isle of Skye may, with great probability, be regarded
as referable to the Upper Laurentian. In other localities in
Great Britain (as in St David's, South Wales; the Malvern Hills;
and the North of Ireland) occur ancient metamorphic deposits
which also are probably referable to the Laurentian series. The
so-called "primitive gneiss" of Norway appears to belong to the
Laurentian, and the ancient metamorphic rocks of Bohemia and
Bavaria may be regarded as being approximately of the same age.
[Illustration: Fig. 21.--Section of Lower Laurentian Limestone
from Hull, Ottawa; enlarged five diameters. The rock is very
highly crystalline, and contains mica and other minerals. The
irregular black masses in it are graphite. (Original.)]
By some geological writers the ancient and highly metamorphosed
sediments of the Laurentian and the succeeding Huronian series
have been spoken of as the "Azoic rocks" (Gr. _a_, without; _zoe_,
life); but even if we were wholly destitute of any evidence of
life during these periods, this name would be objectionable upon
theoretical grounds. If a general name be needed, that of "Eozoic"
(Gr. _eos_, dawn; _zoe_, life), proposed by Principal Dawson, is the
most appropriate. Owing to their metamorphic condition, geologists
long despaired of ever detecting any traces of life in the vast pile
of strata which constitute the Laurentian System. Even before any
direct traces were discovered, it was, however, pointed out that
there were good reasons for believing that the Laurentian seas had
been tenanted by an abundance of living beings. These reasons are
briefly as follows:--(1) Firstly, the Laurentian series consists,
beyond question, of marine sediments which originally differed
in no essential respect from those which were subsequently laid
down in the Cambrian or Silurian periods. (2) In all formations
later than the Laurentian, any limestones which are present can
be shown, with few exceptions, to be _organic_ rocks, and to be
more or less largely made up of the comminuted debris of marine
or fresh-water animals. The Laurentian limestones, in consequence
of the metamorphism to which they have been subjected, are so
highly crystalline (fig. 21) that the microscope fails to detect
any organic structure in the rock, and no fossils beyond those
which will be spoken of immediately have as yet been discovered in
them. We know, however, of numerous cases in which limestones,
of later age, and undoubtedly organic to begin with, have been
rendered so intensely crystalline by metamorphic action that
all traces of organic structure have been obliterated. We have
therefore, by analogy, the strongest possible ground for believing
that the vast beds of Laurentian limestone have been originally
organic in their origin, and primitively composed, in the main,
of the calcareous skeletons of marine animals. It would, in fact,
be a matter of great difficulty to account for the formation
of these great calcareous masses on any other hypothesis. (3)
The occurrence of phosphate of lime in the Laurentian Rocks in
great abundance, and sometimes in the form of irregular beds,
may very possibly be connected with the former existence in the
strata of the remains of marine animals of whose skeleton this
mineral is a constituent. (4) The Laurentian Rocks contain a
vast amount of carbon in the form of black-lead or _graphite_.
This mineral is especially abundant in the limestones, occurring
in regular beds, in veins or strings, or disseminated through
the body of the limestone in the shape of crystals, scales, or
irregular masses. The amount of graphite in some parts of the
Lower Laurentian is so great that it has been calculated as equal
to the quantity of carbon present in an equal thickness of the
Coal-measures. The general source of solid carbon in the crust
of the earth is, however, plant-life; and it seems impossible to
account for the Laurentian graphite, except upon the supposition
that it is metamorphosed vegetable matter. (5) Lastly, the great
beds of iron-ore (peroxide and magnetic oxide) which occur in the
Laurentian series interstratified with the other rocks, point
with great probability to the action of vegetable life; since
similar deposits in later formations can commonly be shown to
have been formed by the deoxidising power of vegetable matter
in a state of decay.
In the words of Principal Dawson, "anyone of these reasons might,
in itself, be held insufficient to prove so great and, at first
sight, unlikely a conclusion as that of the existence of abundant
animal and vegetable life in the Laurentian; but the concurrence
of the whole in a series of deposits unquestionably marine, forms
a chain of evidence so powerful that it might command belief
even if no fragment of any organic or living form or structure
had ever been recognised in these ancient rocks." Of late years,
however, there have been discovered in the Laurentian Rocks certain
bodies which are believed to be truly the remains of animals,
and of which by far the most important is the structure known
under the now celebrated name of _Eozoön_. If truly organic, a
very special and exceptional interest attaches itself to _Eozoön_,
as being the most ancient fossil animal of which we have any
knowledge; but there are some who regard it really a peculiar
form of mineral structure, and a severe, protracted, and still
unfinished controversy has been carried on as to its nature. Into
this controversy it is wholly unnecessary to enter here; and it
will be sufficient to briefly explain the structure of _Eozoön_,
as elucidated by the elaborate and masterly investigations of
Carpenter and Dawson, from the standpoint that it is a genuine
organism--the balance of evidence up to this moment inclining
decisively to this view.
[Illustration: Fig. 22.--Fragment of _Eozoön_, of the natural
size, showing alternate laminæ of loganite and dolomite. (After
Dawson.)]
The structure known as _Eozoön_ is found in various localities
in the Lower Laurentian limestones of Canada, in the form of
isolated masses or spreading layers, which are composed of thin
alternating laminæ, arranged more or less concentrically (fig.
22). The laminæ of these masses are usually of different colours
and composition; one series being white, and composed of carbonate
of lime--whilst the laminæ of the second series alternate with
the preceding, are green in colour, and are found by chemical
analysis to consist of some silicate, generally serpentine or the
closely-related "loganite." In some instances, however, all the
laminæ are calcareous, the concentric arrangement still remaining
visible in consequence of the fact that the laminæ are composed
alternately of lighter and darker coloured limestone.
When first discovered, the masses of _Eozoön_ were supposed to
be of a mineral nature; but their striking general resemblance
to the undoubted fossils which will be subsequently spoken of
under the name of _Stromatopora_ was recognised by Sir William
Logan, and specimens were submitted for minute examination, first
to Principal Dawson, and subsequently to Dr W. B. Carpenter.
After a careful microscopic examination, these two distinguished
observers came to the conclusion that _Eozoön_ was truly organic,
and in this opinion they were afterwards corroborated by other
high authorities (Mr W. K. Parker, Professor Rupert Jones, Mr H.
B. Brady, Professor Gümbel, &c.) Stated briefly, the structure
of _Eozoön_, as exhibited by the microscope, is as follows:--
[Illustration: Fig. 23.--Diagram of a portion of _Eozoön_ cut
vertically. A, B, C, Three tiers of chambers communicating with
one another by slightly constricted apertures: _a a_, The true
shell-wall, perforated by numerous delicate tubes; _b b_. The
main calcareous skeleton ("intermediate skeleton"); c, Passage
of communication ("stolon-passage") from one tier of chambers
to another; d, Ramifying tubes in the calcareous skeleton.
(After Carpenter.)]
The concentrically-laminated mass of _Eozoön_ is composed of
numerous calcareous layers, representing the original skeleton
of the organism (fig. 23, b). These calcareous layers serve to
separate and define a series of chambers arranged in successive
tiers, one above the other (fig. 23, A, B, C); and they are
perforated not only by passages (fig. 23, c), which serve to
place successive tiers of chambers in communication, but also by
a system of delicate branching canals (fig. 23, d). Moreover,
the central and principal portion of each calcareous layer, with
the ramified canal-system just spoken of, is bounded both above
and below by a thin lamina which has a structure of its own, and
which may be regarded as the proper shell-wall (fig. 23, a a).
This proper wall forms the actual lining of the chambers, as well
as the outer surface of the whole mass; and it is perforated with
numerous fine vertical tubes (fig. 24, a a), opening into the
chambers and on to the surface by corresponding fine pores. From
the resemblance of this tubulated layer to similar structures
in the shell of the Nummulite, it is often spoken of as the
"Nummuline layer." The chambers are sometimes piled up one above
the other in an irregular manner; but they are more commonly
arranged in regular tiers, the separate chambers being marked
off from one another by projections of the wall in the form of
partitions, which are so far imperfect as to allow of a free
communication between contiguous chambers. In the original condition
of the organism, all these chambers, of course, must have been
filled with living-matter; but they are found in the present
state of the fossil to be generally filled with some silicate,
such as serpentine, which not only fills the actual chambers,
but has also penetrated the minute tubes of the proper wall and
the branching canals of the intermediate skeleton. In some cases
the chambers are simply filled with crystalline carbonate of
lime. When the originally porous fossil has been permeated by
a silicate, it is possible to dissolve away the whole of the
calcareous skeleton by means of acids, leaving an accurate and
beautiful cast of the chambers and the tubes connected with them
in the insoluble silicate.
[Illustration: Fig. 24.--Portion of one of the calcareous layers
of _Eozoön_, magnified 100 diameters. a a, The proper wall
("Nummuline layer") of one of the chambers, showing the fine
vertical tubuli with which it is penetrated, and which are slightly
bent along the line a' a'. c c, The intermediate skeleton,
with numerous branched canals. The oblique lines are the cleavage
planes of the carbonate of lime, extending across both the
intermediate skeleton and the proper wall. (After Carpenter.)]
The above are the actual appearances presented by _Eozoön_ when
examined microscopically, and it remains to see how far they
enable us to decide upon its true position in the animal kingdom.
Those who wish to study this interesting subject in detail must
consult the admirable memoirs by Dr W. B. Carpenter and Principal
Dawson: it will be enough here to indicate the results which
have been arrived at. The only animals at the present day which
possess a continuous calcareous skeleton, perforated by pores
and penetrated by canals, are certain organisms belonging to
the group of the _Foraminifera_. We have had occasion before
to speak of these animals, and as they are not conspicuous or
commonly-known forms of life, it may be well to say a few words
as to the structure of the living representatives of the group.
The _Foraminifera_ are all inhabitants of the sea, and are mostly
of small or even microscopic dimensions. Their bodies are composed
of an apparently structureless animal substance of an albuminous
nature ("sarcode"), of a gelatinous consistence, transparent, and
exhibiting numerous minute granules or rounded particles. The
body-substance cannot be said in itself to possess any definite
form, except in so far as it may be bounded by a shell; but it
has the power, wherever it may be exposed, of emitting long
thread-like filaments ("pseudopodia"), which interlace with one
another to form a network (fig. 25, b). These filaments can be
thrown out at will, and to considerable distances, and can be
again retracted into the soft mass of the general body-substance,
and they are the agents by which the animal obtains its food.
The soft bodies of the _Foraminifera_ are protected by a shell,
which is usually calcareous, but may be composed of sand-grains
cemented together; and it may consist of a single chamber (fig.
26, a), or of many chambers arranged in different ways (fig.
26, _b-f_). Sometimes the shell has but one large opening into
it--the mouth; and then it is from this aperture that the animal
protrudes the delicate net of filaments with which it seeks its
food. In other cases the entire shell is perforated with minute
pores (fig. 26, e), through which the soft body-substance gains
the exterior, covering the whole shell with a gelatinous film
of animal matter, from which filaments can be emitted at any
point. When the shell consists of many chambers, all of these are
placed in direct communication with one another, and the actual
substance of the shell is often traversed by minute canals filled
with living matter (e.g., in _Calcarina_ and _Nummulina_). The
shell, therefore, may be regarded, in such cases, as a more or
less completely porous calcareous structure, filled to its minutest
internal recesses with the substance of the living animal, and
covered externally with a layer of the same substance, giving
off a network of interlacing filaments.
[Illustration: Fig. 25.--The animal of _Nonionina_, one of the
_Foraminifera_, after the shell has been removed by a weak acid;
b, _Gromia_, a single-chambered Foraminifer (after Schultze),
showing the shell surrounded by a network of filaments derived
from the body substance.]
[Illustration: Fig 26.--Shells of living _Foraminifera_. a,
_Orbulina universa_, in its perfect condition, showing the tubular
spines which radiate from the surface of the shell; b, _Globigerina
bulloides_, in its ordinary condition, the thin hollow spines
which are attached to the shell when perfect having been broken
off; c, Textularia variabilis; d, Peneroplis planatus; e, Rotalia
concamerata; f, _Cristellaria subarcuatula._ [Fig. a is after
Wyville Thomson; the others are after Williamson. All the figures
are greatly enlarged.]]
Such, in brief, is the structure of the living _Foraminifera_;
and it is believed that in _Eozoön_ we have an extinct example of
the same group, not only of special interest from its immemorial
antiquity, but hardly less striking from its gigantic dimensions.
In its original condition, the entire chamber-system of _Eozoön_
is believed to have been filled with soft structureless living
matter, which passed from chamber to chamber through the wide
apertures connecting these cavities, and from tier to tier by
means of the tubuli in the shell-wall and the branching canals
in the intermediate skeleton. Through the perforated shell-wall
covering the outer surface the soft body-substance flowed out,
forming a gelatinous investment, from every point of which radiated
an interlacing net of delicate filaments, providing nourishment
for the entire colony. In its present state, as before said,
all the cavities originally occupied by the body-substance have
been filled with some mineral substance, generally with one of
the silicates of magnesia; and it has been asserted that this
fact militates strongly against the organic nature of _Eozoön_,
if not absolutely disproving it. As a matter of fact, however--as
previously noticed--it is by no means very uncommon at the present
day to find the shells of living species of _Foraminifera_ in which
all the cavities primitively occupied by the body-substance, down
to the minutest pores and canals, have been similarly injected
by some analogous silicate, such as glauconite.
Those, then, whose opinions on such a subject deservedly carry the
greatest weight, are decisively of opinion that we are presented
in the _Eozoön_ of the Laurentian Rocks of Canada with an ancient,
colossal, and in some respects abnormal type of the _Foraminifera_.
In the words of Dr Carpenter, it is not pretended that "the doctrine
of the Foraminiferal nature of _Eozoön_ can be _proved_ in the
demonstrative sense;" but it may be affirmed "that the _convergence
of a number of separate and independent probabilities_, all accordant
with that hypothesis, while a separate explanation must be invented
for each of them on any other hypothesis, gives it that _high
probability_ on which we rest in the ordinary affairs of life, in
the verdicts of juries, and in the interpretation of geological
phenomena generally."
It only remains to be added, that whilst _Eozoön_ is by far the
most important organic body hitherto found in the Laurentian, and
has been here treated at proportionate length, other traces of life
have been detected, which may subsequently prove of great interest
and importance. Thus, Principal Dawson has recently described
under the name of _Archoeosphoerinoe_ certain singular rounded
bodies which he has discovered in the Laurentian limestones, and
which he believes to be casts of the shells of _Foraminifera_
possibly somewhat allied to the existing _Globigerinoe_. The same
eminent palæontologist has also described undoubted worm-burrows
from rocks probably of Laurentian age. Further and more extended
researches, we may reasonably hope, will probably bring to light
other actual remains of organisms in these ancient deposits.
THE HURONIAN PERIOD.
The so-called _Huronian Rocks_, like the Laurentian, have their
typical development in Canada, and derive their name from the
fact that they occupy an extensive area on the borders of Lake
Huron. They are wholly metamorphic, and consist principally of
altered sandstones or quartzites, siliceous, felspathic, or talcose
slates, conglomerates, and limestones. They are largely developed
on the north shore of Lake Superior, and give rise to a broken
and hilly country, very like that occupied by the Laurentians,
with an abundance of timber, but rarely with sufficient soil
of good quality for agricultural purposes. They are, however,
largely intersected by mineral veins, containing silver, gold,
and other metals, and they will ultimately doubtless yield a rich
harvest to the miner. The Huronian Rocks have been identified,
with greater or less certainty, in other parts of North America,
and also in the Old World.
The total thickness of the Huronian Rocks in Canada is estimated
as being not less than 18,000 feet, but there is considerable
doubt as to their precise geological position. In their typical
area they rest unconformably on the edges of strata of _Lower_
Laurentian age; but they have never been seen in direct contact
with the _Upper_ Laurentian, and their exact relations to this
series are therefore doubtful. It is thus open to question whether
the Huronian Rocks constitute a distinct formation, to be
intercalated in point of time between the Laurentian and the
Cambrian groups; or whether, rather, they should not be considered
as the metamorphosed representatives of the Lower Cambrian Rocks
of other regions.
As regards the fossils of the Huronian Rocks, little can be said.
Some of the specimens of _Eozoön Canadense_ which have been
discovered in Canada are thought to come from rocks which are
probably of Huronian age. In Bavaria, Dr Gümbel has described a
species of _Eozoön_ under the name of _Eozoön Bavaricum_, from
certain metamorphic limestones which he refers to the Huronian
formation. Lastly, the late Mr Billings described, from rocks
in Newfoundland apparently referable to the Huronian, certain
problematical limpet-shaped fossils, to which he gave the name
of _Aspidella_.
LITERATURE.
Amongst the works and memoirs which the student may consult with
regard to the Laurentian and Huronian deposits may be mentioned
the following:[10]--
(1) 'Report of Progress of the Geological Survey of Canada from its
Commencement to 1863,' pp. 38-49, and pp. 50-66.
(2) 'Manual of Geology.' Dana. 2d Ed. 1875.
(3) 'The Dawn of Life.' J. W, Dawson. 1876.
(4) "On the Occurrence of Organic Remains in the Laurentian Rocks
of Canada." Sir W. E. Logan. 'Quart. Journ. Geol. Soc.,'
xxi. 45-50.'
(5) "On the Structure of Certain Organic Remains in the Laurentian
Limestones of Canada." J. W. Dawson. 'Quart. Journ. Geol.
Soc.,' xxi. 51-59.
(6) "Additional Note on the Structure and Affinities of Eozoön
Canadense." W. B, Carpenter. 'Quart. Journ. Geol. Soc.,' xxi.
59-66.
(7) "Supplemental Notes on the Structure and Affinities of Eozoön'
Canadense," W. B. Carpenter, 'Quart. Journ. Geol. Soc.,'
xxii. 219-228.
(8) "On the So-Called Eozoönal Rocks." King & Rowney. 'Quart.
Journ. Geol. Soc.,' xxii. 185-218.
(9) 'Chemical and Geological Essays.' Sterry Hunt.
The above list only includes some of the more important memoirs
which may be consulted as to the geological and chemical features
of the Laurentian and Huronian Rocks, and as to the true nature
of _Eozoön_. Those who are desirous of studying the later phases
of the controversy with regard to _Eozoön_ must consult the papers
of Carpenter, Carter, Dawson, King & Rowney, Hahn, and others, in
the 'Quart. Journ. of the Geological Society,' the 'Proceedings
of the Royal Irish Academy,' the 'Annals of Natural History,'
the 'Geological Magazine,' &c. Dr Carpenter's 'Introduction to
the Study of the Foraminifera' should also be consulted.
[Footnote 10: In this and in all subsequently following
bibliographical lists, not only is the selection of works and
memoirs quoted necessarily extremely limited; but only such have,
as a general rule, been chosen for mention as are easily accessible
to students who are in the position of being able to refer to a good
library. Exceptions, however, are occasionally made to this rule,
in favour of memoirs or works of special historical interest. It
is also unnecessary to add that it has not been thought requisite
to insert in these lists the well-known handbooks of geological
and palæontological science; except in such instances as where
they contain special information on special points.]
CHAPTER VIII.
THE CAMBRIAN PERIOD.
The traces of life in the Laurentian period, as we have seen,
are but scanty; but the _Cambrian Rocks_--so called from their
occurrence in North Wales and its borders ("Cambria ")--have
yielded numerous remains of animals and some dubious plants.
The Cambrian deposits have thus a special interest as being the
oldest rocks in which occur any number of well-preserved and
unquestionable organisms. We have here the remains of the first
_fauna_, or assemblage of animals, of which we have at present
knowledge. As regards their geographical distribution, the Cambrian
Rocks have been recognised in many parts of the world, but there
is some question as to the precise limits of the formation, and
we may consider that their most typical area is in South Wales,
where they have been carefully worked out, chiefly by Dr Henry
Hicks. In this region, in the neighbourhood of the promontory
of St David's, the Cambrian Rocks are largely developed, resting
upon an ancient ridge of Pre-Cambrian (Laurentian?) strata, and
overlaid by the lowest beds of the Lower Silurian. The subjoined
sketch-section (fig. 27) exhibits in a general manner the succession
of strata in this locality.
From this section it will be seen that the Cambrian Rocks in
Wales are divided in the first place into a lower and an upper
group. The _Lower Cambrian_ is constituted at the base by a great
series of grits, sandstones, conglomerates, and slates, which
are known as the "Longmynd group," from their vast development
in the Longmynd Hills in Shropshire, and which attain in North
Wales a thickness of 8000 feet or more. The Longmynd beds are
succeeded by the so-called "Menevian group," a series of sandstones,
flags, and grits, about 600 feet in thickness, and containing
a considerable number of fossils. The _Upper Cambrian_ series
consists in its lower portion of nearly 5000 feet of strata,
principally shaly and slaty, which are known as the "Lingula
Flags," from the great abundance in them of a shell referable
to the genus _Lingula_. These are followed by 1000 feet of dark
shales and flaggy sandstones, which are known as the "Tremadoc
slates," from their occurrence near Tremadoc in North Wales;
and these in turn are surmounted, apparently quite conformably,
by the basement beds of the Lower Silurian.
[Illustration: Fig 27. GENERALIZED SECTION OF THE CAMBRIAN ROCKS
IN WALES.]
The above may be regarded as giving a typical series of the Cambrian
Rocks in a typical locality; but strata of Cambrian age are known in
many other regions, of which it is only possible here to allude to
a few of the most important. In Scandinavia occurs a well-developed
series of Cambrian deposits, representing both the lower and
upper parts of the formation. In Bohemia, the Upper Cambrian, in
particular, is largely developed, and constitutes the so-called
"Primordial zone" of Barrande. Lastly, in North America, whilst the
Lower Cambrian is only imperfectly developed, or is represented by
the Huronian, the Upper Cambrian formation has a wide extension,
containing fossils similar in character to the analogous strata
in Europe, and known as the "Potsdam Sandstone." The subjoined
table shows the chief areas where Cambrian Rocks are developed,
and their general equivalency:
TABULAR VIEW OF THE CAMBRIAN FORMATION.
_Britain._ | _Europe._ | _America._
| |
/a. Tremadoc Slates. | a. Primordial zone | a. Potsdam
| | of Bohemia. | Sandstone.
| b. Lingula Flags. | b. Paradoxides | b. Acadian
Upper < | Schists, Olenus | group of New
Cambrian. | | Schists, and | Brunswick.
| | Dictyonema schists |
\ | of Sweden. |
| |
/a. Longmynd Beds. | a. Fucoidal | Huronian
| | Sandstone of Sweden | Formation?
| b. Llanberis Slates.| b. _Eophyton_ |
| | Sandstone of Sweden.|
Lower < c. Harlech Grits. | |
Cambrian. | d. _Oldhamia_ | |
| Slates of Ireland.| |
| e. Conglomerates and| |
| and Sandstones of | |
| Sutherlandshire? | |
\f. Menevian Beds. | |
Like all the older Palæozoic deposits, the Cambrian Rocks, though
by no means necessarily what would be called actually "metamorphic,"
have been highly cleaved, and otherwise altered from their original
condition. Owing partly to their indurated state, and partly to
their great antiquity, they are usually found in the heart of
mountainous districts, which have undergone great disturbance,
and have been subjected to an enormous amount of denudation. In
some cases, as in the Longmynd Hills in Shropshire, they form
low rounded elevations, largely covered by pasture, and with few
or no elements of sublimity. In other cases, however, they rise
into bold and rugged mountains, girded by precipitous cliffs.
Industrially, the Cambrian Rocks are of interest, if only for
the reason that the celebrated Welsh slates of Llanberis are
derived from highly-cleaved beds of this age. Taken as a whole,
the Cambrian formation is essentially composed of arenaceous
and muddy sediments, the latter being sometimes red, but more
commonly nearly black in colour. It has often been supposed that
the Cambrians are a deep-sea deposit, and that we may thus account
for the few fossils contained in them; but the paucity of fossils
is to a large extent imaginary, and some of the Lower Cambrian
beds of the Longmynd Hills would appear to have been laid down
in shallow water; as they exhibit rain-prints, sun-cracks, and
ripple-marks--incontrovertible evidence of their having been a
shore-deposit. The occurrence, of innumerable worm-tracks and
burrows in many Cambrian strata is also a proof of shallow-water
conditions; and the general absence of limestones, coupled with
the coarse mechanical nature of many of the sediments of the
Lower Cambrian, maybe taken as pointing in the same direction.
The _life_ of the Cambrian, though not so rich as in the succeeding
Silurian period, nevertheless consists of representatives of
most of the great classes of invertebrate animals. The coarse
sandy deposits of the formation, which abound more particularly
towards its lower part, naturally are to a large extent barren
of fossils; but the muddy sediments, when not too highly cleaved,
and especially towards the summit of the group, are replete with
organic remains. This is also the case, in many localities at any
rate, with the finer beds of the Potsdam Sandstone in America.
Limestones are known to occur in only a few areas (chiefly in
America), and this may account for the apparent total absence
of corals. It is, however, interesting to note that, with this
exception, almost all the other leading groups of Invertebrates
are known to have come into existence during the Cambrian period.
Fig. 28.--Fragment of _Eophyton Linneanum_, a supposed land-plant.
Lower Cambrian, Sweden, of the natural size.
Of the land-surfaces of the Cambrian period we know nothing;
and there is, therefore, nothing surprising in the fact that
our acquaintance with the Cambrian vegetation is confined to
some marine plants or sea-weeds, often of a very obscure and
problematical nature. The "Fucoidal Sandstone" of Sweden, and the
"Potsdam Sandstone" of North America, have both yielded numerous
remains which have been regarded as markings left by sea-weeds or
"Fucoids;" but these are highly enigmatical in their characters,
and would, in many instances, seem to be rather referable to the
tracks and burrows of marine worms. The first-mentioned of these
formations has also yielded the curious, furrowed and striated
stems which have been described as a kind of land-plant under
the name of _Eopkyton_ (fig. 28). It cannot be said, however,
that the vegetable origin of these singular bodies has been
satisfactorily proved. Lastly, there are found in certain green
and purple beds of Lower Cambrian age at Bray Head, Wicklow,
Ireland, some very remarkable fossils, which are well known under
the name of _Oldhamia_, but the true nature of which is very
doubtful. The commonest form of _Oldhamia_ (fig. 29) consists of
a thread-like stem or axis, from which spring at regular intervals
bundles of short filamentous branches in a fan-like manner. In
the locality where it occurs, the fronds of _Oldhamia_ are very
abundant, and are spread over the surfaces of the strata in tangled
layers. That it is organic is certain, and that it is a calcareous
sea-weed is probable; but it may possibly belong to the sea-mosses
(_Polyzoa_), or to the sea-firs (_Sertularians_).
Amongst the lower forms of animal life (_Protozoa_), we find the
Sponges represented by the curious bodies, composed of netted
fibres, to which the name of _Protospongia_ has been given (fig.
32, a); and the comparatively gigantic, conical, or cylindrical
fossils termed _Archoeocyathus_ by Mr Billings are certainly
referable either to the _Foraminifera_ or to the Sponges. The
almost total absence of limestones in the formation may be regarded
as a sufficient explanation of the fact that the _Foraminifera_
are not more largely and unequivocally represented; though the
existence of greensands in the Cambrian beds of Wisconsin and
Tennessee may be taken as an indication that this class of animals
was by no means wholly wanting. The same fact may explain the
total absence of corals, so far as at present known.
[Illustration: Fig. 29.--A portion of _Oldhamia antiqua_, Lower
Cambrian, Wicklow, Ireland, of the natural size. (After Salter.)]
The group of the _Echinodermata_ (Sea-lilies, Sea-urchins, and
their allies) is represented by a few forms, which are principally
of interest as being the earliest-known examples of the class.
It is also worthy of note that these precursors of a group which
subsequently attains such geological importance, are referable to
no less than three distinct _orders_--the Crinoids or Sea-lilies,
represented by a species of _Dendrocrinus_; the Cystideans by
_Protocystites_; and the Star-fishes by _Palasterina_ and some
other forms. Only the last of these groups, however, appears
to occur in the Lower Cambrian.
[Illustration: Fig. 30.--Annelide-burrows (_Scolithus linearus_)
from the Potsdam Sandstone of Canada, of the natural size. (After
Billings.)]
The Ringed-worms (_Annelida_), if rightly credited with all the
remains usually referred to them, appear to have swarmed in the
Cambrian seas. Being soft-bodied, we do not find the actual worms
themselves in the fossil condition, but we have, nevertheless,
abundant traces of their existence. In some cases we find vertical
burrows of greater or less depth, often expanded towards their
apertures, in which the worm must have actually lived (fig. 30),
as various species do at the present day. In these cases, the
tube must have been rendered more or less permanent by receiving
a coating of mucus, or perhaps a genuine membranous secretion,
from the body of the animal; and it may be found quite empty,
or occupied by a cast of sand or mud. Of this nature are the
burrows which have been described under the names of _Scolithus_
and _Scolecoderma_, and probably the _Histioderma_ of the Lower
Cambrian of Ireland. In other cases, as in _Arenicolites_ (fig.
32, b), the worm seems to have inhabited a double burrow, shaped
like the letter U, and having two openings placed close together
on the surface of the stratum. Thousands of these twin-burrows
occur in some of the strata of the Longmynd, and it is supposed
that the worm used one opening to the burrow as an aperture of
entrance, and the other as one of exit. In other cases, again,
we find simply the meandering trails caused by the worm dragging
its body over the surface of the mud. Markings of this kind are
commoner in the Silurian Rocks, and it is generally more or less
doubtful whether they may not have been caused by other marine
animals, such as shellfish, whilst some of them have certainly
nothing whatever to do with the worms. Lastly, the Cambrian beds
often show twining cylindrical bodies, commonly more or less
matted together, and not confined to the surfaces of the strata,
but passing through them. These have often been regarded as the
remains of sea-weeds, but it is more probable that they represent
casts of the underground burrows of worms of similar habits to
the common lob-worm (_Arenicola_) of the present day.
The _Articulate_ animals are numerously represented in the Cambrian
deposits, but exclusively by the class of _Crustaceans_. Some
of these are little double-shelled creatures, resembling our
living water-fleas (_Ostracoda_). A few are larger forms, and
belong to the same group as the existing brine-shrimps and
fairy-shrimps (_Phyllopoda_). One of the most characteristic of
these is the _Hymenocaris vermicauda_ of the Lingula Flags (fig.
32, d). By far the larger number of the Cambrian _Crustacea_
belong, however, to the remarkable and wholly extinct group of
the _Trilobites_. These extraordinary animals must have literally
swarmed in the seas of the later portion of this and the whole of
the succeeding period; and they survived in greatly diminished
numbers till the earlier portion of the Carboniferous period.
They died out, however, wholly before the close of the Palæozoic
epoch, and we have no Crustaceans at the present day which can be
considered as their direct representatives. They have, however,
relationships of a more or less intimate character with the existing
groups of the Phyllopods, the King-crabs (_Limulus_), and the
Isopods ("Slaters," Wood-lice, &c.) Indeed, one member of the
last-mentioned order, namely, the _Serolis_ of the coasts of
Patagonia, has been regarded as the nearest living ally of the
Trilobites. Be this as it may, the Trilobites possessed a skeleton
which, though capable of undergoing almost endless variations,
was wonderfully constant in its pattern of structure, and we
may briefly describe here the chief features of this.
[Illustration: Fig. 31.--Cambrian Trilobites: a, _Paradoxides
Bohemicus_, reduced in size; b, _Ellipsocephalus Hoffi_; c, _Sao
hirsuta_; d, _Conocorypke Sultzeri_ (all the above, together with
fig. g, are from the Upper Cambrian or "Primordial Zone" of
Bohemia); e, Head-shield of _Dikellocephalus Celticus_, from the
Lingula Flags of Wales; f, Head-shield of _Conocoryphe Matthewi_,
from the Upper Cambrian (Acadian Group) of New Brunswick; g,
_Agnostus rex_, Bohemia; h, Tail-shield of _Dikellocephalus
Minnesotensis_, from the Upper Cambrian (Potsdam Sandstone) of
Minnesota. (After Barrande, Dawson, Salter, and Dale Owen.)]
The upper surface of the body of a Trilobite was defended by a
strong shell or "crust," partly horny and partly calcareous in
its composition. This shell (fig. 31) generally exhibits a very
distinct "trilobation" or division into three longitudinal lobes,
one central and two lateral. It also exhibits a more important and
more fundamental division into three transverse portions, which
are so loosely connected with one another as very commonly to be
found separate. The first and most anterior of these divisions
is a shield or buckler which covers the head; the second or middle
portion is composed of movable rings covering the trunk ("thorax
"); and the third is a shield which covers the tailor "abdomen." The
head-shield (fig. 31, e) is generally more or less semicircular
in shape; and its central portion, covering the stomach of the
animal, is usually strongly elevated, and generally marked by
lateral furrows. A little on each side of the head are placed
the eyes, which are generally crescentic in shape, and resemble
the eyes of insects and many existing Crustaceans in being
"compound," or made up of numerous simple eyes aggregated together.
So excellent is the state of preservation of many specimens of
Trilobites, that the numerous individual lenses of the eyes have
been uninjured, and as many as four hundred have been counted
in each eye of some forms. The eyes may be supported upon
prominences, but they are never carried on movable stalks (as
they are in the existing lobsters and crabs); and in some of the
Cambrian Trilobites, such as the little _Agnosti_ (fig. 31 g),
the animal was blind. The lateral portions of the head-shield
are usually separated from the central portion by a peculiar
line of division (the so-called "facial suture") on each side;
but this is also wanting in some of the Cambrian species. The
backward angles of the head-shield, also, are often prolonged
into spines, which sometimes reach a great length. Following
the head-shield behind, we have a portion of the body which is
composed of movable segments or "body-rings," and which is
technically called the "thorax," Ordinarily, this region is strongly
trilobed, and each ring consists of a central convex portion,
and of two flatter side-lobes. The number of body-rings in the
thorax is very variable (from two to twenty-six), but is fixed
for the adult forms of each group of the Trilobites. The young
forms have much fewer rings than the full-grown ones; and it
is curious to find that the Cambrian Trilobites very commonly
have either a great many rings (as in _Paradoxides_, fig. 31,
a), or else very few (as in _Agnostus_, fig. 31, g). In some
instances, the body-rings do not seem to have been so constructed
as to allow of much movement, but in other cases this region of
the body is so flexible that the animal possessed the power of
rolling itself up completely, like a hedgehog; and many individuals
have been permanently preserved as fossils in this defensive
condition. Finally, the body of the Trilobite was completed by
a tail-shield (technically termed the "pygidium"), which varies
much in size and form, and is composed of a greater or less number
of rings, similar to those which form the thorax, but immovably
amalgamated with one another (fig. 31, h).
The under surface of the body in the Trilobites appears to have
been more or less entirely destitute of hard structures, with the
exception of a well-developed upper lip, in the form of a plate
attached to the inferior side of the head-shield in front. There
is no reason to doubt that the animal possessed legs; but these
structures seem to have resembled those of many living Crustaceans
in being quite soft and membranous. This, at any rate, seems to
have been generally the case; though structures which have been
regarded as legs have been detected on the under surface of one
of the larger species of Trilobites. There is also, at present,
no direct evidence that the Trilobites possessed the two pairs
of jointed feelers ("antennæ") which are so characteristic of
recent Crustaceans.
The Trilobites vary much in size, and the Cambrian formation
presents examples of both the largest and the smallest members
of the order. Some of the young forms may be little bigger than
a millet-seed, and some adult examples of the smaller species
(such as _Agnostus_) may be only a few lines in length; whilst
such giants of the order as _Paradoxides_ and _Asaphus_ may reach
a length of from one to two feet. Judging from what we actually
know as to the structure of the Trilobites, and also from analogous
recent forms, it would seem that these ancient Crustaceans were
mud-haunting creatures, denizens of shallow seas, and affecting
the soft silt of the bottom rather than the clear water above.
Whenever muddy sediments are found in the Cambrian and Silurian
formations, there we are tolerably sure to find Trilobites, though
they are by no means absolutely wanting in limestones. They appear
to have crawled out upon the sea-bottom, or burrowed in the yielding
mud, with the soft under surface directed downwards; and it is
probable that they really derived their nutriment from the organic
matter contained in the ooze amongst which they lived. The vital
organs seem to have occupied the central lobe of the skeleton,
by which they were protected; and a series of delicate leaf-like
paddles, which probably served as respiratory organs, would appear
to have been carried on the under surface of the thorax. That
they had their enemies may be regarded as certain; but we have
no evidence that they were furnished with any offensive weapons,
or, indeed, with any means of defence beyond their hard crust,
and the power, possessed by so many of them, of rolling themselves
into a ball. An additional proof of the fact that they for the
most part crawled along the sea-bottom is found in the occurrence
of tracks and markings of various kinds, which can hardly be
ascribed to any other creatures with any show of probability.
That this is the true nature of some of the markings in question
cannot be doubted at all; and in other cases no explanation so
probable has yet been suggested. If, however, the tracks which have
been described from the Potsdam Sandstone of North America under
the name of _Protichnites_ are really due to the peregrinations
of some Trilobite, they must have been produced by one of the
largest examples of the order.
As already said, the Cambrian Rocks are very rich in the remains
of Trilobites. In the lowest beds of the series (Longmynd Rocks),
representatives of some half-dozen genera have now been detected,
including the dwarf _Agnostus_ and the giant _Paradoxides_. In
the higher beds, the number both of genera and species is largely
increased; and from the great comparative abundance of individuals,
the Trilobites have every right to be considered as the most
characteristic fossils of the Cambrian period,--the more so as
the Cambrian species belong to peculiar types, which, for the
most part, died out before the commencement of the Silurian epoch.
All the remaining Cambrian fossils which demand any notice here
are members of one or other division of the great class of the
_Mollusca_, or "Shell-fish" properly so called. In the Lower
Cambrian Rocks the Lamp-shells (_Brachiopoda_) are the principal
or sole representatives of the class, and appear chiefly in three
interesting and important types--namely, _Lingulella, Discina,_
and _Obolella_. Of these the last (fig. 32, i) is highly
characteristic of these ancient deposits; whilst _Discina_ is
one of those remarkable persistent types which, commencing at
this early period, has continued to be represented by varying
forms through all the intervening geological formations up to the
present day. _Lingulella_ (fig. 32, c), again, is closely allied
to the existing "Goose-bill" Lamp-shell (_Lingula anatina_), and
thus presents us with another example of an extremely long-lived
type. The _Lingulelloe_ and their successors; the _Linguloe_, are
singular in possessing a shell which is of a horny texture, and
contains but a small proportion of calcareous matter. In the Upper
Cambrian Rocks, the _Lingulelloe_ become much more abundant, the
broad satchel-shaped species known as _L. Davisii_ (fig. 32,
e) being so abundant that one of the great divisions of the
Cambrian is termed the "Lingula Flags." Here, also, we meet for
the first time with examples of the genus Orthis (fig. 32, f,
k, l) a characteristic Palæozoic type of the Brachiopods, which
is destined to undergo a vast extension in later ages.
[Illustration: Fig 32.--Cambrian Fossils: a, _Protospongia
fenestrata_, Menevian Group; b, _Arenicolites didymus_, Longmynd
Group; c, _Lingulella ferruginea_, Longmynd and Menevian, enlarged;
d, _Hymenocaris vermicauda_, Lingula Flags; e, _Lingulella Davisii_,
Lingula Flags; f, _Orthis lenticularis_, Lingula Flags; g, _Theca
Davidii_, Tremadoc Slates; h, _Modiolopsis Solvensis_, Tremadoc
Slates; i, _Obolela sagittalis_, interior of valve, Menevian;
j, Exterior of the same; k, _Orthis Hicksii_, Menevian; l,
Cast of the same; m, _Olenus micrurus_, Lingula Flags. (Alter
Salter, Hicks, and Davidson.)]
Of the higher groups of the _Mollusca_ the record is as yet but
scanty. In the Lower Cambrian, we have but the thin, fragile,
dagger-shaped shells of the free-swimming oceanic Molluscs or
"Winged-snails" (_Pteropoda_), of which the most characteristic
is the genus _Theca_ (fig. 32, g). In the Upper Cambrian, in
addition to these, we have a few Univalves (_Gasteropoda_), and,
thanks to the researches of Dr Hicks, quite a small assemblage
of Bivalves (_Lamellibranchiata_), though these are mostly of no
great dimensions (fig. 32, h). Of the chambered _Cephalopoda_
(Cuttle-fishes and their allies), we have but few traces; and these
wholly confined to the higher beds of the formation. We meet,
however, with examples of the wonderful genus _Orthoceras_, with
its straight, partitioned shell, which we shall find in an immense
variety of forms in the Silurian rocks. Lastly, it is worthy of
note that the lowest of all the groups of the _Mollusca_--namely,
that of the Sea-mats, Sea-mosses, and Lace-corals (_Polyzoa_)--is
only doubtfully known to have any representatives in the Cambrian,
though undergoing a large and varied development in the Silurian
deposits.
[Illustration: Fig. 33.--Fragment of _Dictyonema sociale_,
considerably enlarged, showing the horny branches, with their
connecting cross-bars, and with a row of cells on each side.
(Original.)]
An exception, however, may with much probability be made to this
statement in favour of the singular genus _Dictyonema_ (fig.
33), which is highly characteristic of the highest Cambrian beds
(Tremadoc Slates). This curious fossil occurs in the form of
fan-like or funnel-shaped expansions, composed of slightly-diverging
horny branches, which are united in a net-like manner by numerous
delicate cross-bars, and exhibit a row of little cups or cells,
in which the animals were contained, on each side. _Dictyonema_
has generally been referred to the _Graptolites_; but it has a
much greater affinity with the plant-like Sea-firs (_Sertularians_)
or the Sea-mosses (_Polyzoa_), and the balance of evidence is
perhaps in favour of placing it with the latter.
LITERATURE.
The following are the more important and accessible works and
memoirs which may be consulted in studying the stratigraphical
and palæontological relations of the Cambrian Rocks:--
(1) 'Siluria.' Sir Roderick Murchison. 5th ed., pp. 21-46.
(2) 'Synopsis of the Classification of the British Palæozoic Rocks.'
Sedgwick. Introduction to the 3d Fasciculus of the 'Descriptions
of British Palæozoic Fossils in the Woodwardian Museum,'
by F. M'Coy, pp. i-xcviii, 1855.
(3) 'Catalogue of the Cambrian and Silurian Fossils in the Geological
Museum of the University of Cambridge.' Salter. With a Preface
by Prof. Sedgwick. 1873.
(4) 'Thesaurus Siluricus.' Bigsby. 1868.
(5) "History of the Names Cambrian and Silurian." Sterry
Hunt.--'Geological Magazine.' 1873.
(6) 'Système Silurien du Centre de la Bohême.' Barrande. Vol. I.
(7) 'Report of Progress of the Geological Survey of Canada, from its
Commencement to 1863,' pp. 87-109.
(8) 'Acadian Geology.' Dawson. Pp. 641-657.
(9) "Guide to the Geology of New York," Lincklaen; and "Contributions
to the Palæontology of New York," James Hall.--'Fourteenth
Report on the State Cabinet.' 1861.
(10) 'Palæozoic Fossils of Canada.' Billings. 1865.
(11) 'Manual of Geology.' Dana. Pp. 166-182. 2d ed. 1875.
(12) "Geology of North Wales," Ramsay; with Appendix on the
Fossils, Salter.--'Memoirs of the Geological Survey of Great
Britain,' vol. iii. 1866.
(13) "On the Ancient Rocks of the St David's Promontory, South Wales,
and their Fossil Contents." Harkness and Hicks.--' Quart.
Journ. Geol. Soc.,' xxvii. 384-402. 1871.
(14) "On the Tremadoc Rocks in the Neighbourhood of St David's,
South Wales, and their Fossil Contents." Hicks.--'Quart.
Journ. Geol. Soc.,' xxix. 39-52. 1873.
In the above list, allusion has necessarily been omitted to numerous
works and memoirs on the Cambrian deposits of Sweden and Norway,
Central Europe, Russia, Spain, and various parts of North America,
as well as to a number of important papers on the British Cambrian
strata by various well-known observers. Amongst these latter
may be mentioned memoirs by Prof. Phillips, and Messrs Salter,
Hicks, Belt, Plant, Homfray, Ash, Holl, &c.
CHAPTER IX.
THE LOWER SILURIAN PERIOD.
The great system of deposits to which Sir Roderick Murchison
applied the name of "Silurian Rocks" reposes directly upon the
highest Cambrian beds, apparently without any marked unconformity,
though with a considerable change in the nature of the fossils. The
name "Silurian" was originally proposed by the eminent geologist
just alluded to for a great series of strata lying below the Old
Red Sandstone, and occupying districts in Wales and its borders
which were at one time inhabited by the "Silures," a tribe of
ancient Britons. Deposits of a corresponding age are now known
to be largely developed in other parts of England, in Scotland,
and in Ireland, in North America, in Australia, in India, in
Bohemia, Saxony, Bavaria, Russia, Sweden and Norway, Spain, and
in various other regions of less note. In some regions, as in
the neighbourhood of St Petersburg, the Silurian strata are found
not only to have preserved their original horizontality, but
also to have retained almost unaltered their primitive soft and
incoherent nature. In other regions, as in Scandinavia and many
parts of North America, similar strata, now consolidated into
shales, sandstones, and limestones, may be found resting with
a very slight inclination on still older sediments. In a great
many regions, however, the Silurian deposits are found to have
undergone more or less folding, crumpling, and dislocation,
accompanied by induration and "cleavage" of the finer and softer
sediments; whilst in some regions, as in the Highlands of Scotland,
actual "metamorphism" has taken place. In consequence of the
above, Silurian districts usually present the bold, rugged, and
picturesque outlines which are characteristic of the older
"Primitive" rocks of the earth's crust in general. In many instances,
we find Silurian strata rising into mountain-chains of great
grandeur and sublimity, exhibiting the utmost diversity of which
rock-scenery is capable, and delighting the artist with endless
changes of valley, lake, and cliff. Such districts are little
suitable for agriculture, though this is often compensated for
by the valuable mineral products contained in the rocks. On the
other hand, when the rocks are tolerably soft and uniform in
their nature, or when few disturbances of the crust of the earth
have taken place, we may find Silurian areas to be covered with
an abundant pasturage or to be heavily timbered.
Under the head of "Silurian Rocks," Sir Roderick Murchison included
all the strata between the summit of the "Longmynd." beds and the
Old Red Sandstone, and he divided these into the two great groups
of the _Lower_ Silurian and _Upper_ Silurian. It is, however, now
generally admitted that a considerable portion of the basement
beds of Murchison's Silurian series must be transferred---if only
upon palæontological grounds--to the Upper Cambrian, as has here
been done; and much controversy has been carried on as to the proper
nomenclature of the Upper Silurian and of the remaining portion
of Murchison's Lower Silurian. Thus, some would confine the name
"Silurian" exclusively to the Upper Silurian, and would apply the
name of "Cambro-Silurian" to the Lower Silurian, or would include
all beds of the latter age in the "Cambrian" series of Sedgwick.
It is not necessary to enter into the merits of these conflicting
views. For our present purpose, it is sufficient to recognise
that there exist two great groups of rocks between the highest
Cambrian beds, as here defined, and the base of the Devonian or
Old Red Sandstone. These two great groups are so closely allied
to one another, both physically and palæontologically, that many
authorities have established a third or intermediate group (the
"Middle Silurian"), by which a passage is made from one into
the other. This method of procedure involves disadvantages which
appear to outweigh its advantages; and the two groups in question
are not only generally capable of very distinct stratigraphical
separation, but at the same time exhibit, together with the alliances
above spoken of, so many and such important palæontological
differences, that it is best to consider them separately. We
shall therefore follow this course in the present instance; and
pending the final solution of the controversy as to Cambrian and
Silurian nomenclature, we shall distinguish these two groups
of strata as the "Lower Silurian" and the "Upper Silurian."
The _Lower Silurian Rocks_ are known already to be developed
in various regions; and though their _general_ succession in
these areas is approximately the same, each area exhibits
peculiarities of its own, whilst the subdivisions of each are
known by special names. All, therefore, that can be attempted
here, is to select two typical areas--such as Wales and North
America and to briefly consider the grouping and divisions of
the Lower Silurian in each.
In Wales, the line between the Cambrian and Lower Silurian is
somewhat ill-defined, and is certainly not marked by any strong
unconformity. There are, however; grounds for accepting the line
proposed, for palæontological reasons, by Dr Hicks, in accordance
with which the Tremadoc Slates ("Lower Tremadoc" of Salter) become
the highest of the Cambrian deposits of Britain. If we take this
view, the Lower Silurian rocks of Wales and adjoining districts
are found to have the following _general_ succession from below
upwards (fig. 34):--
1. The _Arenig Group_.--This group derives its name from the
Arenig mountains, where it is extensively developed. It consists
of about 4000 feet of slates, shales, and flags, and is divisible
into a lower, middle, and upper division, of which the former
is often regarded as Cambrian under the name of "Upper Tremadoc
Slates."
2. The _Llandeilo Group_.--The thickness of this group varies
from about 4000 to as much as 10,000 feet; but in this latter
case a great amount of the thickness is made up of volcanic ashes
and interbedded traps. The sedimentary beds of this group are
principally slates and flags, the latter occasionally with calcareous
bands; and the whole series can be divided into a lower, middle,
and upper Llandeilo division, of which the last is the most
important. The name of "Llandeilo" is derived from the town of
the same name in Wales, where strata of this age were described
by Murchison.
3. The _Caradoc_ or _Bala Group_.--The alternative names of this
group are also of local origin, and are derived, the one from
Caer Caradoc in Shropshire, the other from Bala in Wales, strata
of this age occurring in both localities. The series is divided
into a lower and upper group, the latter chiefly composed of
shales and flags, and the former of sandstones and shales, together
with the important and interesting calcareous band known as the
"Bala Limestone." The thickness of the entire series varies from
4000 to as much as 12,000 feet, according as it contains more
or less of interstratified igneous rocks.
4. The _Llandovery Group_ (Lower Llandovery of Murchison).--This
series, as developed near the town of Llandovery, in
Caermarthenshire, consists of less than 1000 feet of conglomerates,
sandstones, and shales. It is probable, however, that the little
calcareous band known as the "Hirnant Limestone," together with
certain pale-coloured slates which lie above the Bala Limestone,
though usually referred to the Caradoc series, should in reality
be regarded as belonging to the Llandovery group.
The general succession of the Lower Silurian strata of Wales
and its borders, attaining a maximum thickness (along with
contemporaneous igneous matter) of nearly 30,000 feet, is
diagramatically represented in the annexed sketch-section (fig.
34):--
[Illustration: Fig 34. GENERALIZED SECTION OF THE LOWER SILURIAN
ROCKS OF WALES.]
In North America, both in the United States and in Canada, the
Silurian rocks are very largely developed, and may be regarded
as constituting an exceedingly full and typical series of the
deposits of this period. The chief groups of the Silurian rocks
of North America are as follows, beginning, as before, with the
lowest strata, and proceeding upwards (fig. 35):--
1. _Quebec Group_.--This group is typically developed in the
vicinity of Quebec, where it consists of about 5000 feet of strata,
chiefly variously-coloured shales, together with some sandstones
and a few calcareous bands. It contains a number of peculiar
Graptolites, by which it can be identified without question with
the Arenig group of Wales and the corresponding Skiddaw Slates
of the North of England. It is also to be noted that numerous
Trilobites of a distinct Cambrian _facies_ have been obtained in
the limestones of the Quebec group, near Quebec. These fossils,
however, have been exclusively obtained from the limestones of
the group; and as these limestones are principally calcareous
breccias or conglomerates, there is room for believing that these
primordial fossils are really derived, in part at any rate, from
fragments of an upper Cambrian limestone. In the State of New
York, the Graptolitic shales of Quebec are wanting; and the base
of the Silurian is constituted by the so-called "Calciferous
Sand-rock" and "Chazy Limestone."[11] The first of these is
essentially and typically calcareous, and the second is a genuine
limestone.
[Footnote 11: The precise relations of the Quebec shales with
Graptolites (Levis Formation) to the Calciferous and Chazy beds
are still obscure, though there seems little doubt but that the
Quebec Shales are superior to the Calciferous Sand-rock.]
2. The _Trenton Group_.--This is an essentially calcareous group,
the various limestones of which it is composed being known as
the "Bird's-eye," "Black River," and "Trenton" Limestones, of
which the last is the thickest and most important. The thickness
of this group is variable, and the bands of limestone in it are
often separated by beds of shale.
3. The _Cincinnati Group_ (Hudson River Formation[12]).--This
group consists essentially of a lower series of shales, often
black in colour and highly charged with bituminous matter (the
"Utica Slates "), and of an upper series of shales, sandstones, and
limestones (the "Cincinnati" rocks proper). The exact parallelism
of the Trenton and Cincinnati groups with the subdivisions of the
Welsh Silurian series can hardly be stated positively. Probably
no precise equivalency exists; but there can be no doubt but that
the Trenton and Cincinnati groups correspond, as a whole, with the
Llandeilo and Caradoc groups of Britain. The subjoined diagrammatic
section (fig. 35) gives a general idea of the succession of the
Lower Silurian rocks of North America:--
[Illustration: Fig 35. GENERALIZED SECTION OF THE LOWER SILURIAN
ROCKS OF NORTH AMERICA.]
[Illustration: Fig. 36.--_Licrophycus Ottawaensis_ a "Fucoid,"
from the Trenton Limestone (Lower Silurian) of Canada. (After
Billings.)]
[Footnote 12: There is some difficulty about the precise nomenclature
of this group. It was originally called the "Hudson River Formation;"
but this name is inappropriate, as rocks of this age hardly touch
anywhere the actual Hudson River itself, the rocks so called
formerly being now known to be of more ancient date. There is
also some want of propriety in the name of "Cincinnati Group,"
since the rocks which are known under this name in the vicinity of
Cincinnati itself are the representatives of the Trenton Limestone,
Utica Slates, and the old Hudson River group, inseparably united
in what used to be called the "Blue Limestone Series."].
Of the _life_ of the Lower Silurian period we have record in
a vast number of fossils, showing that the seas of this period
were abundantly furnished with living denizens. We have, however,
in the meanwhile, no knowledge of the land-surfaces of the period.
We have therefore no means of speculating as to the nature of
the terrestrial animals of this ancient age, nor is anything
known with certainty of any land-plants which may have existed.
The only relics of vegetation upon which a positive opinion can
be expressed belong to the obscure group of the "Fucoids," and
are supposed to be the remains of sea-weeds. Some of the fossils
usually placed under this head are probably not of a vegetable
nature at all, but others (fig. 36) appear to be unquestionable
plants. The true affinities of these, however, are extremely
dubious. All that can be said is, that remains which appear to
be certainly vegetable, and which are most probably due to marine
plants, have been recognised nearly at the base of the Lower
Silurian (Arenig), and that they are found throughout the series
whenever suitable conditions recur.
The Protozoans appear to have flourished extensively in the Lower
Silurian seas, though to a large extent under forms which are
still little understood. We have here for the first time the
appearance of Foraminifera of the ordinary type--one of the most
interesting observations in this collection being that made by
Ehrenberg, who showed that the Lower Silurian sandstones of the
neighbourhood of St Petersburg contained casts in glauconite of
Foraminiferous shells, some of which are referable to the existing
genera _Rotalia_ and _Texularia_. True _Sponges_, belonging to
that section of the group in which the skeleton is calcareous,
are also not unknown, one of the most characteristic genera being
_Astylospongia_ (fig. 37). In this genus are included more or
less globular, often lobed sponges, which are believed not to
have been attached to foreign bodies. In the form here figured
there is a funnel-shaped cavity at the summit; and the entire
mass of the sponge is perforated, as in living examples, by a
system of canals which convey the sea-water to all parts of the
organism. The canals by which the sea-water gains entrance open
on the exterior of the sphere, and those by which it again escapes
from the sponge open into the cup-shaped depression at the summit.
[Illustration: Fig. 37.--_Astylospongia proemorsa_, cut vertically
so as to exhibit the canal-system in the interior. Lower Silurian,
Tennessee. (After Ferdinand Roemer.)]
The most abundant, and at the same time the least understood,
of Lower Silurian Protozoans belong, however, to the genera
_Stromatopora_ and _Receptaculites_, the structure of which can
merely be alluded to here. The specimens of _Stromatopora_ (fig.
38) occur as hemispherical, pear-shaped, globular, or irregular
masses, often of very considerable size, and sometimes demonstrably
attached to foreign bodies. In their structure these masses consist
of numerous thin calcareous laminæ, usually arranged concentrically,
and separated by narrow interspaces. These interspaces are generally
crossed by numerous vertical calcareous pillars, giving the vertical
section of the fossil a lattice-like appearance. There are also
usually minute pores in the concentric laminæ, by which the
successive interspaces are placed in communication; and sometimes
the surface presents large rounded openings, which appear to
correspond with the water-canals of the Sponges. Upon the whole,
though presenting some curious affinities to the calcareous Sponges,
_Stromatopora_ is perhaps more properly regarded as a gigantic
_Foraminifer_. If this view be correct, it is of special interest
as being probably the nearest ally of _Eozoön_, the general
appearance of the two being strikingly similar, though their
minute structure is not at all the same. Lastly, in the fossils
known as _Receptaculites_ and _Ischadites_ we are also presented
with certain singular Lower Silurian Protozoans, which may with
great probability be regarded as gigantic _Foraminifera_. Their
structure is very complex; but fragments are easily recognised
by the fact that the exterior is covered with numerous rhomboidal
calcareous plates, closely fitting together, and arranged in
peculiar intersecting curves, presenting very much the appearance
of the engine-turned case of a watch.
[Illustration: Fig. 38.--A small and perfect specimen of
_Stromatopora rugosa_, of the natural size, from the Trenton
Limestone of Canada. (After Billings.)]
Passing next to the sub-kingdom of _Coelenterate_ animals (Zoophytes,
Corals, &c.), we find that this great group, almost or wholly
absent in the Cambrian, is represented in Lower Silurian deposits
by a great number of forms belonging on the one hand to the true
Corals, and en the other hand to the singular family of the
_Graptolites_. If we except certain plant-like fossils which
probably belong rather to the Sertularians or the Polyzoans (e.g.,
_Dictyonema, Dendrograptus_, &c.), the family of the _Graptolites_
may be regarded as exclusively Silurian in its distribution. Not
only is this the case, but it attained its maximum development
almost upon its first appearance, in the Arenig Rocks; and whilst
represented by a great variety of types in the Lower Silurian;
it only exists in the Upper Silurian in a much diminished form.
The _Graptolites_ (Gr. _grapho_, I write; _lithos_, stone) were
so named by Linnæus, from the resemblance of some of them to
written or pencilled marks upon the stone, though the great
naturalist himself did not believe them to be true fossils at
all. They occur as linear or leaf-like bodies, sometimes simple,
sometimes compound and branched; and no doubt whatever can be
entertained as to their being the skeletons of composite organisms,
or colonies of semi-independent animals united together by a common
fleshy trunk, similar to what is observed in the colonies of the
existing Sea-firs (Sertularians). This fleshy trunk or common
stem of the colony was protected by a delicate horny sheath, and
it gave origin to the little flower-like "polypites," which
constituted the active element of the whole assemblage. These
semi-independent beings were, in turn, protected each by a little
horny cup or cell, directly connected with the common sheath
below, and terminating above in an opening through which the
polypite could protrude its tentacled head or could again withdraw
itself for safety. The entire skeleton, again, was usually, if
not universally, supported by a delicate horny rod or "axis,"
which appears to have been hollow, and which often protrudes to
a greater or less extent beyond one or both of the extremities
of the actual colony.
The above gives the elementary constitution of any _Graptolite_,
but there are considerable differences as to the manner in which
these elements are arranged and combined. In some forms the common
stem of the colony gives origin to but a single row of cells
on one side. If the common stem is a simple, straight, or
slightly-curved linear body, then we have the simplest form of
Graptolite known (the genus _Monograptus_); and it is worthy of
note that these simple types do not come into existence till
comparatively late (Llandeilo), and last nearly to the very close
of the Upper Silurian. In other cases, whilst there is still but
a single row of cells, the colony may consist of two of these
simple stems springing from a common point, as in the so-called
"twin Graptolites" (_Didymograptus_, fig. 40). This type is entirely
confined to the earlier portion of the Lower Silurian period
(Arenig and Llandeilo). In other cases, again, there may be four
of such stems springing from a central point (_Tetragraptus_).
Lastly, there are numerous complex forms (such as _Dichograptus,
Loganograptus_, &c.) in which there are eight or more of these
simple branches, all arising from a common centre (fig. 39),
which is sometimes furnished with a singular horny disc. These
complicated branching forms, as well as the _Tetragrapti_, are
characteristic of the horizon of the Arenig group. Similar forms,
often specifically identical, are found at this horizon in Wales,
in the great series of the Skiddaw Slates of the north of England,
in the Quebec group in Canada, in equivalent beds in Sweden, and
in certain gold-bearing slates of the same age in Victoria in
Australia.
[Illustration: Fig. 39.--_Dichograptus octobrachiatus_, a branched,
"unicellular" Graptolite from the Skiddaw and Quebec Groups (Arenig).
(After Hall.)]
In another great group of Graptolites (including the genera
_Diplograptus, Dicranograptus, Climacograptus_, &c.) the common
stem of the colony gives origin, over part or the whole or its
length, to _two_ rows of cells, one on each side (fig. 41). These
"double-celled" Graptolites are highly characteristic of the Lower
Silurian deposits; and, with an exception more apparent than real
in Bohemia, they are exclusively confined to strata of Lower
Silurian age, and are not known to occur in the Upper Silurian.
Lastly, there is a group of Graptolites (_Phyllograptus_, fig.
42) in which the colony is leaf-like in form, and is composed
of _four_ rows of cells springing in a cross-like manner from
the common stem. These forms are highly characteristic of the
Arenig group.
[Illustration: Fig. 40.--Central portion of the colony of
_Didymegraptus divaricatus_, Upper Llandeilo, Dumfresshire.
(Original.)]
[Illustration: Fig. 41.--Examples of _Diplograptus pristis_,
showing variations in the appendages at the base. Upper Llandeilo,
Dumfriesshire. (Original.)]
[Illustration: Fig. 42.--Group of individuals of _Phyllograptus
typus_, from the Quebec group of Canada. (After Hall.) One of
the four rows of cells is hidden on the under surface.]
The Graptolites are usually found in dark-coloured, often black
shales, which sometimes contain so much carbon as to become
"anthracitic." They may be simply carbonaceous; but they are
more commonly converted into iron-pyrites, when they glitter
with the brilliant lustre of silver as they lie scattered on the
surface of the rock, fully deserving in their metallic tracery
the name of "written stones." They constitute one of the most
important groups of Silurian fossils, and are of the greatest
value in determining the precise stratigraphical position of
the beds in which they occur. They present, however, special
difficulties in their study; and it is still a moot point as
to their precise position in the zoological scale. The balance
of evidence is in favour of regarding them as an ancient and
peculiar group of the Sea-firs (Hydroid Zoophytes), but some
regard them as belonging rather to the Sea-mosses (_Polyzoa_).
Under any circumstances, they cannot be directly compared either
with the ordinary Sea-firs or the ordinary Sea-mosses; for these
two groups consist of fixed organisms, whereas the Graptolites
were certainly free-floating creatures, living at large in the
open sea. The only Hydroid Zoophytes or Polyzoans which have
a similar free mode of existence, have either no skeleton at
all, or have hard structures quite unlike the horny sheaths of
the Graptolites.
The second great group of Coelenterate animals (_Actinozoa_)
is represented in the Lower Silurian rocks by numerous Corals.
These, for obvious reasons, are much more abundant in regions
where the Lower Silurian series is largely calcareous (as in
North America) than in districts like Wales, where limestones
are very feebly developed. The Lower Silurian Corals, though
the first of their class, and presenting certain peculiarities,
may be regarded as essentially similar in nature to existing
Corals. These, as is well known, are the calcareous skeletons of
animals--the so-called "Coral-Zoophytes"--closely allied to the
common Sea-anemones in structure and habit. A _simple_ coral (fig.
43) consists of a calcareous cup embedded in the soft tissues of
the flower-like polype, and having at its summit a more or less
deep depression (the "calice") in which the digestive organs
are contained. The space within the coral is divided into
compartments by numerous vertical calcareous plates (the "septa"),
which spring from the inside of the wall of the cup, and of which
some generally reach the centre. _Compound_ corals, again (fig.
44), consist of a greater or less number of structures similar
in structure to the above, but united together in different ways
into a common mass. _Simple_ corals, therefore, are the skeletons
of _single_ and independent polypes; whilst _compound_ corals
are the skeletons of assemblages or colonies of similar polypes,
living united with one another another as an organic community.
[Illustration: Fig. 43.--_Zaphrentis Stokesi_, a simple "cup-coral,"
Upper Silurian, Canada. (After Billings.)]
[Illustration: Fig. 44.--Upper surface of a mass of _Strombodes
pentagonus_. Upper Silurian, Canada. (After Billings.)]
In the general details of their structure, the Lower Silurian
Corals do not differ from the ordinary Corals of the present
day. The latter, however, have the vertical calcareous plates
of the coral ("septa") arranged in multiples of six or five;
whereas the former have these structures arranged in multiples
of four, and often showing a cross-like disposition. For this
reason, the common Lower Silurian Corals are separated to form
a distinct group under the name of _Rugose_ Corals or _Rugosa_.
They are further distinguished by the fact that the cavity of
the coral ("visceral chamber") is usually subdivided by more
or less numerous horizontal calcareous plates or partitions,
which divide the coral into so many tiers or storeys, and which
are known as the "tabulæ" (fig. 45).
[Illustration: Fig. 45.--_Columnaria alveolata_, a Rugose compound
coral, with imperfect septa, but having the corallites partitioned
off into storeys by "tabulæ." Lower Silurian, Canada. (After
Billings.)]
In addition to the Rugose Corals, the Lower Silurian rocks contain
a number of curious compound corals, the tubes of which have
either no septa at all or merely rudimentary ones, but which
have the transverse partitions or "tabulæ" very highly developed.
These are known as the _Tabulate Corals_; and recent researches
on some of their existing allies (such as _Heliopora_) have shown
that they are really allied to the modern Sea-pens, Organ-pipe
Corals, and Red Coral, rather than to the typical stony Corals.
Amongst the characteristic Rugose Corals of the Lower Silurian
may be mentioned species belonging to the genera _Columnaria,
Favistella, Streptelasma_, and _Zaphrentis_; whilst amongst the
"Tabulate" Corals, the principal forms belong to the genera
_Choetetes, Halysites_ (the Chain-coral), _Constellaria_, and
_Heliolites_. These groups of the Corals, however, attain a greater
development at a later period, and they will be noticed more
particularly hereafter.
[Illustration: Fig. 46.--Group of Cystideans. A, _Caryocrinus
ornatus_,[13] Upper Silurian, America; B, _Pleurocystites squamosus_,
showing two short "arms," Lower Silurian, Canada; C, _Pseudocrinus
bifasciatus_, Upper Silurian, England; D, _Lepadocrinus Gebhartii_,
Upper Silurian, America. (After Hall, Billings, and Salter.)]
[Footnote 13: The genus _Caryocrinus_ is sometimes regarded as
properly belonging to the _Crinoids_, but there seem to be good
reasons for rather considering it as an abnormal form of
_Cystidean_.]
Passing onto higher animals, we find that the class of the
_Echinodermata_ is represented by examples of the Star-fishes
(_Asteroidea_), the Sea-lilies (_Crinoidea_), and the peculiar
extinct group of the Cystideans (_Cystoidea_), with one or two of
the Brittle-stars (_Ophiuroidea_)--the Sea-urchins (_Echinoidea_)
being still wanting. The Crinoids, though in some places extremely
numerous, have not the varied development that they possess in
the Upper Silurian, in connection with which their structure will
be more fully spoken of. In the meanwhile, it is sufficient to
note that many of the calcareous deposits of the Lower Silurian
are strictly entitled to the name of "Crinoidal limestones,"
being composed in great part of the detached joints, and plates,
and broken stems, of these beautiful but fragile organisms (see
fig. 12). Allied to the Crinoids are the singular creatures which
are known as _Cystideans_ (fig. 46). These are generally composed
of a globular or ovate body (the "calyx"), supported upon a short
stalk (the "column"), by which the organism was usually attached
to some foreign body. The body was enclosed by closely-fitting
calcareous plates, accurately jointed together; and the stem was
made up of numerous distinct pieces or joints, flexibly united
to each other by membrane. The chief distinction which strikes
one in comparing the Cystideans with the Crinoids is, that the
latter are always furnished, as will be subsequently seen, with
a beautiful crown of branched and feathery appendages, springing
from the summit of the calyx, and which are composed of innumerable
calcareous plates or joints, and are known as the "arms." In the
Cystideans, on the other hand, there are either no "arms" at all,
or merely short, unbranched, rudimentary arms. The Cystideans are
principally, and indeed nearly exclusively, Silurian fossils;
and though occurring in the Upper Silurian in no small numbers,
they are pre-eminently characteristic of the Llandeilo-Caradoc
period of Lower Silurian time. They commenced their existence,
so far as known, in the Upper Cambrian; and though examples are
not absolutely unknown in later periods, they are pre-eminently
characteristic of the earlier portion of the Palæozoic epoch.
[Illustration: Fig. 47.--Lower Silurian Crustaceans. a, _Asaphus
tyrannus_, Upper Llandeilo; b. _Ogygia Buchii_, Upper Llandeilo;
c, _Trinucleus concentricus_, Caradoc; d, _Caryocaris Wrightii_,
Arenig (Skiddaw Slates); e, _Beyrichia complicata_, natural size and
enlarged, Upper Llandeilo and Caradoc; f, _Primitia strangulata_,
Caradoc: g. Head-shield of _Calymene Blumenbachii_, var.
_brevicapitata_, Caradoc; h, Head-shield of _Triarthrus Becki_
(Utica Slates), United States: i, Shield of _Leperditia
Canadensis_, var. _Josephiana_, of the natural size, Trenton
Limestone, Canada; j, The same, viewed from the front. (After
Salter, M'Coy, Rupert Jones, and Dana.)]
The Ringed Worms (_Annelides_) are abundantly represented in the
Lower Silurian, but principally by tracks and burrows similar
in essential respects to those which occur so commonly in the
Cambrian formation, and calling for no special comment. Much more
important are the _Articulate_ animals, represented as heretofore,
wholly by the remains of the aquatic group of the _Crustaceans_.
Amongst these are numerous little bivalved forms--such as species
of _Primitia_ (fig. 47, f), _Beyrichia_ (fig. 47, e), and
_Leperditia_ (fig. 47, i and j). Most of these are very small,
varying from the size of a pin's head up to that of a hemp seed;
but they are sometimes as large as a small bean (fig. 47, i),
and they are commonly found in myriads together in the rock. As
before said, they belong to the same great group as the living
Water-fleas (_Ostracoda_). Besides these, we find the pod-shaped
head-shields of the shrimp-like Phyllopods--such as _Caryocaris_
(fig. 47, d) and _Ceratiocaris_. More important, however, than
any of these are the _Trilobites_, which may be considered as
attaining their maximum development in the Lower Silurian. The
huge _Paradoxides_ of the Cambrian have now disappeared, and with
them almost all the principal and characteristic "primordial"
genera, save _Olenus_ and _Agnostus_. In their place we have a
great number of new forms--some of them, like the great _Asaphus
tyrannus_ of the Upper Llandeilo (fig. 47, a), attaining a
length of a foot or more, and thus hardly yielding in the matter
of size to their ancient rivals. Almost every subdivision of the
Lower Silurian series has its own special and characteristic
species of Trilobites; and the study of these is therefore of
great importance to the geologist. A few widely-dispersed and
characteristic species have been here figured (fig. 47); and
the following may be considered as the principal Lower Silurian
genera--_Asaphus, Ogygia, Cheirurus, Ampyx, Caiymene, Trinucleus,
Lichas, Illoenus, Æglina, Harpes, Remopleurides, Phacops, Acidaspis_,
and _Homalonotus_, a few of them passing upwards under new forms
into the Upper Silurian.
Coming next to the _Mollusca_, we find the group of the Sea-mosses
and Sea-mats (_Polyzoa_) represented now by quite a number of forms.
Amongst these are examples of the true Lace-corals (_Retepora_
and _Fenestella_), with their netted fan-like or funnel-shaped
fronds; and along with these are numerous delicate encrusting
forms, which grew parasitically attached to shells and corals
(_Hippothoa, Alecto_, &c.); but perhaps the most characteristic
forms belong to the genus _Ptilodictya_ (figs. 48 and 49). In
this group the frond is flattened, with thin striated edges,
sometimes sword-like or scimitar-shaped, but often more or less
branched; and it consists of two layers of cells, separated by
a delicate membrane, and opening upon opposite sides. Each of
these little chambers or "cells" was originally tenanted by a
minute animal, and the whole thus constituted a compound organism
or colony.
[Illustration: Fig. 48.--_Ptilodictya falciformis_. a, Small
specimen of the natural size; b, Cross-section, showing the
shape of the frond; c, Portion of the surface, enlarged. Trenton
Limestone and Cincinnati Group, America. (Original.)]
[Illustration: Fig. 49.--A, _Ptilodictya acuta_; B, _Ptilodictya
Schafferi_. a, Fragment, of the natural size; b, Portion,
enlarged to show the cells. Cincinnati Group of Ohio and Canada.
(Original.)]
[Illustration: Fig. 50.--Lower Silurian Brachiopods. a and
a', _Orthis biforata_, Llandeilo-Caradoc, Britain and America:
b, _Orthis flabellulum_, Caradoc, Britain: c, _Orthis subquadrata_,
Cincinnati Group, America; c', Interior of the dorsal valve of
the same: d, _Strophomena deltoidea_, Llandeilo-Caradoc, Britain
and America. (After Meek, Hall, and Salter.)]
The Lamp-shells or _Brachiopods_ are so numerous, and present
such varied types, both in this and the succeeding period of
the Upper Silurian, that the name of "Age of Brachiopods" has
with justice been applied to the Silurian period as a whole. It
would be impossible here to enter into details as to the many
different forms of Brachiopods which present themselves in the
Lower Silurian deposits; but we may select the three genera _Orthis,
Strophomena_, and _Leptoena_ for illustration, as being specially
characteristic of this period, though not exclusively confined to it.
The numerous shells which belong to the extensive and cosmopolitan
genus _Orthis_ (fig. 50, a, b, c, and fig. 51, c and d),
are usually more or less transversely-oblong or subquadrate, the
two valves (as more or less in all the Brachiopods) of unequal
sizes, generally more or less convex, and marked with radiating
ribs or lines. The valves of the shell are united to one another
by teeth and sockets, and there is a straight hinge-line. The beaks
are also separated by a distinct space ("hinge-area"), formed in
part by each valve, which is perforated by a triangular opening,
through which, in the living condition, passed a muscular cord
attaching the shell to some foreign object. The genus _Strophomena_
(fig. 50, d, and 51, a and b) is very like _Orthis_ in
general character; but the shell is usually much flatter, one
or other valve often being concave, the hinge-line is longer,
and the aperture for the emission of the stalk of attachment is
partially closed by a calcareous plate. In _Leptoena_, again
(fig. 51, e), the shell is like _Strophomena_ in many respects,
but generally comparatively longer, often completely semicircular,
and having one valve convex and the other valve concave. Amongst
other genera of Brachiopods which are largely represented in the
Lower Silurian rocks may be mentioned _Lingula, Crania, Discina,
Trematis, Siphonotreta, Acrotreta, Rhynchonella_, and _Athyris_;
but none of these can claim the importance to which the three
previously-mentioned groups are entitled.
[Illustration: Fig. 51.--Lower Silurian Brachiopods, a, _Strophomena
alternata_, Cincinnati Group, America; b, _Strophomena filitexta,
Trenton and Cincinnati Groups, America; c, _Orthis testudinaria_,
Caradoc, Europe, and America; d, d', _Orthis plicateila_, Cincinnati
Group, America; e, e', e'', _Leptoena sericea_, Llandeilo and
Caradoc, Europe and America. (After Meek, Hall, and the Author.)]
The remaining Lower Silurian groups of _Mollusca_ can be but
briefly glanced at here. The Bivalves (_Lamellibranchiata_) find
numerous representatives, belonging to such genera as _Modiolopsis,
Ctenodonta, Orthonota, Paloearca, Lyrodesma, Ambonychia_, and
_Cleidophorus_. The Univalves (_Gasteropoda_) are also very numerous,
the two most important genera being _Murchisonia_ (fig. 52) and
_Pleurotomaria_. In both these groups the outer lip of the shell
is notched; but the shell in the former is elongated and turreted,
whilst in the latter it is depressed. The curious oceanic Univalves
known as the _Heteropods_ are also very abundant, the principal
forms belonging to _Bellerophon_ and _Maclurea_. In the former
(fig. 53) there is a symmetrical convoluted shell, like that of
the Pearly Nautilus in shape, but without any internal partitions,
and having the aperture often expanded and notched behind. The
species of _Maclurea_ (fig. 54) are found both in North America
and in Scotland, and are exclusively confined to the Lower Silurian
period, so far as known. They have the shell coiled into a flat
spiral, the mouth being furnished with a very curious, thick,
and solid lid or "operculum." The Lower Silurian _Pteropods_,
or "Winged snails," are numerous, and belong principally to the
genera _Theca, Conularia_, and _Tentaculites_, the last-mentioned
of these often being extremely abundant in certain strata.
[Illustration: Fig. 52.--_Murchisonia gracilis_, Trenton Limestone,
America. (After Billings.)]
[Illustration: Fig. 53.--Different views of _Bellerophon Argo_,
Trenton Limestone, Canada. (After Billings.)]
[Illustration: Fig. 54.--Different views of _Maclurea crenulata_,
Quebec Group, Newfoundland. (After Billings.)]
[Illustration: Fig. 55.--Fragment of _Orthoceras crebriseptum_,
Cincinnati Group, North America, of the natural size. The lower
figure section showing the air-chambers, and the form and position
of the siphuncle. (After Billings.)]
[Illustration: Fig. 56.--[14] Restoration of Orthoceras, the shell
being supposed to be divided vertically, and only its upper part
being shown. a, Arms; f, Muscular tube ("funnel") by which
water is expelled from the mantle-chamber; c, Air-chambers;
s, Siphuncle.]
[Footnote 14: This illustration is taken from a rough sketch
made by the author many years ago, but he is unable to say from
what original source it was copied.]
Lastly, the Lower Silurian Rocks have yielded a vast number of
chambered shells, referable to animals which belong to the same
great division as the Cuttle-fishes (the _Cephalopoda_), and
of which the Pearly Nautilus is the only living representative
at the present day. In this group of _Cephalopods_ the animal
possesses a well-developed external shell, which is divided into
chambers by shelly partitions ("septa"). The animal lives in
the last-formed and largest chamber of the shell, to which it
is organically connected by muscular attachments. The head is
furnished with long muscular processes or "arms," and can be
protruded from the mouth of the shell at will, or again withdrawn
within it. We learn, also, from the Pearly Nautilus, that these
animals must have possessed two pairs of breathing organs or
"gills;" hence all these forms are grouped together under the
name of the "Tetrabranchiate" Cephalopods (Gr. _tetra_, four;
_bragchia_, gill). On the other hand, the ordinary Cuttle-fishes
and Calamaries either possess an internal skeleton, or if they
have an external shell, it is not chambered; their "arms" are
furnished with powerful organs of adhesion in the form of suckers;
and they possess only a single pair of gills. For this last reason
they are termed the "Dibranchiate" Cephalopods (Gr. _dis_, twice;
_bragchia_, gill). No trace of the true Cuttle-fishes has yet
been found in Lower Silurian deposits; but the Tetrabranchiate
group is represented by a great number of forms, sometimes of
great size. The principal Lower Silurian genus is the well-known
and widely-distributed _Orthoceras_ (fig. 55). The shell in this
genus agrees with that of the existing _Pearly Nautilus_, in
consisting of numerous chambers separated by shelly partitions
(or septa), the latter being perforated by a tube which runs the
whole length of the shell after the last chamber, and is known
as the "siphuncle" (fig. 56, s). The last chamber formed is the
largest, and in it the animal lives. The chambers behind this
are apparently filled with some gas secreted by the animal itself;
and these are supposed to act as a kind of float, enabling the
creature to move with ease under the weight of its shell. The
various air-chambers, though the siphuncle passes through them,
have no direct connection with one another; and it is believed
that the animal has the power of slightly altering its specific
gravity, and thus of rising or sinking in the water by driving
additional fluid into the siphuncle or partially emptying it.
The _Orthoceras_ further agrees with the Pearly Nautilus in the
fact that the partitions or septa separating the different
air-chambers are simple and smooth, concave in front and convex
behind, and devoid of the elaborate lobation which they exhibit
in the Ammonites; whilst the siphuncle pierces the septa either
in the centre or near it. In the Nautilus, however, the shell is
coiled into a flat spiral; whereas in _Orthoceras_ the shell is
a straight, longer or shorter cone, tapering behind, and gradually
expanding towards its mouth in front. The chief objections to
the belief that the animal of the _Orthoceras_ was essentially
like that of the Pearly Nautilus are--the comparatively small
size of the body-chamber, the often contracted aperture of the
mouth, and the enormous size of some specimens of the shell.
Thus, some _Orthocerata_ have been discovered measuring ten or
twelve feet in length, with a diameter of a foot at the larger
extremity. These colossal dimensions certainly make it difficult
to imagine that the comparatively small body-chamber could have
held an animal large enough to move a load so ponderous as its
own shell. To some, this difficulty has appeared so great that
they prefer to believe that the _Orthoceras_ did not live in
its shell at all, but that its shell was an internal skeleton
similar to what we shall find to exist in many of the true
Cuttle-fishes. There is something to be said in favour of this
view, but it would compel us to believe in the existence in Lower
Silurian times of Cuttle-fishes fully equal in size to the giant
"Kraken" of fable. It need only be added in this connection that
the Lower Silurian rocks have yielded the remains of many other
Tetrabranchiate Cephalopods besides _Orthoceras_. Some of these
belong to _Cyrtoceras_, which only differs from _Orthoceras_ in
the bow-shaped form of the shell; others belong to _Phragmoceras_,
_Lituites_, &c.; and, lastly; we have true _Nautili_, with their
spiral shells, closely resembling the existing Pearly Nautilus.
Whilst all the sub-kingdoms of the Invertebrate animals are
represented in the Lower Silurian rocks, no traces of Vertebrate
animals have ever been discovered in these ancient deposits,
unless the so-called "Conodonts" found by Pander in vast numbers
in strata of this age [15] in Russia should prove to be really
of this nature. These problematical bodies are of microscopic
size, and have the form of minute, conical, tooth-shaped spines,
with sharp edges, and hollow at the base. Their original discoverer
regarded them as the horny teeth of fishes allied to the Lampreys;
but Owen came to the conclusion that they probably belonged to
Invertebrates. The recent investigation of a vast number of similar
but slightly larger bodies, of very various forms, in the
Carboniferous rocks of Ohio, has led Professor Newberry to the
conclusion that these singular fossils really are, as Pander
thought, the teeth of Cyclostomatous fishes. The whole of this
difficult question has thus been reopened, and we may yet have
to record the first advent of Vertebrate animals in the Lower
Silurian.
[Footnote 15: According to Pander, the "Conodonts" are found not
only in the Lower Silurian beds, but also in the "Ungulite Grit"
(Upper Cambrian), as well as in the Devonian and Carboniferous
deposits of Russia. Should the Conodonts prove to be truly the
remains of fishes, we should thus have to transfer the first
appearance of vertebrates to, at any rate, as early a period as
the Upper Cambrian.]
CHAPTER X.
THE UPPER SILURIAN PERIOD.
Having now treated of the Lower Silurian period at considerable
length, it will not be necessary to discuss the succeeding group
of the _Upper Silurian_ in the same detail--the more so, as with a
general change of _species_ the Upper Silurian animals belong for
the most part to the same great types as those which distinguish
the Lower Silurian. As compared, also, as regards the total bulk of
strata concerned, the thickness of the Upper Silurian is generally
very much below that of the Lower Silurian, indicating that they
represent a proportionately shorter period of time. In considering
the general succession of the Upper Silurian beds, we shall,
as before, select Wales and America as being two regions where
these deposits are typically developed.
In Wales and its borders the general succession of the Upper
Silurian rocks may be taken to be as follows, in ascending order
(fig. 57):--
(1) The base of the Upper Silurian series is constituted by a
series of arenaceous beds, to which the name of "May Hill Sandstone"
was applied by Sedgwick. These are succeeded by a series of
greenish-grey or pale-grey slates ("Tarannon Shales"), sometimes
of great thickness; and these two groups of beds together form
what may be termed the "_May Hill Group_" (Upper Llandovery of
Murchison). Though not very extensively developed in Britain, this
zone is one very well marked by its fossils; and it corresponds
with the "Clinton Group" of North America, in which similar fossils
occur. In South Wales this group is clearly unconformable to the
highest member of the subjacent Lower Silurian (the Llandovery
group); and there is reason to believe that a similar, though
less conspicuous, physical break occurs very generally between
the base of the Upper and the summit of the Lower Silurian.
(2) The _Wenlock Group_ succeeds the May Hill group, and constitutes
the middle member of the Upper Silurian. At its base it may have
an irregular limestone ("Woolhope Limestone"), and its summit may
be formed by a similar but thicker calcareous deposit ("Wenlock
Limestone"); but the bulk of the group is made up of the argillaceous
and shaly strata known as the "Wenlock Shale." In North Wales
the Wenlock group is, represented by a great accumulation of
flaggy and gritty strata (the "Denbighshire Flags and Grits"),
and similar beds (the "Coniston Flags" and "Coniston Grits")
take the same place in the north of England.
(3) The _Ludlow Group_ is the highest member of the Upper Silurian,
and consists typically of a lower arenaceous and shaly series (the
"Lower Ludlow Rock") a middle calcareous member (the "Aymestry
Limestone"), and an upper shaly and sandy series (the "Upper
Ludlow Rock" and "Downton Sandstone"). At the summit, or close
to the summit, of the Upper Ludlow, is a singular stratum only a
few inches thick (varying from an inch to a foot), which contains
numerous remains of crustaceans and fishes, and is well known
under the name of the "bone-bed." Finally, the Upper Ludlow rock
graduates invariably into a series of red sandy deposits, which,
when of a flaggy character, are known locally as the "Tile-stones."
These beds are probably to be regarded as the highest member
of the Upper Silurian; but they are sometimes looked upon as
passage-beds into the Old Red Sandstone, or as the base of this
formation. It is, in fact, apparently impossible to draw any
actual line of demarcation between the Upper Silurian and the
overlying deposits of the Devonian or Old Red Sandstone series.
Both in Britain and in America the Lower Devonian beds repose
with perfect conformity upon the highest Silurian beds, and the
two formations appear to pass into one another by a gradual and
imperceptible transition.
The Upper Silurian strata of Britain vary from perhaps 3000 or
4000 feet in thickness up to 8000 or 10,000 feet. In North America
the corresponding series, though also variable, is generally of
much smaller thickness, and may be under 1000 feet. The general
succession of the Upper Silurian deposits of North America is
as follows:--
(1) _Medina Sandstone_.--This constitutes the base of the Upper
Silurian, and consists of sandy strata, singularly devoid of life,
and passing below in some localities into a conglomerate ("Oneida
Conglomerate"), which is stated to contain pebbles derived from
the older beds, and which would thus indicate an unconformity
between the Upper and Lower Silurian.
(2) _Clinton Group_.--Above the Medina sandstone are beds of
sandstone and shale, sometimes with calcareous bands, which
constitute what is known as the "Clinton Group." The Medina and
Clinton groups are undoubtedly the equivalent of the "May Hill
Group" of Britain, as shown by the identity of their fossils.
[Illustration: Fig. 57. GENERALIZED SECTION OF THE UPPER SILURIAN
STRATA OF WALES AND SHROPSHIRE.]
(3) _Niagara Group_.--This group consists typically of a series of
argillaceous beds ("Niagara Shale") capped by limestones ("Niagara
Limestone"); and the name of the group is derived from the fact
that it is over limestones of this age that the Niagara river
is precipitated to form the great Falls. In places the Niagara
group is wholly calcareous, and it is continued upwards into a
series of marls and sandstones, with beds of salt and masses
of gypsum (the "Salina Group"), or into a series of magnesian
limestones ("Guelph Limestones"). The Niagara group, as a whole,
corresponds unequivocally with the Wenlock group of Britain.
(4) _Lower Helderberg Group_.--The Upper Silurian period in North
America was terminated by the deposition of a series of calcareous
beds, which derive the name of "Lower Helderberg" from the Helderberg
mountains, south of Albany, and which are divided into several zones,
capable of recognition by their fossils, and known by local names
(Tentaculite Limestone, Water-lime, Lower Pentamerus Limestone,
Delthyris Shaly Limestone, and Upper Pentamerus Limestone). As
a whole, this series may be regarded as the equivalent of the
Ludlow group of Britain, though it is difficult to establish any
precise parallelism. The summit of the Lower Heiderberg group
is constituted by a coarse-grained sandstone (the "Oriskany
Sandstone"), replete with organic remains, which have to a large
extent a Silurian _facies_. Opinions differ as to whether this
sandstone is to be regarded as the highest bed of the Upper Silurian
or the base of the Devonian. We thus see that in America, as
in Britain, no other line than an artificial one can be drawn
between the Upper Silurian and the overlying Devonian.
As regards the _life_ of the Upper Silurian period, we have,
as before, a number of so-called "Fucoids," the true vegetable
nature of which is in many instances beyond doubt. In addition
to these, however, we meet for the first time, in deposits of
this age, with the remains of genuine land-plants, though our
knowledge of these is still too scanty to enable us to construct
any detailed picture of the terrestrial vegetation of the period.
Some of these remains indicate the existence of the remarkable genus
_Lepidodendron_--a genus which played a part of great importance
in the forests of the Devonian and Carboniferous periods, and
which may be regarded as a gigantic and extinct type of the
Club-mosses (_Lycopodiaceoe_). Near the summit of the Ludlow
formation in Britain there have also been found beds charged
with numerous small globular bodies, which Dr Hooker has shown
to be the seed-vessels or "sporangia" of Club-mosses. Principal
Dawson further states that he has seen in the same formation
fragments of wood with the structure of the singular Devonian
Conifer known as _Prototaxites_. Lastly, the same distinguished
observer has described from the Upper Silurian of North America
the remains of the singular land-plants belonging to the genus
_Psilophyton_, which will be referred to at greater length hereafter.
The marine life of the Upper Silurian is in the main constituted
by types of animals similar to those characterising the Lower
Silurian, though for the most part belonging to different species.
The _Protozoans_ are represented principally by _Stromatopora_ and
_Ischadites_, along with a number of undoubted sponges (such as
_Amphispongia, Astroeospongia, Astylospongia_, and _Paloeomanon_).
Amongst the _Coelenterates_, we find the old group of _Graptolites_
now verging on extinction. Individuals still remain numerous,
but the variety of generic and specific types has now become
greatly reduced. All the branching and complex forms of the Arenig,
the twin-Graptolites and _Dicranograpti_ of the Llandeilo, and
the double-celled _Diplograpti_ and _Climacograpti_ of the Bala
group, have now disappeared. In their place we have the singular
_Retiolites_, with its curiously-reticulated skeleton; and several
species of the single-celled genus _Monograptus_, of which a
characteristic species (_M. Priodon_) is here figured. If we
remove from this group the plant-like _Dictyonemoe_, which are
still present, and which survive into the Devonian, no known
species of _Graptolite_ has hitherto been detected in strata
higher in geological position than the Ludlow. This, therefore,
presents us with the first instance we have as yet met with of
the total disappearance and extinction of a great and important
series of organic forms.
[Illustration: Fig. 58.--A, _Monograptus priodon_, slightly enlarged.
B, Fragment of the same viewed from behind. C, Fragment of the
same viewed in front, showing the mouths of the cellules. D,
Cross-section of the same. From the Wenlock Group (Coniston Flags
of the North of England). (Original.)]
The _Corals_ are very numerously represented in the Upper Silurian
rocks some of the limestones (such as the Wenlock Limestone)
being often largely composed of the skeletons of these animals.
Almost all the known forms of this period belong to the two great
divisions of the Rugose and Tabulate corals, the former being
represented by species of _Zaphrentis, Omphyma, Cystiphyllum,
Strombodes, Acervularia, Cyathophyllum_, &c.; whilst the latter
belong principally to the genera _Favosites, Choetetes, Halysites,
Syringopora, Heliolites_, and _Plasmopora_. Amongst the _Rugosa_, the
first appearance of the great and important genus _Cyathophyllum_,
so characteristic of the Palæozoic period, is to be noted; and
amongst the _Tabulata_ we have similarly the first appearance,
in force at any rate, of the widely-spread genus _Favosites_--the
"Honeycomb-corals." The "Chain-corals" (_Halysites_), figured
below (fig. 59), are also very common examples of the Tabulate
corals during this period, though they occur likewise in the
Lower Silurian.
[Illustration: Fig. 59.--a, _Halysites catenularia_, small variety,
of the natural size; b, Fragment of a large variety of the same,
of the natural size; c, Fragment of limestone with the tubes
of _Halysites agglomerata_, of the natural size; d, Vertical
section of two tubes of the same, showing the tabulæ, enlarged.
Niagara Limestone (Wenlock), Canada. (Original.)]
[Illustration: Fig. 60.--Upper Silurian Star-fishes. 1, _Palasterina
primoeva_, Lower Ludlow; 2, _Paloeaster Ruthveni_, Lower Ludlow;
3, _Paloeocoma Colvini_, Lower Ludlow. (After Salter.)]
[Illustration: Fig. 61.--A, _Protaster Sedgwickii_, showing the
disc and bases of the arms; B, Portion of an arm, greatly enlarged.
Lower Ludlow. (After Salter.)]
Amongst the _Echinodermata_, all those orders which have hard parts
capable of ready preservation are more or less largely represented.
We have no trace of the Holothurians or Sea-cucumbers; but this
is not surprising, as the record of the past is throughout almost
silent as to the former existence of these soft-bodied creatures,
the scattered plates and spicules in their skin offering a very
uncertain chance of preservation in the fossil condition. The
Sea-urchins (_Echinoids_) are said to be represented by examples
of the old genus _Paloechinus_. The Star-fishes (_Asteroids_) and
the Brittle-stars (_Ophiuroids_) are, comparatively speaking,
largely represented; the former by species of _Palasterina_ (fig.
60), _Paloeaster_ (fig. 60), _Paloeocoma_ (fig. 60), _Petraster,
Glyptaster_, and _Lepidaster_--and the latter by species of
_Protaster_ (fig. 61), _Paloeodiscus, Acroura_, and _Eucladia_.
The singular _Cystideans_, or "Globe Crinoids," with their globular
or ovate, tesselated bodies (fig. 46, A, C, D,), are also not
uncommon in the Upper Silurian; and if they do not become finally
extinct here, they certainly survive the close of this period by
but a very brief time. By far the most important, however, of
the Upper Silurian Echinodenns, are the Sea-lilies or _Crinoids_.
The limestones of this period are often largely composed of the
fragmentary columns and detached plates of these creatures, and
some of them (such as the Wenlock Limestone of Dudley) have yielded
perhaps the most exquisitely-preserved examples of this group
with which we are as yet acquainted. However varied in their
forms, these beautiful organisms consist of a globular, ovate,
or pear-shaped body (the "calyx"), supported upon a longer or
shorter jointed stem (or "column"). The body is covered externally
with an armour of closely-fitting calcareous plates (fig. 62),
and its upper surface is protected by similar but smaller plates
more loosely connected by a leathery integument. From the upper
surface of the body, round its margin, springs a series of longer
or shorter flexible processes, composed of innumerable calcareous
joints or pieces, movably united with one another. The arms are
typically five in number; but they generally subdivide at least
once, sometimes twice, and they are furnished with similar but
more slender lateral branches or "pinnules," thus giving rise
to a crown of delicate feathery plumes. The "column" is the stem
by which the animal is attached permanently to the bottom of the
sea; and it is composed of numerous separate plates, so jointed
together that whilst the amount of movement between any two pieces
must be very limited, the entire column acquires more or less
flexibility, allowing the organism as a whole to wave backwards and
forwards on its stalk. Into the exquisite _minutioe_ of structure
by which the innumerable parts entering into the composition
of a single Crinoid are adapted for their proper purposes in
the economy of the animal, it is impossible to enter here. No
period, as before said, has yielded examples of greater beauty
than the Upper Silurian, the principal genera represented being
_Cyathocrinus, Platycrinus, Marsupiocrinus, Taxocrinus,
Eucalyptocrinus, Ichthyocrinus, Mariacrinus, Periechocrinus,
Glyptocrinus, Crotalocrinus_, and _Edriocrinus_.
[Illustration: Fig 62.--Upper Silurian Crinoids. a, Calyx and
arms of _Eucalyptocrinus polydactylus_, Wenlock Limestone; b,
_Ichthyocrinus loevis_, Niagara Limestone, America; c, _Taxocrinus
tuberculatus_, Wenlock Limestone. (After M'Coy and Hall.)]
[Illustration: Fig. 63.--_Planolites vulgaris_, the filled-up
burrows of a marine worm. Upper Silurian (Clinton Group), Canada.
(Original.)]
The tracks and burrows of _Annelides_ are as abundant in the
Upper Silurian strata as in older deposits, and have just as
commonly been regarded as plants. The most abundant forms are the
cylindrical, twisted bodies (Planolites), which are so frequently
found on the surfaces of sandy beds, and which have been described
as the stems of sea-weeds. These fossils (fig. 63), however,
can be nothing more, in most cases, than the filled-up burrows
of marine worms resembling the living Lob-worms. There are also
various remains which belong to the group of the tube-inhabiting
Annelides (_Tubicola_). Of this nature are the tubes of _Serpulites_
and _Cornultites_, and the little spiral discs of _Spirorbis
Lewisii_.
[Illustration: Fig. 64.--Upper Silurian Trilobites. a, _Cheirurus
bimucronatus_, Wenlock and Caradoc; b, _Phacops longicaudatus_,
Wenlock, Britain, and America; c, _Phacops Downingioe_, Wenlock
and Ludlow; d, _Harpes ungula_, Upper Silurian, Bohemia. (After
Salter and Barrande.)]
Amongst the _Articulates_, we still meet only with the remains of
_Crustaceans_. Besides the little bivalved _Ostracoda_--which here
are occasionally found of the size of beans--and various _Phyllopods_
of different kinds, we have an abundance of _Trilobites_. These
last-mentioned ancient types, however, are now beginning to show
signs of decadence; and though still individually numerous, there
is a great diminution in the number of generic types. Many of
the old genera, which flourished so abundantly in Lower Silurian
seas, have now died out; and the group is represented chiefly
by species of _Cheirurus, Encrinurus, Harpes, Proetus, Lichas,
Acidaspis, Illoenus, Calymene, Homalonotus_, and _Phacops_--the
last of these, one of the highest and most beautiful of the groups
of Trilobites, attaining here its maximum of development. In the
annexed illustration (fig. 64) some of the characteristic Upper
Silurian Trilobites are represented--all, however, belonging
to genera which have their commencement in the Lower Silurian
period. In addition to the above, the Ludlow rocks of Britain
and the Lower Helderberg beds of North America have yielded the
remains of certain singular Crustaceans belonging to the extinct
order of the _Eurypterida_. Some of these wonderful forms are
not remarkable for their size; but others, such as _Pterygotus
Anglicus_ (fig. 65), attain a length of six feet or more, and
may fairly be considered as the giants of their class. The
Eurypterids are most nearly allied to the existing King-crabs
(_Limuli_), and have the anterior end of the body covered with
a great head-shield, carrying two pairs of eyes, the one simple
and the other compound. The feelers are converted into pincers,
whilst the last pair of limbs have their bases covered with spiny
teeth so as to act as jaws, and are flattened and widened out
towards their extremities so as to officiate as swimming-paddles.
The hinder extremity of the body is composed of thirteen rings,
which have no legs attached to them; and the last segment of
the tail is either a flattened plate or a narrow, sword-shaped
spine. Fragments of the skeleton are easily recognised by the
peculiar scale-like markings with which the surface is adorned,
and which look not at all unlike the scales of a fish. The most
famous locality for these great Crustaceans is Lesmahagow, in
Lanarkshire, where many different species have been found. The
true King-crabs (_Limuli_) of existing seas also appear to have
been represented by at least one form (_Neolimulus_) in the Upper
Silurian.
[Illustration: Fig. 65.--_Pterygotus Anglicus_, viewed from the
under side, reduced in size, and restored. c c, The feelers
(antennæ), terminating in nipping-claws; o o, Eyes; m m,
Three pairs of jointed limbs, with pointed extremities; n n,
Swimming-paddles, the bases of which are spiny and act as jaws.
Upper Silurian, Lanarkshire. (After Henry Woodward.)]
Coming to the _Mollusca_, we note the occurrence of the same
great groups as in the Lower Silurian. Amongst the Sea-mosses
(_Polyzoa_), we have the ancient Lace-corals (_Fenestella_ and
_Retepora_), with the nearly-allied _Glauconome_, and species
of _Ptilodictya_ (fig. 66); whilst many forms often referred
here may probably have to be transferred to the Corals, just as
some so-called Corals will ultimately be removed to the present
group.
[Illustration: Fig. 66.--Upper Silurian Polyzoa. 1, Fan-shaped
frond of _Rhinopora verrucosa_; 1a, Portion of the surface of
the same, enlarged; 2 and 2a, _Phoenopora ensiformis_, of the
natural size and enlarged; 3 and 3a, _Helopora fragilis_, of
the natural size and enlarged; 4 and 4a, _Ptilodictya raripora_,
of the natural size and enlarged. The specimens are all from the
Clinton Formation (May Hill Group) of Canada. (Original.)]
[Illustration: Fig. 67.--_Spirifera hysterica_. The right-hand
figure shows the interior of the dorsal valve with the calcareous
spires for the support of the arms.]
[Illustration: Fig. 68.--Upper Silurian Brachiopods. a a',
_Leptocoelia plano-convexa_, Clinton Group, America; b b',
_Rhynchonella neglecta_, Clinton Group, America; c, _Rhynchonella
cuneata_, Niagara Group, America, and Wenlock Group, Britain;
d d', _Orthis elelgantula_, Llandeilo to Ludlow, America and
Europe; e e', _Atrypa hemispherica_, Clinton Group, America, and
Llandovery and May Hill Groups, Britain; f f', _Atrypa congesta_,
Clinton Group, America; g g', _Orthis Davidsoni_, Clinton Group,
America. (After Hall, Billings, and the Author.)]
The Brachiopods continued to flourish during the Upper Silurian
Period in immense numbers and under a greatly increased variety
of forms. The three prominent Lower Silurian genera _Orthis,
Strophomena_, and _Leptoena_ are still well represented, though
they have lost their former preeminence. Amongst the numerous
types which have now come upon the scene for the first time,
or which have now a special development, are _Spirifera_ and
_Pentamerus_. In the first of these (fig. 69. b, c), one of
the valves of the shell (the dorsal) is furnished in its interior
with a pair of great calcareous spires, which served for the
support of the long and fringed fleshy processes or "arms" which
were attached to the sides of the mouth.[16] In the genus
_Pentamerus_ (fig. 70) the shell is curiously subdivided in its
interior by calcareous plates. The _Pentameri_ commenced their
existence at the very close of the Lower Silurian (Llandovery),
and survived to the close of the Upper Silurian; but they are
specially characteristic of the May Hill and Wenlock groups,
both in Britain and in other regions. One species, _Pentamerus
galeatus_, is common to Sweden, Britain, and America. Amongst
the remaining Upper Silurian Brachiopods are the extraordinary
_Trimerellids_; the old and at the same time modern _Linguloe,
Discinoe_, and _Cranioe_; together with many species of _Atrypa_
(fig. 68, e), _Leptocoelia_ (fig. 68, a), _Rhynchonella_
(fig. 68, b, c), _Meristella_ (fig. 69, a, e, f), _Athyris,
Retzia, Chonetes_, &c.
[Footnote 16: In all the Lamp-shells the mouth is provided with
two long fleshy organs, which carry delicate filaments on their
sides, and which are usually coiled into a spiral. These organs
are known as the "arms," and it is from their presence that the
name of "_Brachiopoda_" is derived (Gr. _brachion_, arm; _podes_,
feet). In some cases the arms are merely coiled away within the
shell, without any support; but in other cases they are carried
upon a more or less elaborate shelly loop, often spoken of as the
"carriage-spring apparatus." In the _Spirifers_, and in other ancient
genera, this apparatus is coiled up into a complicated spiral (fig.
67). It is these "arms," with or without the supporting loops or
spires, which serve as one of the special characters distinguishing
the _Brachiopods_ from the true Bivalves (_Lamellibranchiata_).]
[Illustration: Fig. 69.-a a', Meristella intermedia_, Niagara
Group, America; b, _Spirifera Niagarensis_, Niagara Group, America;
c c', _Spirifera crispa_, May Hill to Ludlow, Britain, and Niagara
Group, America; d, _Strophomena (Streptorhynchus) subplana_,
Niagara Group, America; e, _Meristella naviformis_, Niagara Group,
America; f, _Meristella cylindrica_, Niagara Group, America.
(After Hall, Billings, and the Author.)]
[Illustration: Fig. 70.--_Pentamerus Knightii_. Wenlock and Ludlow.
The right-hand figure shows the internal partitions of the shell.]
[Illustration: Fig. 71.--Upper Silurian Bivalves. A, _Cardiola
interrupta_, Wenlock and Ludlow; B, _Pterinea subfalcata_, Wenlock;
C, _Cardiola fibrosa_, Ludlow. (After Salter and M'Coy.)]
[Illustration: Fig. 72.--Upper Silurian Gasteropods. a, _Platyceras
ventricosum_, Lower Helderberg, America; b, _Euomphalus discors_,
Wenlock, Britain; c, _Holopella obsoleta_ Ludlow, Britain; d,
_Platyschisma helicites_, Upper Ludlow, Britain; e, _Holopella
gracilior_, Wenlock, Britain; f, _Platyceras multisinuatum_, Lower
Helderberg, America; g, _Holopea subconica_, Lower Helderberg,
America; h, h', _Platyostoma Niagarense_, Niagara Group, America.
(After Hall, M'Coy, and Salter.)]
[Illustration: Fig 73.--_Tentaculites ornatus_. Upper Silurian
of Europe and North America.]
The higher groups of the _Mollusca_ are also largely represented
in the Upper Silurian. Apart from some singular types, such as
the huge and thick-shelled _Megalomi_ of the American Wenlock
formation, the Bivalves (_Lamellibranchiata_) present little of
special interest; for though sufficiently numerous, they are rarely
well preserved, and their true affinities are often uncertain.
Amongst the most characteristic genera of this period may be
mentioned _Cardiola_ (fig. 71, A and C) and _Pterinea_ (fig. 71,
B), though the latter survives to a much later date. The Univalves
(_Gasteropoda_) are very numerous, and a few characteristic forms
are here figured (fig. 72). Of these, no genus is perhaps more
characteristic than _Euomphalus_ (fig. 72, b), with its flat
discoidal shell, coiled up into an oblique spiral, and deeply
hollowed out on one side; but examples of this group are both
of older and of more modern date. Another very extensive genus,
especially in America, is Platyceras (fig. 72, a and f),
with its thin fragile shell--often hardly coiled up at all--its
minute spire, and its widely-expanded, often sinuated mouth. The
British _Acroculioe_ should probably be placed here, and the
group has with reason been regarded as allied to the Violet-snails
(_Ianthina_) of the open Atlantic. The species of _Platyostoma_
(fig. 72, h) also belong to the same family; and the entire
group is continued throughout the Devonian into the Carboniferous.
Amongst other well-known Upper Silurian Gasteropods are species
of the genera _Holopea_ (fig. 72, g), _Holopella_ (fig. 72.
e), _Platyschisma_ (fig. 72, d), _Cyclonema, Pleurotomaria,
Murchisonia, Trochonema_, &c. The oceanic Univalves (_Heteropods_)
are represented mainly by species of _Bellerophon_; and the Winged
Snails, or _Pteropods_, can still boast of the gigantic _Thecoe_
and _Conularioe_, which characterise yet older deposits. The
commonest genus of _Pteropoda_, however, is _Tentaculites_ (fig.
73), which clearly belongs here, though it has commonly been
regarded as the tube of an Annelide. The shell in this group
is a conical tube, usually adorned with prominent transverse
rings, and often with finer transverse or longitudinal striæ as
well; and many beds of the Upper Silurian exhibit myriads of
such tubes scattered promiscuously over their surfaces.
The last and highest group of the _Mollusca_--that of the
_Cephalopoda_--is still represented only by _Tetrabranchiate_
forms; but the abundance and variety of these is almost beyond
belief. Many hundreds of different species are known, chiefly
belonging to the straight _Orthoceratites_, but the slightly-curved
_Cyrtoceras_ is only little less common. There are also numerous
forms of the genera _Phragmoceras, Ascoceras, Gyroteras, Lituites_,
and _Nautilus_. Here, also, are the first-known species of the
genus _Goniatites_--a group which attains considerable importance
in later deposits, and which is to be regarded as the precursor
of the _Ammonites_ of the Secondary period.
[Illustration: Fig. 74.--Head-shield of _Pteraspis Banksii_, Ludlow
rocks. (After Murchison.)]
[Illustration: Fig. 75.--A, Spine of _Onchus tenuistriatus_;
B, Shagreen-scales of _Thelodus_. Both from the "bone-bed" of
the Upper Ludlow rocks. (After Murchison.)]
Finally, we find ourselves for the first time called upon to
consider the remains of undoubted vertebrate animals, in the
form of _Fishes_. The oldest of these remains, so far as yet
known, are found in the Lower Ludlow rocks, and they consist of
the bony head-shields or bucklers of certain singular armoured
fishes belonging to the group of the _Ganoids_, represented at
the present day by the Sturgeons, the Gar-pikes of North America,
and a few other less familiar forms. The principal Upper Silurian
genus of these is _Pteraspis_, and the annexed illustration (fig.
74) will give some idea of the extraordinary form of the shield
covering the head in these ancient fishes. The remarkable stratum
near the top of the Ludlow formation known as the "bone-bed" has
also yielded the remains of shark-like fishes. Some of these,
for which the name of _Onchus_ has been proposed, are in the form
of compressed, slightly-curved spines (fig. 75, A), which would
appear to be of the nature of the strong defensive spines implanted
in front of certain of the fins in many living fishes. Besides
these, have been found fragments of prickly skin or shagreen
(_Sphagodus_), along with minute cushion-shaped bodies (_Thelodus_,
fig. 75, B), which are doubtless the bony scales of some fish
resembling the modern Dog-fishes. As the above mentioned remains
belong to two distinct, and at the same time highly-organised,
groups of the fishes, it is hardly likely that we are really
presented here with the first examples of this great class. On
the contrary, whether the so-called "Conodonts" should prove
to be the teeth of fishes or not, we are justified in expecting
that unequivocal remains of this group of animals will still be
found in the Lower Silurian. It is interesting, also, to note
that the first appearance of fishes--the lowest class of vertebrate
animals--so far as known to us at present, does not take place
until after all the great sub-kingdoms of invertebrates have
been long in existence; and there is no reason for thinking that
future discoveries will materially affect the _relative_ order
of succession thus indicated.
LITERATURE.
From the vast and daily-increasing mass of Silurian literature, it
is impossible to do more than select a small number of works which
have a classical and historical interest to the English-speaking
geologist, or which embody researches on special groups of Silurian
animals--anything like an enumeration of all the works and papers
on this subject being wholly out of the question. Apart, therefore,
from numerous and in many cases extremely important memoirs,
by various well-known observers, both at home and abroad, the
following are some of the more weighty works to which the student
may refer in investigating the physical characters and succession
of the Silurian strata and their fossil contents:--
(1) 'Siluria.' Sir Roderick Murchison.
(2) 'Geology of Russia in Europe.' Murchison (with M. de Verneuil
and Count von Keyserling).
(3) 'Bassin Silurien de Bohême Centrale.' Barrande.
(4) 'Introduction to the Catalogue of British Palæozoic Fossils in
the Woodwardian Museum of Cambridge.' Sedgwick.
(5) 'Die Urwelt Russlands.' Eichwald.
(6) 'Report on the Geology of Londonderry, Tyrone,' &c. Portlock.
(7) "Geology of North Wales"--'Mem. Geol. Survey of Great Britain,'
vol. iii. Ramsay.
(8) 'Geology of Canada,' 1863. Sir W. E. Logan; and the 'Reports of
Progress of the Geological Survey' since 1863.
(9) 'Memoirs of the Geological Survey of Great Britain,'
(10) 'Reports of the Geological Surveys of the States of New York,
Illinois, Ohio, Iowa, Michigan, Vermont, Wisconsin, Minnesota,'
&c. By Emmons, Hall, Worthen, Meek, Newberry, Orton, Winchell,
Dale Owen, &c.
(11) 'Thesaurus Siluricus.' Bigsby.
(12) 'British Palæozoic Fossils.' M'Coy.
(13) 'Synopsis of the Silurian Fossils of Ireland,' M'Coy.
(14) "Appendix to the Geology of North Wales"--'Mem. Geol. Survey,'
vol. iii. Salter.
(15) 'Catalogue of the Cambrian and Silurian Fossils in the
Woodwardian Museum of Cambridge.' Salter.
(16) 'Characteristic British Fossils.' Baily.
(17) 'Catalogue of British Fossils.' Morris.
(18) 'Palæozoic Fossils of Canada.' Billings.
(19) 'Decades of the Geological Survey of Canada.' Billings,
Salter, Rupert Jones.
(20) 'Decades of the Geological Survey of Great Britain.' Salter,
Edward, Forbes.
(21) 'Palæontology of New York,' vols. i.-iii. Hall.
(22) 'Palæontology of Illinois.' Meek and Worthen.
(23) 'Palæontology of Ohio.' Meek, Hall, Whitfield, Nicholson.
(24) 'Silurian Fauna of West Tennessee' (Silurische Fauna des
Westlichen Tennessee). Ferdinand Roemer.
(25) 'Reports on the State Cabinet of New York.' Hall.
(26) 'Lethæa Geognostica.' Bronn.
(27) 'Index Palæontologicus.' Bronn.
(28) 'Lethæa Rossica.' Eichwald.
(29) 'Lethæa Suecica.' Hisinger.
(30) 'Palæontologica Suecica.' Angelin.
(31) 'Petrefacta Germaniæ.' Goldfuss.
(32) 'Versteinerungen der Grauwacken-Formation in Sachsen.' Geinitz.
(33) 'Organisation of Trilobites' (Ray Society). Burmeister.
(34) 'Monograph of the British Trilobites' (Palæontographical
Society). Salter.
(35) 'Monograph of the British Merostomata' (Palæontographical Society).
Henry Woodward.
(36) 'Monograph of British Brachiopoda' (Palæontographical Society).
Thomas Davidson.
(37) 'Graptolites of the Quebec Group.' James Hall.
(38) 'Monograph of the British Graptolitidæ.' Nicholson.
(39) 'Monographs on the Trilobites. Pteropods, Cephalopods,
Graptolites,' &c. Extracted from the 'Système Silurien du Centre
de la Bohême.' Barrande.
(40) 'Polypiers Fossiles des Terrains Paleozoiques,' and 'Monograph
of the British Corals' (Palæontographical Society). Milne
Edwards and Jules Haime.
CHAPTER XI.
THE DEVONIAN AND OLD RED SANDSTONE PERIOD.
Between the summit of the Ludlow formation and the strata which
are universally admitted to belong to the Carboniferous series
is a great system of deposits, to which the name of "Old Red
Sandstone" was originally applied, to distinguish them from certain
arenaceous strata which lie above the coal ("New Red Sandstone").
The Old Red Sandstone, properly so called, was originally described
and investigated as occurring in Scotland and in South Wales and
its borders; and similar strata occur in the south of Ireland.
Subsequently it was discovered that sediments of a different mineral
nature, and containing different organic remains, intervened
between the Silurian and the Carboniferous rocks on the continent
of Europe, and strata with similar palæontological characters to
these were found occupying a considerable area in Devonshire.
The name of "Devonian" was applied to these deposits; and this
title, by common usage, has come to be regarded as synonymous
with the name of "Old Red Sandstone." Lastly, a magnificent series
of deposits, containing marine fossils, and undoubtedly equivalent
to the true "Devonian" of Devonshire, Rhenish Prussia, Belgium,
and France, is found to intervene in North America between the
summit of the Silurian and the base of the Carboniferous rocks.
Much difficulty has been felt in correlating the true "Devonian
Rocks" with the typical "Old Red Sandstone"--this difficulty arising
from the fact that though both formations are fossiliferous, the
peculiar fossils of each have only been rarely and partially found
associated together. The characteristic crustaceans and many of the
characteristic fishes of the Old Red are wanting in the Devonian;
whilst the corals and marine shells of the latter do not occur in
the former. It is impossible here to enter into any discussion
as to the merits of the controversy to which this difficulty
has given origin. No one, however, can doubt the importance and
reality of the Devonian series as an independent system of rocks
to be intercalated in point of time between the Silurian and
the Carboniferous. The want of agreement, both lithologically
and palæontologically, between the Devonian and the Old Red,
can be explained by supposing that these two formations, though
wholly or in great part _contemporaneous_, and therefore strict
equivalents, represent deposits in two different geographical
areas, laid down under different conditions. On this view, the
typical Devonian rocks of Europe, Britain, and North America are
the deep-sea deposits of the Devonian period, or, at any rate, are
genuine marine sediments formed far from land. On the other hand,
the "Old Red Sandstone" of Britain and the corresponding "Gaspé
Group" of Eastern Canada represent the shallow-water shore-deposits
of the same period. In fact, the former of these last-mentioned
deposits contains no fossils which can be asserted positively
to be _marine_ (unless the Eurypterids be considered so); and
it is even conceivable that it represents the sediments of an
inland sea. Accepting this explanation in the meanwhile, we may
very briefly consider the general succession of the deposits of
this period in Scotland, in Devonshire, and in North America.
In Scotland the "Old Red" forms a great series of arenaceous and
conglomeratic strata, attaining a thickness of many thousands of
feet, and divisible into three groups. Of these, the _Lower Old
Red Sandstone_ reposes with perfect conformity upon the highest
beds of the Upper Silurian, the two formations being almost
inseparably united by an intermediate series of "passage-beds."
In mineral nature this group consists principally of massive
conglomerates, sandstones, shales, and concretionary limestones;
and its fossils consist chiefly of large crustaceans belonging to
the family of the _Eurypterids_, fishes, and plants. The _Middle
Old Red Sandstone_ consists of flagstones, bituminous shales,
and conglomerates, sometimes with irregular calcareous bands;
and its fossils are principally fishes and plants. It may be
wholly wanting, when the _Upper Old Red_ seems to repose
unconformably upon the lower division of the series. The _Upper
Old Red Sandstone_ consists of conglomerates and grits, along
with a great series of red and yellow sandstones--the fossils,
as before, being fishes and remains of plants. The Upper Old
Red graduates upwards conformably into the Carboniferous series.
The Devonian rocks of Devonshire are likewise divisible into a
lower, middle, and upper division. The _Lower Devonian_ or _Lynton
Group_ consists of red and purple sandstones, with marine fossils,
corresponding to the "Spirifer Sandstein" of Germany, and to the
arenaceous deposits (Schoharie and Cauda-Galli Grits) at the base
of the American Devonian. The _Middle Devonian_ or _Ilfracombe
Group_ consists of sandstones and flags, with calcareous slates
and crystalline limestones, containing many corals. It corresponds
with the great "Eifel Limestone" of the Continent, and, in a
general way, with the Corniferous Limestone and Hamilton group
of North America. The _Upper Devonian_ or _Pilton Group_, lastly,
consists of sandstones and calcareous shales which correspond with
the "Clymenia Limestone" and "Cypridina Shales" of the Continent,
and with the Chemung and Portage groups of North America. It
seems quite possible, also, that the so-called "Carboniferous
Slates" of Ireland correspond with this group, and that the former
would be more properly regarded as forming the summit of the
Devonian than the base of the Carboniferous.
In no country in the world, probably, is there a finer or more
complete exposition of the strata intervening between the Silurian
and Carboniferous deposits than in the United States. The following
are the main subdivisions of the Devonian rocks in the State of
New York, where the series may be regarded as being typically
developed (fig. 67):--
(1) _Cauda-Galli Grit_ and _Schoharie Grit_.--Considering the
"Oriskany Sandstone" as the summit of the Upper Silurian, the
base of the Devonian is constituted by the arenaceous deposits
known by the above names, which rest quite conformably upon the
Silurian, and which represent the Lower Devonian of Devonshire. The
_Cauda-Galli Grit_ is so called from the abundance of a peculiar
spiral fossil (_Spirophyton cauda-Galli_), which is of common
occurrence in the Carboniferous rocks of Britain, and is supposed
to be the remains of a sea-weed.
(2) The _Corniferous_ or _Upper Helderberg Limestone_.--A series
of limestones usually charged with considerable quantities of
siliceous matter in the shape of hornstone or chert (Lat. _cornu_,
horn). The thickness of this group rarely exceeds 300 feet; but
it is replete with fossils, more especially with the remains
of corals. The Corniferous Limestone is the equivalent of the
coral-bearing limestones of the Middle Devonian of Devonshire
and the great "Eifel Limestone" of Germany.
(3) The _Hamilton Group_--consisting of shales at the base
("Marcellus shales"); flags, shales, and impure limestones ("Hamilton
beds") in the middle; and again a series of shales ("Genesee
Slates") at the top. The thickness of this group varies from
200 to 1200 feet, and it is richly charged with marine fossils.
(4) The _Portage Group_.--A great series of shales, flags, and
shaly sandstones, with few fossils.
(5) The _Chemung Group_.--Another great series of sandstones and
shales, but with many fossils. The Portage and Chemung groups
may be regarded as corresponding with the Upper Devonian of
Devonshire. The Chemung beds are succeeded by a great series
of red sandstones and shales--the "Catskill Group"--which pass
conformably upwards into the Carboniferous, and which may perhaps
be regarded as the equivalent of the great sandstones of the
Upper Old Red in Scotland.
Throughout the entire series of Devonian deposits in North America
no unconformability or physical break of any kind has hitherto been
detected; nor is there any marked interruption to the current of
life, though each subdivision of the series has its own fossils.
No completely natural line can thus be indicated, dividing the
Devonian in this region from the Silurian on the one hand, and
the Carboniferous on the other hand. At the same time, there is
the most ample evidence, both stratigraphical and palæontological,
as to the complete independence of the American Devonian series
as a distinct life-system between the older Silurian and the
later Carboniferous. The subjoined section (fig. 76) shows
diagrammatically the general succession of the Devonian rocks
of North America.
[Illustration: Fig. 76. GENERALIZED SECTION OF THE DEVONIAN ROCKS
OF NORTH AMERICA.]
[Illustration: Fig. 77.--Restoration of _Psilophyton princeps_.
Devonian, Canada. (After Dawson.)]
As regards the _life_ of the Devonian period, we are now acquainted
with a large and abundant terrestrial _flora_--this being the
first time that we have met with a land vegetation capable of
reconstruction in any fulness. By the researches of Goeppert,
Unger, Dawson, Carruthers, and other botanists, a knowledge has
been acquired of a large number of Devonian plants, only a few
of which can be noticed here. As might have been anticipated,
the greater number of the vegetable remains of this period have
been obtained from such shallow-water deposits as the Old Red
Sandstone proper and the Gaspè series of North America, and few
traces of plant-life occur in the strictly marine sediments.
Apart from numerous remains, mostly of a problematical nature,
referred to the comprehensive group of the Sea-weeds, a large
number of Ferns have now been recognised, some being, of the
ordinary plant-like type (_Pecopteris, Neuropteris, Alethopteris,
Sphenopteris_, &c.), whilst others belong to the gigantic group
of the "Tree-ferns" (_Psaronius, Caulopteris_, &c.) Besides these
there is an abundant development of the singular extinct types of
the _Lepidodendroids_, the _Sigillarioids_, and the _Calamites_,
all of which attained their maximum in the Carboniferous. Of
these, the _Lepidodendra_ may be regarded as gigantic, tree-like
Club-mosses (_Lycopodiaceoe_); the _Calamites_ are equally gigantic
Horse-tails (_Equisetaceoe_); and the _Sigillarioids_, equally huge
in size, in some respects hold a position intermediate between
the Club-mosses and the Pines (Conifers). The Devonian rocks have
also yielded traces of many other plants (such as _Annularia,
Asterophyllites, Cardiocarpon_, &c.), which acquire a greater
pre-dominance in the Carboniferous period, and which will be
spoken of in discussing the structure of the plants of the
Coal-measures. Upon the whole, the one plant which may be considered
as specially characteristic of the Devonian (though not confined
to this series) is the _Psilophyton_ (fig. 77) of Dr Dawson.
These singular plants have slender branching stems, with sparse
needle-shaped leaves, the young stems being at first coiled up,
crosier-fashion, like the young fronds of ferns, whilst the old
branches carry numerous spore-cases. The stems and branches seem
to have attained a height of two or three feet; and they sprang
from prostrate "root-stocks" or creeping stems. Upon the whole,
Principal Dawson is disposed to regard _Psilophyton_ as a
"generalised type" of plants intermediate between the Ferns and
the Club-mosses. Lastly, the Devonian deposits have yielded the
remains of the first actual _trees_ with which we are as yet
acquainted. About the nature of some of these (_Ormoxylon_ and
_Dadoxylon_) no doubt can be entertained, since their trunks
not only show the concentric rings of growth characteristic of
exogenous trees in general, but their woody tissue exhibits under
the microscope the "discs" which are characteristic of the wood of
the Pines and Firs (see fig. 2). The singular genus _Prototaxites_,
however, which occurs in an older portion of the Devonian series
than the above, is not in an absolutely unchallenged position.
By Principal Dawson it is regarded as the trunk of an ancient
_Conifer_--the most ancient known; but Mr Carruthers regards it
as more probably the stem of a gigantic sea-weed. The trunks
of _Prototaxites_ (fig. 78, A) vary from one to three feet in
diameter, and exhibit concentric rings of growth; but its woody
fibres have not hitherto been clearly demonstrated to possess discs.
Before leaving the Devonian vegetation, it may be mentioned that
the hornstone or chert so abundant in the Corniferous limestone
of North America has been shown to contain the remains of various
microscopic plants (_Diatoms_ and _Desmids_). We find also in
the same siliceous material the singular spherical bodies, with
radiating spines, which occur so abundantly in the chalk flints,
and which are termed _Xanthidia_. These may be regarded as probably
the spore-cases of the minute plants known as _Desmidioe_.
[Illustration: Fig. 78.--A, Trunk of _Prototaxites Logani_, eighteen
inches in diameter, as seen in the cliff near L'Anse Brehaut,
Gaspé; B, Two wood-cells showing spiral fibres and obscure pores,
highly magnified. Lower Devonian, Canada. (After Dawson)]
The Devonian _Protozoans_ have still to be fully investigated.
True Sponges (such as _Astrtoeospongia, Sphoerospongia_, &c.)
are not unknown; but by far the commonest representatives of
this sub-kingdom in the Devonian strata are _Stromatopora_ and
its allies. These singular organisms (fig. 79) are not only very
abundant in some of the Devonian limestones--both in the Old World
and the New--but they often attain very large dimensions. However
much they may differ in minor details, the general structure of
these bodies is that of numerous, concentrically-arranged, thin,
calcareous laminæ, separated by narrow interspaces, which in turn
are crossed by numerous delicate vertical pillars, giving the whole
mass a cellular structure, and dividing it into innumerable minute
quadrangular compartments. Many of the Devonian _Stromatoporoe_
also exhibit on their surface the rounded openings of canals,
which can hardly have served any other purpose than that of
permitting the sea-water to gain ready access to every part of
the organism.
[Illustration: Fig. 79.--a, Part of the under surface of
_Stromatopora tuberculata_, showing the wrinkled basement membrane
and the openings of water-canals, of the natural size; b, Portion
of the upper surface of the same, enlarged; c, Vertical section of
a fragment, magnified to show the internal structure. Corniferous
Limestone, Canada. (Original.)]
[Illustration: Fig. 80.--_Cystiphyllum vesiculosum_, showing a
succession of cups produces by budding from the original coral.
Of the natural size. Devonian, America and Europe. (Original.)]
[Illustration: Fig. 81--_Zaphrentis cornicula_, of the natural
size. Devonian, America. (Original.)]
[Illustration: Fig. 82--_Heliophyllum exiguum_, viewed from in
front and behind. Of the natural size. Devonian, Canada. (Original.)]
[Illustration: Fig. 83.--Portion of a mass of _Crepidophyllum
Archiaci_, of the natural size. Hamilton Formation, Canada. (After
Billings.)]
No true _Graptolites_ have ever been detected in strata of Devonian
age; and the whole of this group has become extinguished--unless we
refer here the still surviving _Dictyonemoe_. The _Coelenterates_,
however, are represented by a vast number of _Corals_, of beautiful
forms and very varied types. The marbles of Devonshire, the Devonian
limestones of the Eifel and of France, and the calcareous strata
of the Corniferous and Hamilton groups of America, are often
replete with the skeletons of these organisms--so much so as to
sometimes entitle the rock to be considered as representing an
ancient coral-reef. In some instances the Corals have preserved
their primitive calcareous composition; and if they are embedded
in soft shales, they may weather out of the rock in almost all
their original perfection. In other cases, as in the marbles
of Devonshire, the matrix is so compact and crystalline that
the included corals can only be satisfactorily studied by means
of polished sections. In other cases, again, the corals have
been more or less completely converted into flint, as in the
Corniferous limestone of North America. When this is the case,
they often come, by the action of the weather, to stand out from
the enclosing rock in the boldest relief, exhibiting to the observer
the most minute details of their organization. As before, the
principal representatives of the Corals are still referable to
the groups of the _Rugosa_ and _Tabulata_. Amongst the Rugose
group we find a vast number of simple "cup-corals," generally
known by the quarrymen as "horns," from their shape. Of the many
forms of these, the species of _Cyathophyllum, Heliophyllum_
(fig. 82), _Zaphrentis_ (fig. 81), and _Cystiphyllum_ (fig. 80),
are perhaps those most abundantly represented--none of these
genera, however, except _Heliophyllum_, being peculiar to the
Devonian period. There are also numerous compound Rugose corals,
such as species of _Eridophyllum, Diphyphyllum, Syringopora,
Phillipsastroea_, and some of the forms of _Cyathophyllum_ and
_Crepidophyllum_ (fig. 83). Some of these compound corals attain
a very large size, and form of themselves regular beds, which
have an analogy, at any rate, with existing coral-reefs, though
there are grounds for believing that these ancient types differed
from the modern reef-builders in being inhabitants of deep water.
The "Tabulate Corals" are hardly less abundant in the Devonian
rocks than the _Rugosa_; and being invariably compound, they
hardly yield to the latter in the dimensions of the aggregations
which they sometimes form.
[Illustration: Fig. 84.--Portion of a mass of _Favosites
Gothlandica_, of the natural size. Upper Silurian and Devonian
of Europe and America. (Original.) Billings.]
[Illustration: Fig. 85.--Fragment of _Favosites hemispherica_,
of the natural size. Upper Silurian and Devonian of America.
(After Billings.)]
The commonest, and at the same time the largest, of these are
the "honeycomb corals," forming the genus _Favosites_ (figs.
84, 85), which derive both their vernacular and their technical
names from their great likeness to masses of petrified honeycomb.
The most abundant species are _Favosites Gothlandica_ and _F.
Hemispherica_, both here figured, which form masses sometimes
not less than two or three feet in diameter. Whilst _Favosites_
has acquired a popular name by its honey-combed appearance, the
resemblance of _Michelinia_ to a fossilised wasp's nest with the
comb exposed is hardly less striking, and has earned for it a
similar recognition from the non-scientific public. In addition
to these, there are numerous branching or plant-like Tabulate
Corals, often of the most graceful form, which are distinctive
of the Devonian in all parts of the world.
The _Echinoderms_ of the Devonian period call for little special
notice. Many of the Devonian limestones are "crinoidal;" and
the _Crinoids_ are the most abundant and widely-distributed
representatives of their class in the deposits of this period.
The _Cystideans_, with doubtful exceptions, have not been recognised
in the Devonian; and their place is taken by the allied group of
the "Pentremites," which will be further spoken of as occurring
in the Carboniferous rocks. On the other hand, the Star-fishes,
Brittle-stars, and Sea-urchins are all continued by types more
or less closely allied to those of the preceding Upper Silurian.
Of the remains of Ringed-worms (_Annelides_), the most numerous
and the most interesting are the calcareous envelopes of some
small tube-inhabiting species. No one who has visited the seaside
can have failed to notice the little spiral tubes of the existing
_Spirorbis_ growing attached to shells, or covering the fronds
of the commoner Sea weeds (especially _Fucus serratus_). These
tubes are inhabited by a small Annelide, and structures of a
similar character occur not uncommonly from the Upper Silurian
upwards. In the Devonian rocks, _Spirorbis_ is an extremely common
fossil, growing in hundreds attached to the outer surface of
corals and shells, and appearing in many specific forms (figs.
86 and 87); but almost all the known examples are of small size,
and are liable to escape a cursory examination.
[Illustration: Fig. 87.--a, _Spirobois omphalodes_, natural size
and enlarged. Devonian, Europe and America; b, _Spirorbis
Arkonensis_, of the natural size and enlarged; c, The same,
with the tube twisted in the reverse direction. Devonian, America.
(Onginal.)]
[Illustration: Fig. 88. a b, _Spirorbis laxus_, enlarged, Upper
Silurian, America; c, _Spirorbis spinulifera_, of the natural
size and enlarged, Devonian, Canada. (After Hall and the Author.)]
[Illustration: Fig. 88.--Devonian Trilobites; a, _Phacops latifrons_,
Devonian of Britain, the Continent of Europe, and South America;
b, _Homalonotus armatus_, Europe; c, _Phacops (Trimerocephalus)
loevis_, Europe; d, Head-shield of _Phacops (Portlockia)
granulatus_, Europe. (After Salter and Burmeister.)]
The _Crustaceans_ of the Devonian are principally _Eurypterids_
and _Trilobites_. Some of the former attain gigantic dimensions,
and the quarrymen in the Scotch Old Red give them the name of
"seraphim" from their singular scale-like ornamentation. The
_Trilobites_, though still sufficiently abundant in some localites,
have undergone a yet further diminution since the close of the
Upper Silurian. In both America and Europe quite a number of
generic types have survived from the Silurian, but few or no
new ones make their appearance during this period in either the
Old World or the New. The _species_, however, are distinct; and
the principal forms belong to the genera _Phacops_ (fig. 88, a,
c, d), _Homalonotus_ (fig. 88, b), _Proetus_, and _Bronteus_.
The species figured above under the name of _Phacops latifrons_
(fig. 88, a), has an almost world-wide distribution, being found
in the Devonian of Britain, Belgium, France, Germany, Russia,
Spain, and South America; whilst its place is taken in North
America by the closely-allied _Phacops rana_. In addition to the
_Trilobites_, the Devonian deposits have yielded the remains of a
number of the minute _Ostracoda_, such as _Entomis_ ("_Cypridina_"),
_Leperditia_, &c., which sometimes occur in vast numbers, as
in the so-called "_Cypridina_ Slates" of the German Devonian.
There are also a few forms of _Phyllopods_ (_Estheria_). Taken
as a whole, the Crustacean fauna of the Devonian period presents
many alliances with that of the Upper Silurian, but has only
slight relationships with that of the Lower Carboniferous.
Besides _Crustaceans_, we meet here for the first time with the
remains of _air-breathing Articulates_, in the shape of _Insects_.
So far, these have only been obtained from the Devonian rocks of
North America, and they indicate the existence of at least four
generic types, all more or less allied to the existing May-flies
(_Ephemeridoe_). One of these interesting primitive insects, namely,
_Platephemera antiqua_ (fig. 89), appears to have measured five
inches in expanse of wing; and another (_Xelloneura antiquorum_) has
attached to its wing the remains of a "stridulating-organ" similar
to that possessed by the modern Grasshoppers--the instrument, as
Principal Dawson remarks, of "the first music of living things
that Geology as yet reveals to us."
[Illustration: Fig. 89.--Wing of _Platephemera antiqua_ Devonian,
America. (After Dawson.)]
Amongst the _Mollusca_, the Devonian rocks have yielded a great
number of the remains of Sea-mosses (_Polyzoa_). Some of these
belong to the ancient type _Ptilodictya_, which seems to disappear
here, or to the allied _Clathropora_ (fig. 90), with its fenestrated
and reticulated fronds. We meet also with the graceful and delicate
stems of _Ceriopora_ (fig. 91).
[Illustration: Fig. 90.--Fragment of _Clathropora intertexta_,
of the natural size and enlarged. Devonian, Canada. (Original.)]
[Illustration: Fig. 91.--Fragment of _Ceriopora Hamiltonensis_,
of the natural size and enlarged. Devonian, Canada. (Original.)]
[Illustration: Fig. 92.--Fragment of _Fenestella magnifica_, of
the natural size and enlarged. Devonian, Canada. (Original.)]
[Illustration: Fig. 93.--Fragment of _Retepora Phillipsi_, of
the natural size and enlarged. Devonian, Canada. (Original.)]
[Illustration: Fig. 94.--Fragment of _Fenestella cribrosa_, of
the natural size and enlarged. Dovonian, Canada. (Original.)]
The majority of the Devonian _Polyzoa_ belong, however, to the
great and important Palæozoic group of the Lace-corals (_Fenestella_,
figs. 92 and 94, _Retepora_, fig. 93, _Polypora_, and their allies).
In all these forms there is a horny skeleton, of a fan-like or
funnel-shaped form, which grew attached by its base to some foreign
body. The frond consists of slightly-diverging or nearly parallel
branches, which are either united by delicate cross-bars, or which
bend alternately from side to side, and become directly united
with one another at short intervals--in either case giving origin
to numerous oval or oblong perforations, which communicate to the
whole plant-like colony a characteristic netted and lace-like
appearance. On one of its surfaces--sometimes the internal, sometimes
the external--the frond carries a number of minute chambers or
"cells," which are generally borne in rows on the branches, and
of which each originally contained a minute animal.
[Illustration: Fig. 95.--_Spirifera sculptilis_. Devonian, Canada.
(After Billings.)]
[Illustration: Fig. 96.--_Spirifera mucronata_. Devonian, America.
(After Billings.)]
[Illustration: Fig. 97.--_Atrypa reticularis_. Upper Silurian
and Devonian of Europe and America. (After Billings.)]
The _Brachiopods_ still continue to be represented in great force
through all the Devonian deposits, though not occurring in the
true Old Red Sandstone. Besides such old types as _Orthis,
Strophomena, Lingula, Athyris_, and _Rhynchonella_, we find some
entirely new ones; whilst various types which only commenced their
existence in the Upper Silurian, now undergo a great expansion
and development. This last is especially the case with the two
families of the _Spiriferidoe_ and the _Produclidoe_. The
_Spirifers_, in particular, are especially characteristic of
the Devonian, both in the Old and New Worlds--some of the most
typical forms, such as _Spirifera mucronata_ (fig. 96), having
the shell "winged," or with the lateral angles prolonged to such
an extent as to have earned for them the popular name of
"fossil-butterflies." The closely-allied _Spirifera disjunda_
occurs in Britain, France, Spain, Belgium, Germany, Russia, and
China. The family of the _Productidoe_ commenced to exist in the
Upper Silurian, in the genus _Chonetes_, and we shall hereafter
find it culminating in the Carboniferous in many forms of the great
genus _Producta_[17] itself. In the Devonian period, there is an
intermediate state of things, the genus _Chonetes_ being continued
in new and varied types, and the Carboniferous _Produdoe_ being
represented by many forms of the allied group _Productella_.
Amongst other well-known Devonian Brachiopods may be mentioned
the two long-lived and persistent types _Atrypa reticularis_
(fig. 97) and _Strophomena rhomboidalis_ (fig. 98). The former
of these commences in the Upper Silurian, but is more abundantly
developed in the Devonian, having a geographical range that is
nothing less than world-wide; whilst the latter commences in the
Lower Silurian, and, with an almost equally cosmopolitan range,
survives into the Carboniferous period.
[Footnote 17: The name of this genus is often written _Productus_,
just as _Spirifera_ is often given in the masculine gender as
_Spirifer_ (the name originally given to it). The masculine
termination to these names is, however, grammatically incorrect,
as the feminine noun _cochlea_ (shell) is in these cases
_understood_.]
[Illustration: Fig. 98.--_Strophomena rhomboidalis_. Lower Silurian,
Upper Silurian, and Devonian of Europe and America.]
[Illustration: Fig. 99.--Different views of _Platyceras dumosum_,
of the natural size. Devonian, Canada. (Original.)]
The Bivalves (_Lamellibranchiata_) of the Devonian call for no
special comment, the genera _Pterinea_ and _Megalodon_ being,
perhaps, the most noticeable. The Univalves (_Gasteropods_), also,
need not be discussed in detail, though many interesting forms
of this group are known. The type most abundantly represented,
especially in America, is _Platyceras_ (fig. 99), comprising thin,
wide-mouthed shells, probably most nearly allied to the existing
"Bonnet-limpets," and sometimes attaining very considerable
dimensions. We may also note the continuance of the genus
_Euomphalus_, with its discoidal spiral shell. Amongst the
_Heteropods_, the survival of _Bellerophon_ is to be recorded;
and in the "Winged-snails," or _Pteropods_, we find new forms
of the old genera _Tentaculites_ and _Conularia_ (fig. 100).
The latter, with its fragile, conical, and often beautifully
ornamented shell, is especially noticeable.
[Illustration: Fig. 100.--_Conularia ornata, of the natural size.
Devonian, Europe.]
[Illustration: Fig. 101.--_Clymenia Sedgwickii_. Devonian, Europe.]
The remains of _Cephalopoda_ are far from uncommon in the Devonian
deposits, all the known forms being still Tetrabranchiate. Besides
the ancient types _Orthoceras_ and _Cyrtoceras_, we have now
a predominance of the spirally-coiled chambered shells of
_Goniatites_ and _Clymenia_. In the former of these the shell is
shaped like that of the _Nautilus_; but the partitions between the
chambers ("septa") are more or less lobed, folded, or angulated,
and the "siphuncle" runs along the _back_ or convex side of the
shell--these being characters which approximate _Goniatites_ to
the true Ammonites of the later rocks. In _Clymenia_, on the
other hand, whilst the shell (fig. 101) is coiled into a flat
spiral, and the partitions or septa are simple or only slightly
lobed, there is still this difference, as compared with the
_Nautilus_, that the tube of the siphuncle is placed on the _inner_
or concave side of the shell. The species of _Clymenia_ are
exclusively Devonian in their range; and some of the limestones
of this period in Germany are so richly charged with fossils of
this genus as to have received the name of "Clymenien-kalk."
The sub-kingdom of the _Vertebrates_ is still represented by
_Fishes_ only; but these are so abundant, and belong to such
varied types, that the Devonian period has been appropriately
called the "Age of Fishes." Amongst the existing fishes there are
three great groups which are of special geological importance,
as being more or less extensively represented in past time. These
groups are: (1) The _Bony Fishes_ (_Teleostei_), comprising most
existing fishes, in which the skeleton is more or less completely
converted into bone; the tail is symmetrically lobed or divided
into equal moieties; and the scales are usually thin, horny,
flexible plates, which overlap one another to a greater or less
extent. (2) The _Ganoid Fishes_ (_Ganoidei_), comprising the modern
Gar-pikes, Sturgeons, &c., in which the skeleton usually more or
less completely retains its primitive soft and cartilaginous
condition; the tail is generally markedly unsymmetrical, being
divided into two unequal lobes; and the scales (when present)
have the form of plates of bone, usually covered by a layer of
shining enamel. These scales may overlap; or they may be rhomboidal
plates, placed edge to edge in oblique rows; or they have the form
of large-sized bony plates, which are commonly united in the region
of the head to form a regular buckler. (3) The _Placoid Fishes_,
or _Elasmobranchii_, comprising the Sharks, Rays, and _Chimoeroe_
of the present day, in which the skeleton is cartilaginous; the
tail is unsymmetrically lobed; and the scales have the form of
detached bony plates of variable size, scattered in the integument.
It is to the two last of these groups that the Devonian fishes
belong, and they are more specially referable to the _Ganoids_.
The order of the Ganoid fishes at the present day comprises but
some seven or eight genera, the species of which principally or
exclusively inhabit fresh waters, and all of which are confined
to the northern hemisphere. As compared, therefore, with the Bony
fishes, which constitute the great majority of existing forms,
the Ganoids form but an extremely small and limited group. It was
far otherwise, however, in Devonian times. At this period, the
bony fishes are not known to have come into existence at all, and
the Ganoids held almost undisputed possession of the waters. To
what extent the Devonian Ganoids were confined to fresh waters
remains yet to be proved; and that many of them lived in the sea
is certain. It was formerly supposed that the Old Red Sandstone
of Scotland and Ireland, with its abundant fish-remains, might
perhaps be a fresh-water deposit, since the habitat of its fishes
is uncertain, and it contains no indubitable marine fossils. It
has been now shown, however, that the marine Devonian strata
of Devonshire and the continent of Europe contain some of the
most characteristic of the Old Red Sandstone fishes of Scotland;
whilst the undoubted marine deposit of the Corniferous limestone
of North America contains numerous shark-like and Ganoid fishes,
including such a characteristic Old Red genus as _Coccosleus_.
There can be little doubt, therefore, but that the majority of
the Devonian fishes were truly marine in their habits, though
it is probable that many of them lived in shallow water, in the
immediate neighbourhood of the shore, or in estuaries.
[Illustration: Fig. 102.--Fishes of the Devonian rocks of America.
a, Diagram of the jaws and teeth of _Dinichthys Hertzeri_,
viewed from the front, and greatly reduced; b, Diagram of the
skull of _Macropetalichthys Sullivanti_, reduced in size; c,
A portion of the enamelled surface of the skull of the same,
magnified; d, One of the scales of _Onychodus sigmoides_, of
the natural size; e, One of the front teeth of the lower jaw of
the same, of the natural size: f, Fin-spine of _Machoeracanthus
major_, a shark-like fish, reduced in size. (After Newberry.)]
[Illustration: Fig. 103.--_Cephalaspis Lyellii_. Old Red Sandstone,
Scotland. (After Page.)]
[Illustration: Fig. 104.--_Pterichthys cornutus_. Old Red Sandstone,
Scotland. (After Agassiz.)]
The Devonian Galloids belong to a number of groups; and it is
only possible to notice a few of the most important forms here.
The modern group of the Sturgeons is represented, more or less
remotely, by a few Devonian fishes--such as _Asterosteus_; and
the great _Macropetalichthys_ of the Corniferous limestone of
North America is believed by Newberry to belong to this group. In
this fish (fig. 102, b) the skull was of large size, its outer
surface being covered with a tuberculated enamel; and, as in the
existing Sturgeons, the mouth seems to have been wholly destitute
of teeth. Somewhat allied, also, to the Sturgeons, is a singular
group of armoured fishes, which is highly characteristic of the
Devonian of Britain and Europe, and less so of that of America.
In these curious forms the head and front extremity of the body
were protected by a buckler composed of large enamelled plates,
more or less firmly united to one another; whilst the hinder end
of the body was naked, or was protected with small scales. Some
forms of this group--such as _Pteraspis_ and _Coccosteus_--date
from the Upper Silurian; but they attain their maximum in the
Devonian, and none of them are known to pass upwards into the
overlying Carboniferous rocks. Amongst the most characteristic
forms of this group may be mentioned _Cephalaspis_ (fig. 103) and
_Pterichthys_ (fig. 104). In the former of these the head-shield is
of a crescentic shape, having its hinder angles produced backwards
into long "horns," giving it the shape of a "saddler's knife."
No teeth have been discovered; but the body was covered with
small ganoid scales, and there was an unsymmetrical tail-fin.
In _Pterichthys_--which, like the preceding, was first brought
to light by the labours of Hugh Miller--the whole of the head
and the front part of the body were defended by a buckler of
firmly-united enamelled plates, whilst the rest of the body was
covered with small scales. The form of the "pectoral fins" was
quite unique--these having the shape of two long, curved spines,
somewhat like wings, covered by finely-tuberculated ganoid plates.
All the preceding forms of this group are of small size; but
few fishes, living or extinct, could rival the proportions of
the great _Dinichthys_, referred to this family by Newberry.
In this huge fish (fig. 102, a) the head alone is over three
feet in length, and the body is supposed to have been twenty-five
or thirty feet long. The head was protected by a massive cuirass
of bony plates firmly articulated together, but the hinder end
of the body seems to have been simply enveloped in a leathery
skin. The teeth are of the most formidable description, consisting
in both jaws of serrated dental plates behind, and in front of
enormous conical tusks (fig. 102, a). Though immensely larger,
the teeth of _Dinichthys_ present a curious resemblance to those
of the existing Mud-fishes (_Lepidosiren_).
In another great group of Devonian Ganoids, we meet with fishes
more or less closely allied to the living _Polypteri_ (fig. 105)
of the Nile and Senegal. In this group (fig. 106) the pectoral
fins consist of a central scaly lobe carrying the fin-rays on
both sides, the scales being sometimes rounded and overlapping
(fig. 106), or more commonly rhomboidal and placed edge to edge
(fig. 105, A). Numerous forms of these "Fringe-finned" Ganoids
occur in the Devonian strata, such as _Holoptychius, Glyotoloemus,
Osteolepis, Phaneropleuron_, &c. To this group is also to be
ascribed the huge _Onychodus_ (fig. 102, d and e), with its
large, rounded, overlapping scales, an inch in diameter, and its
powerful pointed teeth. It is to be remembered, however, that
some of these "Fringe-finned" Ganoids are probably referable
to the small but singular group of the "Mud-fishes" (_Dipnoi_),
represented at the present day by the singular _Lepidosiren_
of South America and Africa, and the _Ceratodus_ of the rivers
of Queensland.
[Illustration: Fig. 105.--A, _Polypterus_, a recent Ganoid
fish; B, _Osteolepis_, a Devonian Ganoid; a a, Pectoral fins,
showing the fin-rays arranged round a central lobe.]
[Illusration: Fig. 106.--_Holoptychius nobilissimus_, restored.
Old Red Sandstone, Scotland. A, Scale of the same.]
Leaving the Ganoid fishes, it still remains to be noticed that
the Devonian deposits have yielded the remains of a number of
fishes more or less closely allied to the existing Sharks, Rays,
and _Chimoeroe_ (the _Elasmobranchii_). The majority of the forms
here alluded to are allied not to the true Sharks and Dog-fishes,
but to the more peaceable "Port Jackson Sharks," with their blunt
teeth, adapted for crushing the shells of Molluscs. The collective
name of "Cestracionts" is applied to these; and we have evidence of
their past existence in the Devonian seas both by their teeth, and
by the defensive spines which were implanted in front of a greater
or less number of the fins. These are bony spines, often variously
grooved, serrated, or ornamented, with hollow bases, implanted
in the integument, and capable of being erected or depressed
at will. Many of these "fin-spines" have been preserved to us
in the fossil condition, and the Devonian rocks have yielded
examples belonging to many genera. As some of the true Sharks
and Dog-fishes, some of the Ganoids, and even some Bony Fishes,
possess similar defences, it is often a matter of some uncertainty
to what group a given spine is to be referred. One of these spines,
belonging to the genus _Machoeracanthus_, from the Devonian rocks
of America, has been figured in a previous illustration (fig.
102, f).
In conclusion, a very few words may be said as to the validity of
the Devonian series as an independent system of rocks, preserving
in its successive strata the record of an independent system
of life. Some high authorities have been inclined to the view
that the Devonian formation has in nature no actual existence,
but that it is made up partly of beds which should be referred
to the summit of the Upper Silurian, and partly of beds which
properly belong to the base of the Carboniferous. This view seems
to have been arrived at in consequence of a too exclusive study
of the Devonian series of the British Isles, where the physical
succession is not wholly clear, and where there is a striking
discrepancy between the organic remains of those two members
of the series which are known as the "Old Red Sandstone" and
the "Devonian" rocks proper. This discrepancy, however, is not
complete; and, as we have seen, can be readily explained on the
supposition that the one group of rocks presents us with the
shallow water and littoral deposits of the period, while in the
other we are introduced to the deep-sea accumulations of the
same period. Nor can the problem at issue be solved by an appeal
to the phenomena of the British area alone, be the testimony of
these what it may. As a matter of fact, there is at present no
sufficient ground for believing that there is any irreconcilable
discordance between the succession of rocks and of life in Britain
during the period which elapsed between the deposition of the
Upper Ludlow and the formation of the Carboniferous Limestone,
and the order of the same phenomena during the same period in
other regions. Some of the Devonian types of life, as is the
case with all great formations, have descended unchanged from
older types; others pass upwards unchanged to the succeeding
period: but the fauna and flora of the Devonian period are, as
a whole, quite distinct from those of the preceding Silurian or
the succeeding Carboniferous; and they correspond to an equally
distinct rock-system, which in point of time holds an intermediate
position between the two great groups just mentioned. As before
remarked, this conclusion may be regarded as sufficiently proved
even by the phenomena of the British area; but it maybe said to
be rendered a certainty by the study of the Devonian deposits of
the continent of Europe--or, still more, by the investigation of
the vast, for the most part uninterrupted and continuous series
of sediments which commenced to be laid down in North America
at the beginning of the Upper Silurian, and did not cease till,
at any rate, the close of the Carboniferous.
LITERATURE.
The following list comprises the more important works and memoirs
to which the student of Devonian rocks and fossils may refer:--
(1) 'Siluria.' Sir Roderick Murchison.
(2) 'Geology of Russia in Europe.' Murchison (together with De
Verneuil and Count von Keyserling).
(3) "Classification of the Older Rocks of Devon and Cornwall"--'Proc.
Geol. Soc.,' vol. iii., 1839. Sedgwick and Murchison.
(4) "On the Physical Structure of Devonshire;" and on the
"Classification of the Older Stratified Rocks of Devonshire
and Cornwall"--'Trans. Geol. Soc.,' vol. v., 1840. Sedgwick
and Murchison.
(5) "On the Distribution and Classification of the Older or Palæozoic
Rocks of North Germany and Belgium"--'Geol. Trans.,' 2d ser.,
vol. vi., 1842. Sedgwick and Murchison.
(6) 'Report on the Geology of Cornwall, Devon, and West Somerset.'
De la Beche.
(7) 'Memoirs of the Geological Survey of Ireland and Scotland.'
Jukes and Geikie.
(8) "On the Carboniferous Slate (or Devonian Rocks) and the Old
Red Sandstone of South Ireland and North Devon"--'Quart.
Journ. Geol. Soc.,' vol. xxii. Jukes.
(9) "On the Physical Structure of West Somerset and North Devon;"
and on the "Palæontological Value of Devonian Fossils"--'Quart.
Journ. Geol. Soc.,' vol. iii. Etheridge.
(10) "On the Connection of the Lower, Middle, and Upper Old Red
Sandstone of Scotland"--'Trans. Edin. Geol. Soc.,' vol. i.
part ii. Powrie.
(11) 'The Old Red Sandstone,' 'The Testimony of the Rocks,' and
'Footprints of the Creator.' Hugh Miller.
(12) "Report on the 4th Geological District"--'Geology of New York,'
vol. iv. James Hall.
(13) 'Geology of Canada,' 1863. Sir W. E. Logan.
(14) 'Acadian Geology.' Dawson.
(15) 'Manual of Geology.' Dana.
(16) 'Geological Survey of Ohio,' vol. i.
(17) 'Geological Survey of Illinois,' vol. i.
(18) 'Palæozoic Fossils of Cornwall, Devon, and West Somerset.'
Phillips.
(19) 'Recherches sur les Poissons Fossiles.' Agassiz.
(20) 'Poissous de l'Old Red.' Agassiz.
(21) "On the Classification of Devonian Fishes"--' Mem. Geol. Survey
of Great Britain,' Decade X. Huxley.
(22) 'Monograph of the Fishes of the Old Red Sandstone of Britain'
(Palæontographical Society). Powrie and Lankester.
(23) 'Fishes of the Devonian System, Palæontology of Ohio.' Newberry.
(24) 'Monograph of British Trilobites' (Palæontographical Society);
Salter.
(25) 'Monograph of British Merostomata' (Palæontographical Society).
Henry Woodward.
(26) 'Monograph of British Brachiopoda' (Palæontographical Society).
Davidson.
(27) 'Monograph of British Fossil Corals' (Palæontographical Society).
Milne-Edwards and Haime.
(28) 'Polypiers Foss. des Terrains Paléozoiques.' Milne-Edwards
and Jules Haime.
(29) "Devonian Fossils of Canada West"--'Canadian Journal,' new ser.,
vols. iv.-vi. Billings.
(30) 'Palæontology of New York,' vol. iv. James Hall.
(31) 'Thirteenth, Fifteenth, and Twenty-third Annual Reports on the
State Cabinet.' James Hall.
(32) 'Palæozoic Fossils of Canada,' vol. ii. Billings.
(33) 'Reports on the Palæontology of the Province of Ontario for 1874
and 1875.' Nicholson.
(34) "The Fossil Plants of the Devonian and Upper Silurian Formations
of Canada"--'Geol. Survey of Canada.' Dawson.
(35) 'Petrefacta Germaniæ.' Goldfuss.
(36) 'Versteinerungen der Grauwacken-formation.' &c. Geinitz.
(37) 'Beitrag zur Palæontologie des Thüringer-Waldes.' Richter and
Unger.
(38) 'Ueber die Placodermen der Devonischen System.' Pander.
(39) 'Die Gattungen der Fossilen Pflanzen.' Goeppert.
(40) 'Genera et Species Plantarum Fossilium.' Unger.
CHAPTER XII.
THE CARBONIFEROUS PERIOD.
Overlying the Devonian formation is the great and important series
of the _Carboniferous Rocks_, so called because workable beds
of coal are more commonly and more largely developed in this
formation than in any other. Workable coal-seams, however, occur
in various other formations (Jurassic, Cretaceous, Tertiary), so
that coal is not an exclusively Carboniferous product; whilst
even in the Coal-measures themselves the coal bears but a very
small proportion to the total thickness of strata, occurring
only in comparatively thin beds intercalated in a great series
of sandstones, shales, and other genuine aqueous sediments.
Stratigraphically, the Carboniferous rocks usually repose conformably
upon the highest Devonian beds, so that the line of demarcation
between the Carboniferous and Devonian formations is principally
a palæontological one, founded on the observed differences in
the fossils of the two groups. On the other hand, the close of
the Carboniferous period seems to have been generally, though
not universally, signalised by movements of the crust of the
earth, so that the succeeding Permian beds often lie unconformably
upon the Carboniferous sediments.
Strata of Carboniferous age have been discovered in almost every
large land-area which has been sufficiently investigated; but
they are especially largely developed in Britain, in various
parts of the continent of Europe, and in North America. Their
general composition, however, is, comparatively speaking, so
uniform, that it will suffice to take a comprehensive view of
the formation without considering any one area in detail, though
in each region the subdivisions of the formation are known by
distinctive local names. Taking such a comprehensive view, it is
found that the Carboniferous series is generally divisible into a
_Lower_ and essentially calcareous group (the "Sub-Carboniferous" or
"Carboniferous Limestone"); a _Middle_ and principally arenaceous
group (the "Millstone Grit"); and an Upper group, of alternating
shales and sandstones, with workable seams of coal (the
"Coal-measures").
I. The _Carboniferous, Sub-Carboniferous_, or _Mountain Limestone
Series_ constitutes the general base of the Carboniferous system.
As typically developed in Britain, the Carboniferous Limestone
is essentially a calcareous formation, sometimes consisting of a
mass of nearly pure limestone from 1000 to 2000 feet in thickness,
or at other times of successive great beds of limestone with
subordinate sandstones and shales. In the north of England the
base of the series consists of pebbly conglomerates and coarse
sandstones; and in Scotland generally, the group is composed
of massive sandstones with a comparatively feeble development
of the calcareous element. In Ireland, again, the base of the
Carboniferous Limestone is usually considered to be formed by
a locally-developed group of grits and shales (the "Coomhola
Grits" and "Carboniferous Slate"), which attain the thickness
of about 5000 feet, and contain an intermixture of Devonian with
Carboniferous types of fossils. Seeing that the Devonian formation
is generally conformable to the Carboniferous, we need feel no
surprise at this intermixture of forms; nor does it appear to be
of great moment whether these strata be referred to the former
or to the latter series. Perhaps the most satisfactory course
is to regard the Coomhola Grits and Carboniferous Slates as
"passage-beds" between the Devonian and Carboniferous; but any
view that may be taken as to the position of these beds, really
leaves unaffected the integrity of the Devonian series as a distinct
life-system, which, on the whole, is more closely allied to the
Silurian than to the Carboniferous. In North America, lastly,
the Sub-Carboniferous series is never purely calcareous, though
in the interior of the continent it becomes mainly so. In other
regions, however, it consists principally of shales and sandstones,
with subordinate beds of limestone, and sometimes with this beds
of coal or deposits of clay-ironstone.
II. _The Millstone Grit_.--The highest beds of the Carboniferous
Limestone series are succeeded, generally with perfect conformity,
by a series of arenaceous beds, usually known as the _Millstone
Grit_. As typically developed in Britain, this group consists of
hard quartzose sandstones, often so large-grained and coarse in
texture as to properly constitute fine conglomerates. In other
cases there are regular conglomerates, sometimes with shales,
limestones, and thin beds of coal--the thickness of the whole
series, when well developed, varying from 1000 to 5000 feet. In
North America, the Millstone Grit rarely reaches 1000 feet in
thickness; and, like its British equivalent, consists of coarse
sandstones and grits, sometimes with regular conglomerates. Whilst
the Carboniferous Limestone was undoubtedly deposited in a tranquil
ocean of considerable depth, the coarse mechanical sediments
of the Millstone Grit indicate the progressive shallowing of
the Carboniferous seas, and the consequent supervention of
shore-conditions.
III. _The Coal-measures_.--The Coal-measures properly so called
rest conformably upon the Millstone Grit, and usually consist of
a vast series of sandstones, shales, grits, and coals, sometimes
with beds of limestone, attaining in some regions a total thickness
of from 7000 to nearly 14,000 feet. Beds of workable coal are
by no means unknown in some areas in the inferior group of the
Sub-Carboniferous; but the general statement is true, that coal is
mostly obtained from the true Coal-measures--the largest known, and
at present most productive coal-fields of the world being in Great
Britain, North America, and Belgium. Wherever they are found, with
limited exceptions, the Coal-measures present a singular _general_
uniformity of mineral composition. They consist, namely, of an
indefinite alternation of beds of sandstone, shale, and coal,
sometimes with bands of clay-ironstone or beds of limestone,
repeated in no constant order, but sometimes attaining the enormous
aggregate thickness of 14,000 feet, or little short of 3 miles.
The beds of coal differ in number and thickness in different
areas, but they seldom or never exceed one-fiftieth part of the
total bulk of the formation in thickness. The characters of the
coal itself, and the way in which the coal-beds were deposited,
will be briefly alluded to in speaking of the vegetable life
of the period. In Britain, and in the Old World generally, the
Coal-measures are composed partly of genuine terrestrial
deposits--such as the coal--and partly of sediments accumulated
in the fresh or brackish waters of vast lagoons, estuaries, and
marshes. The fossils of the Coal-measures in these regions are
therefore necessarily the remains either of terrestrial plants
and animals, or of such forms of life as inhabit fresh or brackish
waters, the occurrence of strata with marine fossils being quite
a local and occasional phenomenon. In various parts of North
America, on the other hand, the Coal-measures, in addition to
sandstones, shales, coal-seams, and bands of clay-ironstone,
commonly include beds of limestone, charged with marine remains,
and indicating marine conditions. The subjoined section (fig. 107)
gives, in a generalised form, the succession of the Carboniferous
strata in such a British area as the north of England, where
the series is developed in a typical form.
As regards the _life_ of the Carboniferous period, we naturally
find, as has been previously noticed, great differences in different
parts of the entire series, corresponding to the different mode of
origin of the beds. Speaking generally, the Lower Carboniferous
(or the Sub-Carboniferous) is characterised by the remains of
marine animals; whilst the Upper Carboniferous (or Coal-measures)
is characterised by the remains of plants and terrestrial animals.
In all those cases, however, in which marine beds are found in
the series of the Coal-measures, as is common in America, then
we find that the fossils agree in their general characters with
those of the older marine deposits of the period.
[Illustration: Fig. 107. GENERALIZED SECTION OF THE CARBONIFEROUS
STRATA OF THE NORTH OF ENGLAND.]
Owing to the fact that coal is simply compressed and otherwise
altered vegetable matter, and that it is of the highest economic
value to man, the Coal-measures have been more thoroughly explored
than any other group of strata of equivalent thickness in the
entire geological series. Hence we have already a very extensive
acquaintance with the _plants_ of the Carboniferous period; and
our knowledge on this subject is daily undergoing increase. It
is not to be supposed, however, that the remains of plants are
found solely in Coal-measures; for though most abundant towards
the summit, they are found in less numbers in all parts of the
series. Wherever found, they belong to the same great types of
vegetation; but, before reviewing these, a few words must be
said as to the origin and mode of formation of _coal_.
The coal-beds, as before mentioned, occur interstratified with
shales, sandstones, and sometimes limestones; and there may,
within the limits of a single coal-field, be as many as 80 or
100 of such beds, placed one above the other at different levels,
and varying in thickness from a few inches up to 20 or 30 feet.
As a general rule, each bed of coal rests upon a bed of shale or
clay, which is termed the "under-clay," and in which are found
numerous roots of plants; whilst the strata immediately on the
top of the coal may be shaly or sandy, but in either case are
generally charged with the leaves and stems of plants, and often
have upright trunks passing vertically through them. When we
add to this that the coal itself is, chemically, nearly wholly
composed of carbon, and that its microscopic structure shows it
to be composed almost entirely of fragments of stems, leaves,
bark, seeds, and vegetable _débris_ derived from _land-plants_,
we are readily enabled to understand how the coal was formed.
The "_under-clay_" immediately beneath the coal-bed represents
an old land-surface--sometimes, perhaps, the bottom of a swamp
or marsh, covered with a luxuriant vegetation; the _coal bed_
itself represents the slow accumulation, through long periods,
of the leaves, seeds, fruits, stems, and fallen trunks of this
vegetation, now hardened and compressed into a fraction of its
original bulk by the pressure of the superincumbent rocks; and
the strata of sand or shale above the coal-bed--the so-called
"roof" of the coal--represent sediments quietly deposited as the
land, after a long period of repose, commenced to sink beneath
the sea. On this view, the rank and long-continued vegetation
which gave rise to each coal-bed was ultimately terminated by
a slow depression of the surface on which the plants grew. The
land-surface then became covered by the water, and aqueous sediments
were accumulated to a greater or less thickness upon the dense
mass of decaying vegetation below, enveloping any trunks of trees
which might still be in an erect position, and preserving between
their layers the leaves and branches of plants brought down from
the neighbouring land by streams, or blown into the wafer by the
wind. Finally, there set in a slow movement of elevation,--the
old land again reappeared above the water; a new and equally
luxuriant vegetation flourished upon the new land-surface; and
another coal-bed was accumulated, to be preserved ultimately in
a similar fashion. Some few beds of coal may have been formed by
drifted vegetable matter brought down into the ocean by rivers, and
deposited directly on the bottom of the sea; but in the majority
of cases the coal is undeniably the result of the slow growth and
decay of plants _in situ_: and as the plants of the coal are
not _marine_ plants, it is necessary to adopt some such theory
as the above to account for the formation of coal-seams. By this
theory, as is obvious, we are compelled to suppose that the vast
alluvial and marshy flats upon which the coal-plants grew were
liable to constantly-recurring oscillations of level, the successive
land-surfaces represented by the successive coal-beds of any
coal-field being thus successively buried beneath accumulations
of mud or sand. We have no need, however, to suppose that these
oscillations affected large areas at the same time; and geology
teaches us that local elevations and depressions of the land
have been matters of constant occurrence throughout the whole
of past time.
All the varieties of coal (bituminous coal, anthracite; cannel-coal,
&c.) show a more or less distinct "lamination"--that is to say,
they are more or less obviously composed of successive thin layers,
differing slightly in colour and texture. All the varieties of coal,
also, consist chemically of _carbon_, with varying proportions of
certain gaseous constituents and a small amount of incombustible
mineral or "ash." By cutting thin and transparent slices of coal,
we are further enabled, by means of the microscope, to ascertain
precisely not only that the carbon of the coal is derived from
vegetables, but also, in many cases, what kinds of plants, and what
parts of these, enter into the formation of coal. When examined
in this way, all coals are found to consist more or less entirely
of vegetable matter; but there is considerable difference in
different coals as to the exact nature of this. By Professor
Huxley it has been shown that many of the English coals consist
largely of accumulations of rounded discoidal sacs or bags, which
are unquestionably the seed-vessels or "spore-cases" of certain
of the commoner coal-plants (such as the _Lepidodendra_). The
best bituminous coals seem to be most largely composed of these
spore-cases; whilst inferior kinds possess a progressively increasing
amount of the dull carbonaceous substance which is known as "mineral
charcoal," and which is undoubtedly composed of "the stems and
leaves of plants reduced to little more than their carbon." On
the other hand, Principal Dawson finds that the American coals
only occasionally exhibit spore-cases to any extent, but consist
principally of the cells, vessels, and fibres of the bark,
integumentary coverings, and woody portions of the Carboniferous
plants.
The number of plants already known to have existed during the
Carboniferous period is so great, that nothing more can be done
here than to notice briefly the typical and characteristic _groups_
of these--such as the Ferns, the Calamites, the Lepidodendroids,
the Sigillarioids, and the Conifers.
[Illustration: Fig. 108.--_Odontopteris Schlotheimii_. Carboniferous,
Europe and North America.]
[Illustration: Fig. 109.--_Calamites cannoeformis_. Carboniferous
Rocks, Europe and North America.]
In accordance with M. Brongniart's generalisation, that the Palæozoic
period is, botanically speaking, the "Age of Acrogens," we find
the Carboniferous plants to be still mainly referable to the
Flowerless or "Cryptogamous" division of the vegetable kingdom.
The flowering or "Phanerogamous" plants, which form the bulk
of our existing vegetation, are hardly known, with certainty,
to have existed at all in the Carboniferous era, except as
represented by trees related to the existing Pines and Firs,
and possibly by the Cycads or "false palms."[18] Amongst the
"Cryptogams," there is no more striking or beautiful group of
Carboniferous plants than the _Ferns_. Remains of these are found
all through the Carboniferous, but in exceptional numbers in
the Coal-measures, and include both herbaceous forms like the
majority of existing species, and arborescent forms resembling
the living Tree-ferns of New Zealand. Amongst the latter, together
with some new types, are examples of the genera _Psaronius_ and
_Caulopteris_, both of which date from the Devonian. The simply
herbaceous ferns are extremely numerous, and belong to such
widely-distributed and largely-represented genera as _Neuropteris,
Odontopteris_ (fig. 108), _Alethopteris, Pecopteris, Sphenopteris,
Hymenophyllites_, &c.
[Footnote 18: Whilst the vegetation of the Coal-period was mainly
a terrestrial one, aquatic plants are not unknown. Sea-weeds
(such as the _Spirophyton cauda-Galli_) are common in some of
the marine strata; whilst coal, according to the researches of
the Abbé Castracane, is asserted commonly to contain the siliceous
envelopes of Diatoms.]
The fossils known as _Calamites_ (fig. 109) are very common in
the Carboniferous deposits, and have given occasion to an abundance
of research and speculation. They present themselves as prostrate
and flattened striated stems, or as similar uncompressed stems
growing in an erect position, and sometimes attaining a length
of twenty feet or more. Externally, the stems are longitudinally
ribbed, with transverse joints at regular intervals, these joints
giving origin to a whorl or branchlets, which mayor may not give
origin to similar whorls of smaller branchlets still. The stems,
further, were hollow, with transverse partitions at the joints,
and having neither true wood nor bark, but only a thin external
fibrous shell. There can be little doubt but that the _Calamites_
are properly regarded as colossal representatives of the little
Horse-tails (_Equisetaceoe_) of the present day. They agree with
these not only in the general details of their organisation, but
also in the fact that the fruit was a species of cone, bearing
"spore-cases" under scales. According to Principal Dawson, the
_Calamites_ "grew in dense brakes on the sandy and muddy flats,
subject to inundation, or perhaps even in water; and they had
the power of budding out from the base of the stem, so as to
form clumps of plants, and also of securing their foothold by
numerous cord-like roots proceeding from various heights on the
lower part of the stem."
[Illustration: Fig. 110.--_Lepidodendron Sternbergii_, Carboniferous,
Europe. The central figure represents a portion of the trunk with
its branches, much reduced in size. The right-hand figure is
a portion of a branch with the leaves partially attached to it;
and the left-hand figure represents the end of a branch bearing
a cone of fructification.]
The _Lepidodendroids_, represented mainly by the genus
_Lepidodendron_ itself (fig. 110), were large tree-like plants,
which attain their maximum in the Carboniferous period, but which
appear to commence in the Upper Silurian, are well represented in
the Devonian, and survive in a diminished form into the Permian.
The trunks of the larger species of _Lepidodendron_ at times
reach a length of fifty feet and upwards, giving off branches in
a regular bifurcating manner. The bark is marked with numerous
rhombic or oval scars, arranged in quincunx order, and indicating
the points where the long, needle-shaped leaves were formerly
attached. The fruit consisted of cones or spikes, carried at the
ends of the branches, and consisting of a central axis surrounded
by overlapping scales, each of which supports a "spore-case"
or seed-vessel. These cones have commonly been described under
the name of _Lepidostrobi_. In the structure of the trunk there
is nothing comparable to what is found in existing trees, there
being a thick bark surrounding a zone principally composed of
"scalariform" vessels, this in turn enclosing a large central
pith. In their general appearance the _Lepidodendra_ bring to mind
the existing Araucarian Pines; but they are true "Cryptogams,"
and are to be regarded as a gigantic extinct type of the modern
Club-mosses (_Lycopodiaceoe_). They are amongst the commonest
and most characteristic of the Carboniferous plants; and the
majority of the "spore-cases" so commonly found in the coal appear
to have been derived from the cones of Lepidodendroids.
The so-called _Sigillanoids_, represented mainly by _Sigillaria_
itself (fig. 111), were no less abundant and characteristic of
the Carboniferous forests than the _Lepidodendra_. They commence
their existence, so far as known, in the Devonian period, but
they attain their maximum in the Carboniferous; and--unlike the
Lepidodendroids--they are not known to occur in the Permian period.
They are comparatively gigantic in size, often attaining a height
of from thirty to fifty feet or more; but though abundant and
well preserved, great divergence of opinion prevails as to their
true affinities. The _name_ of Sigillarioids (Lat. _sigilla_,
little seals or images) is derived from the fact that the bark
is marked with seal-like impressions or leaf-scars (fig. 111).
[Illustration: Fig. 111.--Fragment of the external surface of
_Sigillaria Groeseri_, showing the ribs and leaf-scars. The left-hand
figure represents a small portion enlarged. Carboniferous, Europe.]
Externally, the trunks of _Sigillaria_ present strong longitudinal
ridges, with vertical alternating rows of oval leaf-scars indicating
the points where the leaves were originally attached. The trunk
was furnished with a large central pith, a thick outer bark,
and an intermediate woody zone,--composed, according to Dawson,
partly of the disc-bearing fibres so characteristic of Conifers;
but, according to Carruthers, entirely made up of the "scalariform"
vessels characteristic of Cryptogams. The size of the pith was
very great, and the bark seems to have been the most durable
portion of the trunk. Thus we have evidence that in many cases
the stumps and "stools" of _Sigillarioe_, standing upright in
the old Carboniferous swamps, were completely hollowed out by
internal decay, till nothing but an exterior shell of bark was
left. Often these hollow stumps became ultimately filled up with
sediment, sometimes enclosing the remains of galley-worms,
land-snails, or Amphibians, which formerly found in the cavity
of the trunk a congenial home; and from the sandstone or shale
now filling such trunks some of the most interesting fossils of
the Coal-period have been obtained. There is little certainty
as to either the leaves or fruits of _Sigillaria_, and there
is equally little certainty as to the true botanical position
of these plants. By Principal Dawson they are regarded as being
probably flowering plants allied to the existing "false palms"
or "_Cycads_," but the high authority of Mr Carruthers is to
be quoted in support of the belief that they are Cryptogamic,
and most nearly allied to the Club-mosses.
[Illustration: Fig. 112.--_Stigmaria ficoides_. Quarter natural
size. Carboniferous.]
Leaving the botanical position of _Sigillaria_ thus undecided, we
find that it is now almost universally conceded that the fossils
originally described under the name of _Stigmaria_ are the _roots_
of _Sigillaria_, the actual connection between the two having been
in numerous instances demonstrated in an unmistakable manner.
The _Stigmarioe_ (fig. 112) ordinarily present themselves in
the form of long, compressed or rounded fragments, the external
surface of which is covered with rounded pits or shallow tubercles,
each of which has a little pit or depression in its centre. From
each of these pits there proceeds, in perfect examples, a long
cylindrical rootlet; but in many cases these have altogether
disappeared. In their internal structure, _Stigmaria_ exhibits
a central pith surrounded by a sheath of scalariform vessels,
the whole enclosed in a cellular envelope. The _Stigmarioe_ are
generally found ramifying in the "under-clay," which forms the
floor of a bed of coal, and which represents the ancient soil
upon which the _Sigillarioe_ grew.
[Illustration: Fig. 113.--_Trigonocarpon ovatum_. Coal-measures,
Britain. (After Liudley and Hutton.)]
The _Lepidodendroids and Sigillaroids, though the first were
certainly, and the second possibly, Cryptogamic or flowerless
plants, must have constituted the main mass of the forests of
the Coal period; but we are not without evidence of the existence
at the same time of genuine "trees," in the technical sense of
this term--namely, flowering plants with large woody stems. So
far as is certainly known, all the true trees of the Carboniferous
formation were _Conifers_, allied to the existing Pines and Firs.
They are recognised by the great size and concentric woody rings
of their prostrate, rarely erect trunks, and by the presence
of disc-bearing fibres in their wood, as demonstrated by the
microscope; and the principal genera which have been recognised
are _Dadoxylon, Paloeoxylon, Araucarioxylon_, and _Pinites_.
Their fruit is not known with absolute certainty, unless it be
represented, as often conjectured, by _Trigonocarpon_ (fig. 113).
The fruits known under this name are nut-like, often of considerable
size, and commonly three- or six-angled. They probably originally
possessed a fleshy envelope; and if truly referable to the
_Conifers_, they would indicate that these ancient evergreens
produced berries instead of cones, and thus resembled the modern
Yews rather than Pines. It seems, further, that the great group
of the _Cycads_, which are nearly allied to the _Conifers_, and
which attained such a striking prominence in the Secondary period,
probably commenced its existence during the Coal period; but
these anticipatory forms are comparatively few in number, and
for the most part of somewhat dubious affinities.
CHAPTER XIII.
THE CARBONIFEROUS PERIOD--Continued.
ANIMAL LIFE OF THE CARBONIFEROUS.
We have seen that there exists a great difference as to the mode
of origin of the Carboniferous sediments, some being purely marine,
whilst others are terrestrial; and others, again, have been formed
in inland swamps and morasses, or in brackish-water lagoons,
creeks, or estuaries. A corresponding difference exists necessarily
in the animal remains of these deposits, and in many regions
this difference is extremely well marked and striking. The great
marine limestones which characterise the lower portion of the
Carboniferous series in Britain, Europe, and the eastern portion
of America, and the calcareous beds which are found high up in
the Carboniferous in the western States of America, may, and
do, often contain the remains of drifted plants; but they are
essentially characterised by marine fossils; and, moreover, they
can be demonstrated by the microscope to be almost wholly composed
of the remains of animals which formerly inhabited the ocean. On
the other hand, the animal remains of the beds accompanying the
coal are typically the remains of air-breathing, terrestrial,
amphibious, or aerial animals, together with those which inhabit
fresh or brackish waters. Marine fossils may be found in the
Coal-measures, but they are invariably confined to special horizons
in the strata, and they indicate temporary depressions of the
land beneath the sea. Whilst the distinction here mentioned is
one which cannot fail to strike the observer, it is convenient
to consider the animal life of the Carboniferous as a whole: and
it is simply necessary, in so doing, to remember that the marine
fossils are in general derived from the inferior portion of the
system; whilst the air-breathing, fresh-water, and brackish-water
forms are almost exclusively derived from the superior portion
of the same.
[Illustration: Fig. 114.--Transparent slice of Carboniferous
Limestone, from Spergen Hill, Indiana, U.S., showing numerous
shells of _Endothyra_ (_Rotalia_), _Baiteyi_ slightly enlarged.
(Original.)]
[Illustration: Fig. 115.--_Fusulina cylindrica_, Carboniferous
Limestone, Russia.]
The Carboniferous _Protozoans_ consist mainly of _Foraminifera_
and _Sponges_. The latter are still very insufficiently known,
but the former are very abundant, and belong to very varied types.
Thin slices of the limestones of the period, when examined by the
microscope, very commonly exhibit the shells of _Foraminifera_
in greater or less plenty. Some limestones, indeed, are made up of
little else than these minute and elegant shells, often belonging
to types, such as the Textularians and Rotalians, differing little
or not at all from those now in existence. This is the case, for
example, with the Carboniferous Limestone of Spergen Hill in
Indiana (fig. 114), which is almost wholly made up of the spiral
shells of a species of _Endothyra_. In the same way, though to a
less extent, the black Carboniferous marbles of Ireland, and
the similar marbles of Yorkshire, the limestones of the west
of England and of Derbyshire, and the great "Scar Limestones" of
the north of England, contain great numbers of Foraminiferous
shells; whilst similar organisms commonly occur in the shale-beds
associated with the limestones throughout the Lower Carboniferous
series. One of the most interesting of the British Carboniferous
forms is the _Saccammina_ of Mr Henry Brady, which is sometimes
present in considerable numbers in the limestones of Northumberland,
Cumberland, and the west of Scotland, and which is conspicuous
for the comparatively large size of its spheroidal or pear-shaped
shell (reaching from an eighth to a fifth of an inch in size).
More widely distributed are the generally spindle-shaped shells
of _Fusulina_ (fig. 115), which occur in vast numbers in the
Carboniferous Limestone of Russia, Armenia, the Southern Alps,
and Spain, similar forms occurring in equal profusion in the
higher limestones which are found in the Coal-measures of the
United States, in Ohio, Illinois, Indiana, Missouri, &c. Mr Henry
Brady, lastly, has shown that we have in the _Nummulina Pristina_
of the Carboniferous Limestone of Namur a genuine _Nummulite_,
precursor of the great and important family of the Tertiary
Nummulites.
[Illustration: Fig. 116--Corals of the Carboniferous Limestone.
a. _Cyathophyllum paracida_, showing young corallites budded
forth from the disc of the old one; a', One of the corallites
of the same, seen in cross-section; b, Fragment of a mass of
_Lithostrotion irregulare_; b', One of the corallites of the
same, divided transversely; c, Portion of the simple cylindrical
coral of _Amplexus coralloides_; c', Transverse section of the
same species; d, _Zaphrentis vermicularis_, showing the depression
or "fossula" on one side of the cup; e, Fragrent of a mass of
_Syringopora ramulosa_; f, Fragment of _Coetetes tumidus_; f',
Portion of the same of the same, enlarged. From the Carboniferous
Limestone of Britain and Belgium. (After Thomson, De Koninck,
Milne-Edwards and Haime, and the Author.)]
The sub-kingdom of the _Coelenterates_, so far as certainly known,
is represented only by _Corals_;[19] but the remains of these are
so abundant in many of the limestones of the Carboniferous formation
as to constitute a feature little or not at all less conspicuous
than that afforded by the Crinoids. As is the case in the preceding
period, the Corals belong, almost exclusively, to the groups of
the _Rugosa_ and _Tabulata_; and there is a general and striking
resemblance and relationship between the coral-fauna of the Devonian
as a whole, and that of the Carboniferous. Nevertheless, there
is an equally decided and striking amount of difference between
these successive faunas, due to the fact that the great majority
of the Carboniferous _species_ are new; whilst some of the most
characteristic Devonian _genera_ have nearly or quite disappeared,
and several new genera now make their appearance for the first
time. Thus, the characteristic Devonian types _Heliophyllum,
Pachyphyllum, Chonophyllum, Acervularia, Spongophyllum, Smithia,
Endophyllum_, and _Cystiphyllum_, have now disappeared; and the
great masses of _Favosites_ which are such a striking feature
in the Devonian limestones, are represented but by one or two
degenerate and puny successors. On the other hand, we meet in
the Carboniferous rocks not only with entirely new genera--such
as _Axophyllum, Lophophyllum_, and _Londsdaleia_--but we have an
enormous expansion of certain types which had just begun to exist
in the preceding period. This is especially well seen in the Case
of the genus _Lithostrotion_ (fig. 116, b), which more than any
other may be considered as the predominant Carboniferous group of
Corals. All the species of _Lithostrotion_ are compound, consisting
either of bundles of loosely-approximated cylindrical stems, or of
similar "coral-lites" closely aggregated together into astræiform
colonies, and rendered polygonal by mutual pressure. This genus
has a historical interest, as having been noticed as early as in
the year 1699 by Edward Lhwyd; and it is geologically important
from its wide distribution in the Carboniferous rocks of both the
Old and New Worlds. Many species are known, and whole beds of
limestone are often found to be composed of little else than
the skeletons of these ancient corals, still standing upright
as they grew. Hardly less characteristic of the Carboniferous
than the above is the great group of simple "cup-corals," of
which _Clisiophyllum_ is the central type. Amongst types which
commenced in the Silurian and Devonian, but which are still well
represented here, may be mentioned _Syringopora_ (fig. 116, e),
with its colonies of delicate cylindrical tubes united at intervals
by cross-bars; _Zaphrentis_ (fig. 116, d), with its cup-shaped
skeleton and the well-marked depression (or "fossula") on one side
of the calice; _Amplexus_ (fig. 116, c), with its cylindrical,
often irregularly swollen coral and short septa; _Cyathophyllum_
(fig. 116, a), sometimes simple, sometimes forming great masses
of star-like corallites; and _Choetetes_, with its branched stems,
and its minute, "tabulate" tubes (fig. 116, f). The above,
together with other and hardly less characteristic forms, combine
to constitute a coral-fauna which is not only in itself perfectly
distinctive, but which is of especial interest, from the fact that
almost all the varied types of which it is composed disappeared
utterly before the close of the Carboniferous period. In the
first marine sediments of a calcareous nature which succeeded to
the Coal-measures (the magnesian limestones of the Permian), the
great group of the _Rugose corals_, which flourished so largely
throughout the Silurian, Devonian, and Carboniferous periods,
is found to have all but disappeared, and it is never again
represented save sporadically and by isolated forms.
[Footnote 19: A singular fossil has been described by Professor
Martin Duncan and Mr Jenkins from the Carboniferous rocks under
the name of _Paloeocoryne_, and has been referred to the Hydroid
Zoophytes (_Corynida_). Doubt, however, has been thrown by other
observers on the correctness of this reference.]
[Illustration: Fig. 117.--_Platycrinus tricontadactylus_, Lower
Carboniferous. The left-hand figure shows the calyx, arms, and
upper part of the stem; and the figure next this shows the surface
of one of the joints of the column. The right-hand figure shows
the proboscis. (After M'Coy.)]
[Illustration: Fig. 118.--A, _Pentremites pyriformis_, side-view
of the body ("calyx"); B, The same viewed from below, showing the
arrangement of the plates; C, Body of _Pentremites conoideus_,
viewed from above. Carboniferous.]
Amongst the _Echinoderms_, by far the most important forms are
the Sea-lilies and the Sea-urchins--the former from their great
abundance, and the latter from their singular structure; but the
little group of the "Pentremites" also requires to be noticed.
The Sea-lilies are so abundant in the Carboniferous rocks, that it
has been proposed to call the earlier portion of the period the
"Age of Crinoids." Vast masses of the limestones of the period
are "crinoidal," being more or less extensively composed of the
broken columns, and detached plates and joints of Sea-lilies,
whilst perfect "heads" may be exceedingly rare and difficult
to procure. In North America the remains of Crinoids are even
more abundant at this horizon than in Britain, and the specimens
found seem to be commonly more perfect. The commonest of the
Carboniferous Crinoids belong to the genera _Cyathocrinus,
Actinocrinus, Platycrinus_, (fig. 117), _Poteriocrinus, Zeacrinus_,
and _Forbesiocrinus_. Closely allied to the Crinoids, or forming
a kind of transition between these and the Cystideans, is the
little group of the "Pentremites," or _Blastoids_ (fig. 118).
This group is first known to have commenced its existence in
the Upper Silurian, and it increased considerably in numbers
in the Devonian; but it was in the seas of the Carboniferous
period that it attained its maximum, and no certain representative
of the family has been detected in any later deposits. The
"Pentremites" resemble the Crinoids in having a cup-shaped body
(fig. 118, A) enclosed by closely-fitting calcareous plates,
and supported on a short stem or "column," composed of numerous
calcareous pieces flexibly articulated together. They differ from
the Crinoids, however, in the fact that the upper surface of
the body does not support the crown of branched feathery "arms,"
which are so characteristic of the latter. On the contrary, the
summit of the cup is closed up in the fashion of a flower-bud,
whence the technical name of _Blastoidea_ applied to the group
(Gr. _blastos_, a bud; _eidos_, form). From the top of the cup
radiate five broad, transversely-striated areas (fig. 118, C),
each with a longitudinal groove down its middle; and along each
side of each of these grooves there seems to have been attached
a row of short jointed calcareous filaments or "pinnules."
[Illustration: Fig. 119.--_Paloechinus ellipticus_, one of the
Carboniferous Sea-urchins. The left-hand figure shows one of the
"ambulacral areas" enlarged, exhibiting the perforated plates.
The right-land figure exhibits a single plate from one of the
"inter-ambulacral areas." (After M'Coy.)]
A few Star-fishes and Brittle-stars are known to occur in the
Carboniferous rocks; but the only other Echinodemls of this period
which need be noticed are the Sea-urchins (_Echinoids_). Detached
plates and spines of these are far from rare in the Carboniferous
deposits; but anything like perfect specimens are exceedingly
scarce. The Carboniferous Sea-urchins agree with those of the
present day in having the body enclosed in a shell formed by
an enormous number of calcareous plates articulated together.
The shell may be regarded as, typically, nearly spherical in
shape, with the mouth in the centre of the base, and the excretory
opening or vent at its summit. In both the ancient forms and the
recent ones, the plates of the shell are arranged in ten zones
which generally radiate from the summit to the centre of the base.
In five of these zones--termed the "ambulacral areas"--the plates
are perforated by minute apertures or "pores," through which
the animal can protrude the little water-tubes ("tube-feet") by
which its locomotion is carried on. In the other five zones--the
so-called "inter-ambulacral areas"--the plates are of larger
size, and are not perforated by any apertures. In all the modern
Sea-urchins each of these ten zones, whether perforate or
imperforate, is composed of two rows of plates; and there are
thus twenty rows of plates in all. In the Palæozoic Sea-urchins,
on the other hand, the "ambulacral areas" are often like those of
recent forms, in consisting of _two_ rows of perforated plates
(fig. 119); but the "inter-ambulacral areas" are always quite
peculiar in consisting each of three, four, five, or more rows
of large imperforate plates, whilst there are sometimes four
or ten rows of plates in the "ambulacral areas" also: so that
there are many more than twenty rows of plates in the entire
shell. Some of the Palæozoic Sea-urchins, also, exhibit a very
peculiar singularity of structure which is only known to exist
in a very few recently-discovered modern forms (viz., _Calveria_
and _Phormosoma_). The plates of the inter-ambulacral areas,
namely, overlap one another in an imbricating manner, so as to
communicate a certain amount of flexibility to the shell; whereas
in the ordinary living forms these plates are firmly articulated
together by their edges, and the shell forms a rigid immovable
box. The Carboniferous Sea-urchins which exhibit this extraordinary
peculiarity belong to the genera _Lepidechinus_ and _Lepidesthes_,
and it seems tolerably certain that a similar flexibility of
the shell existed to a less degree in the much more abundant
genus _Archoeocidaris_. The Carboniferous Sea-urchins, like the
modern ones, possessed movable spines of greater or less length,
articulated to the exterior of the shell; and these structures
are of very common occurrence in a detached condition. The most
abundant genera are _Archoeocidaris_ and _Paloechinus_; but the
characteristic American forms belong principally to _Melonites,
Oligoporus_, and _Lepidechinus_.
[Illustration: Fig. 120.--_Spirorbis (Microconchus) Carbonarius_,
of the natural size, attached to a fossil plant, and magnified.
Carboniferous Britain and North America. (After Dawson.)]
Amongst the _Annelides_ it is only necessary to notice the little
spiral tubes of _Spirorbis Carbonarius_ (fig. 120), which are
commonly found attached to the leaves or stems of the Coal-plants.
This fact shows that though the modern species of _Spirorbis_
are inhabitants of the sea, these old representatives of the
genus must have been capable of living in the brackish waters
of lagoons and estuaries.
[Illustration: Fig. 121.--_Prestwichia rotundata_, a Limuloid
Crustacean. Coal-measures, Britain. (After Henry Woodward.)]
[Illustration: Fig. 122.--Crustaceans of the Carboniferous Rocks.
a, _Phillipsia seminifera_, of the natural size--Mountain Limestone,
Europe; b, One valve of the shell of _Estheria tenella_, of the
natural size and enlarged--Coal-measures, Europe; c, Bivalved
shell of _Entomoconchus Scouleri_, of the natural size--Mountain
Limestone, Europe; d, _Dithyrocaris Scouleri_, reduced in
size--Mountain Limestone, Ireland; e, _Paloeocaris typus_, slightly
enlarged--Coal-measures, North America; f, _Anthrapaloemon gracilis_,
of the natural size--Coal-measures, North America. (After De
Koninck, M'Coy, Rupert Jones, and Meek and Worthen.)]
The _Crustaceans_ of the Carboniferous rocks are numerous, and
belong partly to structural types with which we are already familiar,
and partly to higher groups which come into existence here for the
first time. The gigantic _Eurypterids_ of the Upper Silurian and
Devonian are but feebly represented, and make their final exit
here from the scene of life. Their place, however, is taken by
peculiar forms belonging to the allied group of the _Xiphosura_,
represented at the present day by the King-crabs or "Horse-shoe
Crabs" (_Limulus_). Characteristic forms of this group appear
in the Coal-measures both of Europe and America; and though
constituting three distinct genera (_Prestwichia, Belinurus_,
and _Euproöps_), they are all nearly related to one another. The
best known of them, perhaps, is the _Prestwichia rotundala_ of
Coalbrookdale, here figured (fig. 121). The ancient and formerly
powerful order of the _Trilobites_ also undergoes its final
extinction here, not surviving the deposition of the Carboniferous
Limestone series in Europe, but extending its range in America
into the Coal-measures. All the known Carboniferous forms are
small in size and degraded in point of structure, and they are
referable to but three genera (_Phillipsia, Griffithides_, and
_Brachymetopus_), belonging to a single family. The _Phillipsia
seminifera_ here figured (fig. 122, a) is a characteristic species
in the Old World. The Water-fleas (_Ostracoaa_) are extremely
abundant in the Carboniferous rocks, whole strata being often
made up of little else than the little bivalved shells of these
Crustaceans. Many of them are extremely small, averaging about
the size of a millet-seed; but a few forms, such as _Entomoconchus
Scouleni_ (fig. 122, c), may attain a length of from one to
three quarters of an inch. The old group of the _Phyllopods_
is is likewise still represented in some abundance, partly by
tailed forms of a shrimp-like appearance, such as _Dithyrocaris_
(fig. 122, d), and partly by the curious striated _Estherioe_
and their allies, which present a curious resemblance to the
true Bivalve Molluscs (fig. 122, b). Lastly, we meet for the
first time in the Carboniferous rocks with the remains of the
highest of all the groups of _Crustaceans_--namely, the so-called
"Decapods," in which there are five pairs of walking-limbs, and
the hinder end of the body ("abdomen") is composed of separate
rings, whilst the anterior end is covered by a head-shield or
"carapace." All the Carboniferous Decapods hitherto discovered
resemble the existing Lobsters, Prawns, and Shrimps (the _Macrura_),
in having a long and well-developed abdomen terminated by an
expanded tail-fin. The _Paloeocaris typus_ (fig. 122, e) and the
_Anthrapaloemon gracilis_ (fig. 122, f), from the Coal-measures
of Illinois, are two of the best understood and most perfectly
preserved of the few known representatives of the "Long-tailed"
Decapods in the Carboniferous series. The group of the Crabs
or "Short-tailed" Decapods (_Brachyura_), in which the abdomen
is short, not terminated by a tail-fin, and tucked away out of
sight beneath the body, is at present not known to be represented
at all in the Carboniferous deposits.
[Illustration: Fig. 123.--_Cyclophthalmus senior_. A fossil Scorpion
from the Coal-measures of Bohemia.]
[Illustration: Fig. 124.--_Xylobius Sigillarioe_, a Carboniferous
Myriapod. a, A specimen, of the natural size; b, Anterior
portion of the same, enlarged; c, Posterior portion, enlarged.
From the Coal-measures of Nova Scotia. (After Dawson.)]
[Illustration: Fig. 125--_Haplophlebium Barnesi_, a Carboniferous
insect, from the Coal-meastures of Nova Scotia. (After Dawson.)]
In addition to the water-inhabiting group of the Crustaceans, we
find the articulate animals to be represented by members belonging
to the air-breathing classes of the _Arachnida, Myriapoda_, and
_Insecta_. The remains of these, as might have been expected, are
not known to occur in the marine limestones of the Carboniferous
series, but are exclusively found in beds associated with the Coal,
which have been deposited in lagoons, estuaries, or marshes, in
the immediate vicinity of the land, and which actually represent
an old land-surface. The _Arachnids_ are at present the oldest
known of their class, and are represented both by true Spiders
and Scorpions. Remains of the latter (fig. 123) have been found
both in the Old and New Worlds, and indicate the existence in
the Carboniferous period of Scorpions differing but very little
from existing forms. The group of the _Myriapoda_, including
the recent Centipedes and Galley-worms, is likewise represented
in the Carboniferous strata, but by forms in many respects very
unlike any that are known to exist at the present day. The most
interesting of these were obtained by Principal Dawson, along
with the bones of Amphibians and the shells of Land-snails, in
the sediment filling the hollow trunks of _Sigillaria_, and they
belong to the genera _Xylobius_ (fig. 124) and Archiulus. Lastly,
the true _insects_ are represented by various forms of Beetles
(_Coleoptera_), _Orthoptera_ (such as Cockroaches), and
_Neuropterous_ insects resembling those which we have seen to
have existed towards the close of the Devonian period. One of the
most remarkable of the latter is a huge May-fly (_Haplophlebium
Barnesi_, fig. 125), with netted wings attaining an expanse of
fully seven inches, and therefore much exceeding any existing
Ephemerid in point of size.
[Illustration: Fig. 126.--Carboniferous _Polyzoa_. a, Fragment
of _Polypora dendroides_, of the natural size, Ireland; a' Small
portion of the same, enlarged to show the cells; b, Glauconome
pulcherrima_, a fragment, of the natural size, Ireland; b',
Portion of the same, enlarged; c, The central screw-like axis
of _Archimedes Wortheni_, of the natural size--Carboniferous,
America; c', Portion of the exterior of the frond of the same,
enlarged; c'', Portion of the interior of the frond of the
same showing the mouths of the cells, enlarged. (After M'Coy and
Hall.)]
The lower groups of the _Mollusca_ are abundantly represented
in the marine strata of the Carboniferous series by _Polyzoans_
and _Brachiopods_. Amongst the former, although a variety of other
types are known, the majority still belong to the old group of
the "Lace-corals" (_Fenestellidoe_), some of the characteristic
forms of which are here figured (fig. 126). The graceful netted
fronds of _Fenestella, Retepora_, and _Polypora_ (fig. 126, a)
are highly characteristic, as are the slender toothed branches
of _Glauconome_ (fig. 126, b). A more singular form, however,
is the curious _Archimedes_ (fig. 126, c), which is so
characteristic of the Carboniferous formation of North America.
In this remarkable type, the colony consists of a succession of
funnel-shaped fronds, essentially similar to _Fenestella_ in
their structure, springing in a continuous spiral from a strong
screw-like vertical axis. The outside of the fronds is simply
striated; but the branches exhibit on the interior the mouths of
the little cells in which the semi-independent beings composing
the colony originally lived.
[Illustration: Fig. 127.--Carboniferous _Braciopoda. a, _Producta
semireticulata_, showing the slightly concave dorsal valve; a'
Side view of the same, showing the convex ventral valve; b,
_Producta longispina_; c, _Orthis resupinata_; d, _Terebratula
hastata_; e, _Athyris subtilita_; f, _Chonetes Hardrensis_; g,
_Rhynchonella pleurodon_; h, _Spirifera trigonalis_. Most of
these forms are widely distributed in the Carboniferous Limestone
of Britain, Europe, America, &c. All the figures are of the natural
size. (After Davidson, De Koninck, and Meek.)]
The _Brachiopods_ are extremely abundant, and for the most part
belong to types which are exclusively or principally Palæozoic
in their range. The old genera _Strophomena, Orthis_ (fig. 127,
c), _Athyris_ (fig. 127, e), _Rhynchonella_ (fig. 127, g),
and _Spirifera_ (fig. 127, h), are still well represented--the
latter, in particular, existing under numerous specific forms,
conspicuous by their abundance and sometimes by their size. Along
with these ancient groups, we have representatives--for the first
time in any plenty--of the great genus _Terebratula_ (fig. 127,
d), which underwent a great expansion during later periods,
and still exists at the present day. The most characteristic
Carboniferous Brachiopods, however, belong to the family of the
_Productidoe_, of which the principal genus is _Producta_ itself.
This family commenced its existence in the Upper Silurian with
the genus _Chonetes_, distinguished by its spinose hinge-margin.
This genus lived through the Devonian, and flourished in the
Carboniferous (fig. 127, f). The genus _Producta_ itself,
represented in the Devonian by the nearly allied _Productella_,
appeared first in the Carboniferous, at any rate, in force, and
survived into the Permian; but no member of this extensive family
has yet been shown to have over-lived the Palæozoic period. The
_Productoe_ of the Carboniferous are not only exceedingly abundant,
but they have in many instances a most extensive geographical range,
and some species attain what may fairly be considered-gigantic
dimensions. The shell (fig. 127, a and b) is generally more
or less semicircular, with a straight hinge-margin, and having
its lateral angles produced into larger or smaller ears (hence
its generic name--"_cochlea producta_"). One valve (the ventral)
is usually strongly convex, whilst the other (the dorsal) is flat
or concave, the surface of both being adorned with radiating
ribs, and with hollow tubular spines, often of great length.
The valves are not locked together by teeth, and there is no
sign in the fully-grown shell of an opening in or between the
valves for the emission of a muscular stalk for the attachment
of the shell to foreign objects. It is probable, therefore, that
the _Productoe_, unlike the ordinary Lamp-shells, lived an
independent existence, their long spines apparently serving to
anchor them firmly in the mud or ooze of the sea-bottom; but Mr
Robert Etheridge, jun.; has recently shown that in one species
the spines were actually employed as organs of adhesion, whereby
the shell was permanently attached to some extraneous object,
such as the stem of a Crinoid. The two species here figured are
interesting for their extraordinarily extensive geographical
range--_Producta semireticulata_ (fig. 127, a) being found
in the Carboniferous rocks of Britain, the continent of Europe,
Central Asia, China, India, Australia, Spitzbergen, and North
and South America; whilst _P. Longispina_ (fig. 127, b) has
a distribution little if at all less wide.
[Illustration: Fig. 128.--_Pupa (Dendropupa) vetusta_, a
Carboniferous Land-snail from the Coal-measures of Nova Scotia.
a, The shell, of the natural size; b, The same, magnified;
c, Apex of the shell, enlarged; d, Portion of the surface,
enlarged. (After Dawson.)]
The higher _Mollusca_ are abundantly represented in the Carboniferous
rocks by Bivalves (_Lamellibranchs_), Univalves (_Gasteropoda_),
Winged-snails (_Pteropoda_), and _Cephalopods_. Amongst the Bivalves
we may note the great abundance of Scallops (_Aviculopecten_ and
other allied forms), together with numerous other types--some of
ancient origin, others represented here for the first time. Amongst
the Gasteropods, we find the characteristically Palæozoic genera
_Macrocheilus_ and _Loxonema_, the almost exclusively Palæozoic
_Euomphalus_, and the persistent, genus _Pleurotomaria_; whilst
the free-swimming Univalves (_Heteropoda_)are represented by
_Bellerophon_ and _Porcellia_, and the _Pteropoda_ by the old
genus _Conularia_. With regard to the Carboniferous Univalves,
it is also of interest to note here the first appearance of true
air-breathing or terrestrial Molluscs, as discovered by Dawson
and Bradley in the Coal-measures of Nova Scotia and Illinois. Some
of these (_Conulus priscus_) are true Land-snails, resembling the
existing _Zonites_; whilst others (_Pupa vetusta_, fig. 128) appear
to be generically inseparable from the "Chrysalis-shells" (_Pupa_)
of the present day. All the known forms--three in number--are of
small size, and appear to have been local in their distribution
or in their preservation. More important, however, than any of
the preceding, are the _Cephalopoda_, represented, as before,
exclusively by the chambered shells of the Tetrabranchiates.
The older and simpler type of these, with simple plain septa,
and mostly a central siphuncle, is represented by the straight
conical shells of the ancient genus Orthoceras, and the bow-shaped
shells of the equally ancient _Cyrtoceras_--some of the former
attaining a great size. The spirally-curved discoidal shells
of the persistent genus _Nautilus_ are also not unknown, and
some of these likewise exhibit very considerable dimensions.
Lastly, the more complex family of the _Ammonitidoe_, with lobed
or angulated septa, and a dorsally-placed siphuncle (situated on
the convex side of the curved shells), now for the first time
commences to acquire a considerable prominence. The principal
representative of this group is the genus _Goniatites_ (fig.
129), which commenced its existence in the Upper Silurian, is well
represented in the Devonian, and attains its maximum here. In this
genus, the shell is spirally curved, the septa are strongly lobed
or angulated, though not elaborately frilled as in the Ammonites,
and the siphuncle is dorsal. In addition to _Goniatites_, the
shells of true _Ammonites_, so characteristic of the Secondary
period, have been described by Dr Waagen as occurring in the
Carboniferous rocks of India.
[Illustration: Fig. 129.--_Goniatites (Aganides) Fossoe_.
Carboniferous Limestone.]
[Illustration: Fig. 130.--_Amblypterus macropterus_. Carboniferous.]
Coming finally to the _Vertebrata_, we have in the first place
to very briefly consider the Carboniferous _fishes_. These are
numerous; but, with the exception of the still dubious "Conodonts,"
belong wholly to the groups of the _Ganoids_ and the _Placoids_
(including under the former head remains which perhaps are truly
referable to the group of the _Dipnoi_ or Mud-fishes). Amongst the
_Ganoids_, the singular buckler-headed fishes of the Upper Silurian
and Devonian (_Cephalaspidoe_) have apparently disappeared; and
the principal types of the Carboniferous belong to the groups
respectively represented at the present day by the Gar pike
(_Lepidosteus_) of the North American lakes, and the _Polypterus_
of the rivers of Africa. Of the former, the genera _Paloeoniscus_
and _Amblypterus_ (fig. 130), with their small rhomboidal and
enamelled scales, and their strongly unsymmetrical tails, are
perhaps the most abundant. Of the latter, the most important are
species belonging to the genera _Megalichthys_ and _Rhizodus_,
comprising large fishes, with rhomboidal scales, unsymmetrical
("heterocercal") tails, and powerful conical teeth. These fishes
are sometimes said to be "sauroid," from their presenting some
Reptilian features in their organisation, and they must have been
the scourges of the Carboniferous seas. The remains of _Placoid_
fishes in the Carboniferous strata are very numerous, but consist
wholly of teeth and fin-spines, referable to forms more or less
closely allied to our existing Port Jackson Sharks, Dog-fishes,
and Rays. The teeth are of very various shapes and sizes,--some
with sharp, cutting edges (_Petalodus, Cladodus_, &c.); others in
the form of broad crushing plates, adapted, like the teeth of the
existing Port Jackson Shark (_Cestracion Philippi_), for breaking
down the hard shells of Molluscs and Crustaceans. Amongst the many
kinds of these latter, the teeth of _Psammodus_ and _Cochliodus_
(fig. 131) may be mentioned as specially characteristic. The
fin-spines are mostly similar to those so common in the Devonian
deposits, consisting of hollow defensive spines implanted in
front of the pectoral or other fins, usually slightly curved,
often superficially ribbed or sculptured, and not uncommonly
serrated or toothed. The genera _Ctenacanthus, Gyracanthus,
Homacanthus_, &c., have been founded for the reception of these
defensive weapons, some of which indicate fishes of great size
and predaceous habits.
[Illustration: Fig. 131.--Teeth of _Cochliodus contortus_.
Carboniferous Limestone, Britain.]
[Illustration: Fig. 132.--a, Upper surface of the skull of
_Anthracosaurus Russelli_, one-sixth of the natural size: b,
Part of one of the teeth cut across, and highly magnified to
show the characteristic labyrinthine structure; c, One of the
integumentary shields or scales, one-half of the natural size.
Coal-measures, Northumberland. (After Atthey.)]
In the Devonian rocks we meet with no other remains of
Vertebrated animals save fishes only; but the Carboniferous
deposits have yielded remains of the higher group
of the _Amphibians_. This class, comprising our existing
Frogs, Toads, and Newts, stands to some extent in a position midway
between the class of the fishes and that of the true
reptiles, being distinguished from the latter by the fact
that its members invariably possess gills in their early
condition, if not throughout life; whilst they are separated from
the former by always possessing true lungs when adult, and
by the fact that the limbs (when present at all) are never in
the form of fins. The Amphibians, therefore, are all
water-breathers when young, and have respiratory organs adapted
for an aquatic mode of life; whereas, when grown up, they
develop lungs, and with these the capacity for breathing air
directly. Some of them, like the Frogs and Newts, lose their
gills altogether on attaining the adult condition; but others,
such as the living _Proteus_ and _Menobranchus_, retain
their gills even after acquiring their lungs, and are thus fitted
indifferently for an aquatic or terrestrial existence. The name of
"Amphibia," though applied to the whole class, is thus not
precisely appropriate except to these last-mentioned forms
(Gr. _amphi_, both; _bios_, life). The Amphibians also
differ amongst themselves according as to whether they keep
permanently the long tail which they all possess when young (as
do the Newts and Salamanders), or lose this appendage when
grown up (as do the Frogs and Toads). Most of them have
naked skins, but a few living and many extinct forms have
hard structures in the shape of scales developed in the integument.
All of them have well-ossified skeletons, though some
fossil types are partially deficient in this respect; and all of
them which possess limbs at all have these appendages supported
by bones essentially similar to those found in the limbs
of the higher Vertebrates. All the Carboniferous Amphibians
belong to a group which has now wholly passed away--namely,
that of the _Labyrinthodonts_. In the marine strata which
form the base of the Carboniferous series these creatures have only
been recognised by their curious hand-shaped footprints, similar
in character to those which occur in the Triassic rocks, and which
will be subsequently spoken of under the name of _Cheirotherium_.
In the Coal-measures of Britain, the continent of Europe, and
North America, however, many bones of these animals have
been found, and we are now tolerably well acquainted with a
considerable number of forms. All of them seem to have
belonged to the division of Amphibians in which the long tail
of the young is permanently retained; and there is evidence
that some of them kept the gills also throughout life. The skull
is of the characteristic Amphibian type (fig. 132, a), with
two occipital condyles, and having its surface singularly pitted
and sculptured; and the vertebræ are hollowed out at both
ends. The lower surface of the body was defended by an armour
of singular integumentary shields or scales (fig. 132, c);
and an extremely characteristic feature (from which the entire
group derives its name) is, that the walls of the teeth are deeply
folded, so as to give rise to an extraordinary "labyrinthine"
pattern when they are cut across (fig. 132, b). Many of the
Carboniferous Labyrinthodonts are of no great size, some of
them very small, but others attain comparatively gigantic
dimensions, though all fall short in this respect of the huge
examples of this group which occur in the Trias. One of the
largest, and at the same time most characteristic, forms of the
Carboniferous series, is the genus _Anthracosaurus_, the
skull of which is here figured.
No remains of true Reptiles, Birds, or Quadrupeds have as yet
been certainly detected in the Carboniferous deposits in any part
of the world. It should, however, be mentioned, that Professor
Marsh, one of the highest authorities on the subject, has described
from the Coal-formation of Nova Scotia certain vertebræ which
he believes to have belonged to a marine reptile (_Eosaurus
Acadianus_), allied to the great _Ichthyosauri_ of the Lias. Up to
this time no confirmation of this determination has been obtained
by the discovery of other and more unquestionable remains, and
it therefore remains doubtful whether these bones of _Eosaurus_
may not really belong to large Labyrinthodonts.
LITERATURE.
The following list contains some of the more important of the
original sources of information to which the student of Carboniferous
rocks and fossils may refer:--
(1) 'Geology of Yorkshire,' vol. ii.; 'The Mountain Limestone
District.' John Phillips.
(2) 'Siluria.' Sir Roderick Murchison.
(3) 'Memoirs of the Geological Survey of Great Britain and Ireland.'
(4) 'Geological Report on Londonderry,' &c. Portlock.
(5) 'Acadian Geology.' Dawson.
(6) 'Geology of Iowa,' vol. i. James Hall.
(7) 'Reports of the Geological Survey of Illinois' (Geology and
Palæontology). Meek, Worthen, &c.
(8) 'Reports of the Geological Survey of Ohio' (Geology and
Palæontology). Newberry, Cope, Meek, Hall, &c.
(9) 'Description des Animaux fossiles qui se trouvent dans le
Terrain Carbonifère de la Belgique,' 1843; with subsequent
monographs on the genera _Productus_ and _Chonetes_,
on _Crinoids_, on _Corals_, &c. De Koninck.
(10) 'Synopsis of the Carboniferous Fossils of Ireland.' M'Coy.
(11) 'British Palæozoic Fossils.' M'Coy.
(12) 'Figures of Characteristic British Fossils.' Baily.
(13) 'Catalogue of British Fossils.' Morris.
(14) 'Monograph of the Carboniferous Brachiopoda of Britain'
(Palæontographical Society). Davidson.
(15) 'Monograph of the British Carboniferous Corals'
(Palæontographical Society). Milne-Edwards and Haime.
(16) 'Monograph of the Carboniferous Bivalve Entomostraca of
Britain' (Palæontographical Society). Rupert Jones, Kirkby, and
George S. Brady.
(17) 'Monograph of the Carboniferous Foraminifera of Britain'
(Palæontographical Society). H. B. Brady.
(18) "On the Carboniferous Fossils of the West of Scotland"--'Trans.
Geol. Soc.,' of Glasgow, vol. iii., Supplement. Young and
Armstrong.
(19) 'Poissons Fossiles.' Agassiz.
(20) "Report on the Labyrinthodonts of the Coal-measures"--'British
Association Report,' 1873. L. C. Miall.
(21) 'Introduction to the Study of Palæontological Botany.' John
Hutton Balfour.
(22) 'Traité de Paléontologie Végétale.' Schimper.
(23) 'Fossil Flora.' Lindley and Hutton.
(24) 'Histoire des Végétaux Fossiles.' Brongniart.
(25) 'On Calamites and Calamodendron' (Monographs of the
Palæontographical Society). Binney.
(26) 'On the Structure of Fossil Plants found in the Carboniferous
Strata' (Palæontographical Society). Binney.
Also numerous memoirs by Huxley, Davidson, Martin Duncan, Professor
Young, John Young, R. Etheridge, jun., Baily, Carruthers, Dawson,
Binney, Williamson, Hooker, Jukes, Geikie, Rupert Jones, Salter,
and many other British and foreign observers.
CHAPTER XIV.
THE PERMIAN PERIOD.
The Permian formation closes the long series of the Palæozoic
deposits, and may in some respects be considered as a kind of
appendix to the Carboniferous system, to which it cannot be compared
in importance, either as regards the actual bulk of its sediments
or the interest and variety of its life-record. Consisting, as
it does, largely of red rocks--sandstones and marls--for the
most part singularly destitute of organic remains, the Permian
rocks have been regarded as a lacustrine or fluviatile deposit;
but the presence of well-developed limestones with indubitable
marine remains entirely negatives this view. It is, however,
not improbable that we are presented in the Permian formation,
as known to us at present, with a series of sediments laid down
in inland seas of great extent, due to the subsidence over large
areas of the vast land-surfaces of the Coal-measures. This view,
at any rate, would explain some of the more puzzling physical
characters of the formation, and would not be definitely negatived
by any of its fossils.
A large portion of the Permian series, as already remarked, consists
of sandstones and marls, deeply reddened by peroxide of iron, and
often accompanied by beds of gypsum or deposits of salt. In strata
of this nature few or no fossils are found; but their shallow-water
origin is sufficiently proved by the presence of the footprints
of terrestrial animals, accompanied in some cases by well-defined
"ripple-marks." Along with these are occasionally found massive
breccias, holding larger or smaller blocks derived from the older
formations; and these have been supposed to represent an old
"boulder-clay," and thus to indicate the prevalence of an arctic
climate. Beds of this nature must also have been deposited in
shallow water. In all regions, however, where the Permian formation
is well developed, one of its most characteristic members is a
Magnesian limestone, often highly and fantastically concretionary,
but containing numerous remains of genuine marine animals, and
clearly indicating that it was deposited beneath a moderate depth
of salt water.
It is not necessary to consider here whether this formation can
be retained as a distinct division of the geological series. The
name of _Permian_ was given to it by Sir Roderick Murchison,
from the province of Perm in Russia, where rocks of this age are
extensively developed. Formerly these rocks were grouped with
the succeeding formation of the Trias under the common name of
"New Red Sandstone." This name was given them because they contain
a good deal of red sandstone, and because they are superior to the
Carboniferous rocks, while the Old Red Sandstone is inferior.
Nowadays, however, the term "New Red Sandstone" is rarely employed,
unless it be for red sandstones and associated rocks, which are
seen to overlie the Coal-measures, but which contain no fossils by
which their exact age may be made out. Under these circumstances,
it is sometimes convenient to employ the term "New Red Sandstone."
The New Red, however, of the older geologists, is now broken up
into the two formations of the Permian and Triassic rocks--the
former being usually considered as the top of the Palæozoic series,
and the latter constituting the base of the Mesozoic.
In many instances, the Permian rocks are seen to repose unconformably
upon the underlying Carboniferous, from which they can in addition
be readily separated by their lithological characters. In other
instances, however, the Coal-measures terminate upwards in red
rocks, not distinguishable by their mineral characters from the
Permian; and in other cases no physical discordance between the
Carboniferous and Permian strata can be detected. As a general
rule, also, the Permian rocks appear to pass upwards conformably
into the Trias. The division, therefore, between the Permian
and Triassic rocks, and consequently between the Palæozoic and
Mesozoic series, is not founded upon any conspicuous or universal
physical break, but upon the difference in life which is observed
in comparing the marine animals of the Carboniferous and Permian
with those of the Trias. It is to be observed, however, that
this difference can be solely due to the fact that the Magnesian
Limestone of the Permian series presents us with only a small,
and not a typical, portion of the marine deposits which must have
been accumulated in some area at present unknown to us during the
period which elapsed between the formation of the great marine
limestones of the Lower Carboniferous and the open-sea and likewise
calcareous sediments of the Middle Trias.
The Permian rocks exhibit their most typical features in Russia
and Germany, though they are very well developed in parts of
Britain, and they occur in North America. When well developed,
they exhibit three main divisions: a lower set of sandstones,
a middle group, generally calcareous, and an upper series of
sandstones, constituting respectively the Lower, Middle, and Upper
Permians.
In Russia, Germany, and Britain, the Permian rocks consist of
the following members:--
1. The _Lower Permians_, consisting mainly of a great series
of sandstones, of different colours, but usually red. The base
of this series is often constituted by massive breccias with
included fragments of the older rocks, upon which they may happen
to repose; and similar breccias sometimes occur in the upper
portion of the series as well. The thickness of this group varies
a good deal, but may amount to 3000 or 4000 feet.
2. The _Middle Permians_, consisting, in their typical development,
of laminated marls, or "marl-slate," surmounted by beds of magnesian
limestone (the "Zechstein" of the German geologists). Sometimes
the limestones are degenerate or wholly deficient, and the series
may consist of sandy shales and gypsiferous clays. The magnesian
limestone, however, of the Middle Permians is, as a rule, so well
marked a feature that it was long spoken of as _the_ Magnesian
Limestone.
3. The _Upper Permians_, consisting of a series of sandstones
and shales, or of red or mottled marls, often gypsiferous, and
sometimes including beds of limestone.
In North America, the Permian rocks appear to be confined to the
region west of the Mississippi, being especially well developed
in Kansas. Their exact limits have not as yet been made out,
and their total thickness is not more than a few hundred feet.
They consist of sandstones, conglomerates, limestones, marls,
and beds of gypsum.
The following diagrammatic section shows the general sequence of
the Permian deposits in the north of England, where the series
is extensively developed (fig. 133):--
[Illustration: Fig. 133. GENERALISED SECTION OF THE PERMIAN ROCKS
IN THE NORTH OF ENGLAND.]
The record of the _life_ of the Permian period is but a scanty
one, owing doubtless to the special peculiarities of such of the
deposits of this age with which we are as yet acquainted. Red rocks
are, as a general rule, more or less completely unfossiliferous, and
sediments of this nature are highly characteristic of the Permian.
Similarly, magnesian limestones are rarely as highly charged with
organic remains as is the case with normal calcareous deposits,
especially when they have been subjected to concretionary action,
as is observable to such a marked extent in the Permian limestones.
Nevertheless, much interest is attached to the organic remains,
as marking a kind of transition-period between the Palæozoic
and Mesozoic epochs.
[Illustration: Fig. 134.--_Walchia piniformis_, from the Permian
of Saxony, a, Branch; b, Twig, (After Gutbier.)]
The _plants_ of the Permian period, as a whole, have a distinctly
Palæozoic aspect, and are far more nearly allied to those of the
Coal-measures than they are to those of the earlier Secondary
rocks; though the Permian _species_ are mostly distinct from
the Carboniferous, and there are some new genera. Thus, we find
species of _Lepidodendron, Calamites, Equisetites, Asterophyllites,
Annularia_, and other highly characteristic Carboniferous genera.
On the other hand, the _Sigillariods_ of the Coal seem to have
finally disappeared at the close of the Carboniferous period. Ferns
are abundant in the Permian rocks, and belong for the most part to
the well-known Carboniferous genera _Alethopteris, Neuropteris,
Sphenopteris_, and _Pecopteris_. There are also Tree-ferns referable
to the ancient genus _Psaronius_. The _Conifers_ of the Permian
period are numerous, and belong in part to Carboniferous genera.
A characteristic genus, however, is _Walchia_ (fig. 134),
distinguished by its lax short leaves. This genus, though not
exclusively Permian, is mainly so, the best-known species being
the _W. Piniformis_. Here, also, we meet with Conifers which
produce true cones, and which differ, therefore, in an important
degree from the Taxoid Conifers of the Coal-measures. Besides
_Walchia_, a characteristic form of these is the _Ullmania
selaginoides_, which occurs in the Magnesian Limestone of Durham,
the Middle Permian of Westmorland, and the "Kupfer-schiefer" of
Germany. The group of the _Cycads_, which we shall subsequently
find to be so characteristic of the vegetation of the Secondary
period, is, on the other hand, only doubtfully represented in
the Permian deposits by the singular genus _Noeggerathia_.
The _Protozoans_ of the Permian rocks are few in number, and
for the most part imperfectly known. A few _Foraminifera_ have
been obtained from the Magnesian Limestone of England, and the
same formation has yielded some ill-understood Sponges. It does
not seem, however, altogether impossible that some of the singular
"concretions" of this formation may ultimately prove to have an
organic structure, though others would appear to be clearly of
purely inorganic origin. From the Permian of Saxony, Professor
Geinitz has described two species of _Spongillopsis_, which he
believes to be most nearly allied to the existing fresh-water
Sponges (_Spongilla_). This observation has an interest as bearing
upon the mode of deposition and origin of the Permian sediments.
The _Coelenterates_ are represented in the Permian by but a few
Corals. These belong partly to the _Tabulate_ and partly to the
_Rugose_ division; but the latter great group, so abundantly
represented in Silurian, Devonian, and Carboniferous seas, is
now extraordinarily reduced in numbers, the British strata of
this age yielding only species of the single genus _Polycoelia_.
So far, therefore, as at present known, all the characteristic
genera of the Rugose Corals of the Carboniferous had become extinct
before the deposition of the limestones of the Middle Permian.
The _Echinoderms_ are represented by a few _Crinoids_, and by a
Sea-urchin belonging to the genus _Eocidaris_. The latter genus
is nearly allied to the _Archoeocidaris_ of the Carboniferous, so
that this Permian form belongs to a characteristically Palæozoic
type.
A few _Annelides_ (_Spirorbis, Vermilia_, &c.) have been described,
but are of no special importance. Amongst the _Crustaceans_,
however, we have to note the total absence of the great Palæozoic
group of the _Trilobites_; whilst the little _Ostracoda_ and
_Phyllopods_ still continue to be represented. We have also to
note the first appearance here of the "Short-tailed" Decapods or
Crabs (_Brachyura_), the highest of all the groups of _Crustacea_,
in the person of _Hemitrochiscus paradoxus_, an extremely minute
Crab from the Permian of Germany.
[Illustration: Fig. 135.--Brachiopods of the Permian formation.
a, _Producta horrida_; b, _Lingula Credneri_; c, _Terebratula
elongata_; d and e, _Camarophoria globulina_. (After King.)]
Amongst the _Mollusca_, the remains of _Polyzoa_ may fairly be
said to be amongst the most abundant of all the fossils of the
Permian formation, The principal forms of these are the fronds
of the Lace-corals (_Fenestella, Retepora_, and _Synocladia_),
which are very abundant in the Magnesian Limestone of the north
of England, and belong to various highly characteristic species
(such as _Fenestella retiformis, Retepora Ehrenbergi_, and
_Synocladia virgulacea_). The _Brachiopoda_ are also represented
in moderate numbers in the Permian. Along with species of the
persistent genera _Discina, Crania_, and _Lingula_, we still
meet with representatives of the old groups _Spirifera, Athyris_,
and _Streptorhynchus_; and the Carboniferous _Productoe_ yet
survive under well-marked and characteristic types, though in
much-diminished numbers. The species of Brachiopods here figured
(fig. 135) are characteristic of the Magnesian Limestone in Britain
and of the corresponding strata on the Continent. Upon the whole,
the most characteristic Permian _Brachiopods_ belong to the genera
_Producta, Strophalosia_, and _Camarophoria_.
The _Bivalves_ (_Lamellibranchiata_) have a tolerably varied
development in the Permian rocks; but nearly all the old types,
except some of those which occur in the Carboniferous, have now
disappeared. The principal Permian Bivalves belong to the groups
of the Pearl Oysters (_Aviculidoe_) and the _Trigoniadoe_,
represented by genera such as _Bakewellia_ and _Schizodus_; the
true Mussels (_Mytilidoe_), represented by species which have
been referred to _Mytilus_ itself; and the Arks (_Arcadoe_),
represented by species of the genera _Arca_ (fig. 136) and
_Byssoarca_. The first and last of these three families have a
very ancient origin; but the family of the _Trigoniadoe_, though
feebly represented at the present day, is one which attained
its maximum development in the Mesozoic period.
[Illustration: Fig. 136.--_Arca antiqua_. Permian.]
The _Univalves_ (_Gasteropoda_) are rare, and do not demand special
notice. It may be observed, however, that the Palæozoic genera
_Euomphalus, Murchisonia, Loxonema_, and _Macrocheilus_ are still
in existence, together with the persistent genus _Pleurotomaria_.
_Pteropods_ of the old genera _Theca_ and _Conularia_ have been
discovered; but the first of these characteristically Palæozoic
types finally dies out here, and the second only survives but a
short time longer. Lastly, a few _Cephalopods_ have been found,
still wholly referable to the Tetrabranchiate group, and belonging
to the old genera _Orthoceras_ and _Cyrtoceras_ and the long-lived
_Nautilus_.
[Illustration: Fig. 137.--_Platysomus gibbosus_, a "heterocercal"
Ganoid, from the Middle Permian of Russia.]
Amongst _Vertebrates_, we meet in the Permian period not only
with the remains of Fishes and Amphibians, but also, for the
first time, with true Reptiles. The _Fishes_ are mainly _Ganoids_,
though there are also remains of a few Cestraciont Sharks. Not
only are the _Ganoids_ still the predominant group of Fishes, but
all the known forms possess the unsymmetrical ("heterocercal")
tail which is so characteristic of the Palæozoic Ganoids. Most
of the remains of the Permian Fishes have been obtained from the
"Marl-slate" of Durham and the corresponding "Kupfer-schiefer" of
Germany, on the horizon of the Middle Permian; and the principal
genera of the Ganoids are _Paloeoniscus_ and _Platysomus_ (fig.
137).
The _Amphibians_ of the Permian period belong principally to the
order of the _Labyrinthodonts_, which commenced to be represented
in the Carboniferous, and has a large development in the Trias.
Under the name, however, of _Paloeosiren Beinerti_, Professor
Geinitz has described an Amphibian from the Lower Permian of
Germany, which he believes to be most nearly allied to the existing
"Mud-eel" (_Siren lacertina_) of North America, and therefore
to be related to the Newts and Salamanders (_Urodela_).
[Illustration: Fig. 138.--_Protorosaurus Speneri_, Middle Permian,
Thuringia, reduced in size. (After Von Meyer.) [Copied from Dana.]]
Finally, we meet in the Permian deposits with the first undoubted
remains of true _Reptiles_. These are distinguished, as a class,
from the _Amphibians_, by the fact that they are air-breathers
throughout the whole of their life, and therefore are at no time
provided with gills; whilst they are exempt from that metamorphosis
which all the _Amphibia_ undergo in early life, consequent upon
their transition from an aquatic to a more or less purely aerial
mode of respiration. Their skeleton is well ossified; they usually
have horny or bony plates, singly or in combination, developed
in the skin; and their limbs (when present) are never either
in the form of _fins_ or _wings_, though sometimes capable of
acting in either of these capacities, and liable to great
modifications of form and structure. Though there can be no doubt
whatever as to the occurrence of genuine Reptiles in deposits of
unquestionable Permian age, there is still uncertainty as to the
precise number of types which may have existed at this period.
This uncertainty arises partly from the difficulty of deciding
in all cases, whether a given bone be truely Labyrinthodont or
Reptilian, but more especially from the confusion which exists at
present between the Permian and the overlying Triassic deposits.
Thus there are various deposits in different regions which have
yielded the remains of Reptiles, and which cannot in the meanwhile
be definitely referred either to the Permian series or to the
Trias by clear stratigraphical or palæontological evidence. All
that can be done in such cases is to be guided by the characters
of the Reptiles themselves, and to judge by their affinities to
remains from known Triassic or Permian rocks to which of these
formations the beds containing them should be referred; but it
is obvious that this method of procedure is seriously liable
to lead to error. In accordance, however, with this, the only
available mode of determination in some cases, the remains of
_Thecodontosaurus_ and _Palæosaurus_ discovered in the dolomitic
conglomerates near Bristol will be considered as Triassic, thus
leaving _Protorosaurus_[20] as the principal and most important
representative of the Permian Reptiles.[21] The type-species of
the genus _Protorusaurus_ is the _P. Speneri_(fig. 138) of the
"Kupfer-schiefer" of Thuringia, but other allied species have
been detected in the Middle Permian of Germany and the north
of England. This Reptile attained a length of from three to four
feet; and it has been generally referred to the group of the
Lizards (_Lacertilia_), to which it is most nearly allied in
its general structure, at the same time that it differs from
all existing members of this group in the fact that its numerous
conical and pointed teeth were implanted in distinct sockets in
the jaws--this being a Crocodilian character. In other respects,
however, _Protorosaurus_ approximates closely to the living Monitors
(_Varanidoe_); and the fact that the bodies of the vertebræ are
slightly cupped or hollowed out at the ends would lead to the
belief that the animal was aquatic in its habits. At the same
time, the structure of the hind-limbs and their bony supports
proves clearly that it must have also possessed the power of
progression upon the land. Various other Reptilian bones have
been described from the Permian formation, of which some are
probably really referable to Labyrinthodonts, whilst others are
regarded by Professor Owen as referable to the order of the
"Theriodonts," in which the teeth are implanted in sockets, and
resemble those of carnivorous quadrupeds in consisting of three
groups in each jaw (namely, incisors, canines, and molars). Lastly,
in red sandstones of Permian age in Dumfriesshire have been
discovered the tracks of what would appear to have been _Chelonians_
(Tortoises and Turtles); but it would not be safe to accept this
conclusion as certain upon the evidence of footprints alone. The
_Chelichnus Duncani_, however, described by Sir William Jardine
in his magnificent work on the 'Ichnology of Annandale,' bears
a great resemblance to the track of a Turtle.
[Footnote 20: Though commonly spelt as above, it is probable
that the name of this Lizard was really intended to have been
_Proterosaurus_--from the Greek _proteros_, first; and _saura_,
lizard: and this spelling is followed by many writers.]
[Footnote 21: In an extremely able paper upon the subject (Quart.
Journ. Geol. Soc., vol. xxvi.), Mr Etheridge has shown that there
are good physical grounds for regarding the dolomitie conglomerate
of Bristol as of Triassic age, and as probably corresponding in
time with the Muschelkalk of the Continent.]
No remains of Birds or Quadrupeds have hitherto been detected
in deposits of Permian age.
LITERATURE.
The following works may be consulted by the student with regard
to the Permian formation and its fossils:--
(1) "On the Geological Relations and Internal Structure of the
Magnesian Limestone and the Lower Portions of the New Red
Sandstone Series, &c."--'Trans. Geol. Soc.,' ser. 2, vol. iii.
Sedgwick.
(2) 'The Geology of Russia in Europe.' Murchison, De Verneuil, and
Von Keyserling.
(3) 'Siluria,' Murchison.
(4) 'Permische System in Sachsen.' Geinitz and Gutbier.
(5) 'Die Versteinerungen des Deutschen Zechsteingebirges,' Geinitz.
(6) 'Die Animalischen Ueberreste der Dyas.' Geinitz.
(7) 'Monograph of the Permian Fossils of England' (Palæontographical
Society). King.
(8) 'Monograph of the Permian Brachiopoda of Britain'
(Palæontographical Society). Davidson.
(9) "On the Permian Rocks of the North-West of England and their
Extension into Scotland"--'Quart. Journ. Geol. Soc.,' vol. xx.
Murchison and Harkness.
(10) 'Catalogue of the Fossils of the Permian System of the Counties
of Northumberland and Durham.' Howse.
(11) 'Petrefacta Germaniæ.' Goldfuss.
(12) 'Beiträge zur Petrefaktenkunde.' Munster.
(13) 'Ein Beitrag zur Palæontologie des Deutschen Zechsteingebirges.'
Von Schauroth.
(14) 'Saurier aus dem Kupfer-schiefer der Zechstein-formation.' Von
Meyer.
(15) 'Manual of Palæontology.' Owen.
(16) 'Recherches sur les Poissons Fossiles.' Agassiz.
(17) 'Ichnology of Annandale.' Sir William Jardine.
(18) 'Die Fossile Flora der Permischen Formation.' Goeppert.
(19) 'Genera et Species Plantarum Fossilium.' Unger.
(20) "On the Red Rocks of England of older Date than the Trias"
--'Quart. Journ. Geol. Soc.,' vol. xxvii. Ramsay.
CHAPTER XV.
THE TRIASSIC PERIOD.
We come now to the consideration of the great _Mesozoic_, or
Secondary series of formations, consisting, in ascending order,
of the Triassic, Jurassic, and Cretaceous systems. The Triassic
group forms the base of the Mesozoic series, and corresponds
with the higher portion of the New Red Sandstone of the older
geologists. Like the Permian rocks, and as implied by its name,
the _Trias_ admits of a subdivision into three groups--a Lower,
Middle, and Upper Trias. Of these sub-divisions the middle one
is wanting in Britain; and all have received German names, being
more largely and typically developed in Germany than in any other
country. Thus, the Lower Trias is known as the _Bunter Sandstein_;
the Middle Trias is called the _Muschelkalk_; and the Upper Trias
is known as the _Keuper_.
I. The lowest division of the Trias is known as the _Bunter
Sandstein_ (the _Grès bigarré_ of the French), from the generally
variegated colours of the beds which compose it (German, _bunt_,
variegated). The Bunter Sandstein of the continent of Europe
consists of red and white sandstones, with red clays, and thin
limestones, the whole attaining a thickness of about 1500 feet.
The term "marl" is very generally employed to designate the clays
of the Lower and Upper Trias; but the term is inappropriate, as
they may contain no lime, and are therefore not always genuine
marls. In Britain the Bunter Sandstein consists of red and mottled
sandstones, with unconsolidated conglomerates, or "pebble-beds,"
the whole having a thickness of 1000 to 2000 feet. The Bunter
Sandstein, as a rule, is very barren of fossils.
II. The Middle Trias is not developed in Britain, but it is largely
developed in Germany, where it constitutes what is known as the
_Muschelkalk_ (Germ. _Muschel_, mussel; _kalk_, limestone), from
the abundance of fossil shells which it contains. The Muschelkalk
(the _Calcaire coquillier_ of the French) consists of compact
grey or yellowish limestones, sometimes dolomitic, and including
occasional beds of gypsum and rock-salt.
III. The Upper Trias, or _Keuper_ (the _Marnes irisées_ of the
French), as it is generally called, occurs in England; but is
not so well developed as it is in Germany. In Britain, the Keuper
is 1000 feet or more in thickness, and consists of white and
brown sandstones, with red marls, the whole topped by red clays
with rock-salt and gypsum.
The Keuper in Britain is extremely unfossiliferous; but it passes
upwards with perfect conformity into a very remarkable group of
beds, at one time classed with the Lias, and now known under the
names of the Penarth beds (from Penarth, in Glamorganshire), the
Rhætic beds (from the Rhætic Alps), or the _Avicula contorta_ beds
(from the occurrence in them of great numbers of this peculiar
Bivalve). These singular beds have been variously regarded as the
highest beds of the Trias, or the lowest beds of the Lias, or as
an intermediate group. The phenomena observed on the Continent,
however, render it best to consider them as Triassic, as they
certainly agree with the so-called Upper St Cassian or Kössen
beds which form the top of the Trias in the Austrian Alps.
The Penarth beds occur in Glamorganshire, Gloucestershire,
Warwickshire, Staffordshire, and the north of Ireland; and they
generally consist of a small thickness of grey marls, white
limestones, and black shales, surmounted conformably by the lowest
beds of the Lias. The most characteristic fossils which they contain
are the three Bivalves _Cardium Rhoeticum, Avicula contorta_, and
_Pecten Valoniensis_; but they have yielded many other fossils,
amongst which the most important are the remains of Fishes and
small Mammals (_Microlestes_).
In the Austrian Alps the Trias terminates upwards in an extraordinary
series of fossiliferous beds, replete with marine fossils. Sir
Charles Lyell gives the following table of these remarkable
deposits:--
_Strata below the Lias in the Austrian Alps, in descending order._
/ Grey and black limestone, with calcareous
| marls having a thickness of about 50
| feet. Among the fossils, Brachiopoda
1. Koessen beds. | very numerous; some few species common
(Synonyms, Upper | to the genuine Lias; many peculiar.
St Cassian beds of < _Avicula contorta, Pecten Valoniensis_,
Escher and Merian.) | _Cardium Rhoeticum, Avicula_
| _inoequivalvis, Spirifer Münsteri_,
| Dav. Strata containing the above fossils
| alternate with the Dachstein beds, lying
\ next below.
/ White or greyish limestone, often in beds
| three or four feet thick. Total thickness
| of the formation above 2000 feet. Upper
| part fossiliferous, with some strata
2. Dachstein beds. < composed of corals (_Lithodendron_.)
| Lower portion without fossils. Among the
| characteristic shells are _Hemicardium_
| _Wulfeni, Megalodon triqueler_, and
\ other large bivalves.
/ Red, pink, or white marbles, from 800 to
| 1000 feet in thickness, containing more
| than 800 species of marine fossils, for
3. Hallstadt beds | the most part mollusca. Many species of
(or St Cassian). < _Orthoceras_. True _Ammonites_,
| besides _Ceratites_ and
| _Goniatites, Belemnites_ (rare),
| _Porcellia, Pleurotomania, Trochus_,
\ _Monotis salinaria_, &c.
/ A. Black and grey \ Among the fossils
4. A. Guttenstein beds. | limestone 150 feet | are _Ceratites_
B. Werfen beds, base | thick, alternating | _cassianus_,
of Upper Trias? | with the underlying | _Myacites_
Lower Trias of < Werfen beds. > _fassaensis_,
some geologists. | B. Red and green | _Naticella_
| shale and sandstone, | _costata_, &c.
\ with salt and gypsum./
In the United States, rocks of Triassic age occur in several
areas between the Appalachians and the Atlantic seaboard; but
they show no such triple division as in Germany, and their exact
place in the system is uncertain. The rocks of these areas consist
of red sandstones, sometimes shaly or conglomeratic, occasionally
with beds of impure limestone. Other more extensive areas where
Triassic rocks appear at the surface, are found west of the
Mississippi, on the slopes of the Rocky Mountains, where the
beds consist of sandstones and gypsiferous marls. The American
Trias is chiefly remarkable for having yielded the remains of a
small Marsupial (_Dromatherium_), and numerous footprints, which
have generally been referred to Birds (_Brontozoum_), along with
the tracks of undoubted Reptiles (_Otozoum, Anisopus_, &c.)
The subjoined section (fig. 139) expresses, in a diagrammatic
manner, the general sequence of the Triassic rocks when fully
developed, as, for example, in the Bavarian Alps:--
[Illustration: Fig. 139. GENERALIZED SECTION OF THE TRIASSIC ROCKS
OF CENTRAL EUROPE.]
With regard to the _life_ of the Triassic period, we have to
notice a difference as concerns the different members of the group
similar to that which has been already mentioned in connection
with the Permian formation. The arenaceous deposits of the series,
namely, resemble those of the Permian, not only in being commonly
red or variegated in their colour, but also in their conspicuous
paucity of organic remains. They for the most part are either
wholly unfossiliferous, or they contain the remains of plants or
the bones of reptiles, such as may easily have been drifted from
some neighbouring shore. The few fossils which may be considered
as properly belonging to these deposits are chiefly Crustaceans
(_Estheria_) or Fishes, which may well have lived in the waters
of estuaries or vast inland seas. We may therefore conclude,
with considerable probability, that the barren sandy and marly
accumulations of the Bunter Sandstein and Lower Keuper were not
laid down in an open sea, but are probably brackish-water deposits,
formed in estuaries or land-locked bodies of salt water. This at
any rate would appear to be the case as regards these members
of the series as developed in Britain and in their typical areas
on the continent of Europe; and the origin of most of the North
American Trias would appear to be much the same. Whether this view
be correct or not, it is certain that the beds in question were laid
down in _shallow_ water, and in the immediate vicinity of _land_,
as shown by the numerous drifted plants which they contain and
the common occurrence in them of the footprints of air-breathing
animals (Birds, Reptiles, and Amphibians). On the other hand, the
middle and highest members of the Trias are largely calcareous,
and are replete with the remains of undoubted marine animals. There
cannot, therefore, be the smallest doubt but that the Muschelkalk
and the Rhætic or Kössen beds were slowly accumulated in an open
sea, of at least a moderate depth; and they have preserved for
us a very considerable selection from the marine fauna of the
Triassic period.
[Illustration: Fig. 140.--_Zamia spiralis_, a living Cycad.
Australia.]
The _plants_ of the Trias are, on the whole, as distinctively
Mesozoic in their aspect as those of the Permian are Palæozoic.
In spite, therefore, of the great difficulty which is experienced
in effecting a satisfactory stratigraphical separation between
the Permian and the Trias, we have in this fact a proof that the
two formations were divided by an interval of time sufficient
to allow of enormous changes in the terrestrial vegetation of the
world. The _Lepidodendroids, Asterophyllites_, and _Annularioe_,
of the Coal and Permian formations, have now apparently wholly
disappeared: and the Triassic flora consists mainly of Ferns,
Cycads, and Conifers, of which only the two last need special
notice. The _Cycads_ (fig. 140) are true exogenous plants, which
in general form and habit of growth present considerable resemblance
to young Palms, but which in reality are most nearly related to
the Pines and Firs (_Coniferoe_). The trunk is unbranched, often
much shortened, and bears a crown of feathery pinnate fronds.
The leaves are usually "circinate"--they unroll in expanding,
like the fronds of ferns. The seeds are not protected by a
seed-vessel, but are borne upon the edge of altered leaves, or
are carried on the scales of a cone. All the living species of
Cycads are natives of warm countries, such as South America, the
West Indies, Japan, Australia, Southern Asia, and South Africa.
The remains of Cycads, as we have seen, are not known to occur
in the Coal formation, or only to a very limited extent towards
its close; nor are they known with certainty as occurring in
Permian deposits. In the Triassic period, however, the remains
of Cycads belonging to such genera as _Pterophyllum_ (fig. 141,
b), _Zamites_, and _Podozamites_ (fig. 141, c), are sufficiently
abundant to constitute quite a marked feature in the vegetation;
and they continue to be abundantly represented throughout the
whole Mesozoic series. The name "Age of Cycads," as applied to
the Secondary epoch, is therefore, from a botanical point of
view, an extremely appropriate one. The _Conifers_ of the Trias
are not uncommon, the principal form being _Veltzia_ (fig. 141,
a), which possesses some peculiar characters, but would appear
to be most nearly related to the recent Cypresses.
[Illustration: Fig. 141.--Triassic Conifers and Cycads. a, _Voltzia_
(_Schizoneura_) _heterophylla_, portion of a branch, Europe and
America; b, Part of the frond of _Pterophyllum Joegeri_, Europe;
c, Part of the frond of _Podozamites lanceolatus_, America.]
As regards the _Invertebrate animals_ of the Trias, our knowledge
is still principally derived from the calcareous beds which
constitute the centre of the system (the Muschelkalk) on the
continent of Europe, and from the St Cassain and Rhætic beds
still higher in the series; whilst some of the Triassic strata
of California and Nevada have likewise yielded numerous remains
of marine Invertebrates. The _Protozoans_ are represented by
_Foraminifera_ and _Sponges_, and the _Coelenterates_ by a small
number of _Corals_; but these require no special notice. It may be
mentioned, however, that the great Palæozoic group of the _Rugose_
corals has no known representative here, its place being taken
by corals of Secondary type (such as _Montlivaltia, Synastoea_,
&c.)
The _Echinoderms_ are represented principally by _Crinoids_,
the remains of which are extremely abundant in some of the
limestones. The best-known species is the famous "Lily-Encrinite"
(_Encrinus liliiformis_, fig. 142), which is characteristic of the
Muschelkalk. In this beautiful species, the flower-like head is
supported upon a rounded stem, the joints of which are elaborately
articulated with one another; and the fringed arms are composed
each of a double series of alternating calcareous pieces. The
Palæozoic Urchins, with their supernumerary rows of plates, the
Cystideans, and the Pentremites have finally disappeared; but
both Star-fishes and Brittle-stars continue to be represented.
One of the latter--namely, the _Aspidura loricata_ of Goldfuss
(fig. 143)--is highly characteristic of the Muschelkalk.
[Illustration: Fig. 142.--Head and upper part of the column of
_Encrinus liliiformis_. The lower figure shows the articulating
surface of one of the joints of the column. Muschelkalk, Germany.]
[Illustration: Fig. 143.--_Aspidura loricata_, a Triassic Ophiuroid.
Muschelkalk, Germany.]
The remains of _Articulate Animals_ are not very abundant in the
Trias, if we except the bivalved cases of the little Water-fleas
(_Ostracoda_), which are occasionally very plentiful. There are
also many species of the horny, concentrically-striated valves
of the _Estherioe_ (see fig. 122, b), which might easily be
taken for small Bivalve Molluscs. The "Long-tailed" Decapods
of the type of the Lobster, are not without examples but they
become much more numerous in the succeeding Jurassic period.
Remains of insects have also been discovered.
Amongst the _Mollusca_ we have to note the disappearance, amongst
the lower groups, of many characteristic Palæozoic types. Amongst
the _Polyzoans_, the characteristic "Lace-corals," _Fenestella,
Retepora_,[22] _Synocladia, Polypora_, &c., have become apparently
extinct. The same is true of many of the ancient types of
_Brachiopods_, and conspicuously so of the great family of the
_Productidoe_, which played such an important part in the seas
of the Carboniferous and Permian periods.
[Footnote 22: The genus _Retefora_ is really a recent one,
represented by living forms; and the so-called _Reteporoe_ of the
Palæozoic rocks should properly receive another name (_Phyllopora_),
as being of a different nature. The name _Retepora_ has been here
retained for these old forms simply in accordance with general
usage.]
[Illustraton: Fig. 144. Triassic Lamellibranchs. a, _Daonella_
(_Halobia_) _Lommelli_; b, _Pecten Valoniensis_; c, _Myophoria
lineata_; d. _Cardium Rhoeticum_; e. _Avicula contorta_; f. _Avicula
socialis_.]
_Bivalves_ (_Lamellibranchiata_) and _Univalves_ (_Gasteropoda_)
are well represented in the marine beds of the Trias, and some of the
former are particularly characteristic either of the formation as a
whole or of minor subdivisions of it. A few of these characteristic
species are figured in the accompanying illustration (fig. 144).
Bivalve shells of the genera _Daonella_ (fig. 144, a) and _Halobia_
(_Monotis_) are very abundant, and are found in the Triassic
strata of almost all regions. These groups belong to the family
of the Pearl-oysters (_Aviculidoe_), and are singular from the
striking resemblance borne by some of their included forms to
the _Strophomenoe amongst the Lamp-shells, though, of course, no
real relation exists between the two. The little Pearl-oyster,
_Avicula socialis_ (fig. 144, f), is found throughout the greater
part of the Triassic series, and is especially abundant in the
Muschelkalk. The genus _Myophoria_ (fig. 144, c), belonging
to the _Trigoniadoe_, and related therefore to the Permian
_Schizodus_, is characteristically Triassic, many species of the
genus being known in deposits of this age. Lastly, the so-called
"Rhætic" or "Kössen" beds are characterised by the occurrence
in them of the Scallop, _Pecten Valoniensis_ (fig. 144, b);
the small Cockle, _Cardium Rhoeticum_ (fig. 144, d); and the
curiously-twisted Pearl-oyster, _Avicula contorta_ (fig. 144,
e)--this last Bivalve being so abundant that the strata in
question are often spoken of as the "Avicula contorta beds."
[Illustration: Fig. 145.--_Ceratites nodosus_, viewed from the
side and from behind. Muschelkalk.]
Passing over the groups of the _Heteropods_ and _Pteropods_, we
have to notice the _Cephalopoda_, which are represented in the
Trias not only by the chambered shells of _Tetrabranchiates_, but
also, for the first time, by the internal skeletons of _Dibranchiate_
forms. The Trias, therefore, marks the first recognised appearance
of true Cuttle-fishes. All the known examples of these belong
to the great Mesozoic group of the _Belemnitidoe_; and as this
family is much more largely developed in the succeeding Jurassic
period, the consideration of its characters will be deferred till
that formation is treated of. Amongst the chambered _Cephalopods_
we find quite a number of the Palæozoic _Orthoceratites_, some of
them of considerable size, along with the ancient _Cyrtoceras_
and _Goniatites_; and these old types, singularly enough, occur
in the higher portion of the Trias (St Cassian beds), but have,
for some unexplained reason, not yet been recognised in the lower
and equally fossiliferous formation of the Muschelkalk. Along
with these we meet for the first time with true _Ammonites_,
which fill such an extensive place in the Jurassic seas, and
which will be spoken of hereafter. The form, however, which is
most characteristic of the Trias is _Ceratites_ (fig. 145). In
this genus the shell is curved into a flat spiral, the volutions of
which are in contact; and it further agrees with both _Goniatites_
and _Ammonites_ in the fact that the septa or partitions between
the air-chambers are not simple and plain (as in the _Nautilus_
and its allies), but are folded and bent as they approach the
outer wall of the shell. In the _Goniatite_ these foldings of
the septa are of a simply lobed or angulated nature, and in the
_Ammonite_ they are extremely complex; whilst in the _Ceratite_
there is an intermediate state of things, the special feature
of which is, that those foldings which are turned towards the
mouth of the shell are merely rounded, whereas those which are
turned away from the mouth are characteristically toothed. The
genus _Ceratites_, though principally Triassic, has recently
been recognised in strata of Carboniferous age in India.
From the foregoing it will be gathered that one of the most important
points in connection with the Triassic _Mollusca_ is the remarkable
intermixture of Palæozoic and Mesozoic types which they exhibit.
It is to be remembered, also, that this intermixture has hitherto
been recognised, not in the Middle Triassic limestones of the
Muschelkalk, in which--as the oldest Triassic beds with marine
fossils--we should naturally expect to find it, but in the St
Cassian beds, the age of which is considerably later than that
of the Muschelkalk. The intermingling of old and new types of
Shell-fish in the Upper Trias is well brought out in the annexed
table, given by Sir Charles Lyell in his 'Student's Elements of
Geology' (some of the less important forms in the table being
omitted here):--
GENERA OF FOSSIL MOLLUSCA IN THE ST CASSIAN AND HALLSTADT BEDS.
Common to | Characteristic of | Common to
Older Rocks. | Triassic Rocks | Newer Rocks.
| |
Orthoceras. | Ceratites. | Ammonites.
Bactrites. | Cochloceras. | Chemnitzia.
Macrocheilus. | Rhabdoceras. | Cerithium.
Loxonema. | Aulacoceras. | Monodonta.
Holopella. | Naticella. | Sphoera.
Murchisonia. | Platystoma. | Cardita.
Porcellia. | Halobia. | Myoconcha.
Athyris. | Hörnesia. | Hinnites.
Retzia. | Koninckia. | Monotis.
Cyrtina. | Scoliostoma. | Plicatula.
Euomphalus. | Myophoria. | Pachyrisma.
|(The last two are | Thecidium.
|principally but not |
|exclusively Triassic.)|
Thus, to emphasise the more important points alone, the Trias
has yielded, amongst the Gasteropods, the characteristically
Palæozoic _Loxonema, Holopella, Murchisonia, Euomphalus_, and
_Porcellia_, along with typically Triassic forms like _Platystoma_
and _Scoliostoma_, and the great modern groups _Chemnitzia_ and
_Cerithium_. Amongst the Bivalves we find the Palæozoic _Megalodon_
side by side with the Triassic _Halobia_ and _Myophoria_, these
being associated with the _Carditoe, Hinnites, Plicatuloe_, and
_Trigonioe_ of later deposits. The Brachiopods exhibit the Palæozoic
_Athyris, Retzia_, and _Cyrtina_, with the Triassic _Koninckia_
and the modern _Thecidium_. Finally, it is here that the ancient
genera _Orthoceras, Cyrtoceras_, and _Goniatites_ make their last
appearance upon the scene of life, the place of the last of these
being taken by the more complex and almost exclusively Triassic
_Ceratites_, whilst the still more complex genus _Ammonites_ first
appears here in force, and is never again wanting till we reach
the close of the Mesozoic period. The first representatives of
the great Secondary family of the _Belemnites_ are also recorded
from this horizon.
[Illustration: Fig. 146.--a, Dental plate of _Ceratodus serratus_,
Keuper; b, Dental plate of _Ceratodus altus_, Keuper; (After
Agassiz.)]
[Illustration: Fig 147.--_Ceratodus Fosteri_, the Australian
Mud-fish, reduced in size.]
Amongst the _Vertebrate Animals_ of the Trias, the _Fishes_ are
represented by numerous forms belonging to the _Ganoids_ and the
_Placoids_. The Ganoids of the period are still all provided
with unsymmetrical ("heterocercal") tails, and belong principally
to such genera as _Paloeoniscus_ and _Catopterus_. The remains of
Placoids are in the form of teeth and spines, the two principal
genera being the two important Secondary groups _Acrodus_ and
_Hybodus_. Very nearly at the summit of the Trias in England, in
the Rhætic series, is a singular stratum, which is well known as the
"bone-bed," from the number of fish-remains which it contains. More
interesting, however, than the above, are the curious palate-teeth
of the Trias, upon which Agassiz founded the genus _Ceratodus_.
The teeth of Ceratodus (fig. 146) are singular flattened plates,
composed of spongy bone beneath, covered superficially with a
layer of enamel. Each plate is approximately triangular, one
margin (which we now know to be the outer one) being prolonged
into prongs or conical prominences, whilst the surface is more or
less regularly undulated. Until recently, though the master-mind
of Agassiz recognised that these singular bodies were undoubtedly
the teeth of fishes, we were entirely ignorant as to their precise
relation to the animal, or as to the exact affinities of the fish
thus armed. Lately, however, there has been discovered in the
rivers of Queensland (Australia) a living species of _Ceratodus_
(_C. Fosteri_, fig. 147), with teeth precisely similar to those
of its Triassic predecessor; and we thus have become acquainted
with the use of these structures and the manner in which they
were implanted in the mouth. The palate carries two of these
plates, with their longer straight sides turned towards each
other, their sharply-sinuated sides turned outwards, and their
short straight sides or bases directed backwards. Two similar
plates in the lower jaw correspond to the upper, their undulated
surfaces fitting exactly to those of the opposite teeth. There
are also two sharp-edged front teeth, which are placed in the
front of the mouth in the upper jaw; but these have not been
recognised in the fossil specimens. The living _Ceratodus_ feeds
on vegetable matters, which are taken up or tom off from plants
by the sharp front teeth, and then partially crushed between
the undulated surfaces of the back teeth (Günther); and there
need be little doubt but that the Triassic _Ceratodi_ followed
a similar mode of existence. From the study of the living
_Ceratodus_, it is certain that the genus belongs to the same
group as the existing Mud-fishes (_Dipnoi_); and we therefore
learn that this, the highest, group of the entire class of Fishes
existed in Triassic times under forms little or not at all different
from species now alive; whilst it has become probable that the
order can be traced back into the Devonian period.
[Illustration: Fig. 148.--Footprints of a Labyrinthodont
(_Cheirotherium_), from the Triassic Sandstones of Hessberg, near
Hildburghausen, Germany, reduced one-eighth. The lower figure
shows a slab, with several prints, and traversed by reticulated
sun-cracks: the upper figure shows the impression of one of the
hind-feet, one-half of the natural size. (After Sickler.)]
[Illustration: Fig. 149.--Section of the tooth of _Labryinthodon
(Mastodonsaurus) Joegeri_, showing the microscopic structure.
Greatly enlarged. Trias.]
[Illustration: Fig. 150.--a, Skull of _Labyrinthodon Joegeri_,
much reduced in size; b, Tooth of the same. Trias Württemberg.]
The _Amphibians_ of the Trias all belong to the old order of
the _Labyrinthodonts_, and some of them are remarkable for their
gigantic dimensions. They were first known by their footprints,
which were found to occur plentifully in the Triassic sandstones
of Britain and the continent of Europe, and which consisted of
a double series of alternately-placed pairs of hand-shaped
impressions, the hinder print of each pair being much larger
than the one in front (fig. 148). So like were these impressions
to the shape of the human hand, that the at that time unknown
animal which produced them was at once christened _Cheirotherium_,
or "Hand-beast." Further discoveries, however, soon showed that
the footprints of _Cheirotherium_ were really produced by species
of Amphibians which, like the existing Frogs, possessed hind-feet
of a much larger size than the fore-feet, and to which the name
of _Labyrinthodonts_ was applied in consequence of the complex
microscopic structure of the teeth (fig. 149). In the essential
details of their structure, the Triassic Labyrinthodonts did not
differ materially from their predecessors in the Coal-measures
and Permian rocks. They possessed the same frog-like skulls (fig.
150), with a lizard-like body, a long tail, and comparatively
feeble limbs. The hind-limbs were stronger and longer than the
fore-limbs, and the lower surface of the body was protected by an
armour of bony plates. Some of the Triassic Labyrinthodonts must
have attained dimensions utterly unapproached amongst existing
Amphibians, the skull of _Labyrinthodon Joegeri_ (fig. 150) being
upwards of three feet in length and two feet in breadth. Restorations
of some of these extraordinary creatures have been attempted in
the guise of colossal Frogs; but they must in reality have more
closely resembled huge Newts.
Remains of _Reptiles_ are very abundant in Triassic deposits,
and belong to very varied types. The most marked feature, in
fact, connected with the Vertebrate fauna of the Trias, and of
the Secondary rocks in general, is the great abundance of Reptilian
life. Hence the Secondary period is often spoken of as the "Age
of Reptiles." Many of the Triassic reptiles depart widely in
their structure from any with which we are acquainted as existing
on the earth at the present day, and it is only possible here to
briefly note some of the more important of these ancient forms.
Amongst the group of the Lizards (_Lacertilia_), represented by
_Protorosaurus_ in the older Permian strata, three types more
or less certainly referable to this order may be mentioned. One
of these is a small reptile which was found many years ago in
sandstones near Elgin, in Scotland, and which excited special
interest at the time in consequence of the fact that the strata
in question were believed to belong to the Old Red Sandstone
formation. It is, however, now certain that the Elgin sandstones
which contain _Telerpeton Elginense_, as this reptile is termed,
are really to be regarded as of Triassic age. By Professor Huxley,
_Telerpeton_ is regarded as a Lizard, which cannot be considered
as "in any sense a less perfectly-organised creature than the
Gecko, whose swift and noiseless run over walls and ceilings
surprises the traveller in climates warmer than our own." The
"Elgin Sandstones" have also yielded another Lizard, which was
originally described by Professor Huxley under the name of
_Hyperodapedon_, the remains of the same genus having been
subsequently discovered in Triassic strata in India and South
Africa. The Lizards of this group must therefore have at one
time enjoyed a very wide distribution over the globe; and the
living _Sphenodon_ of New Zealand is believed by Professor Huxley
to be the nearest living ally of this family. The _Hyperodapedon_
of the Elgin Sandstones was about six feet in length, with limbs
adapted for terrestrial progression, but with the bodies of the
vertebræ slightly biconcave, and having two rows of palatal teeth,
which become worn down to the bone in old age. Lastly, the curious
_Rhynchosaurus_ of the Trias is also referred, by the eminent
comparative anatomist above mentioned, to the order of the Lizards.
In this singular reptile (fig. 151) the skull is somewhat bird-like,
and the jaws appear to have been destitute of teeth, and to have
been encased in a horny sheath like the beak of a Turtle or a
Bird. It is possible, however, that the palate was furnished
with teeth.
[Illustration: Fig. 151.--Skull of _Rhynchosaurus articeps_. Trias.
(After Owen.)]
The group of the Crocodiles and Alligators (_Crocadilia_),
distinguished by the fact that the teeth are implanted in distinct
sockets and the skin more or less extensively provided with bony
plates, is represented in the Triassic rocks by the _Stagonolepis_
of the Elgin Sandstones. The so-called "Thecodont" reptiles (such
as _Belodon, Thecodontosaurus_, and _Paloeosaurus_, fig. 152,
c, d, e) are also nearly related to the Crocodiles, though
it is doubtful if they should be absolutely referred to this
group. In these reptiles, the teeth are implanted in distinct
sockets in the jaws, their crowns being more or less compressed
and pointed, "with trenchant and finely serrate margins" (Owen).
The bodies of the vertebræ are hollowed out at both ends, but
the limbs appear to be adapted for progression on the land. The
genus _Belodon_ (fig. 152, c) is known to occur in the Keuper
of Germany and in America; and _Paloeosaurus_ (fig. 153. e)
has also been found in the Trias of the same region. Teeth of the
latter, however, are found, along with remains of _Thecodontosaurus_
(fig. 153, d), in a singular magnesian conglomerate near Bristol,
which was originally believed to be of Permian age, but which
appears to be undoubtedly Triassic.
[Illustration: Fig. 152.--Triassic Reptiles. a, Skull of
_Nothosaurus mirabilis_, reduced in size--Muschelkalk, Germany; b,
Tooth of _Simosaurus Gaillardoti_, of the natural size--Muschelkalk,
Germany; c, Tooth of _Beladon Carolinensis_--Trias, America; d,
Tooth of _Thecodontosaurus antiquus_, slightly enlarged--Britain;
e, Tooth of _Paloeosaurus platyodon_, of the natural
size--Britain.]
The Trias has also yielded the remains of the great marine reptiles
which are often spoken of collectively as the "Enaliosaurians"
or "Sea-lizards," and which will be more particularly spoken
of in treating of the Jurassic period, of which they are more
especially characteristic. In all these reptiles the limbs are
flattened out, the digits being enclosed in a continuous skin,
thus forming powerful swimming-paddles, resembling the "flippers"
of the Whales and Dolphins both in their general structure and
in function. The tail is also long, and adapted to act as a
swimming-organ; and there can be no doubt but that these
extraordinary and often colossal reptiles frequented the sea,
and only occasionally came to the land. The Triassic Enaliosaurs
belong to a group of which the later genus _Plesiosaurus_ is
the type (the _Sauropterygia_). One of the best known of the
Triassic genera is _Nothosaurus_ (fig. 152, a), in which the
neck was long and bird-like, the jaws being immensely elongated,
and carrying numerous powerful conical teeth implanted in distinct
sockets. The teeth in _Simosaurus_ (152, b) are of a similar
nature; but the orbits are of enormous size, indicating eyes of
corresponding dimensions, and perhaps pointing to the nocturnal
habits of the animal. In the singular _Placodus_, again, the
teeth are in distinct sockets, but resemble those of many fishes
in being rounded and obtuse (fig. 153), forming broad crushing
plates adapted for the comminution of shell-fish. There is a
row of these teeth all round the upper jaw proper, and a double
series on the palate, but the lower jaw has only a single row of
teeth. _Placodus_ is found in the Muschelkalk, and the characters
of its dental apparatus indicate that it was much more peaceful
in its habits than its associates the Nothosaur and Simosaur.
[Illustration: Fig. 153.--Under surface of the upper jaw and palate
of _Placodus gigas_. Muschelkalk, Germany.]
The Triassic rocks of South Africa and India have yielded the
remains of some extraordinary Reptiles, which have been placed by
Professor Owen in a separate order under the name of _Anomodontia_.
The two principal genera of this group are _Dicynodon_ and
_Oudenodon_, both of which appear to have been large Reptiles,
with well-developed limbs, organised for progression upon the
dry land. In _Oudenodon_ (fig. 154, B) the jaws seem to have
been wholly destitute of teeth, and must have been encased in
a horny sheath, similar to that with which we are familiar in
the beak of a Turtle. In _Dicynodon_ (fig. 154, A), on the other
hand, the front of the upper jaw and the whole of the lower jaw
were destitute of teeth, and the front of the mouth must have
constituted a kind of beak; but the upper jaw possessed on each
side a single huge conical tusk, which is directed downwards,
and must have continued to grow during the life of the animal.
[Illustration: Fig. 154.--Triassic Anomodont Reptiles. A, Skull
of _Dicynodon lacerticeps_, showing one of the great maxillary
tusks; B, Skull of _Oudenodon Bainii_, showing the toothless,
beak-like jaws. From the Trias of South Africa. (After Owen.)]
It may be mentioned that the above-mentioned Triassic sandstones
of South Africa have recently yielded to the researches of Professor
Owen a new and unexpected type of Reptile, which exhibits some
of the structural peculiarities which we have been accustomed
to regard as characteristic of the Carnivorous quadrupeds. The
Reptile in question has been named _Cyanodraco_, and it is looked
upon by its distinguished discoverer as the type of a new order,
to which he has given the name of _Theriodontia_. The teeth of
this singular form agree with those of the Carnivorous quadrupeds
in consisting of three distinct groups--namely, front teeth or
_incisors_, eye teeth or _canines_, and back teeth or _molars_.
The canines also are long and pointed, very much compressed, and
having their lateral margins finely serrated, thus presenting a
singular resemblance to the teeth of the extinct "Sabre-toothed
Tiger" (_Machairodus_). The bone of the upper arm (humerus) further
shows some remarkable resemblances to the same bone in the
Carnivorous Mammals. As has been previously noticed, Professor
Owen is of opinion that some of the Reptilian remains of the
Permian deposits will also be found to belong to this group of
the "Theriodonts."
[Illustration: Fig. 155.--Supposed footprint of a Bird, from
the Triassic Sandstones of the Connecticut River. The slab shows
also numerous "rain-prints."]
Lastly, we find in the Triassic rocks the remains of Reptiles
belonging to the great Mesozoic order of the _Deinosauria_. This
order attains its maximum at a later period, and will be spoken of
when the Jurassic and Cretaceous deposits come to be considered.
The chief interest of the Triassic Reptiles of this group arises
from the fact that they are known by their footprints as well as
by their bones; and a question has arisen whether the supposed
footprints of _birds_ which occur in the Trias have not really
been produced by Deinosaurs. This leads us, therefore, to speak
at the same time as to the evidence which we have of the existence
of the class of Birds during the Triassic period. No actual bones
of any bird have as yet been detected in any Triassic deposit;
but we have tolerably clear evidence of their existence at this
time in the form of _footprints_. The impressions in question
are found in considerable numbers in certain red sandstones of
the age of the Trias in the valley of the Connecticut River, in
the United States. They vary much in size, and have evidently been
produced by many different animals walking over long stretches of
estuarine mud and sand exposed at low water. The footprints now
under consideration form a double series of _single_ prints, and
therefore, beyond all question, are the tracks of a _biped_--that
is, of an animal which walked upon two legs. No living animals,
save Man and the Birds, walk habitually on two legs; and there
is, therefore, a _primâ facie_ presumption that the authors of
these prints were Birds. Moreover, each impression consists of
the marks of three toes turned forwards (fig. 155), and therefore
are precisely such as might be produced by Wading or Cursorial
Birds. Further, the impressions of the toes show exactly the
same numerical progression in the number of the joints as is
observable in living Birds--that is to say, the innermost of the
three toes consists of three joints, the middle one of four, and
the outer one of five joints. Taking this evidence collectively,
it would have seemed, until lately, quite certain that these
tracks could only have been formed by Birds. It has, however,
been shown that the Deinosaurian Reptiles possess, in some cases
at any rate, some singularly bird-like characters, amongst which
is the fact that the animal possessed the power of walking,
temporarily at least, on its hind-legs, which were much longer and
stronger than the fore-limbs, and which were sometimes furnished
with no more than three toes. As the bones and teeth of Deinosaurs
have been found in the Triassic deposits of North America, it
may be regarded as certain that _some_ of the bipedal tracks
originally ascribed to Birds must have really been produced by
these Reptiles. It seems at the same time almost a certainty
that others of the three-toed impressions of the Connecticut
sandstones were in truth produced by Birds, since it is doubtful
if the bipedal mode of progression was more than an occasional
thing amongst the Deinosaurs, and the greater number of the many
known tracks exhibit no impressions of fore-feet. Upon the whole,
therefore, we may, with much probability, conclude that the great
class of Birds (_Aves_) was in existence in the Triassic period.
If this be so, not only must there have been quite a number of
different forms, but some of them must have been of very large
size. Thus the largest footprints hitherto discovered in the
Connecticut sandstones are 22 inches long and 12 inches wide,
with a proportionate length of stride. These measurements indicate
a foot four times as large as that of the African Ostrich; and the
animal which produced them--whether a Bird or a Deinosaur--must
have been of colossal dimensions.
[Illustration: Fig. 156.--Lower jaw of _Dromatherium sylvestre_.
Trias, North Carolina. (After Emmons.)]
[Illustration: Fig. 157.--a, Molar tooth of _Micro estes antiquus_,
magnified; b, Crown of the same, magnified still further. Trias,
Germany.]
[Illustration: Fig. 158.--The Banded Ant-eater (_Myrmecobius
fasciatus_) of Australia.]
Finally, the Trias completes the tale of the great classes of the
Vertebrate sub-kingdom by presenting us with remains of the first
known of the true Quadrupeds or _Mammalia_. These are at present only
known by their teeth, or, in one instance, by one of the halves of
the lower jaw; and these indicate minute Quadrupeds, which present
greater affinities with the little Banded Anteater (_Myrmecobius
fasciatus_, fig. 158) of Australia than with any other living form.
If this conjecture be correct, these ancient Mammals belonged to
the order of the Marsupials or Pouched Quadrupeds (_Marsupialia_),
which are now exclusively confined to the Australian province,
South America, and the southern portion of North America. In the
Old World, the only known Triassic Mammals belong to the genus
_Microlestes_, and to the probably identical _Hypsiprymnopsis_ of
Professor Boyd Dawkins. The teeth of _Microlestes_ (fig. 157)
were originally discovered by Plieninger in 1847 in the "bone-bed"
which is characteristic of the summit of the Rhætic series both
in Britain and on the continent of Europe; and the known remains
indicate two species. In Britain, teeth of _Microlestes_ have been
discovered by Mr Charles Moore in deposits of Upper Triassic age,
filling a fissure in the Carboniferous limestone near Frome, in
Somersetshire; and a molar tooth of _Hypsiprymnopsis_ was found
by Professor Boyd Dawkins in Rhætic marls below the "bone-bed" at
Watchet, also in Somersetshire. In North America, lastly, there
has been found in strata of Triassic age one of the branches
of the lower jaw of a small Mammal, which has been described
under the name of _Dromatherium sylvestre_ (fig. 156). The fossil
exhibits ten small molars placed side by side, one canine, and
three incisors, separated by small intervals, and it indicates
a small insectivorous animal, probably most nearly related to
the existing _Myrmecobius_.
LITERATURE.
The following list comprises a few of the more important sources of
information as to the Triassic strata and their fossil contents:--
(1) 'Geology of Oxford and the Valley of the Thames.' Phillips.
(2) 'Memoirs of the Geological Survey of Great Britain and Ireland.'
(3) 'Report on the Geology of Londonderry,' &c. Portlock.
(4) "On the Zone of Avicula contorta," &c.--'Quart. Journ. Geol.
Soc.,' vol. xvi., 1860. Dr Thomas Wright.
(5) "On the Zones of the Lower Lias and the Avicula contorta
Zone"--'Quart. Journ. Geol. Soc.,' vol. xvii., 1861. Charles
Moore.
(6) "On Abnormal Conditions of Secondary Deposits," &c.--'Quart.
Journ. Geol. Soc.,' vol. xxiii., 1876-77. Charles Moore.
(7) 'Geognostische Beschreibung des Bayerischen Alpengebirges.'
Gümbel.
(8) 'Lethæa Rossica.' Pander.
(9) 'Lethæa Geognostica.' Bronn.
(10) 'Petrefacta Germaniæ.' Goldfuss.
(11) 'Petrefaktenkunde.' Quenstedt.
(12) 'Monograph of the Fossil Estheriæ' (Palæontographical Society).
Rupert Jones.
(13) "Fossil Remains of Three Distinct Saurian Animals, recently
discovered in the Magnesian Conglomerate near Bristol"--'Trans.
Geol. Soc.,' ser. 2, vol. v., 1840. Riley and Stutchbury.
(14) 'Die Saurier des Muschekalkes.' Von Meyer.
(15) 'Beiträge zur Palæontologie Württembergs.' Von Meyer and
Plieninger.
(16) 'Manual of Palæontology.' Owen.
(17) 'Odontography:' Owen.
(18) 'Report on Fossil Reptiles' (British Association, 1841). Owen.
(19) "On Dicynodon"--'Trans. Geol. Soc.,' vol. iii., 1845. Owen.
(20) 'Descriptive Catalogue of Fossil Reptilia and Fishes in the
Museum of the Royal College of Surgeons, England.' Owen.
(21) "On Species of Labyrinthodon from Warwickshire"--'Trans. Geol.
Soc.,' ser. 2, vol. vi. Owen.
(22) "On a Carnivorous Reptile" (Cynodraco major), &c.--'Quart.
Journ. Geol. Soc.,' vol. xxxii., 1876. Owen.
(23) "On Evidences of Theriodonts in Permian Deposits," &c.--'Quart.
Journ. Geol. Soc.,' vol. xxxii., 1876. Owen.
(24) "On the Stagonolepis Robertsoni," &c.--'Quart. Journ. Geol.
Soc.,' vol. xv., 1859. Huxley.
(25) "On a New Specimen of Telerpeton Elginense"--'Quart. Journ.
Geol. Soc.,' vol. xxiii., 1866. Huxley.
(26) "On Hyperodapedon"--'Quart. Journ. Geol. Soc.,' vol. xxv.,
1869. Huxley.
(27) "On the Affinities between the Deinosaurian Reptiles and
Birds"--'Quart. Journ. Geol. Soc.,' vol. xxvi., 1870. Huxley.
(28) "On the Classification of the Deinosauria," &c.--'Quart. Journ.
Geol. Soc.,' vol. xxvi., 1870. Huxley.
(29) "Palæontologica Indica"--'Memoirs of the Geol. Survey of India.'
(30) "On the Geological Position and Geographical Distribution of the
Dolomitic Conglomerate of the Bristol Area"--'Quart. Journ.
Geol. Soc.,' vol. xxvi., 1870. R. Etheridge, sen.
(31) "Remains of Labyrinthodonta from the Keuper Sandstone of
Warwick"--'Quart. Journ. Geol. Soc.,' vol. xxx., 1874 Miall.
(32) 'Manual of Geology.' Dana.
(33) 'Synopsis of Extinct Batrachia and Reptilia of North America.'
Cope.
(34) 'Fossil Footmarks.' Hitchcock.
(35) 'Ichnology of New England.' Hitchcock.
(36) 'Traité de Paléontologie Végétale.' Schimper.
(37) 'Histoire des Végétaux Fossiles.' Brongniart.
(38) 'Monographie der Fossilen Coniferen.' Goeppert.
CHAPTER XVI.
THE JURASSIC PERIOD.
Resting upon the Trias, with perfect conformity, and with an almost
undeterminable junction, we have the great series of deposits
which are known as the _Oolitic Rocks_, from the common occurrence
in them of oolitic limestones, or as the _Jurassic Rocks_, from
their being largely developed in the mountain-range of the Jura,
on the western borders of Switzerland. Sediments of this series
occupy extensive areas in Great Britain, on the continent of
Europe, and in India. In North America, limestones and marls
of this age have been detected in "the Black Hills, the Laramie
range, and other eastern ridges of the Rocky Mountains; also
over the Pacific slope, in the Uintah, Wahsatch, and Humboldt
Mountains, and in the Sierra Nevada" (Dana); but in these regions
their extent is still unknown, and their precise subdivisions
have not been determined. Strata belonging to the Jurassic period
are also known to occur in South America, in Australia, and in
the Arctic zone. When fully developed, the Jurassic series is
capable of subdivision into a number of minor groups, of which
some are clearly distinguished by their mineral characters, whilst
others are separated with equal certainty by the differences of
the fossils that they contain. It will be sufficient for our
present purpose, without entering into the more minute subdivisions
of the series, to give here a very brief and general account
of the main sub-groups of the Jurassic rocks, as developed in
Britain--the arrangement of the Jura-formation of the continent
of Europe agreeing in the main with that of England.
I. THE LIAS.--The base of the Jurassic series of Britain is formed
by the great calcareo-argillaceous deposit of the "Lias," which
usually rests conformably and almost inseparably upon the Rhætic
beds (the so-called "White Lias"), and passes up, generally
conformably, into the calcareous sandstones of the Inferior Oolite.
The Lias is divisible into the three principal groups of the Lower,
Middle, and Upper Lias, as under, and these in turn contain many
well-marked "zones;" so that the Lias has some claims to be
considered as an independent formation, equivalent to all the
remaining Oolitic rocks. The _Lower Lias_ (_Terrain Sinemurien_ of
D'Orbigny) sometimes attains a thickness of as much as 600 feet,
and consists of a great series of bluish or greyish laminated
clays, alternating with thin bands of blue or grey limestone--the
whole, when seen in quarries or cliffs from a little distance,
assuming a characteristically striped and banded appearance. By
means of particular species of _Ammonites_, taken along with
other fossils which are confined to particular zones, the Lower
Lias may be subdivided into several well-marked horizons. The
_Middle Lias_, or _Marlstone Series_ (_Terrain Liasien_ of
D'Orbigny), may reach a thickness of 200 feet, and consists of
sands, arenaceous marls, and argillaceous limestones, sometimes
with ferruginous beds. The _Upper Lias_ (_Terrain Toarcien_ of
D'Orbigny) attains a thickness of 300 feet, and consists principally
of shales below, passing upwards into arenaceous strata.
II. THE LOWER OOLITES.--Above the Lias comes a complex series of
partly arenaceous and argillaceous, but principally calcareous
strata, of which the following are the more important groups:
a, The _Inferior Oolite_ (_Terrain Bajocien_ of D'Orbigny),
consisting of more than 200 feet of oolitic limestones, sometimes
more or less sandy; b, The _Fuller's Earth_, a series of shales,
clays, and marls, about 120 feet in thickness; c, The _Great
Oolite_ or _Bath Oolite_ (_Terrain Bathonien_ of D'Orbigny),
consisting principally of oolitic limestones, and attaining a
thickness of about 130 feet. The well-known "Stonesfield Slates"
belong to this horizon; and the locally developed "Bradford Clay,"
"Corn brash," and "Forest-marble" may be regarded as constituting
the summit of this group.
III. THE MIDDLE OOLITES.--The central portion of the Jurassic
series of Britain is formed by a great argillaceous deposit,
capped by calcareous strata, as follows: a, The _Oxford Clay_
(_Terrain Callovien_ and _Terrain Oxfordien_ of D'Orbigny),
consisting of dark-coloured laminated clays, sometimes reaching
a thickness of 700 feet, and in places having its lower portion
developed into a hard calcareous sandstone ("Kelloway Rock");
b, The Coral-Rag (_Terrain Corallien_ of D'Orbigny, "Nerinean
Limestone" of the Jura, "Diceras Limestone" of the Alps), consisting,
when typically developed, of a central mass of oolitic limestone,
underlaid and surmounted by calcareous grits.
IV. THE UPPER OOLITES.--a, The base of the Upper Oolites of
Britain is constituted by a great thickness (600 feet or more)
of laminated, sometimes carbonaceous or bituminous clays, which
are known as the _Kimmeridge Clay_ (_Terrain Kimméridgien_ of
D'Orbigny); b, The _Portland Beds_ (_Terrain Portlandien_ of
D'Orbigny) succeed the Kimmeridge clay, and consist inferiorly of
sandy beds surmounted by oolitic limestones ("Portland Stone"),
the whole series attaining a thickness of 150 feet or more, and
containing marine fossils; c, The _Purbeck_ Beds are apparently
peculiar to Great Britain, where they form the summit of the entire
Oolitic series, attaining a total thickness of from 150 to 200
feet. The Purbeck beds consist of arenaceous, argillaceous, and
calcareous strata, which can be shown by their fossils to consist
of a most remarkable alternation of fresh-water, brackish-water,
and purely marine sediments, together with old land-surfaces,
or vegetable soils, which contain the upright stems of trees,
and are locally known as "Dirt-beds."
One of the most important of the Jurassic deposits of the continent
of Europe, which is believed to be on the horizon of the Coral-rag
or of the lower part of the Upper Oolites, is the "_Solenhofen
Slate_" of Bavaria, an exceedingly fine-grained limestone, which
is largely used in lithography, and is celebrated for the number
and beauty of its organic remains, and especially for those of
Vertebrate animals.
The subjoined sketch-section (fig. 159) exhibits in a diagrammatic
form the general succession of the Jurassic rocks of Britain.
Regarded as a whole, the Jurassic formation is essentially marine;
and though remains of drifted plants, and of insects and other
air-breathing animals, are not uncommon, the fossils of the formation
are in the main marine. In the Purbeck series of Britain,
anticipatory of the great river-deposit of the Wealden, there are
fresh-water, brackish-water, and even terrestrial strata, indicating
that the floor of the Oolitic ocean was undergoing upheaval, and
that the marine conditions which had formerly prevailed were nearly
at an end. In places also, as in Yorkshire and Sutherlandshire,
are found actual beds of coal: but the great bulk of the formation
is an indubitable sea-deposit; and its limestones, oolitic as
they commonly are, nevertheless are composed largely of the
comminuted skeletons of marine animals. Owing to the enormous
number and variety of the organic remains which have been yielded
by the richly fossiliferous strata of the Oolitic series, it will
not be possible here to do more than to give an outline-sketch
of the principal forms of life which characterise the Jurassic
period as a whole. It is to be remembered, however, that every
minor group of the Jurassic formation has its own peculiar fossils,
and that by the labours of such eminent observers as Quenstedt,
Oppel, D'Orbigny, Wright, De la Beche, Tate, and others, the
entire series of Jurassic sediments admits of a more complete
and more elaborate subdivision into zones characterised by special
life-forms than has as yet been found practicable in the case
of any other rock-series.
[Illustration: Fig. 159. GENERALIZED SECTION OF THE JURASSIC ROCKS
OF ENGLAND.]
[Illustration: Fig. 160.--_Mantellia_ (_Cycadeoidea_) _megalophylla_,
a Cycad from the Purbeck "dirt-bed." Upper Oolites, England.]
The _plants_ of the Jurassic period consist principally of Ferns,
Cycads, and Conifers--agreeing in this respect, therefore, with
those of the preceding Triassic formation. The _Ferns_ are very
abundant, and belong partly to old and partly to new genera. The
_Cycads_ are also very abundant, and, on the whole, constitute the
most marked feature of the Jurassic vegetation, many genera of this
group being known (_Pterophyllum, Otozamites, Zamites, Crossozamia,
Williamsonia, Bucklandia,_ &c.) The so-called "dirt-bed" of the
Purbeck series consists of an ancient soil, in which stand erect
the trunks of Conifers and the silicified stools of Cycads of
the genus _Mantellia_ (fig.160). The _Coniferoe_ of the Jurassic
are represented by various forms more or less nearly allied to
the existing _Araucarioe_; and these are known not only by their
stems or branches, but also in some cases by their cones. We
meet, also, with the remains of undoubted Endogenous plants,
the most important of which are the fruits of forms allied to
the existing Screw-pines (_Pandaneoe_), such as _Podocarya_ and
_Kaidacarpum_. So far, however, no remains of Palms have been
found; nor are we acquainted with any Jurassic plants which could
be certainly referred to the great "Angiospermous" group of the
Exogens, including the majority of our ordinary plants and trees.
Amongst animals, the _Protozoans_ are well represented in the
Jurassic deposits by numerous _Foraminifers_ and _Sponges_; as
are the _Coelenterates_ by numerous _Corals_. Remains of these
last-mentioned organisms are extremely abundant in some of the
limestones of the formation, such as the "Coral-rag" and the
Great Oolite; and the former of these may fairly be considered
as an ancient "reef." The _Rugose Corals_ have not hitherto been
detected in the Jurassic rocks; and the "_Tabulate Corals_,"
so-called, are represented only by examples of the modern genus
_Millepora_. With this exception, all the Jurassic Corals belong
to the great group which predominates in recent seas (_Zoantharia
sclerodermata_); and the majority belong to the important
reef-building family of the "Star-corals" (_Astroeidoe_). The
form here figured (_Thecosmilia annularis_, fig. 161) is one
of the characteristic species of the Coral-rag.
[Illustration: Fig. 161.--_Thecosmilia annularis_, Coral-rag,
England.]
[Illustration: Fig. 162.--_Pentacrinus fasciculos_, Lias. The
left-hand figure shows a few or the joints of the column; the
middle figure shows the arms, and the summit of the column with
its side-arms; and the right-hand figure shows the articulating
surface of one of the column-joints.]
The _Echinoderms_ are very numerous and abundant fossils in the
Jurassic series, and are represented by Sea-lilies, Sea-urchins,
Star-fishes, and Brittle-stars. The _Crinoids_ are still common,
and some of the limestones of the series are largely composed
of the _débris_ of these organisms. Most of the Jurassic forms
resemble those with which we are already familiar, in having
the body permanently attached to some foreign object by means
of a longer or shorter jointed stalk or "column." One of the
most characteristic Jurassic genera of these "stalked" Crinoids
(though not exclusively confined to this period) is _Pentacrinus_
(fig. 162). In this genus, the column is five-sided, with whorls
of "side-arms;" and the arms are long, slender, and branched.
The genus is represented at the present day by the beautiful
"Medusa-head Pentacrinite" (_Pentacrinus caput-medusoe_). Another
characteristic Oolitic genus is _Apiocrinus_, comprising the
so-called "Pear Encrinites." In this group the column is long
and rounded, with a dilated base, and having its uppermost joints
expanded so as to form, with the cup itself, a pear-shaped mass,
from the summit of which spring the comparatively short arms.
Besides the "stalked" Crinoids, the Jurassic rocks have yielded
the remains of the higher group of the "free" Crinoids, such as
_Saccosoma_. These forms resemble the existing "Feather-stars"
(_Comatula_) in being attached when young to some foreign body by
means of a jointed stem, from which they detach themselves when
fully grown to lead an independent existence. In this later stage
of their life, therefore, they closely resemble the Brittle-stars
in appearance. True Star-fishes (_Asteroids_) and Brittle-stars
(_Ophiuroids_) are abundant in the Jurassic rocks, and the
Sea-urchins (_Echinoids_) are so numerous and so well preserved
as to constitute quite a marked feature of some beds of the series.
All the Oolitic urchins agree with the modern _Echinoids_ in
having the shell composed of no more than twenty rows of plates.
Many different genera are known, and a characteristic species
of the Middle Oolites (_Hemicidaris crenularis_, fig. 163) is
here figured.
[Illustration: Fig. 163.--_Hemicidaris crenularis_, showing the
great tubercles on which the spines were supported. Middle Oolites.]
Passing over the _Annelides_, which, though not uncommon, are
of little special interest, we come to the _Articulates_, which
also require little notice. Amongst the _Crustaceans_, whilst
the little Water-fleas (_Ostracoda_) are still abundant, the
most marked feature is the predominance which is now assumed by
the _Decapods_--the highest of the known groups of the class.
True Crabs (_Brachyura_) are by no means unknown; but the principal
Oolitic Decapods belonged to the "Long-tailed" group (_Macrura_),
of which the existing Lobsters, Prawns, and Shrimps are members.
The fine-grained lithographic slates of Solenhofen are especially
famous as a depot for the remains of these Crustaceans, and a
characteristic species from this locality (_Eryon arctiformis_,
fig. 164) is here represented. Amongst the air-breathing
_Articulates_, we meet in the Oolitic rocks with the remains of
Spiders (_Arachnida_), Centipedes (_Myriapoda_), and numerous
true Insects (_Insecta_). In connection with the last-mentioned
of these groups, it is of interest to note the occurrence of
the oldest known fossil Butterfly--the _Paloeontina Oolitica_
of the Stonesfield slate--the relationships of which appear to
be with some of the living Butterflies of Tropical America.
[Illustration: Fig. 164.--_Eryon arctiformis_, a "Long-tailed
Decapod," from the Middle Oolites (Solenhofen Slate).]
Coming to the _Mollusca_, the _Polyzoans_, numerous and beautiful
as they are, must be at once dismissed; but the _Brachiopods_
deserve a moment's attention. The Jurassic Lamp-shells (fig.
165) do not fill by any means such a predominant place in the
marine fauna of the period, as in many Palæozoic deposits, but
they are still individually numerous. The two ancient genera
_Leptoena_ (fig. 165, a) and _Spirifera_ (fig. 165, b), dating
the one from the Lower and the other from the Upper Silurian,
appear here for the last time upon the scene, but they have not
hitherto been recognised in deposits later than the Lias. The
great majority of the Jurassic _Brachiopods_, however, belong to
the genera _Terebratula_ (fig. 165, c, e, f) and _Rhynchonella_
(fig. 165. d), both of which are represented by living forms
at the present day. The _Terebratuloe_, in particular, are very
abundant, and the species are often confined to special horizons
in the series.
[Illustration: Fig. 165.--Jurassic Brachiopod. a. _Leptoena
Liassica_, enlarged, the small cross below the figure indicating
the true size of the shell--Lias; b, _Spirifera rostrata_, Lias;
c, _Terebratula quadrifida_, Lias; d, d', _Rhynchonella varians_,
Fulter's Earth and Kelloway Rock; e, _Terebratula sphoeroidalis_,
Inferior Oolite; f, _Terebratula digona_, Bradford Clay,
Forest-marble, and Great Oolite. (After Davidson).]
[Illustration: Fig. 166.--_Ostrea Marshii_. Middle and Lower
Oolites.]
[Illustration: Fig. 167.--_Gryphoea incurva_. Lias.]
Remains of _Bivalves_ (_Lamellibranchiata_) are very numerous in
the Jurassic deposits, and in many cases highly characteristic.
In the marine beds of the Oolites, which constitute by far the
greater portion of the whole formation, the Bivalyes are of course
marine, and belong to such genera as _Trigonia, Lima, Pholadomya,
Cardinia, Avicula, Hippopodium_, &c.; but in the Purbeck beds, at
the summit of the series, we find bands of Oysters alternating
with strata containing fresh-water or brackish-water Bivalves,
such as _Cyrenoe_ and _Corbuloe_. The predominant Bivalves of
the Jurassic, however, are the _Oysters_, which occur under many
forms, and often in vast numbers, particular species being commonly
restricted to particular horizons. Thus of the true Oysters,
_Ostrea distorta_ is characteristic of the Purbeck series, where
it forms a bed twelve feet in thickness, known locally as the
"Cinder-bed;" _Ostrea expansa_ abounds in the Portland beds;
_Ostrea deltoidea_ is characteristic of the Kimmeridge clay;
_Ostrea gregaria_ predominates in the Coral-rag; _Ostrea acuminata_
characterises the small group of the Fuller's Earth; whilst the
plaited _Ostrea Marshii_ (fig. 166) is a common shell in the
Lower and Middle Oolites. Besides the more typical Oysters, the
Oolitic rocks abound in examples of the singularly unsymmetrical
forms belonging to the genera _Exogyra_ and _Gryphoea_ (fig.
167). In the former of these are included Oysters with the beaks
"reversed"--that is to say, turned towards the hinder part of
the shell; whilst in the latter are Oysters in which the lower
valve of the shell is much the largest, and has a large incurved
beak, whilst the upper valve is small and concave. One of the
most characteristic _Exogyroe_ is the _E. Virgula_ of the Oxford
Clay, and of the same horizon on the Continent; and the _Gryphoea
incurva_ (fig. 167) is equally abundant in, and characteristic
of, the formation of the Lias. Lastly, we may notice the
extraordinary shells belonging to the genus _Diceras_ (fig. 168),
which are exclusively confined to the Middle Oolites. In this
formation in the Alps they occur in such abundance as to give
rise to the name of "Calcaire à Dicerates," applied to beds of
the same age as the Coral-rag of Britain. The genus _Diceras_
belongs to the same family as the "Thorny Clams" (Chama) of the
present day--the shell being composed of nearly equally-sized
valves, the beaks of which are extremely prominent and twisted
into a spiral. The shell was attached to some foreign body by
the beak of one of its valves.
[Illustration: Fig. 168.--_Diceras arietina_. Middle Oolite.]
[Illustration: Fig. 169.--_Nerinoea Goodhallii_, one-fourth of the
natural size. The left-hand figure shows the appearance presented
by the shell when vertically divided. Coral-rag, England.]
Amongst the Jurassic Univalves (_Gasteropoda_) there are many
examples of the ancient and long-lived _Pleurotomaria_; but on
the whole the Univalves begin to have a modern aspect. The
round-mouthed ("holostomatous"), vegetable-eating Sea-snails,
such as the Limpets (_Patellidoe_), the Nerites (_Nerita_), the
_Turritelloe, Chemnitzioe_, &c., still hold a predominant place.
The two most noticeable genera of this group are _Cerithium_
and _Nerinoea_--the former of these attaining great importance
in the Tertiary and Recent seas, whilst the latter (fig. 169)
is highly characteristic of the Jurassic series, though not
exclusively confined to it. One of the limestones of the Jura,
believed to be of the age of the Coral-rag (Middle Oolite) of
Britain, abounds to such an extent in the turreted shells of
_Nerinoea_ as to have gained the name of "Calcaire à Nérinées."
In addition to forms such as the preceding, we now for the first
time meet, in any force, with the Carnivorous Univalves, in which
the mouth of the shell is notched or produced into a canal, giving
rise to the technical name of "siphonostomatous" applied to the
shell. Some of the carnivorous forms belong to extinct types,
such as the _Purpuroidea_ of the Great Oolite; but others are
referable to well-known existing genera. Thus we meet here with
species of the familiar groups of the Whelks (_Buccinum_), the
Spindle-shells (_Fusus_), the Spider-shells (_Pteroceras_), _Murex,
Rostellaria_, and others which are not at present known to occur
in any earlier formation.
Amongst the Wing-shells (_Pteropoda_), it is sufficient to mark
the final appearance in the Lias of the ancient genus _Conularia_.
[Illustration: Fig. 170.--_Ammonites Humphresianus_. Inferior
Oolite.]
[Illustration: Fig. 171.--_Ammonites bifrons_. Lias.]
Lastly, the order of the _Cephalopoda_, in both its Tetrabranchiate
and Dibranchiate sections, undergoes a vast development in the
Jurassic period. The old and comparatively simple genus _Nautilus_
is still well represented, one species being very similar to the
living Pearly Nautilus (_N. Pompilius_); but the _Orthocerata_
and _Goniatites_ of the Trias have finally disappeared; and the
great majority of the Tetrabranchiate forms are referable to
the comprehensive genus _Ammonites_, with its many sub-genera
and its hundreds of recorded species. The shell in _Ammonites_
is in the form of a flat spiral, all the coils of which are in
contact (figs. 170 and 171). The innermost whorls of the shell
are more or less concealed; and the body-chamber is elongated
and narrow, rather than expanded towards the mouth. The tube or
siphuncle which runs through the air-chambers is placed on the
dorsal or _convex_ side of the shell; but the principal character
which distinguishes _Ammonites_ from _Goniatites_ and _Ceratites_ is
the wonderfully complex manner in which the _septa_, or partitions
between the air-chambers, are folded and undulated. To such an
extent does this take place, that the edges of the septa, when
exposed by the removal of the shell-substance, present in an
exaggerated manner the appearance exhibited by an elaborately-dressed
shirt-frill when viewed edgewise. The species of _Ammonites_ range
from the Carboniferous to the Chalk; but they have not been found
in deposits older than the Secondary, in any region except India;
and they are therefore to be regarded as essentially Mesozoic
fossils. Within these limits, each formation is characterised by
particular species, the number of individuals being often very
great, and the size which is sometimes attained being nothing short
of gigantic. In the Lias, particular species of _Ammonites_ may
succeed one another regularly, each having a more or less definite
horizon, which it does not transgress. It is thus possible to
distinguish a certain number of zones, each characterised by
a particular Ammonite, together with other associated fossils.
Some of these zones are very persistent and extend over very
wide areas, thus affording valuable aid to the geologist in his
determination of rocks. It is to be remembered, however, that
there are other species which are not thus restricted in their
vertical range, even in the same formations in which definite
zones occur.
[Illustartion: Fig. 172.--_Beloteuthis subcostata_ Jurassic (Lias).]
The Cuttle-fishes or _Dibranchiate Cephalopods_ constitute a
feature in the life of the Jurassic period little less conspicuous
and striking than that afforded by the multitudinous and varied
chambered shells of the _Ammonitidoe_. The remains by which these
animals are recognised are necessarily less perfect, as a rule,
than those of the latter, as no external shell is present (except
in rare and more modern groups), and the internal skeleton is
not necessarily calcareous. Nevertheless, we have an ample record
of the Cuttle-fishes of the Jurassic period, in the shape of
the fossilised jaws or beak, the ink-bag, and, most commonly
of all, the horny or calcareous structure which is embedded in
the soft tissues, and is variously known as the "pen" or "bone."
The beaks of Cuttle-fishes, though not abundant, are sufficiently
plentiful to have earned for themselves the general title of
"Rhyncholites;" and in their form and function they resemble
the horny, parrot-like beak of the existing Cephalopods. The
ink-bag or leathery sac in which the Cuttle-fishes store up the
black pigment with which they obscure the water when attacked,
owes its preservation to the fact that the colouring-matter which
it contains is finely-divided carbon, and therefore nearly
indestructible except by heat. Many of these ink-bags have been
found in the Lias; and the colouring-matter is sometimes so well
preserved that it has been, as an experiment, employed in painting
as a fossil "sepia." The "pens" of the Cuttle-fishes are not
commonly preserved, owing to their horny consistence, but they
are not unknown. The form here figured (_Beloteuthis subcostata_,
fig. 172) belonged to an old type essentially similar to our modern
Calamaries, the skeleton of which consists of a horny shaft and
two lateral wings, somewhat like a feather in general shape. When,
on the other hand, the internal skeleton is calcareous, then it is
very easily preserved in a fossil condition; and the abundance of
remains of this nature in the Secondary rocks, combined with their
apparent total absence in Palæozoic strata, is a strong presumption
in favour of the view that the order of the Cuttle-fishes did
not come into existence till the commencement of the Mesozoic
period. The great majority of the skeletons of this kind which are
found in the Jurassic rocks belong to the great extinct family
of the "Belemnites" (_Belemnitidoa_), which, so far as known, is
entirely confined to rocks of Secondary age. From its pointed,
generally cylindro-conical form, the skeleton of the Belemnite is
popularly known as a "thunderbolt". (fig. 173, C). In its perfect
condition--in which it is, however, rarely obtainable--the skeleton
consists of a chambered conical shell (the "phragmacone"), the
partitions between the chambers of which are pierced by a marginal
tube or "siphuncle." This conical shell--curiously similar in its
structure to the _external_ shell of the Nautilus--is extended
forwards into a horny "pen," and is sunk in a corresponding conical
pit (fig. 173, B), excavated in the substance of a nearly cylindrical
fibrous body or "guard," which projects backwards for a longer or
shorter distance, and is the part most usually found in a fossil
condition. Many different kinds of _Belemnites_ are known, and
their guards literally swarm in many parts of the Jurassic series,
whilst some specimens attain very considerable dimensions. Not
only is the internal skeleton known, but specimens of _Belemnites_
and the nearly allied _Belemnoteuthis_ have been found in some
of the fine-grained sediments of the Jurassic formation, from
which much has been learnt even as to the anatomy of the soft
parts of the animal. Thus we know that the Belemnites were in
many respects comparable with the existing Calamaries or Squids,
the body being furnished with lateral fins, and the head carrying
a circle of ten "arms," two of which were longer than the others
(fig. 173, A). The suckers on the arms were provided, further,
with horny hooks; there was a large ink-sac; and the mouth was
armed with horny mandibles resembling in shape the beak of a
parrot.
[Illustration: Fig. 173.--A, Restoration of the animal of the
Belemnite; B, Diagram showing the complete skeleton of a Belemnite,
consisting of the chambered phragmacone (a), the guard (b), and
the horny pen (c); C, Specimen of _Belemnites canaliculatus_,
from the Inferior Oolite. (After Phillips.)]
[Illustration: Fig. 174.--_Tetragonolepis (restored), and scales
of the same. Lias.]
Coming next to the _Vertebrates_, we find that the Jurassic _Fishes_
are still represented by _Ganoids_ and _Placoids_. The Ganoids,
however, unlike the old forms, now for the most part possess
nearly or quite symmetrical ("homocercal") tails. A characteristic
genus is _Tetragonolepis_ (fig. 174), with its deep compressed
body, its rhomboidal, closely-fitting scales, and its single
long dorsal fin. Amongst the _Placoids_ the teeth of true Sharks
(_Notidanus_) occur for the first time; but by far the greater
number of remains referable to this group are still the fin-spines
and teeth of "Cestracionts," resembling the living Port-Jackson
Shark. Some of these teeth are pointed (_Hybodus_); but others
are rounded, and are adapted for crushing shell-fish. Of these
latter, the commonest are the teeth of _Acrodus_ (fig. 175), of
which the hinder ones are of an elongated form, with a rounded
surface, covered with fine transverse striæ proceeding from a
central longitudinal line. From their general form and striation,
and their dark colour, these teeth are commonly called "fossil
leeches" by the quarrymen.
[Illustration: Fig. 175.--Tooth of _Acrodus nobilis_. Lias.]
The Amphibian group of the _Labyrinthodonts_, which was so
extensively developed in the Trias, appears to have become extinct,
no representative of the order having hitherto been detected in
rocks of Jurassic age.
[Illustration: Fig. 176.--_Ichthyosaurus communis. Lias.]
Much more important than the Fishes of the Jurassic series are
the _Reptiles_, which are both very numerous, and belong to a
great variety of types, some of these being very extraordinary
in their anatomical structure. The predominant group is that
of the "Enaliosaurs" or "Sea-lizards," divided into two great
orders, represented respectively by the _Ichthyosaurus_ and the
_Plesiosaurus_.
The _Ichthyosauri_ or "Fish-Lizards" are exclusively Mesozoic
in their distribution, ranging from the Lias to the Chalk, but
abounding especially in the former. They were huge Reptiles, of
a fish-like form, with a hardly conspicuous neck (fig. 176),
and probably possessing a simply smooth or wrinkled skin, since
no traces of scales or bony integumentary plates have ever been
discovered. The tail was long, and was probably furnished at its
extremity with a powerful expansion of the skin, constituting a
tail-fin similar to that possessed by the Whales. The limbs are
also like those of Whales in the essentials of their structure,
and in their being adapted to act as swimming-paddles. Unlike
the Whales, however, the Ichthyosaurs possessed the hind-limbs
as well as the fore-limbs, both pairs having the bones flattened
out and the fingers completely enclosed in the skin, the arm
and leg being at the same time greatly shortened. The limbs are
thus converted into efficient "flippers," adapting the animal
for an active existence in the sea. The different joints of the
backbone (vertebræ) also show the same adaptation to an aquatic
mode of life, being hollowed out at both ends, like the biconcave
vertebræ of Fishes. The spinal column in this way was endowed
with the flexibility necessary for an animal intended to pass
the greater part of its time in water. Though the _Ichthyosaurs_
are undoubtedly marine animals, there is, however, reason to
believe that they occasionally came on shore, as they possess
a strong bony arch, supporting the fore-limbs, such as would
permit of partial, if laborious, terrestrial progression. The
head is of enormous size, with greatly prolonged jaws, holding
numerous powerful conical teeth lodged in a common groove. The
nature of the dental apparatus is such as to leave no doubt as
to the rapacious and predatory habits of the Ichthyosaurs--an
inference which is further borne out by the examination of their
petrified droppings, which are known to geologists as "coprolites,"
and which contain numerous fragments of the bones and scales
of the Ganoid fishes which inhabited the same seas. The orbits
are of huge size; and as the eyeball was protected, like that
of birds, by a ring of bony plates in its outer coat, we even
know that the pupils of the eyes were of correspondingly large
dimensions. As these bony plates have the function of protecting
the eye from injury under sudden changes of pressure in the
surrounding medium, it has been inferred, with great probability,
that the Ichthyosaurs were in the habit of diving to considerable
depths in the sea. Some of the larger specimens of _Ichthyosaurus_
which have been discovered in the Lias indicate an animal of
from 20 to nearly 40 feet in length; and many species are known
to have existed, whilst fragmentary remains of their skeletons
are very abundant in some localities. We may therefore safely
conclude that these colossal Reptiles were amongst the most
formidable of the many tyrants of the Jurassic seas.
[Illustration: Fig. 177.--_Plesiosaurus dolichodeirus_, restored.
Lias.]
The _Plesiosaurus_ (fig. 177) is another famous Oolitic Reptile,
and, like the preceding, must have lived mainly or exclusively in
the sea. It agrees with the Ichthyosaur in some important features
of its organisation, especially in the fact that both pairs of
limbs are converted into "flippers" or swimming-paddles, whilst
the skin seems to have been equally destitute of any scaly or bony
investiture. Unlike the _Ichthyosaur_, however, the Plesiosaur
had the paddles placed far back, the tail being extremely short,
and the neck greatly lengthened out, and composed of from twenty
to forty vertebræ. The bodies of the vertebræ, also, are not
deeply biconcave, but are flat, or only slightly cupped. The
head is of relatively small size, with smaller orbits than those
of the _Ichthyosaur_, and with a snout less elongated. The jaws,
however, were armed with numerous conical teeth, inserted in
distinct sockets. As regards the habits of the Plesiosaur, Dr
Conybeare arrives at the following conclusions: "That it was
aquatic is evident from the form of its paddles; that it was
marine is almost equally so from the remains with which it is
universally associated; that it may have occasionally visited
the shore, the resemblance of its extremities to those of the
Turtles may lead us to conjecture: its movements, however, must
have been very awkward on land; and its long neck must have impeded
its progress through the water, presenting a strong contrast to
the organisation which so admirably fits the _Ichthyosaurus_
to cut through the waves." As its respiratory organs were such
that it must of necessity have required to obtain air frequently,
we may conclude "that it swam upon or near the surface, arching
back its long neck like a swan, and occasionally darting it down
at the fish which happened to float within its reach. It may
perhaps have lurked in shoal water along the coast, concealed
amongst the sea-weed; and raising its nostrils to a level with
the surface from a considerable depth, may have found a secure
retreat from the assaults of powerful enemies; while the length
and flexibility of its neck may have compensated for the want
of strength in its jaws, and its incapacity for swift-motion
through the water."
About twenty species of _Plesiosaurus_ are known, ranging from
the Lias to the Chalk, and specimens have been found indicating
a length of from eighteen to twenty feet. The nearly related
"_Pliosaurs_," however, with their huge heads and short necks,
must have occasionally reached a length of at least forty feet--the
skull in some species being eight, and the paddles six or seven
feet long, whilst the teeth are a foot in length.
[Illustration: Fig. 178.--_Pterodactylus crassirostis_. From the
Lithographic Slates of Solenhofen (Middle Oolite). The figure is
"restored," and it seems certain that the restoration is incorrect
in the comparatively unimportant particular, that the hand should
consist of no more than four fingers, three short and one long,
instead of five, as represented.]
Another extraordinary group of Jurassic Reptiles is that of the
"Winged Lizards" or _Pterosauria_. These are often spoken of
collectively as "Pterodactyles," from _Pterodactylus_, the type-genus
of the group. As now restricted, however, the genus _Pterodactylus_
is more Cretaceous than Jurassic, and it is associated in the
Oolitic rocks with the closely allied genera _Dimorphodon_ and
_Rhamphorhynchus_. In all three of these genera we have the same
general structural organisation, involving a marvellous combination
of characters, which we are in the habit of regarding as peculiar
to Birds on the one hand, to Reptiles on another hand, and to the
Flying Mammals or Bats in a third direction. The "Pterosaurs"
are "Flying" Reptiles, in the true sense of the term, since they
were indubitably possessed of the power of active locomotion
in the air, after the manner of Birds. The so-called "Flying"
Reptiles of the present day, such as the little _Draco volans_
of the East Indies and Indian Archipelago, possess, on the other
hand, no power of genuine flight, being merely able to sustain
themselves in the air through the extensive leaps which they take
from tree to tree, the wing-like expansions of the skin simply
exercising the mechanical function of a parachute. The apparatus
of flight in the "Pterosaurs" is of the most remarkable character,
and most resembles the "wing" of a Bat, though very different in
some important particulars. The "wing" of the Pterosaurs is like
that of Bats, namely, in consisting of a thin leathery expansion of
the skin which is attached to the sides of the body, and stretches
between the fore and hind limbs, being mainly supported by an
enormous elongation of certain of the digits of the hand. In
the Bats, it is the four outer fingers which are thus lengthened
out; but in the Pterosaurs, the wing-membrane is borne by a single
immensely-extended finger (fig. 178). No trace of the actual
wing-membrane itself has, of course, been found fossilised; but
we could determine that the "Pterodactyles" possessed the power
of flight, quite apart from the extraordinary conformation of
the hand. The proofs of this are to be found partly in the fact
that the breast-bone was furnished with an elevated ridge or
keel, serving for the attachment of the great muscles of flight,
and still more in the fact that the bones were hollow and were
filled with air--a peculiarity wholly confined amongst living
animals to Birds only. The skull of the Pterosaurs is long, light,
and singularly bird-like in appearance--a resemblance which is
further increased by the comparative length of the neck and the
size of the vertebræ of this region (fig. 178). The jaws, however,
unlike those of any existing Bird, were, with one exception to be
noticed hereafter, furnished with conical teeth sunk in distinct
sockets; and there was always a longer or shorter tail composed
of distinct vertebræ; whereas in all existing Birds the tail
is abbreviated, and the terminal vertebræ are amalgamated to
form a single bone, which generally supports the great feathers
of the tail.
Modern naturalists have been pretty generally agreed that the
_Pterosaurs_ should be regarded as a peculiar group of the Reptiles;
though they have been and are still regarded by high authorities,
like Professor Seeley, as being really referable to the Birds, or
as forming a class by themselves. The chief points which separate
them from Birds, as a class, are the character of the apparatus
of flight, the entirely different structure of the fore-limb, the
absence of feathers, the composition of the tail out of distinct
vertebræ, and the general presence of conical teeth sunk in distinct
sockets in the jaws. The gap between the Pterosaurs and the Birds
has, however, been greatly lessened of late by the discovery
of fossil animals (_Ichthyornis_ and _Hesperornis_) with the
skeleton proper to Birds combined with the presence of teeth
in the jaws, and by the still more recent discovery of other
fossil animals (_Pteranodon_) with a Pterosaurian skeleton, but
without teeth; whilst the undoubtedly feathered _Archoeopteryx_
possessed a long tail composed of separate vertebræ. Upon the
whole, therefore, the relationships of the Pterosaurs cannot
be regarded as absolutely settled. It seems certain, however,
that they did not possess feathers--this implying that they were
cold-blooded animals; and their affinities with Reptiles in this,
as in other characters, are too strong to be overlooked.
[Illustration: Fig. 179--_Rhamphorhynchus Bucklandi_, restored.
Bath Oolite, England. (After the late Professor Phillips.)]
The _Pterosaurs_ are wholly Mesozoic, ranging from the Lias to
the Chalk inclusive; and the fine-grained Lithographic Slate of
Solenhofen has proved to be singularly rich in their remains.
The genus _Pterodactylus_ itself has the jaws toothed to the
extremities with equal-sized conical teeth, and its species range
from the Middle Oolites to the Cretaceous series, in connection
with which they will be again noticed, together with the toothless
genus _Pteranodon_. The genus _Dimorphodon_ is Liassic, and is
characterised by having the front teeth long and pointed, whilst
the hinder teeth are small and lancet-shaped. Lastly, the singular
genus _Rhamphorhynchus_, also from the Lower Oolites, is
distinguished by the fact that there are teeth present in the
hinder portions of both jaws; but the front portions are toothless,
and may have constituted a horny beak. Like most of the other
Jurassic Pterosaurs, _Rhamphorhynchus_ (fig. 179) does not seem
to have been much bigger than a pigeon, in this respect falling
far below the giant "Dragons" of the Cretaceous period. It differed
from its relatives, not only in the armature of the mouth, but
also in the fact that the tail was of considerable length. With
regard to its habits and mode of life, Professor Phillips remarks
that, "gifted with ample means of flight, able at least to perch
on rocks and scuffle along the shore, perhaps competent to dive,
though not so well as a Palmiped bird, many fishes must have
yielded to the cruel beak and sharp teeth of Rhamphorhynchus.
If we ask to which of the many families of Birds the analogy of
structure and probable way of life would lead us to assimilate
Rhamphorhynchus, the answer must point to the swimming races with
long wings, clawed feet, hooked beak, and habits or violence and
voracity; and for preference, the shortness of the legs, and other
circumstances, may be held to claim for the Stonesfield fossil a
more than fanciful similitude to the groups of Cormorants, and
other marine divers, which constitute an effective part of the
picturesque army of robbers of the sea."
Another extraordinary and interesting group of the Mesozoic Reptiles
is constituted by the _Deinosauria_, comprising a series of mostly
gigantic forms, which range from the Trias to the Chalk. All the
"Deinosaurs" are possessed of the two pairs of limbs proper to
Vertebrate animals, and these organs are in the main adapted for
walking on the dry land. Thus, whilst the Mesozoic seas swarmed
with the huge Ichthyosaurs and Plesiosaurs, and whilst the air
was tenanted by the Dragon-like Pterosaurs, the land-surfaces of
the Secondary period were peopled by numerous forms of Deinosaurs,
some of them of even more gigantic dimensions than their marine
brethren. The limbs of the _Deinosaurs_ are, as just said, adapted
for progression on the land; but in some cases, at any rate, the
hind-limbs were much longer and stronger than the fore-limbs;
and there seems to be no reason to doubt that many of these forms
possessed the power of walking, temporarily or permanently, on their
hind-legs, thus presenting a singular resemblance to Birds. Some
very curious and striking points connected with the structure of
the skeleton have also been shown to connect these strange Reptiles
with the true Birds; and such high authorities as Professors Huxley
and Cope are of opinion that the Deinosaurs are distinctly related
to this class, being in some respects intermediate between the
proper Reptiles and the great wingless Birds, like the Ostrich
and Cassowary. On the other hand, Professor Owen has shown that the
Deinosaurs possess some weighty points of relationship with the
so-called "Pachydermatous" Quadrupeds, such as the Rhinoceros and
Hippopotamus. The most important Jurassic genera of _Deinosauria_
are _Megalosaurus_ and _Cetiosaurus_, both of which extend their
range into the Cretaceous period, in which flourished, as we
shall see, some other well-known members of this order.
[Illustration: Fig. 180.--Skull of _Megalosaurus_, on a scale
one-tenth of nature. Restored. (After Professor Phillips.)]
_Megalosaurus_ attained gigantic dimensions, its thigh and shank
bones measuring each about three feet in length, and its total
length, including the tail, being estimated at from forty to
fifty feet. As the head of the thigh-bone is set on nearly at
right angles with the shaft, whilst all the long bones of the
skeleton are hollowed out internally for the reception of the
marrow, there can be no doubt as to the terrestrial habits of
the animal. The skull (fig. 180) was of large size, four or five
feet in length, and the jaws were armed with a series of powerful
pointed teeth. The teeth are conical in shape, but are strongly
compressed towards their summits, their lateral edges being finely
serrated. In their form and their saw-like edges, they resemble
the teeth of the "Sabre-toothed Tiger" (_Machairodus_), and they
render it certain that the Megalosaur was in the highest degree
destructive and carnivorous in its habits. So far as is known, the
skin was not furnished with any armour of scales or bony plates;
and the fore-limbs are so disproportionately small as compared
with the hind-limbs, that this huge Reptile--like the equally
huge Iguanodon--may be conjectured to have commonly supported
itself on its hind-legs only.
The _Cetiosaur_ attained dimensions even greater than those of
the Megalosaur, one of the largest thigh-bones measuring over
five feet in length and a foot in diameter in the middle, and
the total length of the animal being probably not less than fifty
feet. It was originally regarded as a gigantic Crocodile, but
it has been shown to be a true Deinosaur. Having obtained a
magnificent series of remains of this reptile, Professor Phillips
has been able to determine many very interesting points as to
the anatomy and habits of this colossal animal, the total length
of which he estimates as being probably not less than sixty or
seventy feet. As to its mode of life, this accomplished writer
remarks:--
"Probably when 'standing at ease' not less than ten feet in height,
and of a bulk in proportion, this creature was unmatched in magnitude
and physical strength by any of the largest inhabitants of the
Mesozoic land or sea. Did it live in the sea, in fresh waters,
or on the land? This question cannot be answered, as in the case
of Ichthyosaurus, by appeal to the accompanying organic remains;
for some of the bones lie in marine deposits, others in situations
marked by estuarine conditions, and, out of the Oxfordshire district,
in Sussex, in fluviatile accumulations. Was it fitted to live
exclusively in water? Such an idea was at one time entertained,
in consequence of the biconcave character of the caudal vertebræ,
and it is often suggested by the mere magnitude of the creature,
which would seem to have an easier life while floating in water,
than when painfully lifting its huge bulk, and moving with slow
steps along the ground. But neither of these arguments is valid. The
ancient earth was trodden by larger quadrupeds than our elephant;
and the biconcave character of vertebræ, which is not uniform
along the column in Cetiosaurus, is perhaps as much a character
of a geological period as of a mechanical function of life. Good
evidence of continual life in water is yielded in the case of
Ichthyosaurus and other Enaliosaurs, by the articulating surfaces
of their limb-bones, for these, all of them, to the last phalanx,
have that slight and indefinite adjustment of the bones, with much
intervening cartilage, which fits the leg to be both a flexible
and forcible instrument of natation, much superior to the ordinary
oar-blade of the boatman. On the contrary, in Cetiosaur, as well as
in Megalosaur and Iguanodon, all the articulations are definite,
and made so as to correspond to determinate movements in particular
directions, and these are such as to be suited for walking. In
particular, the femur, by its head projecting freely from the
acetabulum, seems to claim a movement of free stepping more parallel
to the line of the body, and more approaching to the vertical than
the sprawling gait of the crocodile. The large claws concur in this
indication of terrestrial habits. But, on the other hand, these
characters are not contrary to the belief that the animal may have
been amphibious; and the great vertical height of the anterior
part of the tail seems to support this explanation, but it does
not go further.... We have therefore a marsh-loving or river-side
animal, dwelling amidst filicine, cycadaceous, and coniferous
shrubs and trees full of insects and small mammalia. What was
its usual diet? If _ex ungue leonem_, surely _ex dente cibum_.
We have indeed but one tooth, and that small and incomplete. It
resembles more the tooth of Iguanodon than that of any other
reptile; for this reason it seems probable that the animal was
nourished by similar vegetable food which abounded in the vicinity,
and was not obliged to contend with Megalosaurus for a scanty
supply of more stimulating diet."
All the groups of Jurassic Reptiles which we have hitherto been
considering are wholly unrepresented at the present day, and
do not even pass upwards into the Tertiary period. It may be
mentioned, however, that the Oolitic deposits have also yielded
the remains of Reptiles belonging to three of the existing orders
of the class-namely, the Lizards (_Lacertilia_), the Turtles
(_Chelonia_), and the Crocodiles (_Crocodilia_). The Lizards
occur both in the marine strata of the Middle Oolites and also
in the fresh-water beds of the Purbeck series; and they are of
such a nature that their affinities with the typical Lacertilians
of the present day cannot be disputed. The Chelonians, up to
this point only known by the doubtful evidence of footprints
in the Permian and Triassic sandstones, are here represented by
unquestionable remains, indicating the existence of marine Turtles
(the _Chelone planiceps_ of the Portland Stone). No remains of
Serpents (_Ophidians_) have as yet been detected in the Jurassic;
but strata of this age have yielded the remains of numerous
_Crocodilians_, which probably inhabited the sea. The most important
member of this group is _Teleosaurus_, which attained a length of
over thirty feet, and is in some respects allied to the living
Gavials of India.
[Illustration: Fig. 181.--_Archoeopteryx macrura_, showing tail
and tail-feathers, with detached bones. Reduced. From the
Lithographic Slate of Solenhofen.]
[Illustration: Fig. 182.--Restoration of _Archoeopteryx macrura_.
(After Owen.)]
The great class of the Birds, as we have seen, is represented
in rocks earlier than the Oolites simply by the not absolutely
certain evidence of the three-toed footprints of the Connecticut
Trias. In the Lithographic Slate of Solenhofen (Middle Oolite),
there has been discovered, however, the at present unique skeleton
of a Bird well known under the name of the _Archoeopteryx macrura_
(figs. 181, 182). The only known specimen--now in the British
Museum--unfortunately does not exhibit the skull; but the
fine-grained matrix has preserved a number of the other bones
of the skeleton, along with the impressions of the tail and wing
feathers. From these remains we know that _Archoeopteryx_ differed
in some remarkable peculiarities of its structure from all existing
members of the class of Birds. This extraordinary Bird (fig.
182) appears to have been about as big as a Rook--the tail being
long and extremely slender, and composed of separate vertebræ,
each of which supports a single pair of quill-feathers. In the
flying Birds of the present day, as before mentioned, the terminal
vertebræ of the tail are amalgamated to form a single bone
("ploughshare-bone"), which supports a cluster of tail-feathers;
and the tail itself is short. In the embryos of existing Birds
the tail is long, and is made up of separate vertebræ, and the
same character is observed in many existing Reptiles. The tail
of _Archoeopteryx_, therefore, is to be regarded as the permanent
retention of an embryonic type of structure, or as an approximation
to the characters of the Reptiles. Another remarkable point in
connection with _Archoeopteryx_, in which it differs from all
known Birds, is, that the wing was furnished with two free claws.
From the presence of feathers, _Archoeopteryx_ may be inferred to
have been hot-blooded; and this character, taken along with the
structure of the skeleton of the wing, may be held as sufficient
to justify its being considered as belonging to the class of
Birds. In the structure of the tail, however, it is singularly
Reptilian; and there is reason to believe that its jaws were
furnished with teeth sunk in distinct sockets, as is the case
in no existing Bird. This conclusion, at any rate, is rendered
highly probable by the recent discovery of "Toothed Birds"
(_Odonturnithes_) in the Cretaceous rocks of North America.
[Illustration: Fig. 183.--Lower jaw of _Amphitherium_
(_Thylacotherium_) _Prevostii_. Stonesfield Slate (Great Oolite.)]
[Illustration: Fig. 184. Oolitic Mammals.--1, Lower jaw and teeth
of _Phascolotherium_, Stonesfield Slate; 2, Lower jaw and teeth
of _Amphitherium_, Stonesfield Slate; 3, Lower jaw and teeth of
_Triconodon_, Purbeck beds; 4, Lower jaw and teeth of _Plagiaulax_,
Purbeck beds. All the figures are of the natural size.]
The _Mammals_ of the Jurassic period are known to us by a number
of small forms which occur in the "Stonesfield Slate" (Great
Oolite) and in the Purbeck beds (Upper Oolite). The remains of
these are almost exclusively separated halves of the lower jaw,
and they indicate the existence during the Oolitic period in
Europe of a number of small "Pouched animals" (_Marsupials_).
In the horizon of the Stonesfield Slate four genera of these
little Quadrupeds have been described--viz., _Amphilestes,
Amphitherium, Phascolotherium_, and _Stereognathus_. In
_Amphitherium_ (fig. 183), the molar teeth are furnished with
small pointed eminences or "cusps;" and the animal was doubtless
insectivorous. By Professor Owen, the highest living authority on
the subject, _Amphitherium_ is believed to be a small Marsupial,
most nearly allied to the living Banded Ant-eater (_Myrmecobius_)
of Australia (fig. 158). _Amphilestes_ and _Phascolotherium_
(fig. 184) are also believed by the same distinguished anatomist
and palæontologist to have been insect-eating Marsupials, and
the latter is supposed to find its nearest living ally in the
Opossums (_Didelphys_) of America. Lastly, the _Stereognathus_ of
the Stonesfield Slate is in a dubious position. It may have been
a Marsupial; but, upon the whole, Professor Owen is inclined to
believe that it must have been a hoofed and herbivorous Quadruped
belonging to the series of the higher Mammals (_Placentalia_).
In the Middle Purbeck beds, near to the close of the Oolitic
period, we have also evidence of the existence of a number of
small Mammals, all of which are probably Marsupials. Fourteen
species are known, all of small size, the largest being no bigger
than a Polecat or Hedgehog. The genera to which these little
quadrupeds have been referred are _Plagiaulax, Spalacotherium,
Triconodon_, and _Galestes_. The first of these (fig. 184, 4)
is believed by Professor Owen to have been carnivorous in its
habits; but other authorities maintain that it was most nearly
allied to the living Kangaroo-rats (_Hypsiprymnus_) of Australia,
and that it was essentially herbivorous. The remaining three
genera appear to have been certainly insectivorous, and find
their nearest living representatives in the Australian Phalangers
and the American Opossums.
Finally, it is interesting to notice in how many respects the
Jurassic fauna of Western Europe approached to that now inhabiting
Australia. At the present day, Australia is almost wholly tenanted
by Marsupials; upon its land-surface flourish _Araucarioe_ and
Cycadaceous plants, and in its seas swims the Port-Jackson Shark
(_Cestracion Philippi_); whilst the Molluscan genus _Trigonia_
is nowadays exclusively confined to the Australian coasts. In
England, at the time of the deposition of the Jurassic rocks,
we must have had a fauna and flora very closely resembling what
we now see in Australia. The small Marsupials, _Amphitherium,
Phascolotherium_, and others, prove that the Mammals were the same
in order; cones of Araucarian pines, with tree-ferns and fronds
of Cycads, occur throughout the Oolitic series; spine-bearing
fishes, like the Port-Jackson Shark, are abundantly represented
by genera such as _Acrodus_ and _Strophodus_; and lastly, the
genus _Trigonia_, now exclusively Australian, is represented
in the Oolites by species which differ little from those now
existing. Moreover, the discovery during recent years of the
singular Mud-fish, the _Ceratodus Fosteri_ in the rivers of
Queensland, has added another and a very striking point of
resemblance to those already mentioned; since this genus of Fishes,
though preeminently Triassic, nevertheless extended its range
into the Jurassic. Upon the whole, therefore, there is reason
to conclude that Australia has undergone since the close of the
Jurassic period fewer changes and vicissitudes than any other
known region of the globe; and that this wonderful continent
has therefore succeeded in preserving a greater number of the
characteristic life-features of the Oolites than any other country
with which we are acquainted.
LITERATURE.
The following list comprises some of the more important sources of
information as to the rocks and fossils of the Jurassic series:--
(1) 'Geology of Oxford and the Thames Valley.' Phillips.
(2) 'Geology of Yorkshire,' vol. ii. Phillips.
(3) 'Memoirs of the Geological Survey of Great Britain.'
(4) 'Geology of Cheltenham.' Murchison, 2d ed. Buckman.
(5) 'Introduction to the Monograph of the Oolitic Asteriadæ'
(Palæontographical Society). Wright.
(6) "Zone of Avicula contorta and the Lower Lias of the South of
England"--'Quart. Journ. Geol. Soc.,' vol. xvi., 1860. Wright.
(7) "Oolites of Northamptonshire"--'Quart. Journ. Geol. Soc.,'
vols. Xxvi. and xxix. Sharp.
(8) 'Manual of Geology.' Dana.
(9) 'Der Jura.' Quenstedt.
(10) 'Das Flötzgebirge Württembergs.' Quenstedt.
(11) 'Jura Formation.' Oppel.
(12) 'Paléontologie du Département de la Moselle.' Terquem.
(13) 'Cours élémentaire de Paléontologie.' D'Orbigny.
(14) 'Paléontologie Française.' D'Orbigny.
(15) 'Fossil Echinodermata of the Oolitic Formation'
(Palæontographical Society). Wright.
(16) 'Brachiopoda of the Oolitic Formation' (Palæontographical
Society). Davidson.
(17) 'Mollusca of the Great Oolite' (Palæontographical Society).
Morris and Lycett.
(18) 'Monograph of the Fossil Trigoniæ' (Palæontographical Society).
Lycett.
(19) 'Corals of the Oolitic Formation' (Palæontographical Society).
Edwards and Haime.
(20) 'Supplement to the Corals of the Oolitic Formation'
(Palæontographical Society). Martin Duncan.
(21) 'Monograph of the Belemnitidæ' (Palæontographical Society).
Phillips.
(22) 'Structure of the Belemnitidæ' (Mem. Geol. Survey). Huxley.
(23) 'Sur les Belemnites.' Blainville.
(24) 'Cephalopoden.' Quenstedt.
(25) 'Mineral Conchology.' Sowerby.
(26) 'Jurassic Cephalopoda' (Palæontologica Indica). Waagen.
(27) 'Manual of the Mollusca.' Woodward.
(28) 'Petrefaktenkunde.' Schlotheim.
(29) 'Bridgewater Treatise.' Buckland.
(30) 'Versteinerungen des Oolithengebirges.' Roemer.
(31) 'Catalogue of British Fossils.' Morris.
(32) 'Catalogue of Fossils in the Museum of Practical Geology.'
Etheridge.
(33) 'Beiträge zur Petrefaktenkunde.' Münster.
(34) 'Petrefacta Germaniæ.' Goldfuss.
(35) 'Lethæa Rossica.' Eichwald.
(36) 'Fossil Fishes' (Decades of the Geol. Survey). Sir Philip Egerton.
(37) 'Manual of Palæontology.' Owen.
(38) 'British Fossil Mammals and Birds.' Owen.
(39) 'Monographs of the Fossil Reptiles of the Oolitic Formation'
(Palæontographical Society). Owen.
(40) 'Fossil Mammals of the Mesozoic Formations' (Palæontographical
Society). Owen.
(41) 'Catalogue of Ornithosauria.' Seeley.
(42) "Classification of the Deinosauria"--'Quart. Journ. Geol. Soc.,'
vol. xxvi., 1870. Huxley.
CHAPTER XVII.
THE CRETACEOUS PERIOD.
The next series of rocks in ascending order is the great and
important series of the Cretaceous Rocks, so called from the
general occurrence in the system of chalk (Lat. _creta_, chalk).
As developed in Britain and Europe generally, the following leading
subdivisions may be recognised in the Cretaceous series:--
1. Wealden, \_ Lower Cretaceous.
2. Lower Greensand or Neocomian, /
3. Gault, \
4. Upper Greensand, |_ Upper Cretaceous.
5. Chalk, |
6. Maestricht beds, /
I. _Wealden_.--The _Wealden_ formation, though of considerable
importance, is a local group, and is confined to the southeast
of England, France, and some other parts of Europe. Its name is
derived from the _Weald_, a district comprising parts of Surrey,
Sussex, and Kent, where it is largely developed. Its lower portion,
for a thickness of from 500 to 1000 feet, is arenaceous, and is
known as the Hastings Sands. Its Upper portion, for a thickness
of 150 to nearly 300 feet, is chiefly argillaceous, consisting of
clays with sandy layers, and occasionally courses of limestone.
The geological importance of the Wealden formation is very great,
as it is undoubtedly the delta of an ancient river, being composed
almost wholly of fresh-water beds, with a few brackish-water
and even marine strata, intercalated in the lower portion. Its
geographical extent, though uncertain, owing to the enormous
denudation to which it has been subjected, is nevertheless great,
since it extends from Dorsetshire to France, and occurs also in
North Germany. Still, even if it were continuous between all
these points, it would not be larger than the delta of such a
modern river as the Ganges. The river which produced the Wealden
series must have flowed from an ancient continent occupying what
is now the Atlantic Ocean; and the time occupied in the formation
of the Wealden must have been very great, though we have, of
course, no data by which we can accurately calculate its duration.
The fossils of the Wealden series are, naturally, mostly the
remains of such animals as we know at the present day as inhabiting
rivers. We have, namely, fresh-water Mussels (_Unio_), River-snails
(_Paludina_), and other fresh-water shells, with numerous little
bivalved Crustaceans, and some fishes.
II. _Lower Greensand_ (_Néocomien_ of D'Orbigny).--The Wealden
beds pass upward, often by insensible gradations, into the Lower
Greensand. The name Lower Greensand is not an appropriate one,
for green sands only occur sparingly and occasionally, and are
found in other formations. For this reason it has been proposed
to substitute for Lower Greensand the name _Neocomian_, derived
from the town of Neufchâtel--anciently called _Neocomum_--in
Switzerland. If this name were adopted, as it ought to be, the
Wealden beds would be called the Lower Neocomian.
The Lower Greensand or Neocomian of Britain has a thickness of
about 850 feet, and consists of alternations of sands, sandstones,
and clays, with occasional calcareous bands. The general colour
of the series is dark brown, sometimes red; and the sands are
occasionally green, from the presence of silicate of iron.
The fossils of the Lower Greensand are purely marine, and among
the most characteristic are the shells of _Cephalopods_.
The most remarkable point, however, about the fossils of the
Lower Cretaceous series, is their marked divergence from the
fossils of the Upper Cretaceous rocks. Of 280 species of fossils
in the Lower Cretaceous series, only 51, or about 18 per cent, pass
on into the Upper Cretaceous. This break in the life of the two
periods is accompanied by a decided physical break as well; for the
Gault is often, if not always, unconformably superimposed on the
Lower Greensand. At the same time, the Lower and Upper Cretaceous
groups form a closely-connected and inseparable series, as shown
by a comparison of their fossils with those of the underlying
Jurassic rocks and the overlying Tertiary beds. Thus, in Britain
no marine fossil is known to be common to the marine beds of
the Upper Oolites and the Lower Greensand; and of more than 500
species of fossils in the Upper Cretaceous rocks, almost everyone
died out before the formation of the lowest Tertiary strata, the
only survivors being one Brachiopod and a few _Foraminifera_.
III. _Gault_ (_Aptien_ of D'Orbigny).--The lowest member of the
Upper Cretaceous series is a stiff, dark-grey, blue, or brown
clay, often worked for brick-making, and known as the _Gault_,
from a provincial English term. It occurs chiefly in the south-east
of England, but can be traced through France to the flanks of
the Alps and Bavaria. It never exceeds 100 feet in thickness;
but it contains many fossils, usually in a state of beautiful
preservation.
IV. _Upper Greensand_ (_Albien_ of D'Orbigny; _Unterquader_ and
_Lower Plänerkalk_ of Germany).--The Gault is succeeded upward by
the _Upper Greensand_, which varies in thickness from 3 up to 100
feet, and which derives its name from the occasional occurrence
in it of green sands. These, however, are local and sometimes
wanting, and the name "Upper Greensand" is to be regarded as a
_name_ and not a description. The group consists, in Britain,
of sands and clays, sometimes with bands of calcareous grit or
siliceous limestone, and occasionally containing concretions of
phosphate of lime, which are largely worked for agricultural
purposes.
V. _White Chalk_.--The top of the Upper Greensand becomes
argillaceous, and passes up gradually into the base of the great
formation known as the true _Chalk_, divided into the three
subdivisions of the chalk-marl, white chalk without flints, and
white chalk with flints. The first of these is simply argillaceous
chalk, and passes up into a great mass of obscurely-stratified
white chalk in which there are no flints (_Turonien_ of D'Orbigny;
_Mittelquader_ of Germany). This, in turn, passes up into a great
mass of white chalk, in which the stratification is marked by
nodules of black flint arranged in layers (_Sénonien_ of D'Orbigny;
_Oberquader_ of Germany). The thickness of these three subdivisions
taken together is sometimes over 1000 feet, and their geographical
extent is very great. White Chalk, with its characteristic
appearance, may be traced from the north of Ireland to the Crimea,
a distance of about 1140 geographical miles; and, in an opposite
direction, from the south of Sweden to Bordeaux, a distance of
about 840 geographical miles.
VI. In Britain there occur no beds containing Chalk fossils, or
in any way referable to the Cretaceous period, above the true
White Chalk with flints. On the banks of the Maes, however, near
Maestricht in Holland, there occurs a series of yellowish limestones,
of about 100 feet in thickness, and undoubtedly superior to the White
Chalk. These _Maestricht beds_ (_Danien_ of D'Orbigny) contain a
remarkable series of fossils, the characters of which are partly
Cretaceous and partly Tertiary. Thus, with the characteristic
Chalk fossils, _Belemnites, Baculites_, Sea-Urchins, &c., are
numerous Univalve Molluscs, such as Cowries and Volutes, which
are otherwise exclusively Tertiary or Recent.
Holding a similar position to the Maestricht beds, and showing
a similar intermixture of Cretaceous forms with later types, are
certain beds which occur in the island of Seeland, in Denmark,
and which are known as the _Faxöe Limestone_.
Of a somewhat later date than the Maestricht beds is the _Pisolitic
Limestone_ of France, which rests unconformably on the White
Chalk, and contains a large number of Tertiary fossils along with
some characteristic Cretaceous types.
The subjoined sketch-section exhibits the general succession of
the Cretaceous deposits in Britain:--
[Illustration: Fig. 185. GENERALIZED SECTION OF THE CRETACEOUS
SERIES OF BRITAIN.]
In North America, strata of Lower Cretaceous age are well represented
in Missouri, Wyoming, Utah, and in some other areas; but the greater
portion of the American deposits of this period are referable to
the Upper Cretaceous. The rocks of this series are mostly sands,
clays, and limestones--_Chalk_ itself being unknown except in
Western Arkansas. Amongst the sandy accumulations, one of the
most important is the so-called "marl" of New Jersey, which is
truly a "Greensand," and contains a large proportion of glauconite
(silicate of iron and potash). It also contains a little phosphate
of lime, and is largely worked for agricultural purposes. The
greatest thickness attained by the Cretaceous rocks of North
America is about 9000 feet, as in Wyoming, Utah, and Colorado.
According to Dana, the Cretaceous rocks of the Rocky Mountain
territories pass upwards "without interruption into a coal-bearing
formation, several thousand feet thick, on which the following
Tertiary strata lie unconformably." The lower portion of this
"Lignitic formation" appears to be Cretaceous, and contains one
or more beds of Coal; but the upper part of it perhaps belongs
to the Lower Tertiary. In America, therefore, the lowest Tertiary
strata appear to rest conformably upon the highest Cretaceous;
whereas in Europe, the succession at this point is invariably an
unconformable one. Owing, however, to the fact that the American
"Lignitic formation" is a shallow-water formation, it can hardly
be expected to yield much material whereby to bridge over the
great palæontological gap between the White Chalk and Eocene
in the Old World.
Owing to the fact that so large a portion of the Cretaceous formation
has been deposited in the sea, much of it in deep water, the _plants_
of the period have for the most part been found special members
of the series, such as the Wealden beds, the Aix-la-Chapelle
sands, and the Lignitic beds of North America. Even the purely
marine strata, however, have yielded plant-remains, and some of
these are peculiar and proper to the deep-sea deposits of the
series. Thus the little calcareous discs termed "coccoliths," which
are known to be of the nature of calcareous sea-weeds (_Algoe_)
have been detected in the White Chalk; and the flints of the same
formation commonly contain the spore-cases of the microscopic
_Desmids_ (the so-called Xanthidia), along with the siliceous
cases of the equally diminutive _Diatoms_.
The plant-remains of the Lower Cretaceous greatly resemble those
of the Jurassic period, consisting mainly of Ferns, Cycads, and
Conifers. The Upper Cretaceous rocks, however, both in Europe and
in North America, have yielded an abundant flora which resembles
the existing vegetation of the globe in consisting mainly of
Angiospermous Exogens and of Monocotyledons.[23] In Europe the
plant-remains in question have been found chiefly in certain
sands in the neighbourhood of Aix-la-Chapelle, and they consist
of numerous Ferns, Conifers (such as _Cycadopteris_), Screw Pines
(_Pandanus_), Oaks (_Quercus_), Walnut (_Juglans_), Fig (_Ficus_),
and many _Proteaceoe_, some of which are referred to existing
genera (_Dryandra, Banksia, Grevillea_, &c.)
[Footnote 23: The "Flowering plants" are divided into the two
great groups of the Endogens and Exogens. The _Endogens_ (such
as Grasses, Palms, Lilies, &c.) have no true bark, nor rings of
growth, and the stem is said to be "endogenous;" the young plant
also possesses but a single seed-leaf or "cotyledon." Hence these
plants are often simply called "_Monocotyledons_." The _Exogens_,
on the other hand, have a true bark; and the stem increases by
annual additions to the outside, so that rings of growth are
produced. The young plant has two seed-leaves or "cotyledons,"
and these plants are therefore called "_Dicotyledons_." Amongst the
Exogens, the Pines (_Conifers_) and the Cycads have seeds which
are unprotected by a seed-vessel, and they are therefore called
"_Gymnosperms_." All the other Exogens, including the ordinary
trees, shrubs, and flowering plants, have the seeds enclosed in
a seed-vessel, and are therefore called "_Angiosperms_." The
derivation of these terms will be found in the Glossary at the
end of the volume.]
In North America, the Cretaceous strata of New Jersey, Alabama,
Nebraska, Kansas, &c., have yielded the remains of numerous plants,
many of which belong to existing genera. Amongst these may be
mentioned Tulip-trees (_Liriodendron_), Sassafras (fig. 186),
Oaks (_Quercus_), Beeches (_Fagus_), Plane-trees (_Platanus_),
Alders (_Alnus_), Dog-wood (_Cornus_), Willows (_Salix_), Poplars
(_Populus_), Cypresses (_Cupressus_), Bald Cypresses (_Taxodium_),
Magnolias, &c. Besides these, however, there occur other forms
which have now entirely disappeared from North America--as, for
example, species of _Cinnamomum_ and _Araucaria_.
It follows from the above, that the Lower and Upper Cretaceous
rocks are, from a botanical point of view, sharply separated
from one another. The Palæozoic period, as we have seen, is
characterised by the prevalance of "Flowerless" plants
(_Cryptogams_), its higher vegetation consisting almost exclusively
of Conifers. The Mesozoic period, as a whole, is characterised
by the prevalence of the Cryptogamic group of the Ferns, and
the Gymnospermic groups of the Conifers and the Cycads. Up to
the close of the Lower Cretaceous, no Angiospermous Exogens are
certainly known to have existed, and Monocotyledonous plants or
Endogens are very poorly represented. With the Upper Cretaceous,
however, a new era of plant-life, of which our present is but
the culmination, commenced, with a great and apparently sudden
development of new forms. In place of the Ferns, Cycads, and
Conifers of the earlier Mesozoic deposits, we have now an
astonishingly large number of true Angiospermous Exogens, many
of them belonging to existing types; and along with these are
various Monocotyledonous plants, including the first examples of
the great and important group of the Palms. It is thus a matter
of interest to reflect that plants closely related to those now
inhabiting the earth, were in existence at a time when the ocean
was tenanted by Ammonites and Belemnites, and when land and sea
and air were peopled by the extraordinary extinct Reptiles of
the Mesozoic period.
[Illustration: Fig. 186.--Cretaceous Angiosperms. a. _Sassafras
Cretaceum; b, Liriodendron Meekii; c, Leguminosites Marcouanus;
d, Salix Meekii_. (After Dana.)]
As regards animal life, the _Protozoans_ of the Cretaceous period
are exceedingly numerous, and are represented by _Foraminifera_
and _Sponges_. As we have already seen, the White Chalk itself is
a deep-sea deposit, almost entirely composed of the microscopic
shells of _Foraminifers_, along with Sponge-spicules, and organic
_débris_ of different kinds (see fig. 7). The green grains which
are so abundant in several minor subdivisions of the Cretaceous,
are also in many instances really casts in glauconite of the
chambered shells of these minute organisms. A great many species
of _Foraminifera_ have been recognised in the Chalk; but the
three principal genera are _Globigerina, Rotalia_ (fig. 187),
and _Textularia_--groups which are likewise characteristic of
the "ooze" of the Atlantic and Pacific Oceans at great depths.
The flints of the Chalk also commonly contain the shells of
_Foraminifera_. The Upper Greensand has yielded in considerable
numbers the huge _Foraminifera_ described by Dr Carpenter under
the name of _Parkeria_, the spherical shells of which are composed
of sand-grains agglutinated together, and sometimes attain a
diameter of two and a quarter inches. The Cretaceous Sponges are
extremely numerous, and occur under a great number of varieties
of shape and structure; but the two most characteristic genera
are _Siphonia_ and _Ventriculites_, both of which are exclusively
confined to strata of this age. The _Siphonioe_ (fig. 188) consist
of a pear-shaped, sometimes lobed head, supported by a longer
or shorter stern, which breaks up at its base into a number of
root-like processes of attachment. The water gained access to the
interior of the Sponge by a number of minute openings covering
the surface, and ultimately escaped by a single, large,
chimney-shaped aperture at the summit. In some respects these
sponges present a singular resemblance to the beautiful "Vitreous
Sponges" (_Holtenia_ or _Pheronema_) of the deep Atlantic; and,
like these, they were probably denizens of a deep sea, The
_Ventriculites_ of the Chalk (fig. 189) is, however, a genus
still more closely allied to the wonderful flinty Sponges, which
have been shown, by the researches of the Porcupine, Lightning,
and Challenger expeditions, to live half buried in the Calcareous
ooze of the abysses of our great oceans. Many forms of this genus
are known, having "usually the form of graceful vases, tubes, or
funnels, variously ridged or grooved, or otherwise ornamented
on the surface, frequently expanded above into a cup-like lip,
and continued below into a bundle of fibrous roots. The minute
structure of these bodies shows an extremely delicate tracery
of fine tubes, sometimes empty, sometimes filled with loose
calcareous matter dyed with peroxide of iron."--(Sir Wyville
Thomson.) Many of the Chalk sponges, originally calcareous, have
been converted into flint subsequently; but the Ventriculites
are really composed of this substance, and are therefore genuine
"Siliceous Sponges," like the existing Venus's Flower-Basket
(_Euplectella_). Like the latter, the skeleton was doubtless
originally composed, in the young state, of disconnected six-rayed
spicules, which ultimately become fixed together to constitute
a continuous frame-work. The sea-water, as in the recent forms,
must have been admitted to the interior of the Sponge by numerous
apertures on its exterior, subsequently escaping by a single
large opening at its summit.
[Illustration: Fig. 187--_Kotalia Boueana_.]
[Illustration: Fig. 188.--_Siphonia ficus. Upper Greensand. Europe.]
[Illustration: Fig. 189.--_Ventriculites simplex_. White Chalk.
Britain.]
Amongst the _Coelenterates_, the "Hydroid Zoophytes" are represented
by a species of the encrusting genus _Hydractinia_, the horny
polypary of which is so commonly found at the present day adhering
to the exterior of shells. The occurrence of this genus is of
interest, because it is the first known instance in the entire
geological series of the occurrence of an unquestionable Hydroid of
a modern type, though many of the existing forms of these animals
possess structures which are perfectly fitted for preservation in
the fossil condition. The corals of the Cretaceous series are not
very numerous, and for the most part are referable to types such
as _Trochocyathus, Stephanophyllia, Parasmilia, Synhelia_ (fig.
190), &c., which belong to the same great group of corals as the
majority of existing forms. We have also a few "Tabulate Corals"
(_Polytremacis_), hardly, if at all, generically separable from very
ancient forms (_Heliolites_); and the Lower Greensand has yielded
the remains of the little _Holocystis elegans_, long believed to
be the last of the great Palæozoic group of the _Rugosa_.
[Illustration: Fig. 190.--_Synhelia Sharpeana_. Chalk, England.]
As regards the _Echinoderms_, the group of the _Crinoids_ now
exhibits a marked decrease in the number and variety of its types.
The "stalked" forms are represented by _Pentacrinus_ and
_Bourgueticrinus_, and the free forms by Feather-stars like our
existing _Comatuloe_; whilst a link between the stalked and free
groups is constituted by the curious "Tortoise Encrinite
(_Marsupites_). By far the most abundant Cretaceous Echinoderms,
however, are Sea-urchins (_Echinoids_); though several Star-fishes
are known as well. The remains of Sea-urchins are so abundant
in various parts of the Cretaceous series, especially in the
White Chalk, and are often so beautifully preserved, that they
constitute one of the most marked features of the fauna of the
period. From the many genera of Sea-urchins which occur in strata
of this age, it is difficult to select characteristic types;
but the genera _Galerites_ (fig. 191), _Discoidea_ (fig. 192),
_Micraster, Ananchytes, Diadema, Salenia_, and _Cidaris_, may
be mentioned as being all important Cretaceous groups.
Coming to the _Annulose Animals_ of the Cretaceous period, there
is little special to remark. The _Crustaceans_ belong for the
most part to the highly-organised groups of the Lobsters and the
Crabs (the Macrurous and Brachyurous Decapods); but there are
also numerous little _Ostracodes_, especially in the fresh-water
strata of the Wealden. It should further be noted that there
occurs here a great development of the singular _Crustaceous_
family of the Barnacles (_Lepadidoe_), whilst the allied family
of the equally singular Acorn-shells (_Balanidoe_) is feebly
represented as well.
[Illustration: Fig. 191.--_Galerites albogalerus_, viewed from
below, from the side, and from above. White Chalk.]
[Illustration: Fig. 192.--_Discoidea cylindrica_; under, side,
and upper aspect. Upper Greensand.]
Passing on to the _Mollusca_, the class of the Sea-mats and
Sea-mosses (_Polyzoa_) is immensely developed in the Cretaceous
period, nearly two hundred species being known to occur in the
Chalk. Most of the Cretaceous forms belong to the family of the
_Escharidoe_, the genera _Eschara_ and _Escharina_ (fig. 193)
being particularly well represented. Most of the Cretaceous
_Polyzoans_ are of small size, but some attain considerable
dimensions, and many simulate Corals in their general form and
appearance.
The Lamp-shells (_Brachiopods_) have now reached a further stage
of the progressive decline, which they have been undergoing ever
since the close of the Palæozoic period. Though individually not
rare, especially in certain minor subdivisions of the series,
the number of generic types has now become distinctly diminished,
the principal forms belonging to the genera _Terebratula,
Terebratella_ (fig. 194), _Terebratulina, Rhynchonella_, and
_Crania_ (fig. 195). In the last mentioned of these, the shell
is attached to foreign bodies by the substance of one of the
valves (the ventral), whilst the other or free valve is more
or less limpet-shaped. All the above-mentioned genera are in
existence at the present day; and one _species_--namely,
_Terebratulina striata_--appears to be undistinguishable from
one now living--the _Terebratulina caputserpentis_.
[Illustration: Fig. 193.--A small fragment of _Escharina Oceani_,
of the natural size; and a portion of the same enlarged. Upper
Greensand.]
[Illustration: Fig. 194.--_Terebratella Astieriana_. Gault.]
Whilst the Lamp-shells are slowly declining, the Bivalves
(_Limellibranchs_) are greatly developed, and are amongst the
most abundant and characteristic fossils of the Cretaceous period.
In the great river-deposit of the Wealden, the Bivalves are forms
proper to fresh water, belonging to the existing River-mussels
(_Unio_), _Cyrena_ and _Cyclas_; but most of the Cretaceous
Lamellibranchs are marine. Some of the most abundant and
characteristic of these belong to the great family of the Oysters
(_Ostreidoe_). Amongst these are the genera _Gryphtoea_ and
_Exogyra_, both of which we have seen to occur abundantly in the
Jurassic; and there are also numerous true Oysters (_Ostrea_,
fig. 196) and Thorny Oysters (_Spondylus_, fig. 197). The genus
_Trigonia_, so characteristic of the Mesozoic deposits in general,
is likewise well represented in the Cretaceous strata. No single
genus of Bivalves is, however, so highly characteristic of the
Cretaceous period as _Inoceramus_, a group belonging to the family
of the Pearl-mussels (_Aviculidoe_). The shells of this genus
(fig. 198) have the valves unequal in size, the larger valve often
being much twisted, and both valves being marked with radiating
ribs or concentric furrows. The hinge-line is long and straight,
with numerous pits for the attachment of the ligament which serves
to open the shell. Some of the _Inocerami_ attain a length of
two or three feet, and fragments of the shell are often found
perforated by boring Sponges. Another extraordinary family of
Bivalves, which is exclusively confined to the Cretaceous rocks,
is that of the _Hippuritidoe_. All the members of this group
(fig. 199) were attached to foreign objects, and lived associated
in beds, like Oysters. The two valves of the shell are always
altogether unlike in sculpturing, appearance, shape, and size;
and the cast of the interior of the shell is often extremely
unlike the form of the outer surface. The type-genus of the family
is _Hippurites_ itself (fig. 199), in which the shell is in the
shape of a straight or slightly-twisted horn, sometimes a foot
or more in length, constituted by the attached lower valve, and
closed above by a small lid-like free upper valve. About a hundred
species of the family of the _Hippuritidoe_ are known, all of these
being Cretaceous, and occurring in Britain (one species only), in
Southern Europe, the West Indies, North America, Algeria, and
Egypt. Species of this family occur in such numbers in certain
compact marbles in the south of Europe, of the age of the Upper
Cretaceous (Lower Chalk), as to have given origin to the name
of "Hippurite Limestones," applied to these strata.
[Illustration: Fig. 195.--_Crania Ignabergensis_. The left-hand
figure shows the perfect shell, attached by its ventral valve
to a foreign body; the middle figure shows the exterior of the
limpet-shaped dorsal valve; and the right-hand figure represents
the interior of the attached valve. White Chalk.]
[Illustration: Fig. 196.--_Ostrea Couloni_. Lower Greensand.]
[Illustration: Fig. 197.--_Spondylus spinosus_. White Chalk.]
[Illustration: Fig. 198.--_Inoceramus sulcatus_. Gault.]
The Univalves (_Gasteropods_) of the Cretaceous period are not
very numerous, nor particularly remarkable. Along with species of
the persistent genus _Pleurotomaria_ and the Mesozoic _Nerinoea_,
we meet with examples of such modern types as _Turritella_ and
_Natica_, the Staircase-shells (_Solarium_), the Wentle-traps
(_Scalaria_), the Carrier-shells (_Phorus_), &c. Towards the close
of the Cretaceous period, and especially in such transitional strata
as the Maestricht beds, the Faxöe Limestone, and the Pisolitic
Limestone of France, we meet with a number of carnivorous
("siphonostomatous") Univalves, in which the mouth of the shell is
notched or produced into a canal. Amongst these it is interesting
to recognise examples of such existing genera as the Volutes
(_Voluta_, fig. 200), the Cowries (_Cyproea_), the Mitre-shells
(_Mitra_), the Wing - shells (_Strombus_), the Scorpion-shells
(_Pteroceras_), &c.
[Illustration: Fig. 199.--_Hippurites Toucasiana_. A large
individual, with two smaller ones attached to it. Upper Cretaceous,
South of Europe.]
[Illustration: Fig. 200.--_Voluta elongata_. White Chalk.]
Upon the whole, the most characteristic of all the Cretaceous
Molluscs are the _Cephalopods_, represented by the remains of
both _Tetrabranchiate_ and _Dibranchiate_ forms. Amongst the
former, the long-lived genus _Nautilus_ (fig. 201) again reappears,
with its involute shell, its capacious body-chamber, its simple
septa between the air-chambers, and its nearly or quite central
siphuncle. The majority of the chambered _Cephalopods_ of the
Cretaceous belong, however, to the complex and beautiful family
of the _Ammonitidoe_, with their elaborately folded and lobed
septa and dorsally-placed siphuncle. This family disappears wholly
at the close of the Cretaceous period; but its approaching
extinction, so far from being signalised by any slow decrease
and diminution in the number of specific or generic types, seems
to have been attended by the development of whole series of new
forms. The genus _Ammonites_ itself, dating from the Carboniferous,
has certainly passed its prime, but it is still represented by
many species, and some of these attained enormous dimensions
(two or three feet in diameter). The genus _Ancyloceras_ (fig.
202), though likewise of more ancient origin (Jurassic), is
nevertheless very characteristic of the Cretaceous. In this genus
the first portion of the shell is in the form of a flat spiral,
the coils of which are not in contact; and its last portion is
produced at a tangent, becoming ultimately bent back in the form
of a crosier. Besides these pre-existent types, the Cretaceous
rocks have yielded a great number of entirely new forms of the
_Ammonitidoe_, which are not known in any deposits of earlier or
later date. Amongst the more important of these may be mentioned
_Crioceras, Turrilites, Scaphites, Hamites, Ptychoceras_, and
_Baulites_. In the genus _Crioceras_ (fig. 204, d), the shell
consists of an open spiral, the volutions of which are not in
contact, thus resembling a partially-unrolled _Ammonite_ or the
inner portion of an _Ancyloceras_. In _Turrilites_ (fig. 203), the
shell is precisely like that of the _Ammonite_ in its structure;
but instead of forming a flat spiral, it is coiled into an elevated
turreted shell, the whorls of which are in contact with one another.
In the genus _Scaphites_ (fig. 204, e), the shell resembles that
of _Ancyloceras_ in consisting of a series of volutions coiled
into a flat spiral, the last being detached from the others,
produced, and ultimately bent back in the form of a crosier; but
the whorls of the enrolled part of the shell are in contact,
instead of being separate as in the latter. In the genus _Hamites_
(fig. 204, f), the shell is an extremely elongated cone, which
is bent upon itself more than once, in a hook-like manner, all
the volutions being separate. The genus _Ptychoteras_ (fig. 204,
a) is very like _Hamites_, except that the shell is only bent
once; and the two portions thus bent are in contact with one
another. Lastly, in the genus _Baculites_ (fig. 204, b and
c) the shell is simply a straight elongated cone, not bent
in any way, but possessing the folded septa which characterise
the whole Ammonite family. The _Baculite_ is the simplest of
all the forms of the _Ammonitidoe_; and all the other forms,
however complex, may be regarded as being simply produced by the
bending or folding of such a conical septate shell in different
ways. The _Baculite_, therefore, corresponds, in the series of
the _Ammonitidoe_, to the _Orthoceras_ in the series of the
_Nautilidoe_. All the above-mentioned genera are characteristically,
or exclusively, Cretaceous, and they are accompanied by a number
of other allied forms, which cannot be noticed here. Not a single
one of these genera, further, has hitherto been detected in any
strata higher than the Cretaceous. We may therefore consider that
these wonderful, varied, and elaborate forms of _Ammonitidoe_
constitute one of the most conspicuous features in the life of
the Chalk period.
[Illustration: Fig. 201.--Different views of _Nautilus Danicus_.
Faxöe Limestone (Upper Cretaceous), Denmark.]
[Illustration: Fig. 202.--_Ancyloceras Matheronianus_. Gault.]
The _Dibranchiate Cephalopods_ are represented partly by the
beak-like jaws of unknown species of Cuttle-fishes and partly
by the internal skeletons of Belemnites. Amongst the latter,
the genus _Belemnites_ itself holds its place in the lower part
of the Cretaceous series; but it disappears in the upper portion
of the series, and its place is taken by the nearly-allied genus
_Belemnitella_ (fig. 205), distinguished by the possession of
a straight fissure in the upper end of the guard. This also
disappears at the close of the Cretaceous period; and no member
of the great Mesozoic family of the _Belemnitidoe_ has hitherto
been discovered in any Tertiary deposit, or is known to exist
at the present day.
[Illustration: Fig. 203.--_Turrilites catenatus_. The lower figure
represents the entire shell; the upper figure represents the
base of the shell seen from below. Gault.]
[Illustration: Fig. 204.--a, _Ptychoceras Emericianum_,
reduced--Lower Greensand; b, _Baculites anceps_, reduced--Chalk;
c, Portion of the same, showing the folded edges of the septa;
d, _Crioceras cristatum_, reduced--Gault; e, _Scaphites oequalis_,
natural size--Chalk; f, _Hamites rotundus_, restored--Gault.]
Passing on next to the _Vertebrate Animals_ of the Cretaceous
period, we find the _Fishes_ represented as before by the Ganoids
and the Placoids, to which, however, we can now add the first
known examples of the great group of the _Bony Fishes_ or
_Teleosteans_, comprising the great majority of existing forms.
The _Ganoid_ fishes of the Cretaceous (_Lepidotus, Pycnodus_,
&c.) present no features of special interest. Little, also, need
be said about the _Placoid_ fishes of this period. As in the
Jurassic deposits, the remains of these consist partly of the
teeth of genuine Sharks (_Lamna, Odontaspis_, &c.) and partly
of the teeth and defensive spines of Cestracionts, such as the
living Port-Jackson Shark. The pointed and sharp-edged teeth of
true Sharks are very abundant in some beds, such as the Upper
Greensand, and are beautifully preserved. The teeth of some forms
(_Carcharias_, &c.) attain occasionally a length of three or four
inches, and indicate the existence in the Cretaceous seas of
huge predaceous fishes, probably larger than any existing Sharks.
The remains of _Cestracionts_ consist partly of the flattened
teeth of genera such as _Acrodus_ and _Ptychodus_ (the latter
confined to rocks of this age), and partly of the pointed teeth
of _Hybodus_, a genus which dates from the Trias. In this genus
the teeth (fig. 206) consist of a principal central cone, flanked
by minor lateral cones; and the fin-spines (fig. 207) are
longitudinally grooved, and carry a series of small spines on
their hinder or concave margin. Lastly, the great modern order
of the Bony Fishes or _Teleosteans_ makes its first appearance
in the Upper Cretaceous rocks, where it is represented by forms
belonging to no less than three existing groups--namely, the
Salmon family (_Salmonidoe_), the Herring family (_Clupeidoe_),
and the Perch family (_Percidoe_). All these fishes have thin,
horny, overlapping scales, symmetrical ("homocercal") tails,
and bony skeletons. The genus _Beryx_ (fig. 208, 1) is one
represented by existing species at the present day, and belongs
to the Perch family. The genus _Osmeroides_, again (fig. 208,
2), is supposed to be related to the living Smelts (_Osmerus_),
and, therefore, to belong to the Salmon tribe.
[Illustration: Fig. 205.--Guard of _Belemnitella mucronata_. White
Chalk.]
[Illustration: Fig. 206.--Tooth of _Hybodus_.]
[Illustration: Fig. 207.--Fin-spine of _Hybodus_. Lower Greensand.]
[Illustration: Fig. 208.--1, _Beryx Lewesiensis_, a Percoid fish
from the Chalk; 2, _Osmeroides Mantelli_, a Salmonoid fish from
the Chalk.]
No remains of _Amphibians_ have hitherto been detected in any part
of the Cretaceous series; but _Reptiles_ are extremely numerous,
and belong to very varied types. As regards the great extinct groups
of Reptiles which characterise the Mesozoic period as a whole, the
huge "Enaliosaurs" or "Sea-Lizards" are still represented by the
_Ichthyosaur_ and the _Plesiosaur_. Nearly allied to the latter
of these is the _Elasmosaurus_ of the American Cretaceous, which
combined the long tail of the Ichthyosaur with the long neck
of the Plesiosaur. The length of this monstrous Reptile could not
have been less than fifty feet, the neck consisting of over sixty
vertebræ and measuring over twenty feet in length. The extraordinary
Flying Reptiles of the Jurassic are likewise well represented in
the Cretaceous rocks by species of the genus _Pterodactylus_
itself, and these later forms are much more gigantic in their
dimensions than their predecessors. Thus some of the Cretaceous
Pterosaurs seem to have had a spread of wing of from twenty to
twenty-five feet, more than realising the "Dragons" of fable in
point of size. The most remarkable, however, of the Cretaceous
_Pterosaurs_ are the forms which have recently been described
by Professor Marsh under the generic title of _Pteranodon_. In
these singular forms--so far only known as American--the animal
possessed a skeleton in all respects similar to that of the typical
Pterodactyles, except that the jaws are completely destitute of
teeth. There is, therefore, the strongest probability that the
jaws were encased in a horny sheath, thus coming to resemble the
beak of a Bird. Some of the recognised species of _Pteranodon_
are very small; but the skull of one species (_P. Longiceps_)
is not less than a yard in length, and there are portions of
the skull of another species which would indicate a length of
four feet for the cranium. These measurements would point to
dimensions larger than those of any other known Pterosaurs.
The great Mesozoic order of the _Deinosaurs_ is largely represented
in the Cretaceous rocks, partly by genera which previously existed
in the Jurassic period, and partly by entirely new types. The great
delta-deposit of the Wealden, in the Old World, has yielded the
remains of various of these huge terrestrial Reptiles, and very
many others have been found in the Cretaceous deposits of North
America. One of the most celebrated of the Cretaceous Deinosaurs
is the _Iguanodon_, so called from the curious resemblance of
its teeth to those of the existing but comparatively diminutive
_Iguana_. The teeth (fig. 209) are soldered to the inner face
of the jaw, instead of being sunk in distinct sockets; and they
have the form of somewhat flattened prisms, longitudinally ridged
on the outer surface, with an obtusely triangular crown, and
having the enamel crenated on one or both sides. They present
the extraordinary feature that the crowns became worn down flat
by mastication, showing that the _Iguanodon_ employed its teeth
in actually chewing and triturating the vegetable matter on which
it fed. There can therefore be no doubt but that the _Iguanodon_,
in spite of its immense bulk, was an herbivorous Reptile, and lived
principally on the foliage of the Cretaceous forests amongst which
it dwelt. Its size has been variously estimated at from thirty to
fifty feet, the thigh-bone in large examples measuring nearly
five feet in length, with a circumference of twenty-two inches
in its smallest part. With the strong and massive hind-limbs are
associated comparatively weak and small fore-limbs; and there
seems little reason to doubt that the _Iguanodon_ must have walked
temporarily or permanently upon its hind-limbs, after the manner of
a Bird. This conjecture is further supported by the occurrence in
the strata which contain the bones of the _Iguanodon_ of gigantic
three-toed foot-prints, disposed _singly_ in a double track. These
prints have undoubtedly been produced by some animal walking on
two legs; and they can hardly, with any probability, be ascribed
to any other than this enormous Reptile. Closely allied to the
_Iguanodon_ is the _Hadrosaurus_ of the American Cretaceous, the
length of which is estimated at twenty-eight feet. _Iguanodon_
does not appear to have possessed any integumentary skeleton; but
the great _Hyloeosaurus_ of the Wealden seems to have been furnished
with a longitudinal crest of large spines running down the back,
similar to that which is found in the comparatively small Iguanas
of the present day. The _Megalosaurus_ of the Oolites continued
to exist in the Cretaceous period; and, as we have previously
seen, it was carnivorous in its habits. The American _Loelaps_
was also carnivorous, and, like the Megalosaur, which it very
closely resembles, appears to have walked upon its hind-legs,
the fore-limbs being disproportionately small.
[Illustration: Fig. 209.--Teeth of Iguanodon Mantellii. Wealden,
Britain.]
Another remarkable group of Reptiles, exclusively confined to
the Cretaceous series, is that of the _Mosasauroids_, so called
from the type-genus _Mosasaurus_. The first species of _Mosasaurus_
known to science was the _M. Camperi_ (fig. 210), the skull of
which--six feet in length--was discovered in 1780 in the Maestricht
Chalk at Maestricht. As this town stands on the river Meuse,
the name of _Mosasaurus_ ("Lizard of the Meuse") was applied
to this immense Reptile. Of late years the remains of a large
number of Reptiles more or less closely related to _Mosasaurus_, or
absolutely belonging to it, have been discovered in the Cretaceous
deposits of North America, and have been described by Professors
Cope and Marsh. All the known forms of this group appear to have
been of large size--one of them, _Mosasaurus princeps_, attaining
the length of seventy-five or eighty feet, and thus rivalling
the largest of existing Whales in its dimensions. The teeth in
the "Mosasauroids" are long, pointed, and slightly curved; and
instead of being sunk in distinct sockets, they are firmly
amalgamated with the jaws, as in modern Lizards. The palate also
carried teeth, and the lower jaw was so constructed as to allow
of the mouth being opened to an immense width, somewhat as in the
living Serpents. The body was long and snake-like, with a very
long tail, which is laterally compressed, and must have served as
a powerful swimming-apparatus. In addition to this, both pairs
of limbs have the bones connecting them with the trunk greatly
shortened; whilst the digits were enclosed in the integuments,
and constituted paddles, closely resembling in structure the
"flippers" of Whales and Dolphins. The neck is sometimes moderately
long, but oftener very short, as the great size and weight of
the head would have led one to anticipate. Bony plates seem in
some species to have formed an at any rate partial covering to
the skin; but it is not certain that these integumentary appendages
were present in all. Upon the whole, there can be no doubt but
that the Mosasauroid Reptiles--the true "Sea-serpents" of the
Cretaceous period--were essentially aquatic in their habits,
frequenting the sea, and only occasionally coming to the land.
[Illustration: Fig. 210.--Skull of _Mosasaurus Camperi_, greatly
reduced. Maestricht Chalk.]
The "Mosasauroids" have generally been regarded as a greatly
modified group of the Lizards (_Lacertilia_). Whether this reference
be correct or not--and recent investigations render it dubious--the
Cretaceous rocks have yielded the remains of small Lizards not widely
removed from existing forms. The recent order of the _Chelonians_
is also represented in the Cretaceous rocks, by forms closely
resembling living types. Thus the fresh-water deposits of the
Wealden have yielded examples of the "Terrapins" or "Mud-Turtles"
(_Emys_); and the marine Cretaceous strata have been found to
contain the remains of various species of Turtles, one of which
is here figured (fig. 211). No true Serpents (_Ophidia_) have
as yet been detected in the Cretaceous rocks; and this order
does not appear to have come into existence till the Tertiary
period. Lastly, true Crocodiles are known to have existed in
considerable numbers in the Cretaceous period. The oldest of
these occur in the fresh-water deposit of the Wealden; and they
differ from the existing forms of the group in the fact that the
bodies of the vertebræ, like those of the Jurassic Crocodiles,
are bi-concave, or hollowed out at both ends. In the Greensand
of North America, however, occur the remains of Crocodiles which
agree with all the living species in having the bodies of the
vertebræ in the region of the back hollowed out in front and
convex behind.
[Illustration: Fig. 211.--Carapace of _Chelone Benstedi_. Lower
Chalk. (After Owen.)]
_Birds_ have not hitherto been shown, with certainty, to have
existed in Europe during the Cretaceous period, except in a few
instances in which fragmentary remains belonging to this class
have been discovered. The Cretaceous deposits of North America
have, however, been shown by Professor Marsh to contain a
considerable number of the remains of Birds, often in a state
of excellent preservation. Some of these belong to Swimming or
Wading Birds, differing in no point of special interest from
modern birds of similar habits. Others, however, exhibit such
extraordinary peculiarities that they merit more than a passing
notice. One of the forms in question constitutes the genus
_Ichthyornis_ of Marsh, the type-species of which (_I. Dispar_)
was about as large as a Pigeon. In two remarkable respects, this
singular Bird differs from all known living members of the class.
One of these respects concerns the jaws, both of which exhibit the
Reptilian character of being armed with numerous small pointed
_teeth_ (fig. 212, a), sunk in distinct sockets. No existing
bird possesses teeth; and this character forcibly recalls the
Bird-like Pterosaurs, with their toothed jaws. _Ichthyornis_,
however, possessed fore-limbs constructed strictly on the type
of the "wing" of the living Birds; and it cannot, therefore, be
separated from this class. Another extraordinary peculiarity
of _Ichthyornis_ is, that the bodies of the _vertebrie_ (fig.
212, c) were _bi-concave_, as is the case with many extinct
Reptiles and almost all Fishes, but as does not occur in any
living Bird. There can be little doubt that _Ichthyornis_ was
aquatic in its habits, and that it lived principally upon fishes;
but its powerful wings at the same time indicate that it was
capable of prolonged flight. The tail of _Ichthyornis_ has,
unfortunately, not been discovered; and it is at present impossible
to say whether this resembled the tail of existing Birds, or
whether it was elongated and composed of separate vertebræ, as
in the Jurassic _Archoeopteryx_.
Still more wonderful than _Ichthyornis_ is the marvellous bird
described by Marsh under the name of _Hesperornis regalis_. This
presents us with a gigantic diving bird, somewhat resembling the
existing "Loons" (_Colymbus_), but agreeing with _Ichthyornis_
in having the jaws furnished with conical, recurved, pointed
teeth (fig. 212, b). Hence these forms are grouped together in
a new sub-class, under the name of _Odontornithes_ or "Toothed
Birds." The teeth of _Hesperornis_ (fig. 212, d) resemble those
of _Ichthyornis_ in their general form; but instead of being
sunk in distinct sockets, they are simply implanted in a deep
continuous groove in the bony substance of the jaw. The front of
the upper jaw does not carry teeth, and was probably encased in
a horny beak. The breast-bone is entirely destitute of a central
ridge or keel, and the wings are minute and quite rudimentary; so
that _Hesperornis_, unlike _Ichthyornis_, must have been wholly
deprived of the power of flight, in this respect approaching the
existing Penguins. The tail consists of about twelve vertebræ,
of which the last three or four are amalgamated to form a flat
terminal mass, there being at the same time clear indications
that the tail was capable of up and down movement in a vertical
plane, this probably fitting it to serve as a swimming-paddle or
rudder. The legs were powerfully constructed, and the feet were
adapted to assist the bird in rapid motion through the water. The
known remains of _Hesperornis regalis_ prove it to have been a
swimming and diving bird, of larger dimensions than any of the
aquatic members of the class of Birds with which we are acquainted
at the present day. It appears to have stood between five and six
feet high, and its inability to fly is fully compensated for by the
numerous adaptations of its structure to a watery life. Its teeth
prove it to have been carnivorous in its habits, and it probably
lived upon fishes. It is a curious fact that two Birds agreeing
with one another in the wholly abnormal character of possessing
teeth, and in other respects so entirely different, should, like
_Ichthyornis_ and _Hesperornis_, have lived not only in the same
geological period, but also in the same geographical area; and
it is equally curious that the area inhabited by these toothed
Birds should at the same time have been tenanted by winged and
bird-like Reptiles belonging to the toothed genus _Pterodactylus_
and the toothless genus _Pteranodon_.
[Illustration: Fig. 212.--Toothed Birds (_Odontornithes_) of the
Cretaceous Rocks of America. a. Left lower jaw of _Ichthyornis
dispar_, slightly enlarged; b, Left lower jaw of _Hesperornis
regalis_, reduced to nearly one-fourth of the natural size; c.
Cervical vertebra of _Ichthyornis dispar_, front view, twice
the natural size; c', Side view of the same; d, Tooth of
_Hesperornis regalis_, enlarged to twice the natural size. (After
Marsh.)]
No remains of _Mammals_, finally, have as yet been detected in
any sedimentary accumulations of Cretaceous age.
LITERATURE.
The following list comprises some of the more important works and
memoirs which may be consulted with reference to the Cretaceous
strata and their fossil contents:--
(1) 'Memoirs of the Geological Survey of Great Britain.'
(2) 'Geology of England and Wales.' Conybeare and Phillips.
(3) 'Geology of Yorkshire,' vol. ii. Phillips.
(4) 'Geology of Oxford and the Thames Valley.' Phillips.
(5) 'Geological Excursions through the Isle of Wight.' Mantell.
(6) 'Geology of Sussex.' Mantell.
(7) 'Report on Londonderry,' &c. Portlock.
(8) 'Recherches sur le Terrain Crétacé Supérieur de l'Angleterre
et de l'Irlande.' Barrois.
(9) "Geological Survey of Canada"--'Report of Progress, 1872-73.'
(10) 'Geological Survey of California.' Whitney.
(11) 'Geological Survey of Montana, Idaho, Wyoming, and Utah.'
Hayden and Meek.
(12) 'Report on Geology,' &c. (British North American Boundary
Commission). G. M. Dawson.
(13) 'Manual of Geology.' Dana.
(14) 'Lethæa Rossica.' Eichwald.
(15) 'Petrefacta Germaniæ.' Goldfuss.
(16) 'Fossils of the South Downs.' Mantell.
(17) 'Medals of Creation.' Mantell.
(18) 'Mineral Conchology.' Sowerby.
(19) 'Lethæa Geognostica.' Bronn.
(20) 'Malacostracous Crustacea of the British Cretaceous Formation'
(Palæontographical Society). Bell.
(21) 'Brachiopoda of the Cretaceous Formation' (Palæontographical
Society). Davidson.
(22) 'Corals of the Cretaceous Formation' (Palæontographical
Society). Milne-Edwards and Haime.
(23) 'Supplement to the Fossil Corals' (Palæontographical Society).
Martin Duncan.
(24) 'Echinodermata or the Cretaceous Formation' (Palæontographical
Society). Wright.
(25) 'Monograph of the Belemnitidæ' (Palæontographical Society).
Phillips.
(26) 'Monograph of the Trigoniæ' (Palæontographical Society).
Lycett.
(27) 'Fossil Cirripedes' (Palæontographical Society). Darwin.
(28) 'Fossil Mollusca of the Chalk of Britain' (Palæontographical
Society). Sharpe.
(29) 'Entomostraca of the Cretaceous Formation' (Palæontographical
Society). Rupert Jones.
(30) 'Monograph of the Fossil Reptiles of the Cretaceous Formation'
(Palæontographical Society). Owen.
(31) 'Manual of Palæontology.' Owen.
(32) 'Synopsis of Extinct Batrachia and Reptilia.' Cope.
(33) "Structure of the Skull and Limbs in Mosasauroid
Reptiles"--'American Journ. Sci. and Arts, 1872.' Marsh.
(34) "On Odontornithes"--'American Journ. Sci. and Arts, 1875.'
Marsh.
(35) 'Ossemens Fossiles.' Cuvier.
(36) 'Catalogue of Ornithosauria.' Seeley.
(37) 'Paléontologie Française.' D'Orbigny.
(38) 'Synopsis des Echinides fossiles.' Desor.
(39) 'Cat. Raisonné des Echinides.' Agassiz and Desor.
(40) "Echinoids"--'Decades of the Geol. Survey of Britain.'
E. Forbes.
(41) 'Paléontologie Française.' Cotteau.
(42) 'Versteinerungen der Böhmischen Kreide-formation.' Reuss.
(43) "Cephalopoda, Gasteropoda, Pelecypoda, Brachiopoda; &c., of the
Cretaceous Rocks of India"--'Palæontologica Indica,' ser. i.,
iii., v., vi., viii. Stoliczka.
(44) "Cretaceous Reptiles of the United States"--'Smithsonian
Contributions to Knowledge,' vol. xiv. Leidy.
(45) 'Invertebrate Cretaceous, and Tertiary Fossils of the Upper
Missouri Country,' 1876. Meek.
CHAPTER XVIII.
THE EOCENE PERIOD.
Before commencing the study of the subdivisions of the Kainozoic
series, there are some general considerations to be noted. In
the first place, there is in the Old World a complete and entire
physical break between the rocks of the Mesozoic and Kainozoic
periods. In no instance in Europe are Tertiary strata to be found
resting conformably upon any Secondary rock. The Chalk has invariably
suffered much erosion and denudation before the lowest Tertiary
strata were deposited upon it. This is shown by the fact that the
actually eroded surface of the Chalk can often be seen; or, failing
this, that we can point to the presence of the chalk-flints in the
Tertiary strata. This last, of course, affords unquestionable proof
that the Chalk must have been subjected to enormous denudation
prior to the formation of the Tertiary beds, all the chalk itself
having been removed, and nothing left but the flints, while these
are all rolled and rounded. In the continent of North America,
on the other hand, the lowest Tertiary strata have been shown
to graduate downwards conformably with the highest Cretaceous
beds, it being a matter of difficulty to draw a precise line
of demarcation between the two formations.
In the second place, there is a marked break in the _life_ of
the Mesozoic and Kainozoic periods. With the exception of a few
_Foraminifera_, and one _Brachiopod_ (the latter doubtful), no
Cretaceous species is known to have survived the Cretaceous period;
while several characteristic _families_, such as the _Ammonitidoe,
Belemnitidoe_, and _Hippuritidoe_, died out entirely with the
close of the Cretaceous rocks. In the Tertiary rocks, on the
other hand, not only are all the animals and plants more or less
like existing types, but we meet with a constantly-increasing
number of _living species_ as we pass from the bottom of the
Kainozoic series to the top. Upon this last fact is founded the
modern classification of the Kainozoic rocks, propounded by Sil
Charles Lyell.
The absence in strata of Tertiary age of the chambered Cephalopods,
the Belemnites, the _Hippurites_, the _Inocerami_, and the
diversified types of Reptiles which form such conspicuous features
in the Cretaceous fauna, render the palæontological break between
the Chalk and the Eocene one far too serious to be overlooked. At
the same time, it is to be remembered that the evidence afforded
by the explorations carried out of late years as to the animal
life of the deep sea, renders it certain that the extinction
of marine forms of life at the close of the Cretaceous period
was far less extensive than had been previously assumed. It is
tolerably certain, in fact, that we may look upon some of the
inhabitants of the depths of our existing oceans as the direct,
if modified, descendants of animals which were in existence when
the Chalk was deposited.
It follows from the general want of conformity between the Cretaceous
and Tertiary rocks, and still more from the great difference in
life, that the Cretaceous and Tertiary periods are separated, in
the Old World at any rate, by an enormous lapse of unrepresented
time. How long this interval may have been, we have no means of
judging exactly, but it very possibly was as long as the whole
Kainozoic epoch itself. Some day we shall doubtless find, at some
part of the earth's surface, marine strata which were deposited
during this period, and which will contain fossils intermediate
in character between the organic remains which respectively
characterise the Secondary and Tertiary periods. At present, we
have only slight traces of such deposits--as, for instance, the
Maestricht beds, the Faxöe Limestone, and the Pisolitic Limestone
of France.
CLASSIFICATION OF THE TERTIARY ROCKS.--The classification of the
Tertiary rocks is a matter of unusual difficulty, in consequence
of their occurring in disconnected basins, forming a series of
detached areas, which hold no relations of superposition to one
another. The order, therefore, of the Tertiaries in point of
time, can only be determined by an appeal to fossils; and in
such determination Sir Charles Lyell proposed to take as the
basis of classification the _proportion of living or existing
species of Mollusca which occurs in each stratum or group of
strata_. Acting upon this principle, Sir Charles Lyell divides
the Tertiary series into four groups:--
I. The _Eocene_ formation (Gr. _eos_, dawn; _kainos_, new),
containing the smallest proportion of existing species, and being,
therefore, the oldest division. In this classification, only
the _Mollusca_ are taken into account; and it was found that of
these about three and a half per cent were identical with existing
species.
II. The _Miocene_ formation (Gr. _meion_, less; _kainos_, new),
with more recent species than the Eocene, but _less_ than the
succeeding formation, and less than one-half the total number
in the formation. As before, only the _Mollusca_ are taken into
account, and about 17 per cent of these agree with existing species.
III. The _Pliocene_ formation (Gr. _pleion_, more; _kainos_, new),
with generally _more_ than half the species of shells identical
with existing species--the proportion of these varying from 35
to 50 per cent in the lower beds of this division, up to 90 or
95 per cent in its higher portion.
IV. The _Post-Tertiary Formations_, in which all _the shells
belong to existing species_. This, in turn, is divided into two
minor groups--the _Post-Pliocene_ and _Recent Formations_. In
the _Post-Pliocene_ formations, while all the _Mollusca_ belong
to existing species, most of the _Mammals_ belong to extinct
species. In the Recent period, the quadrupeds, as well as the
shells, belong to living species.
The above, with some modifications, was the original classification
proposed by Sir Charles Lyell for the Tertiary rocks, and now
universally accepted. More recent researches, it is true, have
somewhat altered the proportions of existing species to extinct,
as stated above. The general principle, however, of an increase
in the number of living species, still holds good; and this is as
yet the only satisfactory basis upon which it has been proposed
to arrange the Tertiary deposits.
EOCENE FORMATION.
The Eocene rocks are the lowest of the Tertiary series, and comprise
all those Tertiary deposits in which there is only a small proportion
of existing _Mollusca_--from three and a half to five per cent.
The Eocene rocks occur in several basins in Britain, France,
the Netherlands, and other parts of Europe, and in the United
States. The subdivisions which have been established are extremely
numerous, and it is often impossible to parallel those of one
basin with those of another. It will be sufficient, therefore,
to accept the division of the Eocene formation into three great
groups--Lower, Middle, and Upper Eocene--and to consider some of
the more important beds comprised under these heads in Europe
and in North America.
I. EOCENE OF BRITAIN. (1.) LOWER EOCENE.--The base of the Eocene
series in Britain is constituted by about 90 feet of light-coloured,
sometimes argillaceous sands (_Thanet Sands_), which are of marine
origin. Above these, or forming the base of the formation where these
are wanting, come mottled clays and sands with lignite (_Woolwich
and Reading series_), which are estuarine or fluvio-marine in
origin. The highest member of the Lower Eocene of Britain is the
"London Clay," consisting of a great mass of dark-brown or blue
clay, sometimes with sandy beds, or with layers of "septaria,"
the whole attaining a thickness of from 200 to as much as 500
feet. The London Clay is a purely marine deposit, containing
many marine fossils, with the remains of terrestrial animals and
plants; all of which indicate a high temperature of the sea and
tropical or sub-tropical conditions of the land.
(2.) MIDDLE EOCENE.--The inferior portion of the Middle Eocene
of Britain consists of marine beds, chiefly consisting of sand,
clays, and gravels, and attaining a very considerable thickness
(_Bag-shot and Bracklesham beds_). The superior portion of the
Middle Eocene of Britain, on the other hand, consists of deposits
which are almost exclusively fresh-water or brackish-water in
origin (_Headon and Osborne series_).
The chief Continental formations of Middle Eocene age are the
"Calcaire grossier" of the Paris basin, and the "Nummulitic
Limestone" of the Alps.
(3.) UPPER EOCENE.--If the Headon and Osborne beds of the Isle
of Wight be placed in the Middle Eocene, the only British
representatives of the Upper Eocene are the _Bembridge beds_.
These strata consist of limestones, clays, and marls, which have
for the most part been deposited in fresh or brackish water.
II. EOCENE BEDS OF THE PARIS BASIN.--The Eocene strata are very
well developed in the neighbourhood of Paris, where they occupy
a large area or basin scooped out of the Chalk. The beds of this
area are partly marine, partly freshwater in origin; and the
following table (after Sir Charles Lyell) shows their subdivisions
and their parallelism with the English series:--
GENERAL TABLE OF FRENCH EOCENE STRATA.
UPPER EOCENE.
_French Subdivisions._ _English Equivalents._
A. 1. Gypseous series of Mont 1. Bembridge series.
Montmartre.
A. 2. Calcaire silicieux, or 2. Osborne and Headon series.
Travertin Inférieur.
A. 3. Grès de Beauchamp, or 3. White sand and clay of
Sables Moyens. Barton Cliff, Hants.
MIDDLE EOCENE.
B. 1. Calcaire Grossier. 1. Bagshot and Bracklesham beds.
B. 2. Soissonnais Sands, or 2. Wanting.
Lits Coquilliers.
LOWER EOCENE.
C. 1. Argile de Londres at base 1. London clay.
of Hill of Cassel, near
Dunkirk.
C. 2. Argile plastique and 2. Plastic clay and sand with
lignite. lignite (Woolwich and Reading
series).
C. 3. Stables de Bracheux. 3. Thanet sands.
III. EOCENE STRATA OF THE UNITED STATES.--The lowest member of
the Eocene deposits of North America is the so-called "_Lignitic
Formation_," which is largely developed in Mississippi, Tennessee,
Arkansas, Wyoming, Utah, Colorado, and California, and sometimes
attains a thickness of several thousand feet. Stratigraphically,
this formation exhibits the interesting point that it graduates
downwards insensibly and conformably into the Cretaceous, whilst
it is succeeded _uncomformably_ by strata of Middle Eocene age.
Lithologically, the series consists principally of sands and
clays, with beds of lignite and coal, and its organic remains
show that it is principally of fresh-water origin with a partial
intermixture of marine beds. These marine strata of the "Lignitic
formation" are of special interest, as showing such a commingling
of Cretaceous and Tertiary types of life, that it is impossible
to draw any rigid line in this region between the Mesozoic and
Kainozoic systems. Thus the marine beds of the Lignitic series
contain such characteristic Cretaceous forms as _Inoceramus_
and _Ammonites_, along with a great number of Univalves of a
distinctly Tertiary type (Cones, Cowries, &c.) Upon the whole,
therefore, we must regard this series of deposits as affording a
kind of transition between the Cretaceous and the Eocene, holding
in some respects a position which may be compared with that held
by the Purbeck beds in Britain as regards the Jurassic and
Cretaceous.
The Middle Eocene of the United States is represented by the
_Claiborne_ and _Jackson_ beds. The _Claiborne series_ is extensively
developed at Claiborne, Alabama, and consists of sands, clays,
lignites, marls, and impure limestones, containing marine fossils
along with numerous plant-remains. The _Jackson series_ is
represented by lignitic clays and marls which occur at Jackson,
Mississippi. Amongst the more remarkable fossils of this series
are the teeth and bones of Cetaceans of the genus _Zeuglodon_.
Strata of Upper Eocene age occur in North America at Vicksburg,
Mississippi, and are known as the _Vicksburg series_. They consist
of lignites, clays, marls, and limestones. Freshwater deposits
of Eocene age are also largely developed in parts of the Rocky
Mountain region. The most remarkable fossils of these beds are
Mammals, of which a large number of species have been already
determined.
LIFE OF THE EOCENE PERIOD.
The fossils of the Eocene deposits are so numerous that nothing
more can be attempted here than to give a brief and general sketch
of the life of the period, special attention being directed to some
of the more prominent and interesting types, amongst which--as
throughout the Tertiary series--the Mammals hold the first place.
It is not uncommon, indeed, to speak of the Tertiary period as a
whole under the name of the "Age of Mammals," a title at least
as well deserved as that of "Age of Reptiles" applied to the
Mesozoic, or "Age of Molluscs" applied to the Palæozoic epoch.
As regards the _plants_ of the Eocene, the chief point to be
noticed is, that the conditions which had already set in with
the commencement of the Upper Cretaceous, are here continued,
and still further enforced. The _Cycads_ of the Secondary period,
if they have not totally disappeared, are exceedingly rare; and
the _Conifers_, losing the predominance which they enjoyed in the
Mesozoic, are now relegated to a subordinate though well-defined
place in the terrestrial vegetation. The great majority of the
Eocene plants are referable to the groups of the Angiospermous
Exogens and the Monocotyledons; and the vegetation of the period,
upon the whole, approximates closely to that now existing upon
the earth. The plants of the European Eocene are, however, in the
main most closely allied to forms which are now characteristic
of tropical or sub-tropical regions. Thus, in the London Clay
are found numerous fruits of Palms (_Napdites_, fig. 213), along
with various other plants, most of which indicate a warm climate
as prevailing in the south of England at the commencement of the
Eocene period. In the Eocene strata of North America occur numerous
plants belonging to existing types--such as Palms, Conifers,
the Magnolia, Cinnamon, Fig. Dog-wood, Maple, Hickory, Poplar,
Plane, &c. Taken as a whole, the Eocene flora of North America
is nearly related to that of the Miocene strata of Europe, as
well as to that now existing in the American area. We conclude,
therefore, that "the forests of the American Eocene resembled
those of the European Miocene, and even of modern America" (Dana).
[Illustration: Fig. 213.--_Napadites ellipticus_, the fruit of
a fossil Palm. London Clay, Isle of Sheppey.]
As regards the _animals_ of the Eocene period, the _Protozoans_
are represented by numerous _Foraminifera_, which reach here their
maximum of development, both as regards the size of individuals and
the number of generic types. Many of the Eocene Foraminifers are of
small size; but even these not uncommonly form whole rock-masses.
Thus, the so-called "Miliolite Limestone" of the Paris basin, largely
used as a building-stone, is almost wholly composed of the shells
of a small species of _Miliola_. The most remarkable, however, of
the many members of this group of animals which flourished in
Eocene times, are the "Nummulites" (_Nummulina_), so called from
their resemblance in shape to coins (Lat. _nummus_, a coin). The
Nummulites are amongst the largest of all known _Foraminifera_,
sometimes attaining a size of three inches in circumference;
and their internal structure is very complex (fig. 214). Many
species are known, and they are particularly characteristic of
the Middle and Upper of these periods--their place being sometimes
taken by _Orbitoides_, a form very similar to the Nummulite in
external appearance, but differing in its internal details. In
the Middle Eocene, the remains of Nummulites are found in vast
numbers in a very widely-spread and easily-recognised formation
known as the "Nummulitic Limestone" (fig. 10). According to Sir
Charles Lyell, "the Nummulitic Limestone of the Swiss Alps rises
to more than 10,000 feet above the level of the sea, and attains
here and in other mountain-chains a thickness of several thousand
feet. It may be said to play a far more conspicuous part than
any other Tertiary group in the solid framework of the earth's
crust, whether in Europe, Asia, or Africa. It occurs in Algeria
and Morocco, and has been traced from Egypt, where it was largely
quarried of old for the building of the Pyramids, into Asia Minor,
and across Persia by Bagdad to the mouths of the Indus. It has
been observed not only in Cutch, but in the mountain-ranges which
separate Scinde from Persia, and which form the passes leading
to Cabul; and it has been followed still further eastward into
India, as far as Eastern Bengal and the frontiers of China."
The shells of Nummulites have been found at an elevation of 16,500
feet above the level of the sea in Western Thibet; and the
distinguished and philosophical geologist just quoted, further
remarks, that "when we have once arrived at the conviction that
the Nummulitic formation occupies a middle and upper place in the
Eocene series, we are struck with the comparatively modern date to
which some of the greatest revolutions in the physical geography
of Europe, Asia, and Northern Africa must be referred. All the
mountain-chains--such as the Alps, Pyrenees, Carpathians, and
Himalayas--into the composition of whose central and loftiest parts
the Nummulitic strata enter bodily, could have had no existence
till after the Middle Eocene period. During that period, the
sea prevailed where these chains now rise; for Nummulites and
their accompanying Testacea were unquestionably inhabitants of
salt water."
[Illustration: Fig. 214.--_Nummulina loevigata_. Middle Eocene.]
The _Coelenterates_ of the Eocene are represented principally
by _Corals_, mostly of types identical with or nearly allied to
those now in existence. Perhaps the most characteristic group
of these is that of the _Turbinolidoe_, comprising a number of
simple "cup-corals," which probably lived in moderately deep
water. One of the forms belonging to this family is here figured
(fig. 215). Besides true Corals, the Eocene deposits have yielded
the remains of the "Sea-pens" (_Pennatulidoe_) and the branched
skeletons of the "Sea-shrubs" (_Gorgontidoe_).
The _Echinoderms_ are represented principally by Sea-urchins, and
demand nothing more than mention. It is to be observed, however,
that the great group of the Sea-lilies (_Crinoids_) is now verging
on extinction, and is but very feebly represented.
Amongst the _Mollusca_, the _Polyzoans_ and _Brachiopods_ also
require no special mention, beyond the fact that the latter are
greatly reduced in numbers, and belong principally to the existing
genera _Terebratula_ and _Rhynchonella_. The Bivalves
(_Lamellibranchs_) and the Univalves (_Gasteropods_) are exceedingly
numerous, and almost all the principal existing genera are now
represented; though less than five percent of the Eocene _species_
are identical with those now living. It is difficult to make any
selection from the many Bivalves which are known in deposits of
this age; but species of _Cardita, Crassatella, Leda, Cyrena, Mactra,
Cardium, Psammobia_, &c., may be mentioned as very characteristic.
The _Caradita planicosta_ here figured (fig. 216) is not only very
abundant in the Middle Eocene, but is very widely distributed,
ranging from Europe to the Pacific coast of North America. The
_Univalves_ of the Eocene are extremely numerous, and generally
beautifully preserved. The majority of them belong to that great
section of the _Gasteropods_ in which the mouth of the shell
is notched or produced into a canal (when the shell is said to be
"siphonostomatous")--this section including the carnivorous and
most highly-organized groups of the class. Not only is this the
case, but a large number of the Eocene Univalves belong to types
which now attain their maximum of development in the warmer regions
of the globe. Thus we find numerous species of Cones (_Conus_),
Volutes (_Voluta_), Cowries (_Cyproea_, fig. 218), Olives and
Rice-shells (_Oliva_), Mitre-shells (_Mitra_), Trumpet-shells
(_Triton_), Auger-shells (_Terebra_), and Fig-shells (_Pyrula_).
Along with these are many forms of _Pleurotoma, Rostellaria_,
Spindle-shells (_Fusus_), Dog-whelks (_Nassa_), _Murices_, and
many round-mouthed ("holostomatous") species, belonging to such
genera as _Turritella, Nerita, Natica, Scalaria_, &c. The genus
_Cerithium_ (fig. 219), most of the living forms of which are found
in warm regions, inhabiting fresh or brackish waters, undergoes a
vast development in the Eocene period, where it is represented
by an immense number of specific forms, some of which attain
very large dimensions. In the Eocene strata of the Paris basin
alone, nearly one hundred and fifty species of this genus have been
detected. The more strictly fresh-water deposits of the Eocene
period have also yielded numerous remains of Univalves such as
are now proper to rivers and lakes, together with the shells of
true Land-snails. Amongst these may be mentioned numerous species
of _Limnoea_ (fig. 220), _Physa_ (fig. 221), _Melania, Paludina,
Planorbis, Helix, Bulimus_, and _Cyclostoma_ (fig. 222).
[Illustration: Fig. 215.--_Turbinolia sulcata_, viewed from one
side, and from above. Eocene.]
[Illustration: Fig. 216.--_Cardita planicosta_. Middle Eocene.]
[Illustration: Fig. 217.--_Typhis tubifer_, a "siphonostomatous"
Univalve. Eocene.]
[Illustration: Fig. 218.--Cyproea elegans. Eocene.]
[Illustration: Fig. 219.--_Cerithium hexagonum_. Eocene.]
With regard to the _Cephalopods_, the chief point to be noticed
is, that all the beautiful and complex forms which peculiarly
characterised the Cretaceous period have here disappeared. We no
longer meet with a single example of the Turrilite, the Baculite,
the Hamite, the Scaphite, or the Ammonite. The only exception
to this statement is the occurrence of one species of Ammonite
in the so-called "Lignitic Formation" of North America; but the
beds containing this may possibly be rather referable to the
Cretaceous--and this exception does not affect the fact that
the _Ammonitidoe_, as a family, had become extinct before the
Eocene strata were deposited. The ancient genus _Nautilus_ still
survives, the sole representative of the once mighty order of the
Tetrabranchiate Cephalopods. In the order of the _Dibranchiates_,
we have a like phenomenon to observe in the total extinction
of the great family of the "Belemnites." No form referable to
this group has hitherto been found in any Tertiary stratum; but
the internal skeletons of Cuttle-fishes (such as _Belosepia_)
are not unknown.
[Illustration: Fig. 220.--_Limnoea pyramidalis_. Eocene.]
[Illustration: Fig. 221.--_Physa columnaris_. Eocene.]
[Illustration: Fig. 222.--_Cyclostoma Arnoudii_. Eocene.]
Remains of _Fishes_ are very abundant in strata of Eocene age,
especially in certain localities. The most famous depot for the
fossil fishes of this period is the limestone of Monte Bolca,
near Verona, which is interstratified with beds of volcanic ashes,
the whole being referable to the Middle Eocene. The fishes here
seem to have been suddenly destroyed by a volcanic eruption,
and are found in vast numbers. Agassiz has described over one
hundred and thirty species of Fishes from this locality, belonging
to seventy-seven genera. All the _species_ are extinct; but about
one-half of the _genera_ are represented by living forms. The
great majority of the Eocene Fishes belong to the order of the
"Bony Fishes" (_Teleosteans_), so that in the main the forms
of Fishes characterising the Eocene are similar to those which
predominate in existing seas. In addition to the above, a few
_Ganoids_ and a large number of _Placoids_ are known to occur
in the Eocene rocks. Amongst the latter are found numerous teeth
of true Sharks, such as _Otodus_ (fig. 224) and _Carcharodon_.
The pointed and serrated teeth of the latter sometimes attain
a length of over half a foot, indicating that these predaceous
fishes attained gigantic dimensions; and it is interesting to
note that teeth, in external appearance very similar to those
of the early Tertiary genus _Carcharodon_, have been dredged
from great depths during the recent expedition of the Challenger.
There also occur not uncommonly the flattened teeth of Rays (fig.
225), consisting of flat bony pieces placed close together, and
forming "a kind of mosaic pavement on both the upper and lower
jaws" (Owen).
[Illustration: Fig. 223.--_Rhombus minimus_, a small fossil Turbot
from the Eocene Tertiary, Monte Bolca.]
[Illustration: Fig. 224.--Tooth of _Otodus obliquus_. Eocene.]
[Illustration: Fig. 225.--Flattened dental plates of a Ray
(_Myliobatis Edwardsii_). Eocene.]
In the class of the _Reptiles_, the disappearance of the
characteristic Mesozoic types is as marked a phenomenon as the
introduction of new forms. The Ichthyosaurs, the Plesiosaurs,
the Pterosaurs, and the Mosasaurs of the Mesozoic, find no
representatives in the Eocene Tertiary; and the same is true of the
Deinosaurs, if we except a few remains from the doubtfully-situated
"Lignitic formation" of the United States, On the other hand, all
the modern orders of Reptiles are known to have existed during
the Eocene period. The _Chelonians_ are represented by true marine
Turtles, by "Terrapins" (_Emydidoe_), and by "Soft Tortoises"
(_Trionycidoe_). The order of the Snakes and Serpents (_Ophidia_)
makes its appearance here, for the first time under several
forms--all of which, however, are referable to the non-venomous
group of the "Constricting Serpents" (_Boidoe_). The oldest of
these is the _Paloeophis toliapicus_ of the London Clay of Sheppey,
first made known to science by the researches of Professor Owen.
The nearly-allied _Paloeophis typhoeus_ of the Eocene beds of
Bracklesham appears to have been a Boa-constrictor-like Snake
of about twenty feet in length. Similar Python-like Snakes
(_Paloeophis, Dinophis_, &c.) have been described from the Eocene
deposits of the United States. True Lizards (_Lacertilians_)
are found in some abundance in the Eocene deposits,--some being
small terrestrial forms, like the common European lizards of the
present day; whilst others equal or exceed the living Monitors
in size. Lastly, the modern order of the _Crocodilia_ is largely
represented in Eocene times, by species belonging to all the
existing genera, together with others referable to extinct types.
As pointed out by Owen, it is an interesting fact that in the
Eocene rocks of the south-west of England, there occur fossil
remains of all the three living types of Crocodilians--namely, the
Gavials, the true Crocodiles, and the Alligators (fig. 226)--though
at the present day these forms are all geographically restricted
in their range, and are never associated together.
[Illustration: Fig. 226.--Upper jaw of Alligator. Eocene Tertiary,
Isle of Wight.]
Almost all the existing orders of _Birds_, if not all, are
represented in the Eocene deposits by remains often very closely
allied to existing types. Thus, amongst the Swimming Birds
(_Natatores_) we find examples of forms allied to the living
Pelicans and Mergansers; amongst the Waders (_Grallatores_) we
have birds resembling the Ibis (the _Numenius gypsorum_ of the
Paris basin); amongst the Running Birds (_Cursores_) we meet with
the great _Gastornis Parisiensis_, which equalled the African
Ostrich in height, and the still more gigantic _Dasornis
Londinensis_; remains of a Partridge represent the Scratching
Birds (_Rasores_); the American Eocene has yielded the bones of
one of the Climbing Birds (_Scansores_), apparently referable
to the Woodpeckers; the _Protornis Glarisiensis_ of the Eocene
Schists of Glaris is the oldest known example of the Perching
Birds (_Insessores_); and the Birds of Prey (_Raptores_) are
represented by Vultures, Owls, and Hawks. The toothed Birds of
the Upper Cretaceous are no longer known to exist; but Professor
Owen has recently described from the London Clay the skull of a very
remarkable Bird, in which there is, at any rate, an approximation
to the structure of _Ichthyornis_ and _Hesperornis_. The bird
in question has been named the _Odontopteryx totiapicus_, its
generic title being derived from the very remarkable characters
of its jaws. In this singular form (fig. 227) the margins of
both jaws are furnished with tooth-like denticulations, which
differ from true teeth in being actually portions of the bony
substance of the jaw itself, with which they are continuous, and
which were probably encased by extensions of the horny sheath
of the bill. These tooth-like processes are of two sizes, the
larger ones being comparable to canines; and they are all directed
forwards, and have a triangular or compressed conical form. From
a careful consideration of all the discovered remains of this
bird, Professor Owen concludes that "_Odontopteryx_ was a
warm-blooded feathered biped, with wings; and further, that it
was web-footed and a fish-eater, and that in the catching of
its slippery prey it was assisted by this Pterosauroid armature
of its jaws." Upon the whole, _Odontopteryx_ would appear to be
most nearly related to the family of the Geese (_Anserinoe_)
or Ducks (_Anatidoe_); but the extension of the bony substance
of the jaws into tooth-like processes is an entirely unique
character, in which it stands quite alone.
[Illustration: Fig. 227.--Skull of _Odontopteryx toliapicus restored.
(After Owen.)]
The known _Mammals_ of the Mesozoic period, as we have seen,
are all of small size; and with one not unequivocal exception,
they appear to be referable to the order of the Pouched Quadrupeds
(_Marsupials_), almost the lowest group of the whole class of
the Mammalia. In the Eocene rocks, on the other hand, numerous
remains of Quadrupeds have been brought to light, representing
most of the great Mammalian orders now in existence upon the
earth, and in many cases indicating animals of very considerable
dimensions. We are, in fact, in a position to assert that the
majority of the great groups of Quadrupeds with which we are
familiar at the present day were already in existence in the
Eocene period, and that their ancient root-stocks were even in
this early time separated by most of the fundamental differences
of structure which distinguish their living representatives.
At the same time, there are some amongst the Eocene quadrupeds
which have a "generalised" character, and which may be regarded
as structural types standing midway between groups now sharply
separated from one another.
The order of the _Marsupials_--including the existing Kangaroos,
Wombats, Opossums, Phalangers, &c.--is poorly represented in
deposits of Eocene age. The most celebrated example of this group
is the _Didelphys gypsorum_ of the Gypseous beds of Montmartre,
near Paris, an Opossum very nearly allied to the living Opossums
of North and South America.
No member of the _Edenates_ (Sloths, Ant-eaters, and Armadillos)
has hitherto been detected in any Eocene deposit. The aquatic order
of the _Sirenians_ (Dugongs and Manatees), with their fish-like
bodies and tails, paddle-shaped forelimbs, and wholly deficient
hind-limbs, are represented in strata of this age by remains of
the ancient "Sea-Cows," to which the name of _Halitherium_ has
been applied. Nearly allied to the preceding is the likewise aquatic
order of the Whales and Dolphins (_Cetaceans_), in which the body
is also fish-like, the hind-limbs are wanting, the fore-limbs are
converted into powerful "flippers" or swimming-paddles, and the
terminal extremity of the body is furnished with a horizontal,
tail-fin. Many existing Cetaceans (such as the Whalebone Whales)
have no true teeth; but others (Dolphins, Porpoises, Sperm Whales)
possess simple conical teeth. In strata of Eocene age, however, we
find a singular group of Whales, constituting the genus _Zeuglodon
(fig. 228), in which the teeth differed from those of all existing
forms in being of two kinds,--the front ones being conical incisors,
whilst the back teeth or molars have serrated triangular crowns,
and are inserted in the jaw by two roots. Each molar (fig. 228,
A) looks as if it were composed of two separate teeth united on
one side by their crowns; and it is this peculiarity which is
expressed by the generic name (Gr. _zeugle_, a yoke; _odous_,
tooth). The best-known species of the genus is the _Zeuglodon
cetoides_ of Owen, which attained a length of seventy feet. Remains
of these gigantic Whales are very common in the "Jackson Beds" of
the Southern United States. So common are they that, according
to Dana, "the large vertebræ, some of them a foot and a half
long and a foot in diameter, were formerly so abundant over the
country, in Alabama, that they were used for making walls, or
were burned to rid the fields of them."
[Illustration: Fig. 228.--_Zeuglodon cetoides_. A, Molar tooth of
the natural size; B, Vertebra, reduced in size. From the Middle
Eocene of the United States. (After Lyell.)]
The great and important order of the Hoofed Quadrupeds (_Ungulata_)
is represented in the Eocene by examples of both of its two principal
sections--namely, those with an uneven number of toes (one or three)
on the foot (_Perissodactyle Ungulates_), and those with an even
number of toes (two or four) to each foot (_Artiodactyle Ungulates_).
Amongst the Odd-toed Ungulates, the living family of the Tapirs
(_Tapirdoe_) is represented by the genus _Coryphodon_ of Owen.
Nearly related to the preceding are the species of _Paloeotherium_,
which have a historical interest as being amongst the first of
the Tertiary Mammals investigated by the illustrious Cuvier.
Several species of _Paloeothere_ are known, varying greatly in
size, the smallest being little bigger than a hare, whilst the
largest must have equalled a good-sized horse in its dimensions. The
species of _Paloeotherium_ appear to have agreed with the existing
Tapirs in possessing a lengthened and flexible nose, which formed
a short proboscis or trunk (fig. 229), suitable as an instrument
for stripping off the foliage of trees--the characters of the
molar teeth showing them to have been strictly herbivorous in
their habits. They differ, however, from the Tapirs, amongst
other characters, in the fact that both the fore and the hind
feet possessed three toes each; whereas in the latter there are
four toes on each fore-foot, and the hind-feet alone are three-toed.
The remains of _Paloeotheria_ have been found in such abundance in
certain localities as to show that these animals roamed in great
herds over the fertile plains of France and the south of England
during the later portion of the Eocene period. The accompanying
illustration (fig. 229) represents the notion which the great
Cuvier was induced by his researches to form as to the outward
appearance of _Paloeotherium magnum_. Recent discoveries, however,
have rendered it probable that this restoration is in some important
respects inaccurate. Instead of being bulky, massive, and more
or less resembling the living Tapirs in form, it would rather
appear that _Paloeotherium magnum_ was in reality a slender,
graceful, and long-necked animal, more closely resembling in
general figure a Llama, or certain of the Antelopes.
[Illustration: Fig. 229.--Outline of _Paloeotherium magnum_,
restored. Upper Eocene, Europe. (After Cuvier.)]
The singular genus _Anchitherium_ forms a kind of transition
between the _Paloeotheria_ and the true Horses (_Equidoe_). The
Horse (fig. 230, D) possesses but one fully-developed toe to
each foot, this being terminated by a single broad hoof, and
representing the _middle_ toe--the _third_ of the typical
five-fingered or five-toed limb of Quadrupeds in general. In
addition, however, to this fully-developed toe, each foot in the
horse carries two rudimentary toes which are concealed beneath the
skin, and are known as the "splint-bones." These are respectively
the _second_ and _fourth_ toes, in an aborted condition; and the
first and fifth toes are wholly wanting. In _Hipparion_ (fig.
230, C), the foot is essentially like that of the modern Horses,
except that the second and fourth toes no longer are mere
"splint-bones," hidden beneath the skin; but have now little
hoofs, and hang freely, but uselessly, by the side of the great
middle toe, not being sufficiently developed to reach the ground.
In _Anchitherium_, again (fig. 230, B), the foot is three-toed,
like that of _Hipparion_; but the two lateral toes (the second
and fourth) are so far developed that they now reach the ground.
The _first_ digit (thumb or great toe) is still wanting; as also
is the _fifth_ digit (little finger or little toe). Lastly, the
Eocene rocks have yielded in North America the remains of a small
Equine quadruped, to which Marsh has given the name of _Orohippus_.
In this singular form--which was not larger than a fox--the foot
(fig. 230, A) carries _four_ toes, all of which are hoofed and touch
the ground, but of which the _third_ toe is still the largest. The
_first_ toe (thumb or great toe) is still wanting; but in this
ancient representative of the Horses, the _fifth_ or "little"
toe appears for the first time. As all the above-mentioned forms
succeed one another in point of time, it may be regarded as probable
that we shall yet be able to point, with some certainty, to some
still older example of the _Equidoe_, in which the first digit
is developed, and the foot assumes its typical five-fingered
condition.
[Illustration: Fig. 230.--Skeleton of the foot in various forms
belonging to the family of the _Equidoe_. A, Foot of _Orohippus_,
Eocene; B, Foot of _Anchitherium, Upper Eocene and Lower Miocene;
C, Foot of _Hipparion_, Upper Miocene and Pliocene: D, Foot of
Horse (_Equus_), Pliocene and Recent. The figures indicate the
numbers of the digits in the typical five-fingered hand of Mammals.
(After Marsh.)]
Passing on to the Even-toed or _Artiodactyle Ungulates_, no
representative of the _Hippotamus_ seems yet to have existed, but
there are several forms (_Choeropotamus, Hyopotamus_, &c.) more
or less closely allied to the Pigs (_Suida_); and the singular
group of the _Anoplotheridoe_ may be regarded as forming a kind of
transition between the Swine and the Ruminants. The _Anoplotheria_
(fig. 231) were slender in form, the largest not exceeding a
donkey in size, with long tails, and having the feet terminated
by two hoofed toes each, sometimes with a pair of small accessory
hoofs as well. The teeth exhibit the peculiarity that they are
arranged in a continuous series, without any gap or interval
between the molars and the canines; and the back teeth, like
those of all the Ungulates, are adapted for grinding vegetable
food, their crowns resembling in form those of the true Ruminants.
The genera _Dichobune_ and _Xiphodon_, of the Middle and Upper
Eocene, are closely related to _Anoplotherium_, but are more
slender and deer-like in form. No example of the great Ruminant
group of the Ungulate Quadrupeds has as yet been detected in
deposits of Eocene age.
[Illustration: Fig. 231.--_Anoplotherium commune_. Eocene Tertiary,
France. (After Cuvier.)]
Whilst true Ruminants appear to be unknown, the Eocene strata
of North America have yielded to the researches of Professor
Marsh examples of an extraordinary group (_Dinocerata_), which
may be considered as in some respects intermediate between the
Ungulates and the Proboscideans. In _Dinoceras_ itself (fig.
232) we have a large animal, equal in dimensions to the living
Elephants, which it further resembles in the structure of the
massive limbs, except that there are only four toes to each foot.
The upper jaw was devoid of front teeth, but there were two very
large canine teeth, in the form of tusks directed perpendicularly
downwards; and there was also a series of six small molars on each.
Each upper jaw-bone carried a bony projection, which was probably
of the nature of a "horn-core," and was originally sheathed in
horn. Two similar, but smaller, horn-cores are carried on the
nasal bones; and two much larger projections, also probably of
the nature of horn-cores, were carried upon the forehead. We may
thus infer that _Dinoceras_ possessed three pairs of horns, all
of which resembled the horns of the Sheep and Oxen in consisting
of a central bony "core," surrounded by a horny sheath. The nose
was not prolonged into a proboscis or "trunk," as in the existing
Elephants; and the tail was short and slender. Many forms of
the _Dinocerata_ are known; but all these singular and gigantic
quadrupeds appear to have been confined to the North American
continent, and to be restricted to the Eocene period.
[Illustration: Fig. 232.--Skull of _Dinoceras mirabilis_, greatly
reduced. Eocene, North America. (After Marsh.)]
The important order of the Elephants (_Proboscidea_) is also not
known to have come into existence during the Eocene period. On the
other hand, the great order of the Beasts of Prey (_Carnivora_)
is represented in Eocene strata by several forms belonging to
different types. Thus the _Ardocyon_ presents us with an Eocene
Carnivore more or less closely allied to the existing Racoons;
the _Paloeonyctis_ appears to be related to the recent Civet-cats;
the genus _Hyoenodon_ is in some respects comparable to the living
Hyænas; and the _Canis Parisiensis_ of the gypsum-bearing beds
of Montmartre may perhaps be allied to the Foxes.
[Illustration: Fig. 233.--Portion of the skeleton of _Vespertilio
Parisienis_. Eocene Tertiary, France.]
The order of the Bats (_Cheiroptera_) is represented in Eocene
strata of the Paris basin (Gypseous series of Montmartre) by
the _Vespertilio Parisiensis_ (fig. 233), an insect-eating Bat
very similar to some of the existing European forms. Lastly, the
Eocene deposits have yielded more or less satisfactory evidence
of the existence in Europe at this period of examples of the
orders of the Gnawing Mammals (_Rodentia_), the Insect-eating
Mammals (_Insectivora_), and the Monkeys (_Quadrumana_).[24]
[Footnote 24: A short list of the more important works relating to
the Eocene rocks and fossils will be given after all the Tertiary
deposits have been treated of.]
CHAPTER XIX.
THE MIOCENE PERIOD.
The Miocene rocks comprise those Tertiary deposits which contain
less than about 35 per cent of existing species of shells
(_Mollusca_), and more than 5 per cent--or those deposits in
which the proportion of living shells is less than of extinct
species. They are divisible into a _Lower Miocene_ (_Oligocene_)
and an _Upper Miocene_ series.
In _Britain_, the Miocene rocks are very poorly developed, one
of their leading developments being at Bovey Tracy in Devonshire,
where there occur sands, clays, and beds of lignite or imperfect
coal. These strata contain numerous plants, amongst which are
Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially
those belonging to the genus Sequoia (the "Red-Foods"). These
Bovey Tracy lignites are of Lower Miocene age, and they are
lacustrine in origin. Also of Lower Miocene age are the so-called
"Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a
thickness of less than 200 feet, and are shown by their numerous
fossils to be principally a true marine formation. Lastly, the
Duke of Argyll, in 1851, showed that there existed at Ardtun, in
the island of Mull, certain Tertiary strata containing numerous
remains of plants; and these also are now regarded as belonging
to the Lower Miocene.
In _France_, the Lower Miocene is represented in Auvergne, Cantal,
and Velay, by a great thickness of nearly horizontal strata of
sands, sandstone, clays, marls, and limestones, the whole of
fresh-water origin. The principal fossils of these lacustrine
deposits are _Mammalia_, of which the remains occur in great
abundance. In the valley of the Loire occur the typical European
deposits of Upper Miocene age. These are known as the "Faluns,"
from a provincial term applied to shelly sands, employed to spread
upon soils which are deficient in lime; and the Upper Miocene
is hence sometimes spoken of as the "Falunian" formation. The
Faluns occur in scattered patches, which are rarely more than 50
feet in thickness, and consist of sands and marls. The fossils
are chiefly marine; but there occur also land and fresh-water
shells, together with the remains of numerous Mammals. About 25
per cent of the shells of the Faluns are identical with existing
species. The sands, limestones, and marls of the Department of
Gers, near the base of the Pyrenees, rendered famous by the number
or Mammalian remains exhumed from them by M. Lartet, also belong
to the age of the Faluns.
In _Switzerland_, between the Alps and the Jura, there occurs
a great series of Miocene deposits, known collectively as the
"Molasse," from the soft nature of a greenish sandstone, which
constitutes one of its chief members. It attains a thickness of
many thousands of feet, and rises into lofty mountains, some
of which--as the Rigi--are more than 6000 feet in height. The
middle portion of the Molasse is of marine origin, and is shown
by its fossils to be of the age of the Faluns; but the lower
and upper portions of the formation are mainly or entirely of
fresh-water origin. The Lower Molasse (of Lower Miocene age)
has yielded about 500 species of plants, mostly of tropical or
sub-tropical forms. The Upper Molasse has yielded about the same
number of plants, with about 900 species of Insects, such as
wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c.
In _Belgium_, strata of both Lower and Upper Miocene age are
known,--the former (_Rupelian Clays_) containing numerous marine
fossils; whilst the latter (_Bolderberg Sands_) have yielded
numerous shells corresponding with those of the Faluns.
In _Austria_, Miocene strata are largely developed, marine beds
belonging to both the Lower and Upper division of the formation
occurring extensively in the Vienna basin. The well-known Brown
Coals of Radaboj, in Croatia, with numerous plants and insects,
are also of Lower Miocene age.
In _Germany_, deposits belonging to both the Lower and Upper
division of the Miocene formation are extensively developed.
To the former belong the marine strata of the Mayence basin,
and the marine _Rupelian Clay_ near Berlin; whilst a celebrated
group of strata belonging to the Upper Miocene occurs near
Epplesheim, in Hesse-Darmstadt, and is well known for the number
of its Mammalian remains.
In _Greece_, at Pikermé, near Athens, there occurs a celebrated
deposit of Upper Miocene age, well known to palæontologists through
the researches of M. M. Wagner, Roth, and Gaudry upon the numerous
Mammalia which it contains. In _Italy_, also, strata of both Lower
and Upper Miocene age are well developed in the neighbourhood
of Turin.
In the _Siwâlik Hills_, in India, at the southern foot of the
Himalayas, occurs a series of Upper Miocene strata, which have
become widely celebrated through the researches of Dr Falconer
and Sir Proby Cautley upon the numerous remains of Mammals and
Reptiles which they contain. Beds of corresponding age, with
similar fossils, are known to occur in the island of Perim in
the Gulf of Cambay.
Lastly, Miocene deposits are found in _North America_, in New
Jersey, Maryland, Virginia, Missouri, California, Oregon, &c.,
attaining a thickness of 1500 feet or more. They consist principally
of clays, sands, and sandstones, sometimes of marine and sometimes
of fresh-water origin. Near Richmond, in Virginia, there occurs a
remarkable stratum, wrongly called "Infusorial Earth," which is
occasionally 30 feet in thickness, and consists almost wholly of
the siliceous envelopes of certain low forms of plants (Diatoms),
along with the spicules of Sponges and other siliceous organisms
(see fig. 16). The _White River Group_ of Hayden occurs in the
Upper Missouri region, and is largely exposed over the barren
and desolate district known as the "Mauvaises Terres." They have
a thickness of 1000 feet or more, and contain numerous remains
of Mammals. They are of lacustrine origin, and are believed to
be of the age of the Lower Miocene. Upon the whole, about from
15 to 30 per cent of the _Mollusca_ of the American Miocene are
identical with existing species.
In addition to the regions previously enumerated, Miocene strata
are known to be developed in _Greenland, Iceland, Spitzbergen_,
and in other areas of less importance.
The _life_ of the Miocene period is extremely abundant, and, from
the nature of the deposits of this age, also extremely varied
in its character. The marine beds of the formation have yielded
numerous remains of both Vertebrate and Invertebrate sea-animals;
whilst the fresh-water deposits contain the skeletons of such
shells, fishes, &c., as now inhabit rivers or lakes. Both the
marine and the lacustrine beds have been shown to contain an
enormous number of plants, the latter more particularly; whilst
the Brown Coals of the formation are made up of vegetable matter
little altered from its original condition. The remains of
air-breathing animals, such as Insects, Reptiles, Birds, and
Mammals, are also abundantly found, more especially in the
fresh-water beds.
The _plants_ of the Miocene period are extraordinarily numerous,
and only some of the general features of the vegetation of this
epoch can be indicated here. Our chief sources of information as
to the Miocene plants are the Brown Coals of Germany and Austria,
the Lower and Upper Molasse of Switzerland, and the Miocene strata
of the Arctic regions. The lignites of Austria have yielded very
numerous plants, chiefly of a tropical character--one of the
most noticeable forms being a Palm of the genus _Sabal_ (fig.
234, B), now found in America. The plants of the Lower Miocene of
Switzerland are also mostly of a tropical character, but include
several forms now found in North America, such as a Tulip-tree
(_Liriodendron_) and a Cypress (_Taxodium_). Amongst the more
remarkable forms from these beds may be mentioned Fan-Palms
(_Chamoerops_, fig 234, A), numerous tropical ferns, and two
species of Cinnamon. The plant-remains of the Upper Molasse of
Switzerland indicate an extraordinarily rank and luxuriant
vegetation, composed mainly of plants which now live in warm
countries. Among the commoner plants of this formation may be
enumerated many species of Maple (_Acer_), Plane-trees (_Platanus_
fig. 235), Cinnamon-trees (fig. 236), and other members of the
_Lauraceoe_, many species of _Proteaccoe_ (_Banksia, Grevillea_,
&c.), several species of Sarsaparilla (_Smilax_), Palms, Cypresses,
&c.
[Illustration: Fig. 234.--Miocene Palms A, _Chamoerops Helvetica_;
B, _Sabal major_. Lower Miocene of Switzerland and France.]
[Illustration: Fig. 235.--_Platanus aceroides_, an Upper Miocene
Plane-tree. a, Leaf; b, The core of a bundle of fruits; c,
A single fruit.]
[Illustration: Fig. 236.--_Cinnamomum polymorphum_. a, Leaf;
b, Flower. Upper Miocene.]
In Britain, the Lower Miocene strata of Bovey Tracy have yielded
remains of Ferns, Vines, Fig, Cinnamon, _Proteaccoe_, &c., along
with numerous Conifers. The most abundant of these last is a
gigantic pine--the _Sequoia Couttsioe_--which is very nearly
allied to the huge _Sequoia_ (_Wellingtonia_) _gigantea_ of
California. A nearly-allied form (_Sequoia Langsdorffi_) has been
detected in the leaf-bed of Ardtun, in the Hebrides.
In Greenland, as well as in other parts of the Arctic regions,
Miocene strata have been discovered which have yielded a great
number of plants, many of which are identical with species found
in the European Miocene. Amongst these plants are found many
trees, such as Conifers, Beeches, Oaks, Maples, Plane-trees,
Walnuts, Magnolias, &c., with numerous shrubs, ferns, and other
smaller plants. With regard to the Miocene flora of the Arctic
regions, Sir Charles Lyell remarks that "more than thirty species
of Coniferæ have been found, including several Sequoias (allied
to the gigantic Wellingtonia of California), with species of
_Thujopsis_ and _Salisburia_, now peculiar to Japan. There are
also beeches, oaks, planes, poplars, maples, walnuts, limes, and
even a magnolia, two cones of which have recently been obtained,
proving that this splendid evergreen not only lived but ripened
its fruit within the Arctic circle. Many of the limes, planes,
and oaks were large-leaved species; and both flowers and fruits,
besides immense quantities of leaves, are in many cases preserved.
Among the shrubs are many evergreens, as _Andromeda_, and two
extinct genera, _Daphnogene_ and _M'Clintockia_, with fine leathery
leaves, together with hazel, blackthorn, holly, logwood, and
hawthorn. A species of Zamia (_Zimites_) grew in the swamps,
with _Potamogeton, Sparganium_, and _Menyanthes_; while ivy and
villes twined around the forest-trees, and broad-leaved ferns
grew beneath their shade. Even in Spitzbergen, as far north as
lat. 78° 56', no less than ninety-five species of fossil plants
have been obtained, including _Taxodium_ of two species, hazel,
poplar, alder, beech, plane-tree, and lime. Such a vigorous growth
of trees within 12° of the pole, where now a dwarf willow and a
few herbaceous plants form the only vegetation, and where the
ground is covered with almost perpetual snow and ice, is truly
remarkable."
Taking the Miocene flora as a whole, Dr Heer concludes from his
study of about 3000 plants contained in the European Miocene
alone, that the Miocene plants indicate tropical or sub-tropical
conditions, but that there is a striking inter-mixture of forms
which are at present found in countries widely removed from one
another. It is impossible to state with certainty how many of the
Miocene plants belong to existing species, but it appears that
the larger number are extinct. According to Heer, the American
types of plants are most largely represented in the Miocene flora,
next those of Europe and Asia, next those of Africa, and lastly
those of Australia. Upon the whole, however, the Miocene flora
of Europe is mostly nearly allied to the plants which we now
find inhabiting the warmer parts of the United States; and this
has led to the suggestion that in Miocene times the Atlantic
Ocean was dry land, and that a migration of American plants to
Europe was thus permitted. This view is borne out by the fact
that the Miocene plants of Europe are most nearly allied to the
living plants of the eastern or Atlantic seaboard of the United
States, and also by the occurrence of a rich Miocene flora in
Greenland. As regards Greenland, Dr Heer has determined that
the Miocene plants indicate a temperate climate in that country,
with a mean annual temperature at least 30° warmer than it is
at present.
The present limit of trees is the isothermal which gives the
mean temperature of 500 Fahr. in July, or about the parallel of
67° N. latitude. In Miocene times, however, the Limes, Cypresses,
and Plane-trees reach the 79th degree of latitude, and the Pines
and Poplars must have ranged even further north than this.
The _Invertebrate Animals_ of the Miocene period are very numerous,
but they belong for the most part to existing types, and they
can only receive scanty consideration here. The little shells of
_Foraminifera_ are extremely abundant in some beds, the genera
being in many cases such as now flourish abundantly in our seas.
The principal forms belong to the genera _Textularia_ (fig. 237),
_Robulina, Glandulina, Polystomella, Amplistegina_, &c. Corals
are very abundant, in many instances forming regular "reefs;"
but all the more important groups are in existence at the present
day. The Red Coral (_Corallium_), so largely sought after as an
ornamental material, appears for the first time in deposits of
this age. Amongst the _Echinoderms_, we meet with Heart-Urchins
(_Spatangus_), Cake-Urchins (_Scutella_; fig. 238), and various
other forms, the majority of which are closely allied to forms
now in existence.
[Illustration: Fig. 237.--_Textularia Meyeriana_, greatly enlarged.
Miocene Tertiary.]
Numerous Crabs and Lobsters represent the _Crustacea_; but the most
important of the Miocene Articulate Animals are the _Insects_. Of
these, more than thirteen hundred species have been determined by
Dr Heer from the Miocene strata of Switzerland alone. They include
almost all the existing orders of insects, such as numerous and
varied forms of Beetles (_Coleoptera_), Forest-bugs (_Hemiptera_),
Ants (_Hymenoptera_), Flies (_Diptera_), Termites and Dragon-flies
(_Neuroptera_), Grasshoppers (_Orthoptera_), and Butterflies
(_Lepidoptera_). One of the latter, the well-known _Vanessa Pluto_
of the Brown Coals of Croatia, even exhibits the pattern of the
wing, and to some extent its original coloration; whilst the more
durably-constructed insects are often in a state of exquisite
preservation.
[Illustration: Fig. 238.--Different views of _Scutella subrotunda_,
a Miocene "Cake-Urchin" from the south of France.]
The _Mollusca_ of the Miocene period are very numerous, but call
for little special comment. Upon the whole, they are generically
very similar to the Shell-fish of the present day; whilst, as
before stated, from fifteen to thirty per cent of the _species_
are identical with those now in existence. So far as the European
area is concerned, the Molluscs indicate a decidedly hotter climate
than the present one, though they have not such a distinctly
tropical character as is the case with the Eocene shells. Thus we
meet with many Cones, Volutes, Cowries, Olive-shells, Fig-shells,
and the like, which are decidedly indicative of a high temperature
of the sea. _Polyzoans_ are abundant, and often attain considerable
dimensions; whilst _Brachiopods_, on the other hand, are few in
number. Bivalves and _Univalves_ are extremely plentiful; and
we meet here with the shells of Winged-Snails (_Pteropods_),
belonging to such existing genera as _Hyalea_ (fig. 239) and
_Cleodora_. Lastly, the _Cephalopods_ are represented both by
the chambered shells of _Nautili_ and by the internal skeletons
of Cuttle-fishes (_Spirulirostra_.)
[Illustration: Fig. 239.--Different views of the shell of _Hyalea
Orbignyana_, a Miocene Pteropod.]
The _Fishes_ of the Miocene Period are very abundant but of little
special importance. Besides the remains of Bony Fishes, we meet
in the marine deposits of this age with numerous pointed teeth
belonging to different kinds of Sharks. Some of the genera of
these--such as _Carcharodon_ (fig. 241), _Oxyrhina_ (fig. 240),
_Lamna_, and _Galeocerdo_--are very widely distributed, ranging
through both the Old and New Worlds; and some of the species
attain gigantic dimensions.
Amongst the _Amphibians_ we meet with distinctly modern types,
such as Frogs (_Rana_) and Newts or Salamanders. The most celebrated
of the latter is the famous _Andrias Scheuchzeri_ (fig. 242),
discovered in the year 1725 in the fresh-water Miocene deposits
of OEningen, in Switzerland. The skeleton indicates an animal
nearly five feet in length; and it was originally described by
Scheuchzer, a Swiss physician, in a dissertation published in 1731,
as the remains of one of the human beings who were in existence
at the time of the Noachian Deluge. Hence he applied to it the
name of _Homo diluvii testis_. In reality, however, as shown by
Cuvier, we have here the skeleton of a huge Newt, very closely
allied to the Giant Salamander (_Menopoma maxima_) of Java.
[Illustration: Fig. 240.--Tooth of _Oxyrhina xiphodon_. Miocene.]
[Illustration: Fig. 241.--Tooth of _Carcharodon productus_. Miocene.]
The remains of _Reptiles_ are far from uncommon in the Miocene
rocks, consisting principally of Chelonians and Crocodilians.
The Land-tortoises (_Testudinidoe_) make their first appearance
during this period. The most remarkable form of this group is
the huge _Colossochelys Atlas_ of the Upper Miocene deposits
of the Siwâlik Hills in India, described by Dr Falconer and Sir
Proby Cautley. Far exceeding any living Tortoise in its dimensions,
this enormous animal is estimated as having had a length of about
twenty feet, measured from the tip of the snout to the extremity
of the tail, and to have stood upwards of seven feet high. All the
details of its organisation, however, prove that it must have been
"strictly a land animal, with herbivorous habits, and probably
of the most inoffensive nature." The accomplished palæontologist
just quoted, shows further that some of the traditions of the
Hindoos would render it not improbable that this colossal Tortoise
had survived into the earlier portion of the human period.
Of the _Birds_ of the Miocene period it is sufficient to remark
that though specifically distinct, they belong, so far as known,
wholly to existing groups, and therefore present no points of
special palæontological interest.
The _Mammals_ of the Miocene are very numerous, and only the more
important forms can be here alluded to. Amongst the _Marsupials_,
the Old World still continued to possess species of Opossum
(_Didephys_), allied to the existing American forms. The _Edentates_
(Sloths, Armadillos, and Ant-eaters), at the present day mainly
South American, are represented by two large European forms. One
of these is the large _Macrotherium giganteum_ of the Upper Miocene
of Gers in Southern France, which appears to hare been in many
respects allied to the existing Scaly Ant-eaters or Pangolins,
at the same time that the disproportionately long fore-limbs would
indicate that it possessed the climbing habits of the Sloths.
The other is the still more gigantic _Ancylotherium Pentelici_
of the Upper Miocene of Pikermé, which seems to have been as
large as, or larger than, the Rhinoceros, and which must have
been terrestrial in its habits. This conclusion is further borne
out by the comparative equality of length which subsists between
the fore and hind limbs, and is not affected by the curvature and
crookedness of the claws, this latter feature being well marked
in such existing terrestrial Edentates as the Great Ant-eater.
[Illustration: Fig. 242.--Front portion of the skeleton of _Andrias
Scheuchzeri_, a Giant Salamander from the Miocene Tertiary of
Oeningen, in Switzerland. Reduced in size.]
The aquatic _Sirenians_ and _Cetaceans_ are represented in Miocene
times by various forms of no special importance. Amongst the
former, the previously existing genus _Halitherium_ continued to
survive, and amongst the latter we meet with remains of Dolphins
and of Whales of the "Zeuglodont" family. We may also note here
the first appearance of true "Whalebone Whales," two species
of which, resembling the living "Right Whale" of Arctic seas,
and belonging to the same genus (_Baloena_), have been detected
in the Miocene beds of North America.
The great order of the _Ungulates_ or Hoofed Quadrupeds is very
largely developed in strata of Miocene age, various new types
of this group making their appearance here for the first time,
whilst some of the characteristic genera of the preceding period
are still represented under new shapes. Amongst the Odd-toed
or "Perissodactyle" Ungulates, we meet for the first time with
representatives of the family _Rhinoceridoe_ comprising only
the existing Rhinoceroses. In India in the Upper Miocene beds
of the Siwâlik Hills, and in North America, several species of
Rhinoceros have been detected, agreeing with the existing forms
in possessing three toes to each foot, and in having one or two
solid fibrous "horns" carried upon the front of the head. On
the other hand, the forms of this group which distinguish the
Miocene deposits of Europe appear to have been for the most part
hornless, and to have resembled the Tapirs in having three-toed
hind-feet, but four-toed fore-feet.
The family of the Tapirs is represented, both in the Old and
New Worlds, by species of the genus _Lophiodon_, some of which
were quite diminutive in point of size, whilst others attained
the dimensions of a horse. Nearly allied to this family, also,
is the singular group of quadrupeds which Marsh has described
from the Miocene strata of the United States under the name of
_Brontotheridoe_. These extraordinary animals, typified by
_Brontotherium_ (fig. 243) itself, agree with the existing Tapirs
of South America and the Indian Archipelago in having the fore-feet
four-toed, whilst the hind-feet are three-toed; and a further
point of resemblance is found in the fact (as shown by the form
of the nasal bones) that the nose was long and flexible, forming
a short movable proboscis or trunk, by means of which the animal
was enabled to browse on shrubs or trees. They differ, however,
from the Tapirs, not only in the apparent presence of a long tail,
but also in the possession of a pair of very large "horn-cores,"
carried upon the nasal bones, indicating that the animal possessed
horns of a similar structure to those of the "Hollow-horned"
Ruminants (_e.g._, Sheep and Oxen). _Brontotherium gigas_ is
said to be nearly as large as an Elephant, whilst _B. Ingens_
appears to have attained dimensions still more gigantic. The
well-known genus _Titanotherium_ of the American Miocene would
also appear to belong to this group.
[Illustration: Fig. 243.--Skull of _Brontotherium ingens_. Miocene
Tertiary, United States. (After Marsh.)]
The family of the Horses (_Equidoe_) appears under various forms
in the Miocene, but the most important and best known of these
is _Hipparion_. In this genus the general conformation of the
skeleton is extremely similar to that of the existing Horses,
and the external appearance of the animal must have been very
much the same. The foot of _Hipparion_, however, as has been
previously mentioned, differed from that of the Horse in the
fact that whilst both possess the middle toe greatly developed
and enclosed in a broad hoof, the former, in addition, possessed
two lateral toes, which were sufficiently developed to carry
hoofs, but were so far rudimentary that they hung idly by the
side of the central toe without touching the ground (see fig.
230). In the Horse, on the other hand, these lateral toes, though
present, are not only functionally useless, but are concealed
beneath the skin. Remains of the _Hipparion_ have been found
in various regions in Europe and in India; and from the immense
quantities of their bones found in certain localities, it may
be safely inferred that these Middle Tertiary ancestors of the
Horses lived, like their modern representatives, in great herds,
and in open grassy plains or prairies.
Amongst the Even-toed or _Artiodactyle_ Ungulates, we for the
first time meet with examples of the _Hippopotamus_, with its
four-toed feet, its massive body, and huge tusk-like lower canine
teeth. The Miocene deposits of Europe have not hitherto yielded
any remains of _Hippopotamus_; but several species have been
detected in the Upper Miocene of the Siwâlik Hills by Dr Falconer
and Sir Proby Cautley. These ancient Indian forms, however, differ
from the existing _Hippopotamus amphibius_ of Africa in the fact
that they possessed six incisor teeth in each jaw (fig. 244),
whereas the latter has only four.
[Illustration: Fig. 244.--a, Skull of _Hippopotamus Sivalensis_,
viewed from below, one-eighth of the natural size; b, Molar
tooth of the same, showing the surface of the crown, one-half
of the natural size: c, Front of the lower jaw of the same,
showing the six incisors and the tusk-like canines, one-eighth of
the natural size. Upper Miocene, Siwâlik Hills; (After Falconer
and Cautley.)]
Amongst the other Even-toed Ungulates, the family of the Pigs
(_Suida_) is represented by true Swine (_Sus Erymanthius_), Peccaries
(_Dicotyles antiquus_), and by forms which, like the great
_Elotherium_ of the American Miocene, have no representative at
the present day. The Upper Miocene of India has yielded examples
of the Camels. Small Musk-deer (_Amphitragulus_ and _Dremotherium_)
are known to have existed in France and Greece; and the true Deer
(_Cervidoe_), with their solid bony antlers, appear for the first
time here in the person of species allied to the living Stags
(_Cervus_), accompanied by the extinct genus _Dorcatherium_. The
Giraffes (_Camelopardalidoe_), now confined to Africa, are known to
have lived in India and Greece; and the allied _Helladotherium_, in
some respects intermediate between the Giraffes and the Antelopes,
ranged over Southern Europe from Attica to France. The great
group of the "Hollow-horned" Ruminants (_Cavicornia_), lastly,
came into existence in the Miocene period; and though the typical
families of the Sheep and Oxen are apparently wanting, there are
true Antelopes, together with forms which, if systematically
referable to the _Antilopidoe_, nevertheless are more or less
clearly transitional between this and the family of the Sheep and
Goats. Thus the _Paloeoreas_ of the Upper Miocene of Greece may
be regarded as a genuine Antelope; but the _Tragoceras_ of the
same deposit is intermediate in its characters between the typical
Antelopes and the Goats. Perhaps the most remarkable, however,
of these Miocene Ruminants is the _Sivatherium giganteum_ (fig.
245) of the Siwâlik Hills, in India. In this extraordinary animal
there were two pairs of horns, supported by bony "horn-cores,"
so that there can be no hesitation in referring _Sivatherium_
to the Cavicorn Ruminants. If all these horns had been simple,
there would have been no difficulty in considering _Sivatherium_
as simply a gigantic four-horned Antelope, essentially similar
to the living _Antilope_ (_Tetraceros_) _quadricornis_ of India.
The hinder pair of horns, however, is not only much larger than
the front pair, but each possesses two branches or snags--a
peculiarity not to be paralleled amongst any existing Antelope,
save the abnormal Prongbuck (_Antilocapra_) of North America.
Dr Murie, however, in an admirable memoir on the structure and
relationships of _Sivatherium_, has drawn attention to the fact
that the Prongbuck sheds the _sheath_ of its horns annually,
and has suggested that this may also have been the case with
the extinct form. This conjecture is rendered probable, amongst
other reasons, by the fact that no traces of a horny sheath
surrounding the horn-cores of the Indian fossil have been as
yet detected. Upon the whole, therefore, we may regard the
elephantine _Sivatherium_ as being most nearly allied to the
Prongbuck of Western America, and thus as belonging to the family
of the Antelopes.
[Illustration: Fig. 245.--Skull of _Sivatherium giganteum_, reduced
in size. Miocene, India. (After Murie.)]
It is to the Miocene period, again, to which we must refer the
first appearance of the important order of the Elephants and
their allies (_Proboscideans_), all of which are characterised
by their elongated trunk-like noses, the possession of five toes
to the foot, the absence of canine teeth, the development of two
or more of the incisor teeth into long tusks, and the adaptation
of the molar teeth to a vegetable diet. Only three generic groups
of this order are known-namely, the extinct _Deinotherium_, the
equally extinct _Mastodons_, and the _Elephants_; and all these
three types are known to have been in existence as early as the
Miocene period, the first of them being exclusively confined to
deposits of this age. Of the three, the genus _Deinotherium_
is much the most abnormal in its characters; so much so, that
good authorities regard it as really being one of the Sea-cows
(_Sirenia_)--though this view has been rendered untenable by
the discovery of limb-bones which can hardly belong to any other
animal, and which are distinctly Proboscidean in type. The most
celebrated skull of the Deinothere (fig. 246) is one which was
exhumed from the Upper Miocene deposits of Epplesheim, in
Hesse-Darmstadt, in the year 1836. This skull was four and a half
feet in length, and indicated an animal larger than any existing
species of Elephant. The upper jaw is destitute of incisor or
canine teeth, but is furnished on each side with five molars,
which are opposed to a corresponding series of grinding teeth in
the lower jaw. No canines are present in the lower jaw; but the
front portion of the jaw is abruptly bent downwards, and carries
two huge tusk-like incisor teeth, which are curved downwards and
backwards, and the use of which is rather problematical. Not
only does the Deinothere occur in Europe, but remains belonging
to this genus have also been detected in the Siwâlik Hills, in
India.
[Illustration: Fig. 246.--Skull of _Deinotherium giganteum_, greatly
reduced. From the Upper Micene of Germany.]
The true Elephants (_Elephas_) do not appear to have existed
during the Miocene period in Europe, but several species have
been detected in the Upper Miocene deposits of the Siwâlik Hills,
in India. The fossil forms, though in all cases specifically, and
in some cases even sub-generically, distinct, agree with those
now in existence in the general conformation of their skeleton,
and in the principal characters of their dentition. In all, the
canine teeth are wanting in both jaws; and there are no incisor
teeth in the lower jaw, whilst there are two incisors in the
front of the upper jaw, which are developed into two huge "tusks."
There are six molar teeth on each side of both the upper and lower
jaw, but only one, or at most a part of two, is in actual use
at any given time; and as this becomes worn away, it is pushed
forward and replaced by its successor behind it. The molars are of
very large size, and are each composed of a number of transverse
plates of enamel united together by ivory; and by the process
of mastication, the teeth become worn down to a flat surface,
crossed by the enamel-ridges in varying patterns; These patterns
are different in the different species of Elephants, though constant
for each; and they constitute one of the most readily available
means of separating the fossil forms from one another. Of the
seven Miocene Elephants of India, as judged by the characters of
the molar, teeth, two are allied to the existing Indian Elephant,
one is related to the living African Elephant, and the remaining
four are in some respects intermediate between the true Elephants
and the Mastodons.
[Illustration: Fig. 247.--A, Molar tooth of _Elephas planifrons_,
one-third of the natural size, showing the grinding surface--from
the Upper Miocene of India; B, Profile view of the last upper molar
of _Mastodon Sivalensis_, one-third of the natural size--from
the Upper Miocene of India. (After Falconer.)]
The _Mastodons_, lastly, though quite elephantine in their general
characters, possess molar teeth which have their crowns furnished
with conical eminences or tubercles placed in pairs (fig. 247, B),
instead of having the approximately flat surface characteristic
of the grinders of the Elephants. As in the latter, there are two
upper incisor teeth, which grow permanently during the life of
the animal, and which constitute great tusks; but the Mastodons,
in addition, often possess two lower incisors, which in some
cases likewise grow into small tusks. Three species of _Mastodon_
are known to occur in the Upper Miocene of the Siwâlik Hills
of India; and the Miocene deposits of the European area have
yielded the remains of four species, of which the best known are
the _M. Longirostris_ and the _M. Angustidens_.
Whilst herbivorous Quadrupeds, as we have seen, were extremely
abundant during Miocene times, and often attained gigantic
dimensions, Beasts of Prey (_Carnivora_) were by no means wanting,
most of the principal existing families of the order being
represented in deposits of this age. Thus, we find aquatic Carnivores
belonging to both the living groups of the Seals and Walruses;
true Bears are wanting, but their place is filled by the
closely-allied genus _Amphicyon_, of which various species are
known; Weasels and Otters were not unknown, and the _Hyoenictis_
and _Iditherium_ of the Upper Miocene of Greece are apparently
intermediate between the Civet-cats and the Hyænas; whilst the great
Cats of subsequent periods are more than adequately represented by
the huge "Sabre-toothed Tiger" (_Machairodus_), with its immense
trenchant and serrated canine teeth.
Amongst the _Rodent_ Mammals, the Miocene rocks have yielded
remains of Rabbits, Porcupines (such as the _Hystrix primigenius_
of Greece), Beavers, Mice, Jerboas, Squirrels, and Marmots. All the
principal living groups of this order were therefore differentiated
in Middle Tertiary times.
The _Cheiroptera_ are represented by small insect-eating Bats;
and the order of the Insectivorous Mammals is represented by
Moles, Shrew-mice, and Hedgehogs.
[Illustration: Fig. 248.--Lower jaw of _Pliopithcus antiquus_.
Upper Miocene, France.]
Lastly, the Monkeys (_Quadrumana_) appear to have existed during
the Miocene period under a variety of forms, remains of these
animals having been found both in Europe and in India; but no member
of this order has as yet been detected in the Miocene Tertiary of
the North American continent. Amongst the Old World Monkeys of
the Miocene, the two most interesting are the _Pliopithecus_
and _Dryopithecus_ of France. The former of these (fig. 248)
is supposed to have been most nearly related to the living
_Semnopitheci_ of Southern Asia, in which case it must have possessed
a long tail. The _Mesopithecus_ of the Upper Miocene of Greece is
also one of the lower Monkeys, as it is most closely allied to
the existing Macaques. On the other hand, the _Dryopithecus_
of the French Upper Miocene is referable to the group of the
"Anthropoid Apes," and is most nearly related to the Gibbons
of the present day, in which the tail is rudimentary and there
are no cheek-pouches. _Dryopithecus_ was, also, of large size,
equalling Man in stature, and apparently living amongst the trees
and feeding upon fruits.
CHAPTER XX.
THE PLIOCENE PERIOD.
The highest division of the Tertiary deposits is termed the
_Pliocene_ formation, in accordance with the classification proposed
by Sir Charles Lyell. The Pliocene formations contain from 40 to
95 per cent of existing species of _Mollusca_, the remainders
belonging to extinct species. They are divided by Sir Charles
Lyell into two divisions, the Older Pliocene and Newer Pliocene.
The Pliocene deposits of Britain occur in Suffolk, and are known
by the name of "Crags," this being a local term used for certain
shelly sands, which are employed in agriculture. Two of these
Crags are referable to the Older Pliocene, viz., the White and
Red Crags,--and one belongs to the Newer Pliocene, viz., the
Norwich Crag.
The _White or Coralline Crag_ of Suffolk is the oldest of the
Pliocene deposits of Britain, and is an exceedingly local formation,
occurring in but a single small area, and having a maximum thickness
of not more than 50 feet. It consists of soft sands, with occasional
intercalations of flaggy limestone. Though of small extent and
thickness, the Coralline Crag is of importance from the number
of fossils which it contains. The name "Coralline" is a misnomer;
since there are few true Corals, and the so-called "Corals" of
the formation are really _Polyzoa_, often of very singular forms.
The shells of the Coralline Crag are mostly such as inhabit the
seas of temperate regions; but there occur some forms usually
looked upon as indicating a warm climate.
The _Upper_ or _Red Crag_ of Suffolk--like the Coralline Crag--has
a limited geographical extent and a small thickness, rarely exceeding
40 feet. It consists of quartzose sands, usually deep red or
brown in colour, and charged with numerous fossils.
Altogether more than 200 species of shells are known from the
Red Crag, of which 60 per cent are referable to existing species.
The shells indicate, upon the whole, a temperate or even cold
climate, decidedly less warm than that indicated by the organic
remains of the Coralline Crag. It appears, therefore, that a
gradual refrigeration was going on during the Pliocene period,
commencing in the Coralline Crag, becoming intensified in the Red
Crag, being still more severe in the Norwich Crag, and finally
culminating in the Arctic cold of the Glacial period.
Besides the _Mollusca_, the Red Crag contains the ear-bones of
Whales, the teeth of Sharks and Rays, and remains of the Mastodon,
Rhinoceros, and Tapir.
The _Newer Pliocene_ deposits are represented in Britain by the
_Norwich Crag_, a local formation occurring near Norwich. It
consists of incoherent sands, loams, and gravels, resting in
detached patches, from 2 to 20 feet in thickness, upon an eroded
surface of Chalk. The Norwich Crag contains a mixture of marine,
land, and fresh-water shells, with remains of fishes and bones
of mammals; so that it must have been deposited as a local
sea-deposit near the mouth of an ancient river. It contains
altogether more than 100 marine shells, of which 89 per cent
belong to existing species. Of the Mammals, the two most important
are an Elephant (_Elephas meridionalis_), and the characteristic
Pliocene Mastodon (_M. Arvernensis_), which is hitherto the only
Mastodon found in Britain.
According to the most recent views of high authorities, certain
deposits--such as the so-called "Bridlington Crag" of Yorkshire,
and the "Chillesford beds" of Suffolk--are to be also included
in the Newer Pliocene, upon the ground that they contain a small
proportion of extinct shells. Our knowledge, however, of the
existing Molluscan fauna, is still so far incomplete, that it
may reasonably be doubted if these supposed extinct forms have
actually made their final disappearance, whilst the strata in
question have a strong natural connection with the "Glacial
deposits," as shown by the number of Arctic Mollusca which they
contain. Here, therefore, these beds will be included in the
Post-Pliocene series, in spite of the fact that some of their
species of shells are not known to exist at the present day.
The following are the more important Pliocene deposits which have
been hitherto recognised out of Britain:--
1. In the neighbourhood of Antwerp occur certain "crags," which
are the equivalent of the White and Red Crag in part. The lowest
of these contains less than 50 per cent, and the highest 60 per
cent, of existing species of shells, the remainder being extinct.
2. Bordering the chain of the Apennines, in Italy, on both sides
is a series of low hills made up of Tertiary strata, which are
known as the Sub-Apennine beds. Part of these is of Miocene age,
part is Older Pliocene, and a portion is Newer Pliocene. The
Older Pliocene portion of the Sub-Apennines consists of blue or
brown marls, which sometimes attain a thickness of 2000 feet.
3. In the valley of the Arno, above Florence, are both Older
and Newer Pliocene strata. The former consist of blue clays and
lignites, with an abundance of plants. The latter consist of sands
and conglomerates, with remains of large Carnivorous Mammals,
Mastodon, Elephant, Rhinoceros, Hippopotamus, &c.
4. In Sicily, Newer Pliocene strata are probably more largely
developed than anywhere else in the world, rising sometimes to a
height of 3000 feet above the sea. The series consists of clays,
marls, sands, and conglomerates, capped by a compact limestone,
which attains a thickness of from 700 to 800 feet. The fossils of
these beds belong almost entirely to living species, one of the
commonest being the Great Scallop of the Mediterranean (_Pecten
Jacoboeus_).
5. Occupying an extensive area round the Caspian, Aral, and Azof
Seas, are Pliocene deposits known as the "Aralo-Caspian" beds.
The fossils in these beds are partly freshwater, partly marine,
and partly intermediate in character, and they are in great part
identical with species now inhabiting the Caspian. The entire
formation appears to indicate the former existence of a great
sheet of brackish water, forming an inland sea, like the Caspian,
but as large as, or larger than, the Mediterranean.
6. In the United States, strata of Pliocene age are found in
North and South Carolina. They consist of sands and clays, with
numerous fossils, chiefly _Molluscs_ and _Echinoderms_. From 40
to 60 per cent of the fossils belong to existing species. On
the Loup Fork of the river Platte, in the Upper Missouri region,
are strata which are also believed to be referable to the Pliocene
period, and probably to its upper division. They are from 300 to
400 feet thick, and contain land-shells, with the bones of numerous
Mammals, such as Camels, Rhinoceroses, Mastodons, Elephants, the
Horse, Stag, &c.
As regards the _life_ of the Pliocene period, there are only
two classes of organisms to which our attention need be
directed--namely, the Shell-fish and the Mammals. So far as the
former are concerned, we have to note in the first place that
the introduction of new species of animals upon the globe went
on rapidly during this period. In the Older Pliocene deposits,
the number of shells of existing species is only from 40 to 60
per cent; but in the Newer Pliocene the proportion of living
forms rises to as much as from 80 to 95 per cent. Whilst the
Molluscs thus become rapidly modernised, the Mammals still all
belong to extinct species, though modern generic types gradually
supersede the more antiquated forms of the Miocene. In the second
place, there is good evidence to show that the Pliocene period
was one in which the climate of the northern hemisphere underwent
a gradual refrigeration. In the Miocene period, there is evidence
to show that Europe possessed a climate very similar to that
now enjoyed by the Southern United States, and certainly very
much warmer than it is at present. The presence of Palm-trees
upon the land, and of numerous large Cowries, Cones, and other
shells of warm regions in the sea, sufficiently proves this. In
the Older Pliocene deposits, on the other hand, northern forms
predominate amongst the Shells, though some of the types of hotter
regions still survive. In the Newer Pliocene, again, the Molluscs
are such as almost exclusively inhabit the seas of temperate
or even cold regions; whilst if we regard deposits like the
"Bridlington Crag" and "Chillesford beds" as truly referable to
this period, we meet at the close of this period with shells such
as nowadays are distinctively characteristic of high latitudes. It
might be thought that the occurrence of Quadrupeds such as the
Elephant, Rhinoceros, and Hippopotamus, would militate against
this generalisation, and would rather support the view that the
climate of Europe and the United States must have been a hot
one during the later portion of the Pliocene period. We have,
however, reason to believe that many of these extinct Mammals
were more abundantly furnished with hair, and more adapted to
withstand a cool temperature, than any of their living congeners.
We have also to recollect that many of these large herbivorous
quadrupeds may have been, and indeed probably were, more or less
migratory in their habits; and that whilst the winters of the
later portion of the Pliocene period were cold, the summers might
have been very hot. This would allow of a northward migration
of such terrestrial animals during the summer-time, when there
would be an ample supply of food and a suitably high temperature,
and a southward recession towards the approach of winter.
The chief palæontological interests of the Pliocene deposits,
as of the succeeding Post-Pliocene, centre round the Mammals of
the period; and amongst the many forms of these we may restrict
our attention to the orders of the Hoofed Quadrupeds (_Ungulates_),
the _Proboscideans_, the _Carnivora_, and the _Quadrumana_. Almost
all the other Mammalian orders are more or less fully represented
in Pliocene times, but none of them attains any special interest
till we enter upon the Post-Pliocene.
Amongst the Odd-toed Ungulates, in addition to the remains of
true Tapirs (_Tapirus Arvernensis_), we meet with the bones of
several species of Rhinoceros, of which the _Rhinoceros Etruscus_
and _R. Megarhinus_ (fig. 249) are the most important. The former
of these (fig. 249, A) derives its specific name from its abundance
in the Pliocene deposits of the Val d'Arno, near Florence, and
though principally Pliocene in its distribution, it survived
into the earlier portion of the Post-Pliocene period. _Rhinoceros
Etruscus_ agreed with the existing African forms in having two
horns placed one behind the other, the front one being the longest;
but it was comparatively slight and slender in its build, whilst
the nostrils were separated by an incomplete bony partition. In
the _Rhinoceros megarhinus_ (fig. 249, B), on the other hand, no
such partition exists between the nostrils, and the nasal bones
are greatly developed in size. It was a two-horned form, and is
found associated with _Elephas meridionalis_ and _E. Antiquus_ in
the Pliocene deposits of the Val d'Arno, near Florence. Like the
preceding, it survived, in diminished numbers, into the earlier
portion of the Post-Pliocene period.
[Illustration: Fig. 249.--A. Under surface of the skull of
_Rhinoceros Etruscus_, one-seventh of the natural size--Pliocene,
Italy.; B, Crowns of the three true molars of the upper jaw, left
side, of _Rhinoceros megarhinus_ (_R. Leptorhinus_, Falconer),
one-half of the natural size--Pliocene, France. (After Falconer.)]
The Horses (_Equidoe_) are represented, both in Europe and America,
by the three-toed Hipparions, which survive from the Miocene,
but are now verging upon extinction. For the first time, also,
we meet with genuine Horses (_Equus_), in which each foot is
provided with a single complete toe only, encased in a single
broad hoof. One of the American species of this period (the _Equus
excelsus_) quite equalled the modern Horse in stature; and it
is interesting to note the occurrence of indigenous horses in
America at such a comparatively late geological epoch, seeing
that this continent certainly possessed none of these animals
when first discovered by the Spaniards.
Amongst the Even-toed Ungulates, we may note the occurrence of
Swine (_Suida_), of forms allied to the Camels (_Camelidoe_), and
of various kinds of Deer (_Cervidoe_); but the most interesting
Pliocene Mammal belonging to this section is the great _Hippopotamus
major_ of Britain and Europe. This well-known species is very
closely allied to the living _Hippopotamus amphibius_ of Africa,
from which it is separated only by its larger dimensions, and by
certain points connected with the conformation of the skeleton.
It is found very abundantly in the Pliocene deposits of Italy and
France, associated with the remains of the Elephant, Mastodon,
and Rhinoceros, and it survived into the earlier portion of the
Post-Pliocene period. During this last-mentioned period, it extended
its range northwards, and is found associated with the Reindeer,
the Bison, and other northern animals. From this fact it has been
inferred, with great probability, that the _Hippotamus major_
was furnished with a long coat of hair and fur, thus differing
from its nearly hairless modern representative, and resembling
its associates, the Mammoth and the Woolly Rhinoceros.
[Illustration: Fig. 250.--Third milk-molar of the left side of
the upper jaw of _Mastodon Arvernensis_, showing the grinding
surface. Pliocene.]
Passing on to the Pliocene Proboscideans, we find that the great
_Deinotheria_ of the Miocene have now wholly disappeared, and the
sole representatives of the order are Mastodons and Elephants.
The most important member of the former group is the _Mastodon
Arvernensis_ (fig. 250), which ranged widely over Southern Europe
and England, being generally associated with remains of the _Elephas
meridionalis, E. antiquus, Rhinoceros megarhinus_, and _Hippopotamus
major_. The lower jaw seems to have been destitute of incisor
teeth; but the upper incisors are developed into great tusks,
which sometimes reach a length of nine feet, and which have the
simple curvature of the tusks of the existing Elephants. Amongst
the Pliocene Elephants the two most important are the _Elephas
meridionalis_ and the _Elephas antiquus_. Of these, the _Elephas
meridionalis_ (fig. 251) is found abundantly in the Pliocene
deposits of Southern Europe and England, and also survived into
the earlier portion of the Post-Pliocene period. Its molar teeth
are of the type of those of the existing African Elephant, the
spaces enclosed by the transverse enamel-plates being more or
less lozenge-shaped, whilst the curvature of the tusks is simple.
The _Elephas antiquus_ (fig. 252) is very generally associated
with the preceding, and it survived to an even later stage of
the Post-Pliocene period. The molar teeth are of the type of the
existing Indian Elephant, with comparatively thin enamel-ridges,
placed closer together than in the African type; whilst the tusks
were nearly straight.
[Illustration: Fig. 251.--Molar tooth of _Elephas meridionalis_,
one-third of the natural size. Pliocene and Post-Pliocene.]
[Illustration: Fig. 252.--Molar tooth of _Elephas antiquus_,
one-third of the natural size. Pliocene and Post-Pliocene.]
Amongst the Pliocene _Carnivores_, we meet with true Bears (_Ursus
Arvernensis_), Hyænas (such as _Hyoena Hipparionum_), and genuine
Lions (such as the _Felis angustus_ of North America); but the
most remarkable of the beasts of prey of this period is the great
"Sabre-toothed Tiger" (_Machairodus_), species of which existed
in the earlier Miocene, and survived to the later Post-Pliocene.
In this remarkable form we are presented with perhaps the most
highly carnivorous type of all known beasts of prey. Not only
are the jaws shorter in proportion even than those of the great
Cats of the present day, but the canine teeth (fig. 253) are
of enormous size, greatly flattened so as to assume the form
of a poignard, and having their margins finely serrated. A part
from the characters of the skull, the remainder of the skeleton,
so far as known, exhibits proofs that the Sabre-toothed Tiger
was extraordinarily muscular and powerful, and in the highest
degree adapted for a life of rapine. Species of _Machairodus_
must have been as large as the existing Lion; and the genus is
not only European, but is represented both in South America and
in India, so that the geographical range of these predaceous
beasts must have been very extensive.
[Illustration: Fig. 253.--A, Skull of _Machairodus cultridens_,
without the lower jaw, reduced in size; B, Canine tooth of the
same, one-half the natural size. Pliocene, France.]
Lastly, we may note that the Pliocene deposits of Europe have
yielded the remains of Monkeys (_Quadrumana_), allied to the
existing _Semnopitheci_ and Macaques.
LITERATURE.
The following list comprises a small selection of some of the
more important and readily accessible works and memoirs relating
to the Tertiary rocks and their fossils. With few exceptions,
foreign works relating to the Tertiary strata of the continent
of Europe or their organic remains have been omitted:--
(1) 'Elements of Geology.' Lyell.
(2) 'Students' Elements of Geology.' Lyell.
(3) 'Manual of Palæontology.' Owen.
(4) 'British Fossil Mammals and Birds.' Owen.
(5) 'Traité de Paléontologie.' Pictet.
(6) 'Cours Elémentaire de Paléontologie.' D'Orbigny.
(7) "Probable Age of the London Clay," &c.--'Quart. Journ. Geol.
Soc.,' vol. iii. Prestwich.
(8) 'Structure and Probable Age of the Bagshot Sands'--Ibid., vol.
iii. Prestwich.
(9) 'Tertiary Formations of the Isle of Wight'--Ibid., vol. ii.
Prestwich.
(10) 'Structure of the Strata between the London Clay and the
Chalk,' &c.--Ibid., vols. vi., viii., and x. Prestwich.
(11) 'Correlation of the Eocene Tertiaries of England, France,
and Belgium'--Ibid., vol. xxvii. Prestwich.
(12) 'On the Fluvio-marine Formations of the Isle of Wight'--Ibid.,
vol. ix. Edward Forbes.
(13) 'Newer Tertiary Deposits of the Sussex Coast'--Ibid., vol.
xiii. Godwin-Austen.
(14) 'Kainozoic Formations of Belgium'--Ibid., vol. xxii.
Godwin-Austen.
(15) 'Tertiary Strata of Belgium and French Flanders'--Ibid.,
vol. viii. Lyell.
(16) 'On Tertiary Leaf-beds in the Isle of Mull'--Ibid., vol. vii.
The Duke of Argyll.
(17) 'Newer Tertiaries of Suffolk and their Fauna'--Ibid., vol.
xxvi. Ray Lankester.
(18) 'Lower London Tertiaries of Kent'--Ibid., vol. xxii. Whitaker.
(19) "Guide to the Geology of London"--'Mem. Geol. Survey.'
Whitaker.
(20) 'Memoirs of the Geological Survey of Great Britain.'
(21) 'Introductory Outline of the Geology of the Crag District'
(Supplement to Crag Mollusca, Palæontographical Society). S. V.
Wood, jun., and F. w. Harmer.
(22) "Tertiary Fluvio-marine Deposits of the Isle of Wight." Edward
Forbes. Edited by Godwin-Austen; with Descriptions of the
Fossils by Morris, Salter, and Rupert Jones--'Memoirs of the
Geological Survey.'
(23) 'Geological Excursions round the Isle of Wight.' Mantell.
(24) 'Catalogue of British Fossils.' Morris.
(25) 'Catalogue of Fossils in the Museum of Practical Geology.'
Etheridge.
(26) 'Monograph of the Crag Polyzoa' (Palæontographical Society). Busk.
(27) 'Monograph of the Tertiary Brachiopoda' (Ibid.) Davidson.
(28) 'Monograph of the Tertiary Malacostracous Crustacea' (Ibid.)
Bell.
(29) 'Monograph of the Tertiary Corals' (Ibid.) Milne-Edwards and
Haime.
(30) 'Supplement to the Tertiary Corals' (Ibid.) Martin Duncan.
(31) 'Monograph of the Eocene Mollusca' (Ibid.) Fred. E. Edwards.
(32) 'Monograph of the Eocene Mollusca' (Ibid.) Searles V. Wood.
(33) 'Monograph of the Crag Mollusca' (Ibid.) Searles V. Wood.
(34) 'Monograph of the Tertiary Entomostraca' (Ibid.) Rupert Jones.
(35) 'Monograph of the Foraminifera of the Crag' (Ibid.) Rupert Jones,
Parker, and H. B. Brady.
(36) 'Monograph of the Radiaria of the London Clay' (Ibid.) Edward
Forbes.
(37) 'Monograph of the Cetacea of the Red Crag' (Ibid.) Owen.
(38) 'Monograph of the Fossil Reptiles of the London Clay' (Ibid.)
Owen and Bell.
(39) "On the Skull of a Dentigerous Bird from the London Clay of
Sheppey"--'Quart. Journ. Geol. Soc.,' vol. xxix. Owen.
(40) 'Ossemens Fossiles.' Cuvier.
(41) 'Fauna Antiqua Sivalensis.' Falconer and Sir Proby Cautley.
(42) 'Palæontological Memoirs.' Falconer.
(43) 'Animaux Fossiles et Géologie de l'Attique.' Gaudry.
(44) "Principal Characters of the Dinocerata"--'American Journ. of
Science and Arts,' vol. xi. Marsh.
(45) 'Principal Characters of the Brontotheridæ' (Ibid.) Marsh.
(46) 'Principal Characters of the Tillodontia' (Ibid.) Marsh.
(47) "Extinct Vertebrata of the Eocene of Wyoming"--'Geological
Survey of Montana,' &c., 1872. Cope.
(48) "Ancient Fauna of Nebraska"--'Smithsonian Contributions to
Knowledge,' vol. vi. Leidy.
(49) 'Manual of Geology.' Dana.
(50) "Palæontology and Evolution" (Presidential Address to the
Geological Society of London, 1870)--'Quart. Journ. Geol.
Soc.,' vol. xxvi. Huxley.'
(51) 'Mineral Conchology.' Sowerby.
(52) 'Description des Coquilles Fossiles,' &c. Deshayes.
(53) 'Description des Coquilles Tertiaires de Belgique.' Nyst.
(54) 'Fossilen Polypen des Wiener Tertiär-beckens.' Reuss.
(55) 'Palæontologische Studien über die älteren Tertiär-schichten
der Alpen.' Reuss.
(56) 'Land und Süss-wasser Conchylien der Vorwelt.' Sandberger.
(57) 'Flora Tertiaria Helvetica.' Heer.
(58) 'Flora Fossilis Arctica.' Heer.
(59) 'Recherches sur le Climat et la Végétation du Pays
Tertiaire.' Heer.
(60) 'Fossil Flora of Great Britain.' Lindley and Hutton.
(61) 'Fossil Fruits and Seeds of the London Clay.' Bowerbank.
(62) "Tertiary Leaf-beds of the Isle of Mull"--'Quart. Journ.
Geol. Soc.,' vol. vii. Edward Forbes.
(63) 'The Geology of England and Wales.' Horace B. Woodward.[25]
[Footnote 25: This work--published whilst these sheets were going
through the press--gives to the student a detailed view of all the
strata of England and Wales, with their various sub-divisions,
from the base of the Palæozoic to the top of the Tertiary.]
CHAPTER XXI.
THE QUATERNARY PERIOD.
THE POST-PLIOCENE PERIOD.
Later than any of the Tertiary formations are various detached
and more or less superficial accumulations, which are generally
spoken of as the _Post-Tertiary formations_, in accordance with
the nomenclature of Sir Charles Lyell--or as the _Quaternary
formations_, in accordance with the general usage of Continental
geologists. In all these formations we meet with no _Mollusca_
except such as are now alive--with the partial and very limited
exception of some of the oldest deposits of this period, in which
a few of the shells occasionally belong to species not known
to be in existence at the present day. Whilst the _Shell-fish_
of the Quaternary deposits are, generally speaking, identical
with existing forms, the _Mammals_ are sometimes referable to
living, sometimes to extinct species. In accordance with this,
the Quaternary formations are divided into two groups: (1) The
_Post-Pliocene_, in which the shells are almost invariably referable
to existing species, but some of the _Mammals are extinct_; and
(2) the _Recent_, in which _the shells and the Mammals alike
belong to existing species_. The Post-Pliocene deposits are often
spoken of as the Pleistocene formations (Gr. _pleistos_, most;
_kainos_, new or recent), in allusion to the fact that the great
majority of the living beings of this period belong to the species
characteristic of the "new" or Recent period.
The _Recent_ deposits, though of the highest possible interest,
do not properly concern the palæontologist strictly so-called, but
the zoologist, since they contain the remains of none but existing
animals. They are "Pre-historic," but they belong entirely to
the existing terrestrial order. The _Post-Pliocene_ deposits, on
the other hand, contain the remains of various extinct Mammals;
and though Man undoubtedly existed in, at any rate, the later
portion of this period, if not throughout the whole of it, they
properly form part of the domain of the palæontologist.
The Post-Pliocene deposits are extremely varied, and very widely
distributed; and owing to the mode of their occurrence, the ordinary
geological tests of age are in their case but very partially
available. The subject of the classification of these deposits
is therefore an extremely complicated one; and as regards the age
of even some of the most important of them, there still exists
considerable difference of opinion. For our present purpose, it
will be convenient to adopt a classification of the Post-Pliocene
deposits founded on the relations which they bear in time to the
great "Ice-age" or "Glacial period;" though it is not pretended
that our present knowledge is sufficient to render such a
classification more than a provisional one.
In the early Tertiary period, as we have seen, the climate of the
northern hemisphere, as shown by the Eocene animals and plants,
was very much hotter than it is at present--partaking, indeed, of a
sub-tropical character. In the Middle Tertiary or Miocene period,
the temperature, though not so high, was still much warmer than
that now enjoyed by the northern hemisphere; and we know that the
plants of temperate regions at this time flourished within the
Arctic circle. In the later Tertiary or Pliocene period, again,
there is evidence that the northern hemisphere underwent a further
progressive diminution of temperature; though the climate of Europe
generally seems at the close of the Tertiary period to have been
if anything warmer, or at any rate not colder, than it is at
the present day. With the commencement of the Quaternary period,
however, this diminution of temperature became more decided; and
beginning with a temperate climate, we find the greater portion
of the northern hemisphere to become gradually subjected to all
the rigours of intense Arctic cold. All the mountainous regions
of Northern and Central Europe, of Britain, and of North America,
became the nurseries of huge ice-streams, and large areas of the
land appear to have been covered with a continuous ice-sheet.
The Arctic conditions of this, the well-known "Glacial period,"
relaxed more than once, and were more than once re-established
with lesser intensity. Finally, a gradual but steadily progressive
amelioration of temperature took place; the ice slowly gave way,
and ultimately disappeared altogether; and the climate once more
became temperate, except in high northern latitudes.
The changes of temperature sketched out above took place slowly
and gradually, and occupied the whole of the Post-Pliocene period.
In each of the three periods marked out by these changes--in
the early temperate, the central cold, and the later temperate
period--certain deposits were laid down over the surface of the
northern hemisphere; and these deposits collectively constitute the
Post-Pliocene formations. Hence we may conveniently classify all
the accumulations of this age under the heads of (1) _Pre-Glacial_
deposits, (2) _Glacial_ deposits, and (3) _Post-Glacial_ deposits,
according as they were formed before, during, or after the "Glacial
period." It cannot by any means be asserted that we can definitely
fix the precise relations in time of all the Post-Pliocene deposits
to the Glacial period. On the contrary, there are some which
hold a very disputed position as regards this point; and there
are others which do not admit of definite allocation in this
manner at all, in consequence of their occurrence in regions
where no "Glacial Period" is known to have been established.
For our present purpose, however, dealing as we shall have to do
principally with the northern hemisphere, the above classification,
with all its defects, has greater advantages than any other that
has been yet proposed.
I. PRE-GLACIAL DEPOSITS.--The chief pre-glacial deposit of Britain
is found on the Norfolk coast, reposing upon the Newer Pliocene
(Norwich Crag), and consists of an ancient land-surface which
is known as the "Cromer Forest-bed."
This consists of an ancient soil, having embedded in it the stumps
of many trees, still in an erect position, with remains of living
plants, and the bones of recent and extinct quadrupeds. It is
overlaid by fresh-water and marine beds, all the shells of which
belong to existing species, and it is finally surmounted by true
"glacial drift." While all the shells and plants of the Cromer
Forest-bed and its associated strata belong to existing species,
the Mammals are partly living, partly extinct. Thus we find the
existing Wolf (_Canis lupus_), Red Deer (_Cervus elaphus_), Roebuck
(_Cervus capreolus_), Mole (_Talpa Europtoea_), and Beaver (_Castor
fiber_), living in western England side by side with the
_Hippopotamus major, Elephas antiquus, Elephas meridionalis,
Rhinoceros Etruscus_, and _R. Megarhinus_ of the Pliocene period,
which are not only extinct, but imply an at any rate moderately
warm climate. Besides the above, the Forest-bed has yielded the
remains of several extinct species of Deer, of the great extinct
Beaver (_Trogontherium Cuvieri_), of the Caledonian Bull or "Urus"
(_Bos primigenius_), and of a Horse (_Equus fossilis_), little
if at all distinguishable from the existing form.
The so-called "Bridlington Crag" of Yorkshire, and the "Chillesford
Beds" of Suffolk, are probably to be regarded as also belonging
to this period; though many of the shells which they contain
are of an Arctic character, and would indicate that they were
deposited in the commencement of the Glacial period itself. Owing,
however, to the fact that a few of the shells of these deposits
are not known to occur in a living condition, these, and some
other similar accumulations, are sometimes considered as referable
to the Pliocene period.
II. GLACIAL DEPOSITS.--Under this head is included a great series
of deposits which are widely spread over both Europe and America,
and which were formed at a time when the climate of these countries
was very much colder than it is at present, and approached more
or less closely to what we see at the present day in the Arctic
regions. These deposits are known by the general name of the
_Glacial deposits_, or by the more specialised names of the Drift,
the Northern Drift, the Boulder-clay, the Till, &c.
These glacial deposits are found in Britain as far south as the
Thames, over the whole of Northern Europe, in all the more elevated
portions of Southern and Central Europe, and over the whole of
North America, as far south as the 39th parallel. They generally
occur as sands, clays, and gravels, spread in widely-extended
sheets over all the geological formations alike, except the most
recent, and are commonly spoken of under the general term of
"Glacial drift." They vary much in their exact nature in different
districts, but they universally consist of one, or all, of the
following members:--
1. _Unstratified_ clays, or loams, containing numerous angular
or sub-angular blocks of stone, which have often been transported
for a greater or less distance from their parent rock, and which
often exhibit polished, grooved, or striated surfaces. These
beds are what is called _Boulder-clay_, or _Till_.
2. Sands, gravels, and clays, often more or less regularly
_stratified_, but containing erratic blocks, often of large size,
and with their edges _unworn_, derived from considerable distances
from the place where they are now found. In these beds it is
not at all uncommon to find fossil shells; and these, though of
existing species, are generally of an Arctic character, comprising
a greater or less number of forms which are now exclusively found
in the icy waters of the Arctic seas. These beds are often spoken
of as "Stratified Drift."
3. _Stratified_ sands and gravels, in which the pebbles are _worn_
and rounded, and which have been produced by a rearrangement of
ordinary glacial beds by the sea. These beds are commonly known
as "Drift-gravels," or "Regenerated Drift".
Some of the last-mentioned of these are doubtless post-glacial;
but, in the absence of fossils, it is often impossible to arrive at
a positive opinion as to the precise age of superficial accumulations
of this nature. It is also the opinion of high authorities that a
considerable number of the so-called "cave-deposits," with the
bones of extinct Mammals, truly belong to the Glacial period,
being formed during warm intervals when the severity of the Arctic
cold had become relaxed. It is further believed that some, at
any rate, of the so-called "high-level" river-gravels and
"brick-earths" have likewise been deposited during mild or warm
intervals in the great age of ice; and in two or three instances
this has apparently been demonstrated--deposits of this nature,
with the bones of extinct animals and the implements of man,
having been shown to be overlaid by true Boulder-clay.
The fossils of the undoubted Glacial deposits are principally
shells, which are found in great numbers in certain localities,
sometimes with _Foraminifera_, the bivalved cases of Ostracode
Crustaceans, &c. Whilst some of the shells of the "Drift" are such
as now live in the seas of temperate regions, others, as previously
remarked, are such as are now only known to live in the seas of
high latitudes; and these therefore afford unquestionable evidence
of cold conditions. Amongst these Arctic forms of shells which
characterise the Glacial beds may be mentioned _Pecten Islandicus_
(fig. 254), _Pecten Groenlandicus, Scalaria Groenlandica, Leda
truncata, Astarte borealis, Tellina proxima, Nattra clausa_,
&c.
[Illustration: Fig. 254.--Left valve of _Pecten Islandicus_, Glacial
and Recent.]
III. POST-GLACIAL DEPOSITS.--As the intense cold of the Glacial
period became gradually mitigated, and temperate conditions of
climate were once more re-established, various deposits were
formed in the northern hemisphere, which are found to contain
the remains of extinct Mammals, and which, therefore, are clearly
of Post-Pliocene age. To these deposits the general name of
_Post-Glacial_ formations is given; but it is obvious that, from
the nature of the case, and with our present limited knowledge,
we cannot draw a rigid line of demarcation between the deposits
formed towards the close of the Glacial period, or during warm
"interglacial" periods, and those laid down after the ice had
fairly disappeared. Indeed it is extremely improbable that any
such rigid line of demarcation should ever have existed; and it
is far more likely that the Glacial and Post-Glacial periods,
and their corresponding deposits, shade into one another by an
imperceptible gradation. Accepting this reservation, we may group
together, under the general head of "Post-Glacial Deposits,"
most of the so-called "Valley-gravels," "Brick-earths," and
"Cave-deposits," together with some "raised beaches" and various
deposits of peat. Though not strictly within the compass of this
work, a few words may be said here as to the origin and mode of
formation of the Brick-earths, Valley-gravels, and Cave-deposits,
as the subject will thus be rendered more clearly intelligible.
Every river produces at the present day beds of fine mud and
loam, and accumulations of gravel, which it deposits at various
parts of its course--the gravel generally occupying the lowest
position, and the finer sands and mud coming above. Numerous
deposits of a similar nature are found in most countries in various
localities, and at various heights above the present channels of
our rivers. Many of these fluviatile (Lat. _fluvius_, a river)
deposits consist of fine loam, worked for brick-making, and known
as "Brick-earths;" and they have yielded the remains of numerous
extinct Mammals, of which the Mammoth (_Elephas primigenius_) is
the most abundant. In the valley of the Rhine these fluviatile
loams (known as "Loess") attain a thickness of several hundred
feet, and contain land and fresh-water shells of existing species.
With these occur the remains of Mammals, such as the Mammoth and
Woolly Rhinoceros. Many of these Brick-earths are undoubtedly
Post-Glacial, but others seem to be clearly "inter-glacial;" and
instances have recently been brought forward in which deposits
of Brick-earth containing bones and shells of fresh-water Molluscs
have been found to be overlaid by regular unstratified boulder-clay.
The so-called "Valley-gravels," like the Brick-earths, are fluviatile
deposits, but are of a coarser nature, consisting of sands and
gravels. Every river gives origin to deposits of this kind at
different points along the course of its valley; and it is not
uncommon to find that there exist in the valley of a single river
two or more sets of these gravel-beds, formed by the river itself,
but formed at times when the river ran at different levels, and
therefore formed at different periods. These different accumulations
are known as the "high-level" and "low-level" gravels; and a
reference to the accompanying diagram will explain the origin
and nature of these deposits (fig. 255). When a river begins
to occupy a particular line of drainage, and to form its own
channel, it will deposit fluviatile sands and gravels along its
sides. As it goes on deepening the bed or valley through which
it flows, it will deposit other fluviatile strata at a lower
level beside its new bed. In this way have arisen the terms
"high-level" and "low-level" gravels. We find, for instance, a
modern river flowing through a valley which it has to a great
extent or entirely formed itself; by the side of its immediate
channel we may find gravels, sand, and loam (fig. 255, 2 2')
deposited by the river flowing in its present bed. These are
_recent_ fluviatile or alluvial deposits. At some distance from
the present bed of the river, and at a higher level, we may find
other sands and gravels, quite like the recent ones in character
and origin, but formed at a time when the stream flowed at a higher
level, and before it had excavated its valley to its present
depth. These (fig. 255, 3 3') are the so-called "_low-level_
gravels" of a river. At a still higher level, and still farther
removed from the present bed of the river, we may find another
terrace, composed of just the same materials as the lower one,
but formed at a still earlier period, when the excavation of
the valley had proceeded to a much less extent. These (fig. 255,
4 4') are the so-called "_high-level_ gravels" of a river, and
there may be one or more terraces of these.
[Illustration: Fig. 255.--Recent and Post-Pliocene Alluvial Deposits.
1, Peat of the recent period; 2, Gravel of the modern river:
2', Loam of the modern river; 3. Lower-level valley-gravel with
bones of extinct Mammals (Post-Pliocene); 3', Loam of the same
age as 3; 4. Higher-level valley-gravel (Post-Pliocene); 4',
Loam of the same age as 4; 5. Upland gravels of various kinds
(often glacial drift); 6, Older rock. (After Sir Charles Lyell.)]
The important fact to remember about these fluviatile deposits
is this--that here the ordinary geological rule is reversed. The
high-level gravels are, of course, the highest, so far as their
actual elevation above the sea is concerned; but geologically the
lowest, since they are obviously much older than the low-level
gravels, as these are than the recent gravels. How much older
the high-level gravels may be than the low-level ones, it is
impossible to say. They occur at heights varying from 10 to 100
feet above the present river-channels, and they are therefore
older than the recent gravels by the time required by the river
to dig out its own bed to this depth. How long this period may
be, our data do not enable us to determine accurately; but if
we are to calculate from the observed rate of erosion of the
actually existing rivers, the period between the different
valley-gravels must be a very long one.
The lowest or recent fluviatile deposits which occur beside the
bed of the present river, are referable to the Recent period,
as they contain the remains of none but living Mammals. The two
other sets of gravels are Post-Pliocene, as they contain the
bones of extinct Mammals, mixed with land and fresh-water shells
of existing species. Among the more important extinct Mammals
of the low-level and high-level valley-gravels may be mentioned
the _Elephas antiquus_, the Mammoth (_Elephas primigenius_),
the Woolly Rhinoceros (_R. Tichorhinus_), the Hippopotamus, the
Cave-lion, and the Cave-bear. Along with these are found
unquestionable traces of the existence of Man, in the form of
rude flint implements of undoubted human workmanship.
The so-called "Cave-deposits," again, though exhibiting peculiarities
due to the fact of their occurrence in caverns or fissures in the
rocks, are in many respects essentially similar to the older
valley-gravels. Caves, in the great majority of instances, occur
in limestone. When this is not the case, it will generally be
found that they occur along lines of sea-coast, or along lines
which can be shown to have anciently formed the coast-line. There
are many caves, however, in the making of which it can be shown
that the sea has had no hand; and these are most of the caves
of limestone districts. These owe their origin to the solvent
action upon lime of water holding carbonic acid in solution.
The rain which falls upon a limestone district absorbs a certain
amount of carbonic acid from the air, or from the soil. It then
percolates through the rock, generally along the lines of jointing
so characteristic of limestones, and in its progress it dissolves
and carries off a certain quantity of carbonate of lime. In this
way, the natural joints and fissures in the rock are widened, as
can be seen at the present day in any or all limestone districts.
By a continuance of this action for a sufficient length of time,
caves may ultimately be produced. Nothing, also, is commoner
in a limestone district than for the natural drainage to take
the line of some fissure, dissolving the rock in its course. In
this way we constantly meet in limestone districts with springs
issuing from the limestone rock--sometimes as large rivers--the
waters of which are charged with carbonate of lime, obtained by
the solution of the sides of the fissure through which the waters
have flowed. By these and similar actions, every district in which
limestones are extensively developed will be found to exhibit
a number of natural caves, rents, or fissures. The first element,
therefore, in the production of cave-deposits, is the existence
of a period in which limestone rocks were largely dissolved, and
caves were formed in consequence of the then existing drainage
taking the line of some fissure.
Secondly, there must have been a period in which various deposits
were accumulated in the caves thus formed. These cavern-deposits
are of very various nature, consisting of mud, loam, gravel,
or breccias of different kinds. In all cases, these materials
have been introduced into the cave at some period subsequent to,
or contemporaneous with, the formation of the cave. Sometimes
the cave communicates with the surface by a fissure through which
sand, gravel, &c., may be washed by rains or by floods from some
neighbouring river. Sometimes the cave has been the bed of an
ancient stream, and the deposits have been formed as are fluviatile
deposits at the surface. Or, again, the river has formerly flowed
at a greater elevation than it does at present, and the cave
has been filled with fluviatile deposits by the river at a time
prior to the excavation of its bed to the present depth (fig.
256). In this last case, the cave-deposits obviously bear exactly
the same relation in point of antiquity to recent deposits, as
do the low-level and high-level valley-gravels to recent
river-gravels. In any case, it is necessary for the physical
geography of the district to change to some extent, in order
that the cave-deposits should be preserved. If the materials
have been introduced by a fissure, the cave will probably become
ultimately filled to the roof, and the aperture of admission
thus blocked up. If a river has flowed through the cave, the
surface configuration of the district must be altered so far
as to divert the river into a new channel. And if the cave is
placed in the side of a river-valley, as in fig. 256, the river
must have excavated its channel to such a depth that it can no
longer wash out the contents of the cave even in high floods.
[Illustration: Fig 256.--Diagrammatic section across a river-valley
and cave. _a a_, Recent valley-gravels near the channel (b) of
the existing river; c, Cavern, partly filled with cave-earth;
_d d_, High-level gravels, filling fissures in the limestone,
which perhaps communicate in some instances with the cave, and
form a channel by which materials of various kinds were introduced
into it; _e e_, Inclined beds of limestone.]
If the cave be entirely filled, the included deposits generally
get more or less completely cemented together by the percolation
through them of water holding carbonate of lime in solution. If
the cave is only partially filled, the dropping of water from
the roof holding lime in solution, and its subsequent evaporation,
would lead to the formation over the deposits below of a layer of
stalagmite, perhaps several inches, or even feet, in thickness.
In this way cave-deposits, with their contained remains, may
be hermetically sealed up and preserved without injury for an
altogether indefinite period of time.
In all caves in limestone in which deposits containing bones are
found, we have then evidence of three principal sets of changes.
(1.) A period during which the cave was slowly hollowed out by
the percolation of acidulated water; (2.) A period in which the
cave became the channel of an engulfed river, or otherwise came
to form part of the general drainage-system of the district; (3.)
A period in which the cave was inhabited by various animals.
As a typical example of a cave with fossiliferous Post-Pliocene
deposits, we may take Kent's Cavern, near Torquay, in which a
systematic and careful examination has revealed the following
sequence of accumulations in descending order:--
(a) Large blocks of limestone, which lie on the floor of the
cave, having fallen from the roof, and which are sometimes cemented
together by stalagmite.
(b) A layer of black mould, from three to twelve inches thick,
with human bones, fragments of pottery, stone and bronze implements,
and the bones of animals now living in Britain. This, therefore,
is a _recent_ deposit.
(c) A layer of stalagmite, from sixteen to twenty inches thick,
but sometimes as much as five feet, containing the bones of Man,
together with those of extinct Post-Pliocene Mammals.
(d) A bed of red cave-earth, sometimes four feet in thickness,
with numerous bones of extinct Mammals (Mammoth, Cave-bear, &c.),
together with human implements of flint and horn.
(e) A second bed of stalagmite, in places twelve feet in thickness,
with bones of the Cave-bear.
(f) A red-loam and cave-breccia, with remains of the Cave-bear
and human implements.
The most important Mammals which are found in cave-deposits in
Europe generally, are the Cave-bear, the Cave-lion, the Cave-hyæna,
the Reindeer, the Musk-ox, the Glutton, and the Lemming--of which
the first three are probably identical with existing forms, and
the remainder are certainly so--together with the Mammoth and
the Woolly Rhinoceros, which are undoubtedly extinct. Along with
these are found the implements, and in some cases the bones, of
Man himself, in such a manner as to render it absolutely certain
that an early race of men was truly contemporaneous in Western
Europe with the animals above mentioned.
IV. UNCLASSIFIED POST-PLIOCENE DEPOSITS.--Apart from any of the
afore mentioned deposits, there occur other accumulations--sometimes
superficial, sometimes in caves--which are found in regions where
a "Glacial period" has not been fully demonstrated, or where
such did not take place; and which, therefore, are not amenable
to the above classification. The most important of these are
known to occur in South America and Australia; and though their
numerous extinct Mammalia place their reference to the Post-Pliocene
period beyond doubt, their relations to the glacial period and
its deposits in the northern hemisphere have not been precisely
determined.
CHAPTER XXII.
THE POST-PLIOCENE PERIOD--_Continued_.
As regards the _life_ of the Post-Pliocene period, we have, in
the first place, to notice the effect produced throughout the
northern hemisphere by the gradual supervention of the Glacial
period. Previous to this the climate must have been temperate or
warm-temperate; but as the cold gradually came on, two results were
produced as regards the living beings of the area thus affected.
In the first place, all those Mammals which, like the Mammoth, the
Woolly Rhinoceros, the Lion, the Hyæna, and the Hippopotamus,
require, at any rate, moderately warm conditions, would be forced
to migrate southwards to regions not affected by the new state
of things. In the second place, Mammals previously inhabiting
higher latitudes, such as the Reindeer, the Musk-ox, and the
Lemming, would be enabled by the increasing cold to migrate
southwards, and to invade provinces previously occupied by the
Elephant and the Rhinoceros. A precisely similar, but more
slowly-executed process, must have taken place in the sea, the
northern Mollusca moving southwards as the arctic conditions of
the Glacial period became established, whilst the forms proper
to temperate seas receded. As regards the readily locomotive
Mammals, also, it is probable that this process was carried on
repeatedly in a partial manner, the southern and northern forms
alternately fluctuating backwards and forwards over the same
area, in accordance with the fluctuations of temperature which
have been shown by Mr James Geikie to have characterised the
Glacial period as a whole. We can thus readily account for the
intermixture which is sometimes found of northern and southern
types of Mammalia in the same deposits, or in deposits apparently
synchronous, and within a single district. Lastly, at the final close
of the arctic cold of the Glacial period, and the re-establishment
of temperate conditions over the northern hemisphere, a reversal
of the original process took place--the northern Mammals retiring
within their ancient limits, and the southern forms pressing
northwards and reoccupying their original domains.
The _Invertebrate_ animals of the Post-Pliocene deposits require
no further mention--all the known forms, except a few of the shells
in the lowest beds of the formation, being identical with species
now in existence upon the globe. The only point of importance in
this connection has been previously noticed--namely, that in
the true Glacial deposits themselves a considerable number of
the shells belong to northern or Arctic types.
As regards the _Vertebrate_ animals of the period, no extinct
forms of Fishes, Amphibians, or Reptiles are known to occur,
but we meet with both extinct Birds and extinct Mammals. The
remains of the former are of great interest, as indicating the
existence during Post-Pliocene times, at widely remote points
of the southern hemisphere, of various wingless, and for the
most part gigantic, Birds. All the great wingless Birds of the
order _Cursores_ which are known as existing at the present day
upon the globe, are restricted to regions which are either wholly
or in great part south of the equator. Thus the true Ostriches are
African; the Rheas are South American; the Emeus are Australian;
the Cassowaries are confined to Northern Australia, Papua, and the
Indian Archipelago; the species of _Apteryx_ are natives of New
Zealand; and the Dodo and Solitaire (wingless, though probably
not true _Cursores_), both of which have been exterminated within
historical times, were inhabitants of the islands of Mauritius
and Rodriguez, in the Indian Ocean. In view of these facts, it
is noteworthy that, so far as known, all the Cursorial Birds
of the Post-Pliocene period should have been confined to the
same hemisphere as that inhabited by the living representatives
of the order. It is still further interesting to notice that
the extinct forms in question are only found in geographical
provinces which are now, or have been within historical times,
inhabited by similar types. The greater number of the remains
of these have been discovered in New Zealand, where there now
live several species of the curious wingless genus _Apteryx_;
and they have been referred by Professor Owen to several generic
groups, of which _Dinornis_ is the most important (fig. 257).
Fourteen species of _Dinornis_ have been described by the
distinguished palæontologist just mentioned, all of them being
large wingless birds of the type of the existing Ostrich, having
enormously powerful hind-limbs adapted for running, but with
the wings wholly rudimentary, and the breast-bone devoid of the
keel or ridge which characterises this bone in all birds which
fly. The largest species is the _Dinornis giganteus_, one of
the most gigantic of living or fossil birds, the shank (tibia)
measuring a yard in length, and the total height being at least
ten feet. Another species, the _Dinornis Elephantopus_ (fig.
257), though not standing more than about six feet in height,
was of an even more ponderous construction--"the framework of
the skeleton being the most massive of any in the whole class of
Birds," whilst "the toe-bones almost rival those of the Elephant"
(Owen). The feet in _Dinornis_ were furnished with three toes,
and are of interest as presenting us with an undoubted Bird big
enough to produce the largest of the foot-prints of the Triassic
Sandstones of Connecticut. New Zealand has now been so far explored,
that it seems questionable if it can retain in its recesses any
living example of _Dinornis_; but it is certain that species
of this genus were alive during the human period, and survived
up to quite a recent date. Not only are the bones very numerous
in certain localities, but they are found in the most recent
and superficial deposits, and they still contain a considerable
proportion of animal matter; whilst in some instances bones have
been found with the feathers attached, or with the horny skin of
the legs still adhering to them. Charred bones have been found
in connection with native "ovens;" and the traditions of the
Maories contain circumstantial accounts of gigantic wingless
Birds, the "Moas," which were hunted both for their flesh and
their plumage. Upon the whole, therefore, there can be no doubt
but that the Moas of New Zealand have been exterminated at quite a
recent period--perhaps within the last century--by the unrelenting
pursuit of Man,--a pursuit which their wingless condition rendered
them unable to evade.
[Illustration: Fig. 257.--Skeleton of _Dinornis elephantopus_,
greatly reduced. Post-Pliocene, New Zealand. (After Owen.)]
In Madagascar, bones have been discovered of another huge wingless
Bird, which must have been as large as, or larger than, the _Dinornis
giganteus_, and which has been described under the name of _Æpiornis
maximus_. With the bones have been found eggs measuring from
thirteen to fourteen inches in diameter, and computed to have
the capacity of three Ostrich eggs. At least two other smaller
species of _Æpiornis_ have been described by Grandidier and
Milne-Edwards as occurring in Madagascar; and they consider the
genus to be so closely allied to the _Dinornis_ of New Zealand,
as to prove that these regions, now so remote, were at one time
united by land. Unlike New Zealand, where there is the _Apteryx_,
Madagascar is not known to possess any living wingless Birds;
but in the neighbouring island of Mauritius the wingless Dodo
(_Didus ineptus_) has been exterminated less than three hundred
years ago; and the little island of Rodriguez, in the same
geographical province, has in a similar period lost the equally
wingless Solitaire (_Pezophaps_), both of these, however, being
generally referred to the _Rasores_.
The _Mammals_ of the Post-Pliocene period are so numerous, that
in spite of the many points of interest which they present, only
a few of the more important forms can be noticed here, and that
but briefly. The first order that claims our attention is that
of the _Marsupials_, the headquarters of which at the present
day is the Australian province. In Oolitic times Europe possessed
its small Marsupials, and similar forms existed in the same area
in the Eocene and Miocene periods; but if size be any criterion,
the culminating point in the history of the order was attained
during the Post-Pliocene period in Australia. From deposits of
this age there has been disentombed a whole series of remains of
extinct, and for the most part gigantic, examples of this group
of Quadrupeds. Not to speak of Wombats and Phalangers, two forms
stand out prominently as representatives of the Post-Pliocene
animals of Australia. One of these is _Diprotodon_ (fig. 258),
representing, with many differences, the well-known modern group
of the Kangaroos. In its teeth, _Diprotodon_ shows itself to
be closely allied to the living, grass-eating Kangaroos; but
the hind-limbs were not so disproportionately long. In size,
also, _Diprotodon_ must have many times exceeded the dimensions
of the largest of its living successors, since the skull measures
no less than three feet in length. The other form in question
is _Thylacoleo_ (fig. 259), which is believed by Professor Owen
to belong to the same group as the existing "Native Devil"
(_Dasyurus_) of Van Diemen's Land, and therefore to have been
flesh-eating and rapacious in its habits, though this view is
not accepted by others. The principal feature in the skull of
_Thylacoleo_ is the presence, on each side of each jaw, of a
single huge tooth, which is greatly compressed, and has a cutting
edge. This tooth is regarded by Owen as corresponding to the
great cutting tooth of the jaw of the typical Carnivores, but
Professor Flower considers that _Thylacoleo_ is rather related to
the Kangaroo-rats. The size of the crown of the tooth in question
is not less than two inches and a quarter; and whether carnivorous
or not, it indicates an animal of a size exceeding that of the
largest of existing Lions.
[Illustration: Fig. 258.--Skull of _Diprotodon Australis_, greatly
reduced. Post-Pliocene, Australia.]
[Illustration: Fig. 259.--Skull of _Thylacoleo_. Post-Pliocene,
Australia. Greatly reduced. (After Flower.)]
The order of the _Edentates_, comprising the existing Sloths,
Ant-eaters, and Armadillos, and entirely restricted at the present
day to South America, Southern Asia, and Africa, is one alike
singular for the limited geographical range of its members, their
curious habits of life, and the well-marked peculiarities of
their anatomical structure. South America is the metropolis of
the existing forms; and it is an interesting fact that there
flourished within Post-Pliocene times in this continent, and to
some extent in North America also, a marvellous group of extinct
Edentates, representing the living Sloths and Armadillos, but
of gigantic size. The most celebrated of these is the huge
_Megatherium Cuvieri_ (fig. 260) of the South American Pampas.
The Megathere was a colossal Sloth-like animal which attained a
length of from twelve to eighteen feet, with bones more massive
than those of the Elephant. Thus the thigh-bone is nearly thrice
the thickness of the same bone in the largest of existing Elephants,
its circumference at its narrowest point nearly equalling its
total length; the massive bones of the shank (tibia and fibula)
are amalgamated at their extremities; the heel-bone (calcaneum)
is nearly half a yard in length; the haunch-bones (ilia) are
from four to five feet across at their crests; and the bodies
of the vertebræ at the root of the tail are from five to seven
inches in diameter, from which it has been computed that the
circumference of the tail at this part might have been from five
to six feet. The length of the fore-foot is about a yard, and
the toes are armed with powerful curved claws. It is known now
that the Megathere, in spite of its enormous weight and ponderous
construction, walked, like the existing Ant-eaters and Sloths,
upon the outside edge of the fore-feet, with the claws more or
less bent inwards towards the palm of the hand. As in the great
majority of the Edentate order, incisor and canine teeth are
entirely wanting, the front of the jaws being toothless. The
jaws, however, are furnished with five upper and four lower molar
teeth on each side. These grinding teeth are from seven to eight
inches in length, in the form of four-sided prisms, the crowns of
which are provided with well-marked transverse ridges; and they
continue to grow during the whole life of the animal. There are
indications that the snout was prolonged, and more or less flexible;
and the tongue was probably prehensile. From the characters of
the molar teeth it is certain that the Megathere was purely
herbivorous in its habits; and from the enormous size and weight
of the body, it is equally certain that it could not have imitated
its modern allies, the Sloths, in the feat of climbing, back
downwards, amongst the trees. It is clear, therefore, that the
Megathere sought its sustenance upon the ground; and it was
originally supposed to have lived upon roots. By a masterly piece
of deductive reasoning, however, Professor Owen showed that this
great "Ground-Sloth" must have truly lived upon the foliage of
trees, like the existing Sloths--but with this difference, that
instead of climbing amongst the branches, it actually uprooted
the tree bodily. In this _tour de force_, the animal sat upon its
huge haunches and mighty tail, as on a tripod, and then grasping
the trunk with its powerful arms, either wrenched it up by the
roots or broke it short off above the ground. Marvellous as this
may seem, it can be shown that every detail in the skeleton of the
Megathere accords with the supposition that it obtained its food
in this way. Similar habits were followed by the allied _Mylodon_
(fig. 261), another of the great "Ground-Sloths," which inhabited
South America during the Post-Pliocene period. In most respects,
the _Mylodon_ is very like the Megathere; but the crowns of the
molar teeth are flat instead of being ridged. The nearly-related
genus _Megalonyx_, unlike the Megathere, but like the Mylodon,
extended its range northwards as far as the United States.
[Illustration: Fig. 260.--_Megatherium Cuvieri_. Post-Pliocene,
South America.]
Just as the Sloths of the present day were formerly represented
in the same geographical area by the gigantic Megatheroids, so
the little banded and cuirassed Armadillos of South America were
formerly represented by gigantic species, constituting the genus
_Glyptodon_. The _Glyptodons_ (fig. 262) differed from the living
Armadillos in having no bands in their armour, so that they must
have been unable to roll themselves up. It is rare at the present
day to meet with any Armadillo over two or three feet in length;
but the length of the _Glyptodon clavipes_, from the tip of the
snout to the end of the tail, was more than nine feet.
[Illustration: Fig. 261.--Skeleton of _Mylodon robustus_.
Post-Pliocene, South America.]
[Illustration: Fig. 262.--Skeleton of _Glyptodon clavipes_.
Post-Pliocene, South America.]
There are no canine or incisor teeth in the _Glyptodon_, but
there are eight molars on each side of each jaw, and the crowns
of these are fluted and almost trilobed. The head is covered
by a helmet of bony plates, and the trunk was defended by an
armour of almost hexagonal bony pieces united by sutures, and
exhibiting special patterns of sculpturing in each species. The
tail was also defended by a similar armour, and the vertebræ were
mostly fused together so as to form a cylindrical bony rod. In
addition to the above-mentioned forms, a number of other Edentate
animals have been discovered by the researches of M. Lund in
the Post-Pliocene deposits of the Brazilian bone-caves. Amongst
these are true Ant-eaters, Armadillos, and Sloths, many of them
of gigantic size, and all specifically or generically distinct
from existing forms.
Passing over the aquatic orders of the _Sirenians_ and _Cetaceans_,
we come next to the great group of the Hoofed Quadrupeds, the
remains of which are very abundant in Post-Pliocene deposits both
in Europe and North America. Amongst the Odd-toed Ungulates the
most important are the Rhinoceroses, of which three species are
known to have existed in Europe during the Post-Pliocene period.
Two of these are the well-known Pliocene forms, the _Rhinoceros
Etruscus_ and the _R. Megarhinus_ still surviving in diminished
numbers; but the most famous is the _Rhinoceros tichorhinus_
(fig. 263), or so-called "Woolly Rhinoceros." This species is
known not only by innumerable bones, but also by a carcass, at
the time of its discovery complete, which was found embedded in
the frozen soil of Siberia towards the close of last century,
and which was partly saved from destruction by the exertions of
the naturalist Pallas. From this, we know that the Tichorhine
Rhinoceros, like its associate the Mammoth, was provided with
a coating of hair, and therefore was enabled to endure a more
severe climate than any existing species. The skin was not thrown
into the folds which characterise most of the existing forms;
and the technical name of the species refers to the fact that
the nostrils were completely separated by a bony partition. The
head carried two horns, placed one behind the other, the front
one being unusually large. As regards its geographical range,
the Woolly Rhinoceros is found in Europe in vast numbers north
of the Alps and Pyrenees, and it also abounded in Siberia; so
that it would appear to be a distinctly northern form, and to
have been adapted for a temperate climate. It is not known to
occur in Pliocene deposits, but it makes its first appearance
in the Pre-Glacial deposits, surviving the Glacial period, and
being found in abundance in Post-Glacial accumulations. It was
undoubtedly a contemporary of the earlier races of men in Western
Europe; and it may perhaps be regarded as being the actual
substantial kernel of some of the "Dragons" of fable.
[Illustration: Fig. 263.--Skull of the Tichorhine Rhinoceros, the
horns being wanting. One-tenth of the natural size. Post-Pliocene
deposits of Europe and Asia.]
The only other Odd-toed Ungulate which needs notice is the so-called
_Equus fossilis_ of the Post-Pliocene of Europe. This made its
appearance before the Glacial period, and appears to be in reality
identical with the existing Horse (_Equus caballus_). True Horses
also occur in the Post-Pliocene of North America; but, from some
cause or another, they must have been exterminated before historic
times.
[Illustration: Fig. 264--Skeleton of the "Irish Elk" (_Cervus
megaceros_). Post-Pliocene, Britain.]
Amongst the Even-toed Ungulates, the great _Hippopotamus major_
of the Pliocene still continued to exist in Post-Pliocene times
in Western Europe; and the existing Wild Boar (_Sus scrofa_),
the parent of our domestic breeds of Pigs, appeared for the first
time. The Old World possessed extinct representatives of its
existing Camels, and lost types of the living Llamas inhabited
South America. Amongst the Deer, the Post-Pliocene accumulations
have yielded the remains of various living species, such as the
Red Deer (_Cervus elaphus_), the Reindeer (_Cervus tarandus_),
the Moose or Elk (_Alces malchis_), and the Roebuck (_Cervus
capreolus_), together with a number of extinct forms. Among the
latter, the great "Irish Elk" (_Cervus megaceros_) is justly
celebrated both for its size and for the number and excellent
preservation of its discovered remains. This extinct species
(fig. 264) has been found principally in peat-mosses and
Post-Pliocene lake-deposits, and is remarkable for the enormous
size of the spreading antlers, which are widened out towards
their extremities, and attain an expanse of over ten feet from
tip to tip. It is not a genuine Elk, but is intermediate between
the Reindeer and the Fallow-deer. Among the existing Deer of the
Post-Pliocene, the most noticeable is the Reindeer, an essentially
northern type, existing at the present day in Northern Europe,
and also (under the name of the "Caribou") in North America. When
the cold of the Glacial period became established, this boreal
species was enabled to invade Central and Western Europe in great
herds, and its remains are found abundantly in cave-earths and
other Post-Pliocene deposits as far south as the Pyrenees.
[Illustration: Fig. 265.--Skull of the Urns (_Bos primigenius_).
Post-Pliocene and Recent. (After Owen.)]
In addition to the above, the Post-Pliocene deposits of Europe
and North America have yielded the remains of various Sheep and
Oxen. One of the most interesting of the latter is the "Urus" or
Wild Bull (_Bos primigenius_, fig. 265), which, though much larger
than any of the existing fossils, is believed to be specifically
undistinguishable from the domestic Ox (_Bos taurus_), and to be
possibly the ancestor of some of the larger European varieties
of oxen. In the earlier part of its existence the Urus ranged
over Europe and Britain in company with the Woolly Rhinoceros
and the Mammoth; but it long survived these, and does not appear
to have been finally exterminated till about the twelfth century.
Another remarkable member of the Post-Pliocene Cattle, also to
begin with an associate of the Mammoth and Rhinoceros, is the
European Bison or "Aurochs" (_Bison priscus_). This "maned" ox
formerly abounded in Europe in Post-Glacial times, and was not
rare even in the later periods of the Roman empire, though much
diminished in numbers, and driven back into the wilder and more
inaccessible parts of the country. At present this fine species
has been so nearly exterminated that it no longer exists in Europe
save in Lithuania, where its preservation has been secured by
rigid protective laws. Lastly, the Post-Pliocene deposits have
yielded the remains of the singular living animal which is known
as the Musk-ox or Musk-sheep (_Ovibos moschatus_). At the present
day, the Musk-ox is an inhabitant of the "barren grounds" of
Arctic America, and it is remarkable for the great length of
its hair. It is, like the Reindeer, a distinctively northern
animal; but it enjoyed during the Glacial period a much wider
range than it has at the present day, the conditions suitable
for its existence being then extended over a considerable portion
of the northern hemisphere. Thus remains of the Musk-Ox are found
in greater or less abundance in Post-Pliocene deposits over a
great part of Europe, extending even to the south of France;
and closely-related forms are found in similar deposits in the
United States.
[Illustration: Fig. 266.--Skeleton of the Mammoth (_Elephas
primigenius_). Portions of the integument still adhere to the
head, and the thick skin of the soles is still attached to the
feet. Post-Pliocene.]
Coming to the _Proboscideans_, we find that the _Mastodons_ seem
to have disappeared in Europe at the close of the Pliocene period,
or at the very commencement of the Post-Pliocene. In the New World,
on the other hand, a species of Mastodon (_M. Americanus_ or _M.
Ohioticus_) is found abundantly in deposits of Post-Pliocene
age, from Canada to Texas. Very perfect skeletons of this species
have been exhumed from morasses and swamps, and large individuals
attained a length (exclusive of the tusks) of seventeen feet and
a height of eleven feet, the tusks being twelve feet in length.
Remains of _Elephants_ are also abundant in the Post-Pliocene
deposits of both the Old and the New World. Amongst these, we
find in Europe the two familiar Pliocene species _E. Meridionales_
and _E. Antiquus_ still surviving, but in diminished numbers.
With these are found in vast abundance the remains of the
characteristic Elephant of the Post-Pliocene, the well-known
"Mammoth" (Elephas primigenius_), which is accompanied in North
America by the nearly-allied, but more southern species, the
_Elephas Americanus_. The Mammoth (fig. 266) is considerably
larger than the largest of the living Elephants, the skeleton
being over sixteen feet in length, exclusive of the tusks, and
over nine feet in height. The tusks are bent almost into a circle,
and are sometimes twelve feet in length, measured along their
curvature. In the frozen soil of Siberia several carcasses of
the Mammoth have been discovered with the flesh and skin still
attached to the bones, the most celebrated of these being a Mammoth
which was discovered at the beginning of this century at the
mouth of the Lena, on the borders of the Frozen Sea, and the
skeleton of which is now preserved at St Petersburg (fig. 266).
From the occurrence of the remains of the Mammoth in vast numbers
in Siberia, it might have been safely inferred that this ancient
Elephant was able to endure a far more rigorous climate than its
existing congeners. This inference has, however, been rendered
a certainty by the specimens just referred to, which show that
the Mammoth was protected against the cold by a thick coat of
reddish-brown wool, some nine or ten inches long, interspersed
with strong, coarse black hair more than a foot in length. The
teeth of the Mammoth (fig.267) are of the type of those of the
existing Indian Elephant, and are found in immense numbers in
certain localities. The Mammoth was essentially northern in its
distribution, never passing south of a line drawn through the
Pyrenees, the Alps, the northern shores of the Caspian, Lake
Baikal, Kamschatka, and the Stanovi Mountains (Dawkins). It occurs
in the Pre-Glacial forest-bed of Cromer in Norfolk, survived the
Glacial period, and is found abundantly in Post-Glacial deposits
in France, Germany, Britain, Russia in Europe, Asia, and North
America, being often associated with the Reindeer, Lemming, and
Musk-ox. That it survived into the earlier portion of the human
period is unquestionable, its remains having been found in a
great number of instances associated with implements of human
manufacture; whilst in one instance a recognisable portrait of
it has been discovered, carved on bone.
[Illustration: Fig. 267.--Molar tooth of the Mammoth (_Elephas
primigenius_), upper jaw, right side, one-third of the natural
size. a, Grinding surface; b, Side view. Post-Pliocene.]
Amongst other Elephants which occur in Post-Pliocene deposits
may be mentioned, as of special interest, the pigmy Elephants
of Malta. One of these--the _Elephas Melitensis_, or so-called
"Donkey-Elephant"--was not more than four and a half feet in
height. The other--the _Elephas Falconeri_, of Busk--was still
smaller, its average height at the withers not exceeding two
and a half to three feet.
[Illustration: Fig. 268.--Skull of _Ursus spelpeus_. Post-Pliocene,
Europe. One-sixth of the natural size.]
Whilst herbivorous animals abounded during the Post-Pliocene,
we have ample evidence of the coexistence with them of a number
of Carnivorous forms, both in the New and the Old World. The
Bears are represented in Europe by at least three species, two
of which--namely, the great Grizzly Bear (_Ursus ferox_) and
the smaller Brown Bear (_Ursus arctos_)--are in existence at the
present day. The third species is the celebrated Cave-bear (_Ursus
speloeus_, fig. 268), which is now extinct. The Cave-bear exceeded
in its dimensions the largest of modern Bears; and its remains,
as its name implies; have been found mainly in cavern-deposits.
Enormous numbers of this large and ferocious species must have
lived in Europe in Post-Glacial times; and that they survived
into the human period, is clearly shown by the common association
of their bones with the implements of man. They are occasionally
accompanied by the remains of a Glutton (the _Gulo speloeus_),
which does not appear to be really separable from the existing
Wolverine or Glutton of northern regions (the _Gulo luscus_).
In addition, we meet with the bones of the Wolf, Fox, Weasel,
Otter, Badger, Wild Cat, Panther, Hyæna, and Lion, &c., together
with the extinct _Machairodus_ or "Sabre-toothed Tiger." The
only two of these that deserve further mention are the Hyæna
and the Lion. The Cave-hyæna (_Hyoena speloea_, fig. 269) is
regarded by high authorities as nothing more than a variety of
the living Spotted Hyæna (_H. Crocuta_) of South Africa. This
well-known species inhabited Britain and a considerable portion
of Europe during a large part of the Post-Pliocene period; and
its remains often occur in great abundance. Indeed, some caves,
such as the Kirkdale Cavern in Yorkshire, were dens inhabited
during long periods by these animals, and thus contain the remains
of numerous individuals and of successive generations of Hyænas,
together with innumerable gnawed and bitten bones of their prey.
That the Cave-hyæna was a contemporary with Man in Western Europe
during Post-Glacial times is shown beyond a doubt by the common
association of its bones with human implements.
[Illustration: Fig. 269.--Skull of _Hyoena speloea_, one-fourth
of the natural size. Post-Phocene, Europe.]
Lastly, the so-called Cave-lion (_Felis speloea_), long supposed
to be a distinct species, has been shown to be nothing more than
a large variety of the existing Lion (_Felis leo_). This animal
inhabited Britain and Western Europe in times posterior to the
Glacial period, and was a contemporary of the Cave-hyæna, Cave-bear,
Woolly Rhinoceros, and Mammoth. The Cave-lion also unquestionably
survived into the earlier portion of the human period in Europe.
The Post-Pliocene deposits of Europe have further yielded the
remains of numerous _Rodents_--such as the Beaver, the Northern
Lemming, Marmots, Mice, Voles, Rabbits, &c.--together with the
gigantic extinct Beaver known as the _Trogontherium Cuvieri_
(fig. 270). The great _Castoroides Ohioensis_ of the Post-Pliocene
of North America is also a great extinct Beaver, which reached
a length of about five feet. Lastly, the Brazilian bone-caves
have yielded the remains of numerous Rodents of types now
characteristic of South America, such as Guinea-pigs, Capybaras,
tree-inhabiting Porcupines, and Coypus.
[Illustration: Fig. 270.--Lower jaw of _Trogontherium Cuvieri_,
one-fourth of the natural size. Post-Pliocene, Britain.]
The deposits just alluded to have further yielded the remains of
various Monkeys, such as Howling Monkeys, Squirrel Monkeys, and
Marmosets, all of which belong to the group of _Quadrumana_ which
is now exclusively confined to the South American continent--namely,
the "Platyrhine" Monkeys.
We still have very briefly to consider the occurrence of Man
in Post-Pliocene deposits; but before doing so, it will be well
to draw attention to the evidence afforded by the Post-Pliocene
Mammals as to the climate of Western Europe at this period. The
chief point which we have to notice is, that a considerable
revolution of opinion has taken place on this point. It was
originally believed that the presence of such animals as Elephants,
Lions, the Rhinoceros, and the Hippopotamus afforded an irrefragable
proof that the climate of Europe must have been a warm one, at any
rate during Post-Glacial times. The existence, also, of numbers
of Mammoths in Siberia, was further supposed to indicate that
this high temperature extended itself very far north. Upon the
whole, however, the evidence is against this view. Not only is
there great difficulty in supposing that the Arctic conditions of
the Glacial period were immediately followed by anything warmer
than a cold-temperate climate; but there is nothing in the nature
of the Mammals themselves which would absolutely forbid their
living in a temperate climate. The _Hippopotamus major_, though
probably clad in hair, offers some difficulty--since, as pointed
out by Professor Busk, it must have required a climate sufficiently
warm to insure that the rivers were not frozen over in the winter;
but it was probably a migratory animal, and its occurrence may
be accounted for by this. The Woolly Rhinoceros and the Mammoth
are known with certainty to have been protected with a thick
covering of wool and hair; and their extension northwards need
not necessarily have been limited by anything except the absence of
a sufficiently luxuriant vegetation to afford them food. The great
American Mastodon, though not certainly known to have possessed a
hairy covering, has been shown to have lived upon the shoots of
Spruce and Firs, trees characteristic of temperate regions--as
shown by the undigested food which has been found with its skeleton,
occupying the place of the stomach. The Lions and Hyænas, again,
as shown by Professor Boyd Dawkins, do not indicate necessarily
a warm climate. Wherever a sufficiency of herbivorous animals
to supply them with food can live, there they can live also;
and they have therefore no special bearing upon the question of
climate. After a review of the whole evidence, Professor Dawkins
concludes that the nearest approach at the present day to the
Post-Pliocene climate of Western Europe is to be found in the
climate of the great Siberian plains which stretch from the Altai
Mountains to the Frozen Sea. "Covered by impenetrable forests,
for the most part of Birch, Poplar, Larch, and Pines, and low
creeping dwarf Cedars, they present every gradation in climate
from the temperate to that in which the cold is too severe to admit
of the growth of trees, which decrease in size as the traveller
advances northwards, and are replaced by the grey mosses and
lichens that cover the low marshy 'tundras.' The maximum winter
cold, registered by Admiral Von Wrangel at Nishne Kolymsk, on
the banks of the Kolyma, is--65° in January. 'Then breathing
becomes difficult; the Reindeer, that citizen of the Polar region,
withdraws to the deepest thicket of the forest, and stands there
motionless as if deprived of life;' and trees burst asunder with
the cold. Throughout this area roam Elks, Black Bears, Foxes,
Sables, and Wolves, that afford subsistence to the Jakutian and
Tungusian fur-hunters. In the northern part countless herds of
Reindeer, Elks, Foxes, and Wolverines make up for the poverty
of vegetation by the rich abundance of animal life. 'Enormous
flights of Swans, Geese, and Ducks arrive in the spring, and seek
deserts where they may moult and build their nests in safety.
Ptarmigans run in troops amongst the bushes; little Snipes are
busy along the brooks and in the morasses; the social Crows seek
the neighbourhood of new habitations; and when the sun shines
in spring, one may even sometimes hear the cheerful note of the
Finch, and in autumn that of the Thrush.' Throughout this region
of woods, a hardy, middle-sized breed of horses lives under the
mastership and care of man, and is eminently adapted to bear the
severity of the climate.... The only limit to their northern
range is the difficulty of obtaining food. The severity of the
winter through the southern portion of this vast wooded area is
almost compensated for by the summer heat and its marvellous
effect on vegetation."--(Dawkins, 'Monograph of Pleistocene
Mammalia.')
Finally, a few words must be said as to the occurrence of the
remains of Man in Post-Pliocene deposits. That Man existed in
Western Europe and in Britain during the Post-Pliocene period, is
placed beyond a doubt by the occurrence of his bones in deposits
of this age, along with the much more frequent occurrence of
implements of human manufacture. At what precise point of time
during the Post-Pliocene period he first made his appearance is
still a matter of conjecture. Recent researches would render
it probable that the early inhabitants of Britain and Western
Europe were witnesses of the stupendous phenomena of the Glacial
period; but this cannot be said to have been demonstrated. That
Man existed in these regions during the Post-Glacial division
of Post-Pliocene time cannot be doubted for a moment. As to the
physical peculiarities of the ancient races that lived with the
Mammoth and the Woolly Rhinoceros, little is known compared with
what we may some day hope to know. Such information as we have,
however, based principally on the skulls of the Engis, Neanderthal,
Cro-Magnon, and Bruniquel caverns, would lead to the conclusion that
Post-Pliocene Man was in no respect inferior in his organisation
to, or less highly developed than, many existing races. All the
known skulls of this period, with the single exception of the
Neanderthal cranium, are in all respects average and normal in
their characters; and even the Neanderthal skull possessed a
cubic capacity at least equal to that of some existing races.
The implements of Post-Pliocene Man are exclusively of stone or
bone; and the former are invariably of rude shape and _undressed_.
These "palæolithic" tools (Gr. _palaios_; ancient; _lithos_,
stone) point to a very early condition of the arts; since the
men of the earlier portion of the Recent period, though likewise
unacquainted with the metals, were in the habit of polishing
or dressing the stone implements which they fabricated.
It is impossible here to enter further into this subject; and
it would be useless to do so without entering as well into a
consideration of the human remains of the Recent period--a period
which lies outside the province of the present work. So far as
Post-Pliocene Man is concerned, the chief points which the
palæontological student has to remember have been elsewhere
summarised by the author as follows:--
1. Man unquestionably existed during the later portion of what
Sir Charles Lyell has termed the "Post-Pliocene" period. In other
words, Man's existence dates back to a time when several remarkable
Mammals, previously mentioned, had not yet become extinct; but he
does not date back to a time anterior to the present _Molluscan_
fauna.
2. The antiquity of the so-called Post-Pliocene period is a matter
which must be mainly settled by the evidence of Geology proper,
and need not be discussed here.
3. The extinct Mammals with which man coexisted in Western Europe are
mostly of large size, the most important being the Mammoth (_Elephas
primogenius_), the Woolly Rhinoceros (_Rhinoceros tichorhinus_),
the Cave-lion (_Felis speloea_), the Cave-hyæna(_Hyoena speloea),
and the Cave-bear (_Ursus speloeus_). We do not know the causes
which led to the extinction of these Mammals; but we know that
hardly any Mammalian species has become extinct during the historical
period.
4. The extinct Mammals with which man coexisted are referable in
many cases to species which presumably required a very different
climate to that now prevailing in Western Europe. How long a
period, however, has been consumed in the bringing about of the
climatic changes thus indicated, we have no means of calculating
with any approach to accuracy.
5. Some of the deposits in which the remains of man have been
found associated with the bones of extinct Mammals, are such as
to show incontestably that great changes in the physical geography
and surface-configuration of Western Europe have taken place
since the period of their accumulation. We have, however, no
means at present of judging of the lapse of time thus indicated
except by analogies and comparisons which may be disputed.
6. The human implements which are associated with the remains
of extinct Mammals, themselves bear evidence of an exceedingly
barbarous condition of the human species. Post-Pliocene or
"Palæolithic" Man was clearly unacquainted with the use of any
of the metals. Not only so, but the workmanship of these ancient
races was much inferior to that of the later tribes, who were also
ignorant of the metals, and who also used nothing but weapons
and tools of stone, bone, &c.
7. Lastly, it is only with the human remains of the Post-Pliocene
period that the palæontologist proper has to deal. When we enter
the "Recent" period, in which the remains of Man are associated
with those of _existing species of Mammals_, we pass out of the
region of pure palæontology into the domain of the Archæologist
and the Ethnologist.
LITERATURE.
The following are some of the principal works and memoirs to which
the student may refer for information as to the Post-Pliocene
deposits and the remains which they contain, as well as to the
primitive races of mankind:--
(1) 'Elements of Geology.' Lyell.
(2) 'Antiquity of Man.' Lyell.
(3) 'Palæontological Memoirs.' Falconer.
(4) 'The Great Ice-age.' James Geikie.
(5) 'Manual of Palæontology.' Owen.
(6) 'British Fossil Mammals and Birds.' Owen.
(7) 'Cave-Hunting.' Boyd Dawkins.
(8) 'Prehistoric Times.' Lubbock.
(9) 'Ancient Stone Implements.' Evans.
(10) 'Prehistoric Man.' Daniel Wilson.
(11) 'Prehistoric Races of the United States.' Foster.
(12) 'Manual of Geology.' Dana.
(13) 'Monograph of Pleistocene Mammalia' (Palæontographical
Society). Boyd Dawkins and Sanford.
(14) 'Monograph of the Post-Tertiary Entomostraca of Scotland, &c.,
with an Introduction on the Post-Tertiary Deposits of Scotland'
(Ibid.) G. S. Brady, H. W. Crosskey, and D. Robertson.
(15) "Reports on Kent's Cavern"--'British Association Reports.'
Pengelly.
(16) "Reports on the Victoria Cavern, Settle"--'British Association
Reports.' Tiddeman.
(17) 'Ossemens Fossiles.' Cuvier.
(18) 'Reliquiæ Diluvianæ.' Buckland.
(19) "Fossil Mammalia"--'Zoology of the Voyage of the Beagle.'
Owen.
(20) 'Description of the Tooth and Part of the Skeleton of the
_Glyptodon_.' Owen.
(21) "Memoir on the Extinct Sloth Tribe of North
America"--'Smithsonian Contributions to Knowledge.' Leidy.
(22) "Report on Extinct Mammals of Australia"--'British Association,'
1844. Owen.
(23) 'Description of the Skeleton of an Extinct Gigantic Sloth
(_Mylodon robtutus_).' Owen.
(24) "Affinities and Probable Habits of Thylacoleo"--'Quart. Journ.
Geol. Soc.,' vol. xxiv. Flower.
(25) 'Prodromus of the Palæontology of Victoria.' M'Coy.
(26) 'Les Ossemens Fossiles des Cavernes de Liège.' Schmerling.
(27) 'Die Fauna der Pfahlbauten in der Schweiz.' Rütimeyer.
(28) "Extinct and Existing Bovine Animals of Scandinavia"--'Annals
of Natural History,' ser. 2, vol. iv., 1849. Nilsson.
(29) 'Man's Place in Nature.' Huxley.
(30) 'Les Temps Antéhistoriques en Belgique.' Dupont.
(31) "Classification of the Pleistocene Strata of Britain and the
Continent"--'Quart. Journ. Geol. Soc.,' vol. xxviii. Boyd Dawkins.
(32) 'Distribution of the Post-Glacial Mammalia' (Ibid.), vol. xxv.
Boyd Dawkins.
(33) 'On British Fossil Oxen' (Ibid.), vols. xxii. and xxiii. Boyd
Dawkins.
(34) 'British Prehistoric Mammals' (Congress of Prehistoric
Archæology, 1868). Boyd Dawkins.
(35) 'Reliquiæ Aquitanicæ.' Lartet and Christy.
(36) 'Zoologie et Paléontologie Françaises.' Gervais.
(37) 'Notes on the Post-Pliocene Geology of Canada.' Dawson.
(38) "On the Connection between the existing Fauna and Flora of
Great Britain and certain Geological Changes"--'Mem. Geol.
Survey.' Edward Forbes.
(39) 'Cavern-Researches.' M'Enery. Edited by Vivian.
(40) "Quaternary Gravels"--'Quart. Journ. Geol. Soc.,' vol. xxv.
Tylor.
CHAPTER XXIII.
THE SUCCESSION OF LIFE UPON THE GLOBE.
In conclusion, it may not be out of place if we attempt to summarise,
in the briefest possible manner, some of the principal results
which may be deduced as to the succession of life upon the earth
from the facts which have in the preceding portion of this work
been passed in review. That there was a time when the earth was
void of life is universally admitted, though it may be that the
geological record gives us no direct evidence of this. That the
globe of to-day is peopled with innumerable forms of life whose
term of existence has been, for the most part, but as it were
of yesterday, is likewise an assertion beyond dispute. Can we
in any way connect the present with the remote past, and can we
indicate even imperfectly the conditions and laws under which the
existing order was brought about? The long series of fossiliferous
deposits, with their almost countless organic remains, is the
link between what has been and what is; and if any answer to the
above question can be arrived at, it will be by the careful and
conscientious study of the facts of Palæontology. In the present
state of our knowledge, it may be safely said that anything like
a dogmatic or positive opinion as to the precise sequence of
living forms upon the globe, and still more as to the manner in
which this sequence may have been brought about, is incapable of
scientific proof. There are, however, certain general deductions
from the known facts which may be regarded as certainly established.
In the first place, it is certain that there has been a _succession_
of life upon the earth, different specific and generic types
succeeding one another in successive periods. It follows from
this, that the animals and plants with which we are familiar
as living, were not always upon the earth, but that they have
been preceded by numerous races more or less differing from them.
What is true of the species of animals and plants, is true also
of the higher zoological divisions; and it is, in the second
place, quite certain that there has been a similar _succession_
in the order of appearance of the primary groups ("sub-kingdoms,"
"classes," &c.) of animals and vegetables. These great groups
did not all come into existence at once, but they made their
appearance successively. It is true that we cannot be said to
be certainly acquainted with the first _absolute_ appearance of
any great group of animals. No one dare assert positively that
the apparent first appearance of Fishes in the Upper Silurian
is really their first introduction upon the earth: indeed, there
is a strong probability against any such supposition. To whatever
extent, however, future discoveries may push back the first advent
of any or of all of the great groups of life, there is no likelihood
that anything will be found out which will materially alter the
_relative_ succession of these groups as at present known to us.
It is not likely, for example, that the future has in store for
us any discovery by which it would be shown that Fishes were in
existence before Molluscs, or that Mammals made their appearance
before Fishes. The sub-kingdoms of Invertebrate animals were
all represented in Cambrian times--and it might therefore be
inferred that _these_ had all come simultaneously into existence;
but it is clear that this inference, though incapable of actual
disproof, is in the last degree improbable. Anterior to the Cambrian
is the great series of the Laurentian, which, owing to the
metamorphism to which it has been subjected, has so far yielded
but the singular _Eozoön_. We may be certain, however, that others
of the Invertebrate sub-kingdoms besides the Protozoa were in
existence in the Laurentian period; and we may infer from known
analogies that they appeared successively, and not simultaneously.
When we come to smaller divisions than the sub-kingdoms--such
as classes, orders, and families--a similar succession of groups
is observable. The different classes of any given sub-kingdom,
or the different orders of any given class, do not make their
appearance together and all at once, but they are introduced
upon the earth in _succession_. More than this, the different
classes of a sub-kingdom, or the different orders of a class,
_in the main succeed one another in the relative order of their
zoological rank--the lower groups appearing first and the higher
groups last_. It is true that in the Cambrian formation--the
earliest series of sediments in which fossils are abundant--we
find numerous groups, some very low, others very high, in the
zoological scale, which _appear_ to have simultaneously flashed
into existence. For reasons stated above, however, we cannot
accept this appearance as real; and we must believe that many of
the Cambrian groups of animals really came into being long before
the commencement of the Cambrian period. At any rate, in the long
series of fossiliferous deposits of later date than the Cambrian
the above-stated rule holds good as a broad generalisation--that
the lower groups, namely, precede the higher in point of time;
and though there are apparent exceptions to the rule, there are
none of such a nature as not to admit of explanation. Some of
the leading facts upon which this generalisarion is founded will
be enumerated immediately; but it will be well, in the first
place, to consider briefly what we precisely mean when we speak
of "higher" and "lower" groups.
It is well known that naturalists are in the habit of "classifying"
the innumerable animals which now exist upon the globe; or, in
other words, of systematically arranging them into groups. The
precise arrangement adopted by one naturalist may differ in minor
details from that adopted by another; but all are agreed as to
the fundamental points of classification, and all, therefore,
agree in placing certain groups in a certain sequence. What,
then, is the principle upon which this sequence is based? Why,
for example, are the Sponges placed below the Corals; these below
the Sea-urchins; and these, again, below the Shell-fish? Without
entering into a discussion of the principles of zoological
classification, which would here be out of place, it must be
sufficient to say that the sequence in question is based upon
the _relative type of organisation_ of the groups of animals
classified. The Corals are placed above the Sponges upon the
ground that, regarded as a whole, the _plan or type of structure_
of a Coral is more complex than that of a Sponge. It is not in the
slightest degree that the Sponge is in any respect less highly
organised or less perfect, as a Sponge, than is the Coral as a
Coral. Each is equally perfect in its own way; but the structural
pattern of the Coral is the highest, and therefore it occupies a
higher place in the zoological scale. It is upon this principle,
then, that the primary subdivisions of the animal kingdom (the
so-called "sub-kingdoms") are arranged in a certain order. Coming,
again, to the minor subdivisions (classes, orders, &c.) of each
sub-kingdom, we find a different but entirely analogous principle
employed as a means of classification. The numerous animals belonging
to any given sub-kingdom are formed upon the same fundamental
plan of structure; but they nevertheless admit of being arranged
in a regular series of groups. All the Shell-fish, for example,
are built upon a common plan, this plan representing the ideal
Mollusc; but there are at the same time various groups of the
_Mollusca_, and these groups admit of an arrangement in a given
sequence. The principle adopted in this case is simply of _the
relative elaboration of the common type_. The Oyster is built
upon the same ground-plan as the Cuttle-fish; but this plan is
carried out with much greater elaboration, and with many more
complexities, in the latter than in the former: and in accordance
with this, the _Cephalopoda_ constitute a higher group than the
Bivalve Shell-fish. As in the case of superiority of structural
type, so in this case also, it is not in the least that the Oyster
is an _imperfect_ animal. On the contrary, it is just as perfectly
adapted by its organisation to fill its own sphere and to meet
the exigencies of its own existence as is the Cuttle-fish; but
the latter lives a life which is, physiologically, higher than
the former, and its organisation is correspondingly increased
in complexity.
This being understood, it may be repeated that, in the main,
the succession of life upon the globe in point of _time_ has
corresponded with the relative order of succession of the great
groups of animals in _zoological rank_; and some of the more
striking examples of this may be here alluded to. Amongst the
_Echinoderms_, for instance, the two orders generally admitted to
be the "lowest" in the zoological scale--namely, the _Crinoids_
and the _Cystoids_--are likewise the oldest, both, appearing in
the Cambrian, the former slowly dying out as we approach the
Recent period, and the latter disappearing wholly before the
close of the Palæozoic period. Amongst the _Crustaceans_, the
ancient groups of the Trilobites, Ostracodes, Phyllopods,
Eurypterids, and Limuloids, some of which exist at the present
day, are all "low" types; whereas the highly-organised Decapods
do not make their appearance till near the close of the Palæozoic
epoch, and they do not become abundant till we reach Mesozoic
times. Amongst the _Mollusca_, those Bivalves which possess
breathing-tubes (the "siphonate" Bivalves) are generally admitted
to be higher than those which are destitute of these organs (the
"asiphonate" Bivalves); and the latter are especially characteristic
of the Palæozoic period, whilst the former abound in Mesozoic
and Kainozoic formations. Similarly, the Univalves with
breathing-tubes and a corresponding notch in the mouth of the
shell ("siphonostomatous" Univalves) are regarded as higher in
the scale than the round-mouthed vegetable-eating Sea-snails, in
which no respiratory siphons exist ("holostomatous" Univalves);
but the latter abound in the Palæozoic rocks--whereas the former
do not make their appearance till the Jurassic period, and their
higher groups do not seem to have existed till the close of the
Cretaceous. The _Cephalopods_, again--the highest of all the groups
of Mollusca--are represented in the Palæozoic rocks exclusively
by Tetrabranchiate forms, which constitute the lowest of the
two orders of this class; whereas the more highly specialised
Dibranchiates do not make their appearance till the commencement
of the Mesozoic. The Palæozoic Tetrabranchiates, also, are of
a much simpler type than the highly complex _Ammonitidoe_ of
the Mesozoic.
Similar facts are observable amongst the _Vertebrate animals_.
The Fishes are the lowest class of Vertebrates, and they are
the first to appear, their first certain occurrence being in
the Upper Silurian; whilst, even if the Lower Silurian and Upper
Cambrian "Conodonts" were shown to be the teeth of Fishes, there
would still remain the enormously long periods of the Laurentian
and Lower Cambrian, during which there were Invertebrates, but
no Vertebrates. The _Amphibians_, the next class in zoological
order, appears later than the Fishes, and is not represented till
the Carboniferous; whilst its highest group (that of the Frogs
and Toads) does not make its entrance upon the scene till Tertiary
times are reached. The class of the _Reptiles_, again, the next
in order, does not appear till the Permian, and therefore not
till after Amphibians of very varied forms had been in existence
for a protracted period. The _Birds_ seem to be undoubtedly later
than the Reptiles; but, owing to the uncertainty as to the exact
point of their first appearance, it cannot be positively asserted
that they preceded Mammals, as they should have done. Finally,
the Mesozoic types of _Mammals_ are mainly, if not exclusively,
referable to the _Marsupials_, one of the lowest orders of the
class; whilst the higher orders of the "Placental" Quadrupeds
are not with certainty known to have existed prior to the
commencement of the Tertiary period.
Facts of a very similar nature are offered by the succession
of Plants upon the globe. Thus the vegetation of the Palæozoic
period consisted principally of the lowly-organised groups of
the Cryptogamous or Flowerless plants. The Mesozoic formations,
up to the Chalk, are especially characterised by the naked-seeded
Flowering plants--the Conifers and the Cycads; whilst the higher
groups of the Angiospermous Exogens and Monocotyledons characterise
the Upper Cretaceous and Tertiary rocks.
Facts of the above nature--and they could be greatly multiplied--seem
to point clearly to the existence of some law of progression,
though we certainly are not yet in a position to formulate this
law, or to indicate the precise manner in which it has operated.
Two considerations, also, must not be overlooked. In the first
place, there are various groups, some of them highly organised,
which make their appearance at an extremely ancient date, but
which continue throughout geological time almost unchanged, and
certainly unprogressive. Many of these "persistent types" are
known--such as various of the _Foraminifera_, the _Linguloe_, the
_Nautili_, &c.; and they indicate that under given conditions, at
present unknown to us, it is possible for a life-form to subsist
for an almost indefinite period without any important modification
of its structure. In the second place, whilst the facts above
mentioned point to some general law of progression of the great
zoological groups, it cannot be asserted that the primeval types
_of any given group_ are necessarily "lower," zoologically speaking,
than their modern representatives. Nor does this seem to be at
all necessary for the establishment of the law in question. It
cannot be asserted, for example, that the Ganoid and Placoid Fishes
of the Upper Silurian are in themselves less highly organised
than their existing representatives; nor can it even be asserted
that the Ganoid and Placoid orders are low _groups_ of the class
_Pisces_. On the contrary, they are high groups; but then it
must be remembered that these are probably not really the first
Fishes, and that if we meet with Fishes at some future time in
the Lower Silurian or Cambrian, these may easily prove to be
representatives of the lower orders of the class. This question
cannot be further entered into here, as its discussion could be
carried out to an almost unlimited length; but whilst there are
facts pointing both ways, it appears that at present we are not
justified in asserting that the earlier types of each group--so far
as these are known to us, or really are without predecessors--are
_necessarily_ or _invariably_ more "degraded" or "embryonic" in
their structure than their more modern representatives.
It remains to consider very briefly how far Palæontology supports
the doctrine of "Evolution," as it is called; and this, too, is a
question of almost infinite dimensions, which can but be glanced at
here. Does Palæontology teach us that the almost innumerable kinds
of animals and plants which we know to have successively flourished
upon the earth in past times were produced separately and wholly
independently of each other, at successive periods? or does it
point to the theory that a large number of these supposed distinct
forms, have been in reality produced by the slow modification of a
comparatively small number of primitive types? Upon the whole, it
must be unhesitatingly replied that the evidence of Palæontology
is in favour of the view that the succession of life-forms upon
the globe has been to a large extent regulated by some orderly
and constantly-acting law of modification and evolution. Upon
no other theory can we comprehend how the fauna of any given
formation is more closely related to that of the formation next
below in the series, and to that of the formation next above,
than to that of any other series of deposits. Upon no other view
can we comprehend why the Post-Tertiary Mammals of South America
should consist principally of Edentates, Llamas, Tapirs, Peccaries,
Platyrhine Monkeys, and other forms now characterising this
continent; whilst those of Australia should be wholly referable
to the order of Marsupials. On no other view can we explain the
common occurrence of "intermediate" or "transitional" forms of
life, filling in the gaps between groups now widely distinct.
On the other hand, there are facts which point clearly to the
existence of some law other than that of evolution, and probably
of a deeper and more far-reaching character. Upon no theory of
evolution can we find a satisfactory explanation for the constant
introduction throughout geological time of new forms of life,
which do not appear to have been preceded by pre-existent allied
types; The Graptolites and Trilobites have no known predecessors,
and leave no known successors. The Insects appear suddenly in the
Devonian, and the Arachnides and Myriapods in the Carboniferous,
under well-differentiated and highly-specialised types. The
Dibranchiate Cephalopods appear with equal apparent suddenness in
the older Mesozoic deposits, and no known type of the Palæozoic
period can be pointed to as a possible ancestor. The _Hippuritidoe_
of the Cretaceous burst into a varied life to all appearance
almost immediately after their first introduction into existence.
The wonderful Dicotyledonous flora of the Upper Cretaceous period
similarly surprises us without any prophetic annunciation from
the older Jurassic.
Many other instances could be given; but enough has been said
to show that there is a good deal to be said on both sides, and
that the problem is one environed with profound difficulties.
One point only seems now to be universally conceded, and that
is, that the record of life in past time is not interrupted by
gaps other than those due to the necessary imperfections of the
fossiliferous series, to the fact that many animals are incapable
of preservation in a fossil condition, or to other causes of a
like nature. All those who are entitled to speak on this head
are agreed that the introduction of new and the destruction of
old species have been slow and gradual processes, in no sense of
the term "catastrophistic." Most are also willing to admit that
"Evolution" has taken place in the past, to a greater or less
extent, and that a greater or less number of so-called species of
fossil animals are really the modified descendants of pre-existent
forms. _How_ this process of evolution has been effected, to what
extent it has taken place, under what conditions and laws it has
been carried out, and how far it may be regarded as merely auxiliary
and supplemental to some deeper law of change and progress, are
questions to which, in spite of the brilliant generalisations
of Darwin, no satisfactory answer can as yet be given. In the
successful solution of this problem--if soluble with the materials
available to our hands--will lie the greatest triumph that
Palæontology can hope to attain; and there is reason to think
that, thanks to the guiding-clue afforded by the genius of the
author of the 'Origin of Species,' we are at least on the road
to a sure, though it may be a far-distant, victory.
APPENDIX.
TABULAR VIEW OF THE CHIEF DIVISIONS OF THE ANIMAL KINGDOM.
(Extinct groups are marked with an asterisk. Groups not represented
at all as fossils are marked with two asterisks.)
INVERTEBRATE ANIMALS.
SUB-KINGDOM I.--PROTOZOA.
Animal simple or compound; body composed of "sarcode," not definitely
segmented; no nervous system; and no digestive apparatus, beyond
occasionally a mouth and gullet.
CLASS I. GREGARINIDÆ.**
CLASS II. RHIZOPODA.
_Order_ 1. _Monera_.**
" 2. _Amoebea_.**
" 3. _Foraminifera_.
" 4. _Radiolaria_ (Polycystines, &c.)
" 5. _Spongida_ (Sponges).
CLASS III. INFUSORIA.**
SUB-KINGDOM II.--COELENTERATA.
Animal simple or compound; body-wall composed of two principal
layers; digestive canal freely communicating with the general
cavity of the body; no circulating organs, and no nervous system
or a rudimentary one; mouth surrounded by tentacles, arranged,
like the internal organs, in a "radiate" or star-like manner.
CLASS I. HYDROZOA.
_Sub-class_ 1. _Hydroida_ ("Hydroid Zoophytes"). _Ex._
Fresh-water Polypes,** Pipe-corallines (_Tubularia_), Sea-Firs
(_Sertularia_).
_Sub-class_ 2. _Siphonophora_** ("Oceanic Hydrozoa").
_Ex_. Portuguese Man-of-war (_Physalia_).
_Sub-class_ 3. _Discophora_ ("Jelly-fishes"). Only known as
fossils by impressions of their stranded carcasses.
_Sub-class_ 4. _Lucernarida_ ("Sea-blubbers"). Also only
known as fossils by impressions left in fine-grained strata.
_Sub-class_ 5. _Graptolitidoe_* ("Graptolites").
CLASS II. ACTINOZOA.
_Order_ 1. _Zoantharia_. _Ex_. Sea-anemones**
(_Actinidoe_), Star-corals (_Astroeidoe_).
_Order_ 2. _Alcyonaria_. _Ex_. Sea-pens
(_Pennatula_), Organ-pipe Coral (_Tubipora_),
Red Coral (_Corallium_).
_Order_ 3. _Rugosa_ ("Rugose Corals").
" 4. _Ctenophora_.** _Ex_. Venus's Girdle (_Cestum_).
SUB-KINGDOM III.--ANNULOIDA.
Animals in which the digestive canal is completely shut off from
the cavity of the body; a distinct nervous system; a system of
branched "water-vessels," which usually communicate with the
exterior. Body of the adult often "radiate," and never composed
of a succession of definite rings.
CLASS I. ECHINODERMATA.
_Order_ 1. _Crinoidea_ ("Sea-lilies"). _Ex_.
Feather-star (_Comatula_), Stone-lily (_Encrinus_*).
_Order_ 2. _Blastoidea_* ("Pentremites").
" 3. _Cystoidea_* ("Globe-lilies").
" 4. _Ophiuroidea_ ("Brittle-stars"). _Ex_.
Sand-stars (_Ophiura_), Brittle-stars (_Ophiocoma_).
_Order_ 5. _Asteroidea_ ("Star-fishes"). Ex. Cross-fish
(_Uraster_), Sun-star (_Solaster_).
_Order_ 6. _Echinoidea_ ("Sea-urchins"). Ex. Sea-eggs
(_Echinus_), Heart-urchins (_Spatangus_).
_Order_ 7. _Holothuroidea_ ("Sea-cucumbers"). _Ex_.
Trepangs (_Holothuria_).
CLASS II. SCOLECIDA** (Intestinal Worms, Wheel Animalcules, &c.)
SUB-KINGDOM IV.--ANNULOSA.
Animal composed of numerous definite segments placed one behind
the other; nervous system forming a knotted cord placed along
the lower (ventral) surface of the body.
_Division A. Anarthropoda_. No jointed limbs.
CLASS I. GEPHYREA** ("Spoon-worms").
CLASS II. ANNELIDA. ("Ringed-worms"). _Ex_. Leeches**
(_Hirudinea_), Earthworms** (_Oligochoeta_),
Tube-worms (_Tubicola_), Sea-worms and
Sea-centipedes (_Errantia_).
CLASS III. CHÆTOGNATHA** ("Arrow-worms").
_Division B. Arthropoda or Articulata_. Limbs jointed to the body.
CLASS I. CRUSTACEA ("Crustaceans"). _Ex_. Barnacles and
Acorn-shells (_Cirripedia_), Water-fleas (_Ostracoda_),
Brine-shrimps and Fairy-shrimps (_Phyllopoda_), Trilobites*
(_Trilobita_), King-crabs and Eurypterids* (_Merostomata_),
Wood-lice and Slaters (_Isopoda_), Sand-hoppers
(_Amphipoda_), Lobsters, Shrimps, Hermit-crabs, and
Crabs (_Decapoda_).
CLASS II. ARACHNIDA. _Ex._ Mites (_Acarina_), Scorpions
(_Pedipalpi_), Spiders (_Araneida_).
CLASS III. MYRIAPODA. _Ex._ Centipedes (_Chilopoda_),
Millipedes and Galley-worms (_Chilignatha_).
CLASS IV. INSECTA ("Insects"). _Ex_. Field-bugs (_Hemiptera_);
Crickets, Grasshoppers, &c. (_Orthoptera_); Dragon-flies
and May-flies (_Neuroptera_); Goats and House-flies
(_Diptera_); Butterflies and Moths (_Lepidoptera_);
Bees, Wasps, and Ants (_Hymenoptera_); Beetles
(_Coleoptera_).
SUB-KINGDOM V.--MOLLUSCA.
Animal soft-bodied, generally with a hard covering or shell; no
distinct segmentation of the body; nervous system of scattered
masses.
CLASS I. POLYZOA ("Sea-Mosses"). _Ex_. Sea-mats (_Flustra_),
Lace-corals (_Fenestellidoe_*).
CLASS II. TUNICATA** ("Tunicaries"). _Ex_. Sea-squirts
(_Ascidia_).
CLASS III. BRACHIOPODA ("Lamp-shells"). _Ex_. Goose-bill
Lamp-shell (_Lingula_).
CLASS IV. LAMELLIBRANCHIATA ("Bivalves"). _Ex_. Oyster
(_Ostrea_), Mussel (_Mytilus_), Scallop (_Pecten_),
Cockle (_Cardium_).
CLASS V. GASTEROPODA ("Univalves"). _Ex_. Whelks
(_Buccinum_), Limpets (_Patella_), Sea-slugs**
(_Doris_), Land-snails (_Helix_).
CLASS VI. PTEROPODA ("Winged Snails"). Ex. _Hyalea, Cleodora_.
CLASS VII. CEPHALOPODA ("Cuttle-fishes"). _Ex_. Calamary
(_Loligo_), Poulpe (_Octopus_), Paper Nautilus
(_Arganauta_), Pearly Nautilus (_Nautilus_), Belemnites,*
Orthoceratites,* Ammonites.*
VERTEBRATE ANIMALS.
SUB-KINGDOM VI.--VERTEBRATA.
Body composed of definite segments arranged longitudinally one
behind the other; main masses of the nervous system placed dorsally;
a backbone or "vertebral column" in the majority.
CLASS I. PISCES ("Fishes"). _Ex_. Lancelet** (_Amphioxus_);
Lampreys and Hag-fishes (_Marsipobranchii_**); Herring,
Salmon, Perch, &c. (_Teleostei_ or "Bony Fishes");
Gar-pike, Sturgeon, &c. (_Ganoidei_); Sharks, Dog-fishes,
Rays, &c. (_Elasmobranchii_ or "Placoids").
CLASS II. AMPHIBIA ("Amphibians"). Ex. _Labyrinthodontia_,*
Cæcilians,** Newts and Salamanders (_Urodela_), Frogs and
Toads (_Anoura_).
CLASS III. REPTILIA ("Reptiles"). Ex. _Deinosauria_,*
_Pterosauria_,* _Anomodontia_,* Plesiosaurs
(_Sauropterygia_*), Ichthyosaurs (_Ichthyopterygia_*),
Tortoises and Turtles (_Chelonia_), Snakes (_Ophidia_),
Lizards (_Lacertilia_), Crocodiles (_Crocodilia_).
CLASS IV. AVES ("Birds"). _Ex_. Toothed Birds
(_Odontornithes_*); Lizard-tailed Birds (_Archoeopteryx_*);
Ducks, Geese, Gulls, &c. (_Natatores_); Storks, Herons,
Snipes, Plovers, &c. (_Grallatores_); Ostrich, Emeu,
Cassowary, Dinornis,* Æpiornis,* &c. (_Cursores_); Fowls,
Game Birds, and Doves (_Rasores_); Cuckoos, Woodpeckers,
Parrots, &c. (_Scansores_); Crows, Starlings, Finches,
Hummingbirds, Swallows, &c. (_Insessores_); Owls, Hawks,
Eagles, Vultures (_Raptores_).
CLASS V. MAMMALIA ("Quadrupeds"). _Ex_. Duck-mole and Spiny
Ant-eater (_Monotremata_**); Kangaroos, Phalangers,
Opossums, Tasmanian Devil, &c. (_Marsupialia_); Sloths,
Ant-eaters, Armadillos (_Edentata_); Manatees and Dugongs
(_Sirenia_); Whales, Dolphins, Porpoises (_Cetacea_);
Rhinoceros, Tapir, Horses, Hippopotamus, Pigs, Camels and
Llamas, Giraffes, Deer, Antelopes, Sheep, Goats, Oxen
(_Ungulata_); Hyrax (_Hyracoidea_**); Elephants,
Mastodon,* Deinotherium* (_Proboscidea_); Seals,
Walrus, Bears, Dogs, Wolves, Cats, Lions, Tigers, &c.
(_Carnivora_); Hares, Rabbits, Porcupines, Beavers,
Rats, Mice, Lemmings, Squirrels, Marmots, &c. (_Rodentia_);
Bats (_Cheiroptera_); Moles, Shrew-mice, Hedgehogs
(_Insectivora_); Lemurs, Spider-monkeys, Macaques,
Baboons, Apes (_Quadrumana_); Man (_Bimana_).
GLOSSARY.
ABDOMEN (Lat. _abdo_, I conceal). The posterior cavity of the
body, containing the intestines and others of the viscera. In
many Invertebrates there is no separation of the body-cavity
into thorax and abdomen, and it is only in the higher _Annulosa_
that a distinct abdomen can be said to exist.
ABERRANT (Lat. _aberro_, I wander away). Departing from the regular
type.
ABNORMAL (Lat. _ab_, from; _norma_, a rule). Irregular; deviating
from the ordinary standard.
ACRODUS (Gr. _akros_, high; _odous_, tooth). A genus of the
Cestraciont fishes, so called from the elevated teeth.
ACROGENS (Gr. _akros_, high; _gennao_, I produce). Plants which
increase in height by additions made to the summit of the stem
by the union of the bases of the leaves.
ACROTRETA (Gr. _akros_, high; _tretos_, pierced). A genus of
Brachiopods, so called from the presence of a foramen at the summit
of the shell.
ACTINOCRINUS (Gr. _aktin_, a ray; _krinon_, a lily). A genus of
Crinoids.
ACTINOZOA (Gr. _aktin_, a ray; and _zoön_, an animal). That division
of the _Coelenterata_ of which the Sea-anemones may be taken as
the type.
ÆGLINA (_Æglé_, a sea-nymph). A genus of Trilobites.
ÆPIORNIS (Gr. _aipus_, huge; _ornis_, bird). A genus of gigantic
Cursorial birds.
AGNOSTUS (Gr. _a_, not; _gignosko_, I know). A genus of Trilobites.
ALCES (Lat. _alces_, elk). The European Elk or Moose.
ALECTO (the proper name of one of the Furies). A genus of _Polyzoa_.
ALETHOPTERIS (Gr. _alethes_, true; _pteris_, fern). A genus of
Ferns.
ALGÆ. (Lat. _alga_, a marine plant). The order of plants comprising
the Sea-weeds and many fresh-water plants.
ALVEOLUS (Lat. _alvus_, belly). Applied to the sockets of the
teeth.
AMBLYPTERUS (Gr. _amblus_, blunt; _pteron_, fin). An order of
Ganoid Fishes.
AMBONYCHIA (Gr. _ambon_, a boss; _onux_, claw). A genus of Palæozoic
Bivalves.
AMBULACRA (Lat. _ambulacrum_, a place for walking). The perforated
spaces or "avenues" through which are protruded the tube-feet,
by means of which locomotion is effected in the _Echinodermata_.
AMMONITIDÆ. A family of Tetrabranchiate Cephalopods, so called
from the resemblance of the shell of the type-genus, _Ammonites_,
to the horns of the Egyptian God, Jupiter-Ammon.
AMORPHOZOA (Gr. _a_, without; _morphe_, shape; _zoön_, animal).
A name sometimes used to designate the _Sponges_.
AMPHIBIA (Gr. _amphi_, both; _bios_, life). The Frogs, Newts,
and the like, which have gills when young, but can always breathe
air directly when adult.
AMPHICYON (Gr. _amphi_, both--implying doubt; _kuon_, dog). An
extinct genus of _Carnivora_.
AMPHILESTES (Gr. _amphi_, both; _lestes_, a thief). A genus of
Jurassic Mammals.
AMPHISPONGIA (Gr. _amphi_, both; _spoggos_, sponge). A genus of
Silurian sponges.
AMPHISTEGINA (Gr. _amphi_, both; _stegé_, roof). A genus of
_Foraminifera_.
AMPHITHERIUM (Gr. _amphi_, both; _therion_, beast). A genus of
Jurassic Mammals.
AMPHITRAGULUS (Gr. _amphi_, both; dim. of _tragos_, goat). An
extinct genus related to the living Musk-deer.
AMPLEXUS (Lat. an Ambrace). A genus of Rugose Corals.
AMPYX (Gr. _ampux_, a wreath or wheel). A genus of Trilobites.
ANARTHROPODA (Gr. _a_, without; _arthros_, a joint; _pous_, foot).
That division of _Annulose_ animals in which there are no articulated
appendages.
ANCHITHERIUM (Gr. _agchi_, near; _therion_, beast). An extinct
genus of Mammals.
ANCYLOCERAS (Gr. _agkulos_, crooked; _ceras_, horn). A genus of
_Ammonitidoe_.
ANCYLOTHERIUM (Gr. _agkulos_, crooked; _therion_, beast). An extinct
genus of Edentate Mammals.
ANDRIAS (Gr. _andrias_, image of man). An extinct genus of tailed
Amphibians.
ANGIOSPERMS (Gr. _angeion_, a vessel; _sperma_, seed). Plants
which have their seeds enclosed in a seed-vessel.
ANNELIDA (a Gallicised form of _Annulata_). The Ringed Worms,
which form one of the divisions of the _Anarthropoda_.
ANNULARIA (Lat. _annulus_, a ring). A genus of Palæozoic plants,
with leaves in whorls.
ANNULOSA (Lat. _annulus_). The sub-kingdom comprising the
_Anarthropoda_ and the _Arthropoda_ or _Articulata_, in all of
which the body is more or less evidently composed of a succession
of rings.
ANOMODONTIA (Gr. _anomos_, irregular; _odous_, tooth). An extinct
order of Reptiles, often called _Dicynodontia_.
ANOMURA (Gr. _anomos_, irregular; _oura_, tail). A tribe of Decapod
_Crustacea_, of which the Hermit-crab is the type.
ANOPLOTHERIDÆ (Gr. _anoplos_, unarmed; _ther_, beast). A family
of Tertiary Ungulates.
ANOURA (Gr. _a_, without; _oura_, tail). The order of _Amphibia_
comprising the Frogs and Toads, in which the adult is destitute
of a tail. Often, called _Batrachia_.
ANTENNÆ (Lat. _antenna_, a yard-arm). The jointed horns or feelers
possessed by the majority of the _Articulata_.
ANTENNULES (dim. of _Antennoe_). Applied to the smaller pair of
antennæ in the _Crustacea_.
ANTHRACOSAURUS (Gr. _anthrax_, coal; _saura_, lizard). A genus
of Labyrinthodont Amphibians.
ANTHRAPALÆMON (Gr. _anthrax_, coal; _paloemon_, a prawn--originally
a proper name). A genus of long-tailed Crustaceans from the
Coal-measures.
ANTLERS. Properly the branches of the horns of the Deer tribe
(_Cervidoe_), but generally applied to the entire horns.
APIOCRINIDÆ (Gr. _apion_, a pear; _krinon_, lily). A family of
Crinoids--the "Pear-encrinites."
APTERYX (Gr. _a_, without; _pterux_, a wing). A wingless bird
of New Zealand, belong to the order _Cursores_.
AQUEOUS (Lat. _aqua_, water). Formed in or by water.
ARACHNIDA (Gr. _arachne_, a spider). A class of the _Articulata_,
comprising Spiders, Scorpions, and allied animals.
ARBORESCENT. Branched like a tree.
ARCHÆOCIDARIS (Gr. _archaios_, ancient; Lat. _cidaris_, a diadem).
A Palæozoic genus of Sea-urchins, related to the existing _Cidaris_.
ARCHÆOCYATHUS (Gr. _archaios_, ancient; _kuathos_, cup). A genus
of Palæozoic fossils allied to the Sponges.
ARCHÆOPTERYX (Gr. _archaios_, ancient; _pterux_, a wing). The
singular fossil bird which alone constitutes the order of the
_Saururoe_.
ARCTOCYON (Gr. _arctos_, bear; _kuon_, dog). An extinct genus
of Carnivora.
ARENACEOUS. Sandy, or composed of grains of sand.
ARENICOLITES (Lat. _arena_, sand; _colo_, I inhabit). A genus
founded on burrows supposed to be formed by worms resembling
the living Lobworms (_Arenicola_).
ARTICULATA (Lat. _articulus_, a joint). A division of the animal
kingdom, comprising Insects, Centipedes, Spiders, and Crustaceans,
characterised by the possession of jointed bodies or jointed
limbs. The term _Arthropoda_ is now more usually employed.
ARTIODACTYLA (Gr. _artios_, even; _daktulos_, a finger or toe).
A division of the hoofed quadrupeds (_Ungulata_) in which each
foot has an even number of toes (two or four).
ASAPHUS (Gr. _Asaphes_, obscure). A genus of Trilobites.
ASCOCERAS (Gr. _askos_, a leather bottle; _keras_, horn). A genus
of Tetrabranchiate Cephalopods.
ASIPHONATE. Not possessing a respiratory tube or siphon. (Applied
to a division of the _Lamellibranchiate_ Molluscs.)
ASTEROID (Gr. _aster_, a star; and _eidos_, form). Star-shaped,
or possessing radiating lobes or rays like a star-fish.
ASTEROIDEA. An order of _Echinodermata_, comprising the Star-fishes,
characterised by their rayed form.
ASTEROPHYLLITES (Gr. _aster_, a star; _phullon_, leaf). A genus
of Palæozoic plants, with leaves in whorls.
ASTRÆIDÆ (Gr. _Astroea_, a proper name). The family of the
Star-corals.
ASTYLOSPONGIA (Gr. _a_, without; _stulos_, a column; _spoggos_,
a sponge). A genus of Silurian Sponges.
ATHYRIS (Gr. _a_, without; _thura_, door). A genus of Brachiopods.
ATRYPA (Gr. _a_, without; _trupa_, a hole). A genus of Brachiopods.
AVES (Lat. _avis_, a bird). The class of the Birds.
AVICULA (Lat. a little bird). The genus of Bivalve Molluscs
comprising the Pearl-oysters.
AXOPHYLLUM (Gr. _axon_, a pivot; _phullon_, a leaf). A genus of
Rugose Corals.
AZOIC (Gr. _a_, without; _zoé_, life). Destitute of traces of
living beings.
BACULITES (Lat. _baculum_, a staff). A genus of the _Ammonitidoe_.
BALÆNA (Lat. a whale). The genus of the Whalebone Whales.
BALANIDÆ (Gr. _balanos_, an acorn). A family of sessile _Cirripedes_,
commonly called "Acorn-shells."
BATRACHIA (Gr. _batrachos_, a frog). Often loosely applied to
any of the _Amphibia_, but sometimes restricted to the Amphibians
as a class, or to the single order of the _Anoura_.
BELEMNITIDÆ (Gr. _belemnon_, a dart). An extinct group of
Dibranchiate Cephalopods, comprising the Belemnites and their
allies.
BELEMNOTEUTHIS (Gr. _belemnon_, a dart; _teuthis_, a cuttle-fish).
A genus allied to the Belemnites proper.
BELINURUS (Gr. _belos_, a dart; _oura_, tail). A genus of fossil
King-crabs.
BELLEROPHON (Gr. proper name). A genus of oceanic Univalves
(_Heteropoda_).
BELOTEUTHIS (Gr. _belos_, a dart; _teuthis_, a cuttle-fish). An
extinct genus of Dibranchiate Cephalopods.
BEYRICHIA (named after Prof. Beyrich). A genus of Ostracode
Crustaceans.
BILATERAL. Having two symmetrical sides.
BIMANA (Lat. _Bis_, twice; _manus_, a hand). The order of _Mammalia_
comprising man alone.
BIPEDAL (Lat. _bis_, twice; _pes_, foot). Walking upon two legs.
BIVALVE (Lat. _bis_, twice; _valvoe_, folding-doors). Composed of
two plates or valves; applied to the shell of the _Lamellibranchiata_
and _Brachiopoda_, and to the carapace of certain _Crustacea_.
BLASTOIDEA (Gr. _blastos_, a bud; and _eidos_, form). An extinct
order of _Echinodermata_, often called _Pentremites_.
BRACHIOPODA (Gr. _brachion_, an arm; _pous_, the foot). A class
or the _Molluscoida_, often called "Lamp-shells," characterised
by possessing two fleshy arms continued from the sides of the
mouth.
BRACHYURA (Gr. _brachus_, short; _oura_, tail). A tribe of the
Decapod _Crustaceans_ with short tails (_i.e._, the Crabs).
BRADYPODIDÆ. (Gr. _bradus_, slow; _podes_, feet). The family of
_Edentata_ comprising the Sloths.
BRANCHIA (Gr. _bragchia_, the gill of a fish). A respiratory organ
adapted to breathe air dissolved in water.
BRANCHIATE. Possessing gills or branchiæ.
BRONTEUS (Gr. _broné_, thunder--an epithet of Jupiter the Thunderer).
A genus of Trilobites.
BRONTOTHERIUM (Gr. _bronté_, thunder; _therion_ beast). An extinct
genus of Ungulate Quadrupeds.
BRONTOZOUM (Gr. _bronté_, thunder; _zoön_, animal). A genus founded
on the largest footprints of the Triassic Sandstones of Connecticut.
BUCCINUM (Lat. _buccinun_, a trumpet). The genus of Univalves
comprising the Whelks.
CAINOZOIC (_See_ Kainozoic.)
CALAMITES (Lat. _calamus_, a reed). Extinct plants with reed-like
stems, believed to be gigantic representatives of the _Equisetaceoe_.
CALCAREOUS (Lat. _calx_, lime). Composed of carbonate of lime.
CALICE. The little cup in which the polype of a coralligenous
Zoophyte (_Actinozoön_) is contained.
CALYMENE (Gr. _kalumené_, concealed). A genus of Trilobites.
CALYX (Lat. a cup). Applied to the cup-shaped body of a _Crinoid_
(_Echinodermata_).
CAMAROPHORIA (Gr. _kamara_, a chamber; _phero_, I carry). A genus
of Brachiopods.
CAMELOPARDALIDÆ. (Lat. _camelus_, a camel; _pardalis_, a panther).
The family of the Giraffes.
CANINE (Lat. _canis_, a dog). The eye-tooth of Mammals, or the
tooth which is placed at or close to the præmaxillary suture in
the upper jaw, and the corresponding tooth in the lower jaw.
CARAPACE. A protective shield. Applied to the upper shell of
Crabs, Lobsters, and many other _Crustacea_. Also the upper half
of the immovable case in which the body of a Chelonian is protected.
CARCHARODON (Gr. _karcharos_. rough; _odous_, tooth). A genus
of Sharks.
CARDIOCARPON (Gr. _kardia_, the heart; _karpos_, fruit). A genus
of fossil fruit from the Coal-measures.
CARDIUM (Gr. _kardia_, the heart). The genus of Bivalve Molluscs
comprising the Cockles. _Cardinia, Cardiola_, and _Cardita_ have
the same derivation.
CARNIVORA (Lat. _caro_, flesh; _voro_, I devour). An order of
the _Mammalia_. The "Beasts of Prey."
CARNIVOROUS (Lat. _caro_, flesh; _voro_, I devour). Feeding upon
flesh.
CARYOCARIS (Gr. _karua_, a nut; _karis_, a shrimp). A genus of
Phyllopod Crustaceans.
CARYOCRINUS (Gr. _karua_, a nut; _krinon_, a lily). A genus of
Cystideans.
CAUDAL (Lat. _cauda_, the tail). Belonging to the tail.
CAVICORNIA (Lat. _cavus_, hollow; _cornu_, a horn). The
"hollow-horned" Ruminants, in which the horn consists of a central
bony "horn-core" surrounded by a horny sheath.
CENTRUM (Gr. _kentron_, the point round which a circle is described
by a pair of compasses). The central portion or "body" of a vertebra.
CEPHALASPIDÆ. (Gr. _kephale_, head; _aspis_, shield). A family
of fossil fishes.
CEPHALIC (Gr. _kephale_, head). Belonging to the head.
CEPHALOPODA (Gr. _kephale_; and _podes_, feet). A class of the
_Mollusca_, comprising the Cuttle-fishes and their allies, in
which there is a series of arms ranged round the head.
CERATIOCARIS (Gr. _keras_, a horn; _karis_, a shrimp). A genus
of Phyllopod Crustaceans.
CERATITES (Gr. _keras_, a horn). A genus of _Ammonitidoe_.
CERATODUS (Gr. _keras_, a horn; _odous_, tooth). A genus of Dipnoous
fishes.
CERVICAL (Lat. _cervix_, the neck). Connected with or belonging
to the region of the neck.
CERVIDÆ (Lat. _cervus_, a stag). The family of the Deer.
CESTRAPHORI (Gr. _kestra_, a weapon; _phero_, I carry). The group
of the "Cestraciont Fishes," represented at the present day by
the Port-Jackson Shark; so called from their defensive spines.
CETACEA (Gr. _ketos_, a whale). The order of Mammals comprising
the Whales and the Dolphins.
CETIOSAURUS (Gr. _ketos_, whale; _saura_, lizard). A genus of
Deinosaurian Reptiles.
CHEIROPTERA (Gr. _cheir_, hand; _pteron_, wing). The Mammalian
order of the Bats.
CHEIROTHERIUM (Gr. _cheir_, hand; _therion_, beast). The generic
name applied originally to the hand-shaped footprints of
Labyrinthodonts.
CHEIRURUS (Gr. _cheir_, hand; _oura_, tail). A genus of Trilobites.
CHELONIA (Gr. _cheloné_, a tortoise). The Reptilian order of the
Tortoises and Turtles.
CHONETES (Gr. _choné_ or _choané_, a chamber or box). A genus
of Brachiopods.
CIDARIS (Lat. a diadem). A genus of Sea-urchins.
CLADODUS (Gr. _klados_, branch; _odous_, tooth). A genus of Fishes.
CLATHROPORA (Lat. _clathti_, a trellis; _porus_, a pore). A genus
of Lace-corals (_Polyzoa_).
CLISIOPHYLLUM (Gr. _klision_, a hut; _phullon_, leaf). A genus
of Rugose Corals.
CLYMENIA (_Clumene_, a proper name). A genus of Tetrabranchiate
Cephalopods.
COCCOSTEUS (Gr. _kokkos_, berry; _osteon_, bone). A genus of Ganoid
Fishes.
COCHLIODUS (Gr. _kochlion_, a snail-shell; _odous_, tooth). A
genus of Cestraciont Fishes.
COELENTERATA (Gr. _koilos_, hollow; _enteron_, the bowel). The
sub-kingdom which comprises the _Hydrozoa_ and _Actinozoa_. Proposed
by Frey and Leuckhart in place of the old term _Radiata_, which
included other animals as well.
COLEOPTERA (Gr. _koleos_, a sheath; _pteron_, wing). The order
of Insects (Beetles) in which the anterior pair of wings are
hardened, and serve as protective cases for the posterior pair
of membranous wings.
COLOSSOCHELYS (Gr. _kolossos_, a gigantic statue; _chelus_, a
tortoise). A huge extinct Land-tortoise.
COMATULA (Gr. _koma_, the hair). The Feather-star, so called in
allusion to its tress-like arms.
CONDYLE (Gr. _kondulos_, a knuckle). The surface by which one
bone articulates with another. Applied especially to the articular
surface or surfaces by which the skull articulates with the vertebral
column.
CONIFERÆ (Lat. _conus_, a cone; _fero_, I carry). The order of
the Firs, Pines, and their allies, in which the fruit is generally
a "cone" or "fir-apple."
CONULARIA (Lat. _conulus_, a little-cone). An extinct genus of
Pteropods.
COPRALITES (Gr. _kopros_, dung; _lithos_, stone). Properly applied
to the fossilised excrements of animals; but often employed to
designate phosphatic concretions which are not of this nature.
CORALLITE. The corallum secreted by an _Actinozoön_ which consists
of a single polype; or the portion of a composite corallum which
belongs to, and is secreted by, an individual polype.
CORALLUM (from the Latin for Red Coral). The hard structures
deposited in, or by the tissues of an _Actinozoön_,--commonly
called a "coral."
CORIACEOUS (Lat. _corium_. hide). Leathery.
CORYPHODON (Gr. _korus_, helmet; _odous_, tooth). An extinct genus
of Mammals, allied to the Tapirs.
CRANIUM (Gr. _kranion_, the skull). The bony or cartilaginous
case in which the brain is contained.
CRETACEOUS (Lat. _creta_, chalk). The formation which in Europe
contains white chalk as one of its most conspicuous members.
CRINOIDEA (Gr. _krinon_, a lily; _eidos_, form). An order of
_Echinodermata_, comprising forms which are usually stalked, and
sometimes resemble lilies in shape.
CRIOCERAS (Gr. _krios_, a ram; _keras_, a horn). A genus of
_Ammonitidoe_.
CROCODILIA (Gr. _krokodeilos_, a crocodile). An order of Reptiles.
CROSSOPTERYGIDÆ. (Gr. _krossotos_, a fringe; _pterux_, a fin). A
sub-order of Ganoids in which the paired fins possess a central
lobe.
CRUSTACEA (Lat. _crusta_, a crust). A class of Articulate animals,
comprising Crabs, Lobsters, &c., characterised by the possession
of a hard shell or crust, which they cast periodically.
CRYPTOGAMS (Gr. _kruptos_, concealed; _gamos_, marriage). A division
of plants in which the organs of reproduction are obscure and
there are no true flowers.
CTENACANTHUS (Gr. _kteis_, a comb; _akantha_, a thorn). A genus
of fossil fishes, named from its fin-spines.
CTENOID (Gr. _kteis_, a comb; _eidos_, form). Applied to those
scales of fishes the hinder margins of which are fringed with
spines or comb-like projections.
CURSORES (Lat. _curro_, I run). An order of _Aves_, comprising
birds destitute of the power of flight, but formed for running
vigorously (_e.g._, the Ostrich and Emeu).
CUSPIDATE. Furnished with small pointed eminences or "cusps."
CYATHOCRINUS (Gr. _kuathos_, a cup; _krinon_, a lily). A genus
of Crinoids.
CYATHOPHYLLUM (Gr. _kuathos_, a cup; _phullon_, a leaf). A genus
of Rugose Corals.
CYCLOID (Gr. _kuklos_, a circle; _eidos_, form). Applied to those
scales of fishes which have a regularly circular or elliptical
outline with an even margin.
CYCLOPHTHALMUS (Gr. _kuklos_, a circle; _ophthalmos_, eye). A
genus of fossil Scorpions.
CYCLOSTOMI (Gr. _kuklos_, and _stoma_, mouth). Sometimes used
to designate the Hag-fishes and Lampreys, forming the order
_Marsipobranchii_.
CYPRÆA (a name of Venus). The genus of Univalve Molluscs comprising
the Cowries.
CYRTOCERAS (Gr. _kurtos_. crooked; _keras_, horn). A genus of
Tetrabranchiate Cephalopods.
CYSTIPHYLLUM (Gr. _kustis_, a bladder; _phullon_, a leaf). A genus
of Rugose Corals.
CYSTOIDEA (Gr. _kustis_, a bladder; _eidos_, form). The
"Globe-crinoids," an extinct order of _Echinodermata_.
DADOXYLON (Gr. _dadion_, a torch; _xulon_, wood). An extinct genus
of Coniferous trees.
DECAPODA (Gr. _deka_, ten; _podes_, feet). The division of
_Crustacea_ which have ten feet; also the family of Cuttle-fishes,
in which there are ten arms or cephalic processes.
DECIDUOUS (Lat. _decido_, I fall off). Applied to parts which
fall off or are shed during the life of the animal.
DEINOSAURIA (Gr. _deinos_, terrible; _saura_, lizard). An extinct
order of Reptiles.
DEINOTHERIUM (Gr. _deinos_, terrible; _therion_, beast). An extinct
genus of Proboscidean Mammals.
DENDROGRAPTUS (Gr. _dendron_, tree; _grapho_, I write). A genus
of Graptolites.
DESMIDIÆ. Minute fresh-water plants, of a green colour, without
a siliceous epidermis.
DIATOMACEÆ (Gr. _diatemno_, I sever). An order of minute plants
which are provided with siliceous envelopes.
DIBRANCHIATA (Gr. _dis_; twice; _bragchia_, gill). The order
of _Cephalopoda_ (comprising the Cuttle-fishes, &c.) in which
only two gills are present.
DICERAS (Gr. _dis_, twice; _keras_, horn). An extinct genus of
Bivalve Molluscs.
DICTYONEMA (Gr. _diktuon_, a net; _nema_, thread). An extinct
genus of _Polyzoa_.
DICYNODONTIA (Gr. _dis_, twice; _kuon_, dog; _odous_, tooth).
An extinct order of Reptiles.
DIDYMOGRAPTUS (Gr. _didumos_, twin; _grapho_, I write). A genus
of Graptolites.
DIMORPHODON (Gr. _dis_, twice; _morphé_, shape; _oduos_, tooth).
A genus of Pterosaurian reptiles.
DINICHTHYS (Gr. _deinos_, terrible; _ichthus_, fish). An extinct
genus of Fishes.
DINOCERAS (Gr. _deinos_, terrible; _keras_, horn). An extinct
genus of Mammals.
DINOPHIS (Gr. _deinos_, terrible; _ophis_, snake). An extinct
genus of Snakes.
DINORNIS (Gr. _deinos_, terrible; _ornis_, bird). An extinct genus
of Birds.
DIPLOGRAPTUS (Gr. _diplos_, double; _grapho_, I write). A genus
of Graptolites.
DIPNOI (Gr. _dis_, twice; _pnoé_, breath). An order of Fishes,
comprising the Mud-fishes, so called in allusion to their double
mode of respiration.
DIPROTODON (Gr. _dis_, twice; _protos_, first; _odous_, tooth).
A genus of extinct Marsupials.
DIPTERA (Gr. _dis_, twice; _pteron_, wing). An order of Insects
characterised by the possession of two wings.
DISCOID (Gr. _diskos_, a quoit; _eidos_, form). Shaped like a
round plate or quoit.
DOLOMITE (named after M. Dolomieu). Magnesian limestone.
DORSAL (Lat. _dorsum_, the back). Connected with or placed upon
the back.
DROMATHERIUM (Gr. _dromaios_, nimble; _therion_, beast). A genus
of Triassic Mammals.
DRYOPITHECUS (Gr. _drus_, an oak; _pithekos_, an ape). An extinct
genus of Monkeys.
ECHINODERMATA (Gr. _echinos_; and _derma_, skin). A class of
animals comprising the Sea-urchins, Star-fishes, and others, most
of which have spiny skins.
ECHINOIDEA (Gr. _echinos_; and _eidos_, form). An order of
_Echinodermata_, comprising the Sea-urchins.
EDENTATA (Lat. _e_, without; _dens_, tooth). An order of _Mammalia_
often called _Bruta_.
EDENTULOUS. Toothless, without any dental apparatus. Applied to
the mouth of any animal, or to the hinge of the Bivalve Molluscs.
ELASMOBRANCHII (Gr. _elasma_, a plate; _bragchia_, gill). An order
of Fishes, including the Sharks and Rays.
ENALIOSAURIA (Gr. _enalios_, marine; _saura_, lizard), Sometimes
employed as a common term to designate the extinct Reptilian
orders of the _Ichthyosauria_ and _Plesiosauria_.
EOCENE (Gr. _eos_, dawn; _kainos_, new or recent). The lowest
division of the Tertiary rocks, in which species of existing
shells are to a small extent represented.
EOPHYTON (Gr. _eos_, dawn; _phuton_, a plant). A genus of Cambrian
fossils, supposed to be of a vegetable nature.
EOZOÖN (Gr. _eos_, dawn; _zoön_, animal). A genus of chambered
calcareous organisms found in the Laurentian and Huronian formations.
EQUILATERAL (Lat. _oequus_, equal; _latus_, side). Having its
sides equal. Usually applied to the shells of the _Brachiopoda_.
When applied to the spiral shells of the _Foraminifera_, it means
that all the convolutions of the shell lie in the same plane.
EQUISETACEÆ (Lat. _equus_, horse; _seta_, bristle). A group of
Cryptogamous plants, commonly known as "Horse-tails."
EQUIVALVE (Lat. _oequus_, equal; _valvoe_, folding-doors). Applied
to shells which are composed of two equal pieces or valves.
ERRANTIA (Lat. _erro_, I wander). An order of _Annelida_, often
called _Nereidea_, distinguished by their great locomotive powers.
EUOMPHALUS (Gr. _eu_, well; _omphalos_, navel). An extinct genus
of Univalve Molluscs.
EURYPTERIDA (Gr. _eurus_, broad; _pteron_, wing). An extinct
sub-order of _Crustacea_.
EXOGYRA (Gr. _exo_, outside; _guros_, circle). An extinct genus
of Oysters.
FAUNA (Lat. _Fauni_, the rural deities of the Romans). The general
assemblage of the animals of any region or district.
FAVOSITES (Lat. _favus_, a honeycomb). A genus of Tabulate Corals.
FENESTELLIDÆ. (Lat. _fenestella_, a little window). The
"Lace-corals," a group of Palæozoic Polyzoans.
FILICES (Lat. _filix_, a fern). The order of Cryptogamic plants
comprising the Ferns.
FILIFORM (Lat. _filum_, a thread; _forma_, shape). Thread-shaped.
FLORA (Lat. _Flora_, the goddess of flowers). The general assemblage
of the plants of any region or district.
FORAMINIFERA (Lat. _foramen_, an aperture; _fero_, I carry).
An order of Protozoa, usually characterised by the possession
of a shell perforated by numerous pseudopodial apertures.
FRUGIVOROUS (Lat. _frux_, fruit; _voro_, I devour). Living upon
fruits.
FUCOIDS (Lat. _fucus_, sea-weed; Gr. _eidos_, likeness). Fossils,
often of an obscure nature, believed to be the remains of sea-weeds.
FUSULINA (Lat. _fusus_, a spindle). An extinct genus of
_Foraminifera_.
GANOID (Gr, _ganos_, splendour, brightness). Applied to those
scales or plates which are composed of an inferior layer of true
bone covered by a superior layer of polished enamel.
GANOIDEI. An order of Fishes.
GASTEROPODA (Gr. _gaster_, stomach; _pous_, foot). The class
of the Mollusca comprising the ordinary Univalves, in which
locomotion is usually effected by a muscular expansion of the
under surface of the body (the "foot").
GLOBIGERINA (Lat. _globus_, a globe; _gero_, I carry). A genus
of _Foraminifera_.
GLYPTODON (Gr. _glupho_, I engrave; _odous_, tooth). An extinct
genus of Armadillos, so named in allusion to the fluted teeth.
GONIATITES (Gr. _gonia_, angle). A genus of Tetrabranchiate
Cephalopods.
GRALLATORES (Lat. _gralloe_, stilts). The order of the long-legged
Wading Birds.
GRAPTOLITIDÆ. (Gr. _grapho_, I write; _lithos_, stone). An extinct
sub-class of the _Hydrozoa_.
GYMNOSPERMS (Gr. _gumnos_, naked; _sperma_, seed). The Conifers
and Cycads, in which the seed is not protected within a seed-vessel.
HALITHERIUM (Gr. _hals_, sea; _therion_, beast). An extinct genus
of Sea-cows (_Sirenia_).
HAMITES (Lat. _hamus_, a hook). A genus of the _Ammonitidoe_.
HELIOPHYLLUM (Gr. _helios_, the sun; _phullon_, leaf). A genus
of Rugose Corals.
HELLADOTHERIUM (Gr. _Hellas_, Greece; _therion_, beast). An extinct
genus of Ungulate Mammals.
HEMIPTERA (Gr. _hemi_, and _pteron_, wing). An order of Insects
in which the anterior wings are sometimes "hemelytra."
HESPERORNIS (Gr. _Hesperos_, the evening star; _ornis_, bird).
An extinct genus of Birds.
HETEROCERCAL (Gr. _heteros_, diverse; _kerkos_, tail). Applied
to the tail of Fishes when it is unsymmetrical, or composed of
two unequal lobes.
HETEROPODA (Gr. _heteros_, diverse; _podes_, feet). An aberrant
group of the Gasteropods, in which the foot is modified so as
to form a swimming organ.
HIPPARION (Gr. _hipparion_, a little horse). An extinct genus
of _Equidoe_.
HIPPOPOTAMUS (Gr. _hippos_, horse; _potamos_, river). A genus
of Hoofed Quadrupeds--the "River-horses."
HIPPURITIDÆ. (Gr. _hippos_, horse; _oura_, tail). An extinct family
of Bivalve Molluscs.
HOLOPTYCHIUS (Gr. _holos_, whole; _ptucé_, wrinkle). An extinct
genus of Ganoid Fishes.
HOLOSTOMATA (Gr. _holos_, whole; _stoma_, mouth). A division
of _Gasteropodous Molluscs_, in which the aperture of the shell
is rounded, or "entire."
HOLOTHUROIDEA (Gr. _holothourion_, and _eidos_, form). An order
of _Echinodermata_ comprising the Trepangs.
HOMOCERCAL (Gr. _homos_, same; _kerkol_, tail). Applied to the
tail of Fishes when it is symmetrical, or composed of two equal
lobes.
HYBODUNTS (Gr. _hubos_, curved; _odous_, tooth). A group of Fishes
of which _Hybodus_ is the type-genus.
HYDROIDA (Gr. _hudra_; and _eidos_, form). The sub-class of the
_Hydrozoa_, which comprises the animals most nearly allied to
the Hydra.
HYDROZOA (Gr. _hudra_; and _zoön_, animal). The class of the
_Coelenterata_ which comprises animals constructed after the type
of the Hydra.
HYMENOPTERA (Gr. _humen_, a membrane; _pteron_, a wing). An order
of Insects (comprising Bees, Ants, &c.) characterised by the
possession of four membranous wings.
ICHTHYODORULITE (Gr. _ichthus_, fish; _dorus_, spear; _lithos_,
stone). The fossil fin-spine of Fishes.
ICHTHYOPTERYGIA (Gr. _ichthus_; _pterux_, wing). An extinct order
of Reptiles.
ICHTHYORNIS (Gr. _ichthus_, fish; _ornis_, bird). An extinct genus
of Birds.
ICHTHYOSAURIA (Gr. _ichthus_; _saura_, lizard). Synonymous with
_Ichthyopterygia_.
IGUANODON (_Iguana_, a living lizard; Gr. _odous_, tooth). A genus
of Deinosaurian Reptiles.
INCISOR (Lat. _incido_, I cut). The cutting teeth fixed in the
intermaxillary bones of the _Mammalia_, and the corresponding
teeth in the lower jaw.
INEQUILATERAL. Having the two sides unequal, as in the case of
the shells of the ordinary bivalves (_Lamellibranchiata_). When
applied to the shells of the _Foraminifera_, it implies that
the convolutions of the shell do not lie in the same plane, but
are obliquely wound round an axis.
INEQUIVALVE. Composed of two unequal pieces or valves.
INOCERAMUS (Gr. _is_, a fibre; _keramos_, an earthen vessel).
An extinct genus of Bivalve Molluscs.
INSECTA (Lat. _inseco_, I cut into). The class of articulate animals
commonly known as Insects.
INSECTIVORA (Lat. _insectum_, an insect; _voro_, I devour). An
order of Mammals.
INSECTIVOROUS. Living upon Insects.
INSESSORES (Lat. _insedeo_, I sit upon). The order of the Perching
Birds, often called _Passeres_.
INTERAMBULACRA. The rows of plates in an _Echinoid_ which are
not perforated for the emission of the "tube-feet."
INTERMMAXILLÆ or PRÆMAXILLÆ. The two bones which are situated
between the two superior maxillæ in _Vertebrata_. In man, and
some monkeys, the præmaxillæ anchylose with the maxillæ, so as
to be irrecognisable in the adult.
INVERTEBRATA (Lat. _in_, without; _vertebra_, a bone of the back).
Animals without a spinal column or backbone.
ISOPODA. (Gr. _isos_, equal; _podes_, feet). An order of _Crustacea_
in which the feet are like one another and equal.
KAINOZOIC (Gr. _kainos_, recent; _zoe_, life). The Tertiary period
in Geology comprising those formations in which the organic remains
approximate more or less closely to the existing fauna and flora.
LABYRINTHODONTIA (Gr. _laburinthos_, a labyrinth; _odous_, tooth).
An extinct order of _Amphibia_, so called from the complex
microscopic structure of the teeth.
LACERTILIA (Lat. _lacerta_, a lizard). An order of _Reptilia_
comprising the Lizards and Slow-worms.
LAMELLIBRANCHIATA (Lat. _lamella_, a plate; Gr. _bragchia_, gill).
The class of _Mollusca_ comprising the ordinary bivalves,
characterised by the possession of lamellar gills.
LEPIDODENDRON (Gr. _lepis_, a scale; _dendron_, a tree). A genus
of extinct plants, so named from the scale-like scars upon the
stem left by the falling off of the leaves.
LEPIDOPTERA (Gr. _lepis_, a scale; _pteron_, a wing). An order
of Insects, comprising Butterflies and Moths, characterised by
possessing four wings which are usually covered with minute scales.
LEPIDOSIREN (Gr. _lepis_, a scale; _seiren_, a siren--the generic
name of the Mud-eel or _Siren lacertina_). A genus of Dipnoous
fishes, comprising the "Mud-fishes."
LEPIDOSTROBUS (Gr. _lepis_, a scale; _strobilos_, a fir-cone).
A genus founded on the cones of _Lepidodendron_.
LEPTÆNA (Gr. _leptos_. slender). A genus of Brachiopods.
LINGULA (Lat. _lingula_, a little tongue). A genus of Brachiopods.
LYCOPODIACEÆ (Gr. _lupos_, a wolf; _pous_, foot). The group of
Cryptogamic plants generally known as "Club-mosses."
MACHÆRACANTHUS (Gr. _machaira_, a sabre; _acantha_, thorn or spine).
An extinct genus of Fishes.
MACHAIRODUS (Gr. _machaira_, a sabre; _odous_, tooth). An extinct
genus of Carnivora.
MACROTHERIUM (Gr. _makros_, long; _therion_. beast). An extinct
genus of Edentata.
MACRURA (Gr. _makros_, long; _oura_, tail). A tribe of Decapod
_Crustaceans_ with long tails (e.g., the Lobster, Shrimp, &c.)
MAMMALIA (Lat. _mamma_, the breast). The class of Vertebrate animals
which suckle their young.
MANDIBLE (Lat. _mandibulum_, a jaw). The upper pair of jaws in
Insects; also applied to one of the pairs of jaws in _Crustacea_
and Spiders, to the beak of Cephalopods, the lower jaw of
Vertebrates, &c.
MANTLE. The external integument of most of the Mollusca, which
is largely developed, and forms a cloak in which the viscera
are protected. Technically called the "pallium."
MANUS (Lat. the hand). The hand of the higher Vertebrates.
MARSIPOBRANCHII (Gr. _marsipos_, a pouch; _bragchia_, gill).
The order of Fishes comprising the Hag-fishes and Lampreys, with
pouch-like gills.
MARSUPIALIA (Lat. _marsupium_, a pouch). An order of Mammals in
which the females mostly have an abdominal pouch in which the
young are carried.
MASTODON (Gr. _mastos_, nipple; _odous_, tooth). An extinct genus
of Elephantine Mammals.
MEGALONYX (Gr. _megas_, great; _onux_, nail). An extinct genus
of Edentate Mammals.
MEGALOSAURUS (Gr. _megas_, great; _saura_, lizard). A genus of
Deinosaurian Reptiles.
MEGATHERIUM (Gr. _megas_, great; _therion_, beast). An extinct
genus of Edentata.
MESOZOIC (Gr. _mesos_, middle; and _zoe_, life). The Secondary
period in Geology.
MICROLESTES (Gr. _mikros_, little; _lestes_, thief). An extinct
genus of Triassic Mammals.
MILLEPORA (Lat. _mille_, one thousand; _porus_, a pore). A genus
of "Tabulate Corals."
MIOCENE (Gr. _meion_, less; _kainol_, new). The Middle Tertiary
period.
MOLARS (Lat. _mola_, a mill). The "grinders" in man, or the teeth
in diphyodont Mammals which are not preceded by milk-teeth.
MOLLUSCA (Lat. _mollis_, soft). The sub-kingdom which includes
the Shell-fish proper, the _Polyzoa_, the _Tunicata_, and the
Lamp-shells; so called from the generally soft nature of their
bodies.
MOLLUSCOIDA (_Mollusca_; Gr. _eidos_, form). The lower division
of the _Mollusca_, comprising the _Polyzoa, Tunicata_, and
_Brachiopoda_.
MONOGRAPTUS (Gr. _monos_, single; _grapho_, I write). A genus
of Graptolites.
MYLODON (Gr. _mulos_, a mill; _odous_, tooth). An extinct genus
of Edentate Mammals.
MYRIAPODA or MYRIOPODA (Gr. _murios_, ten thousand; _podes_,
feet). A class of _Arthropoda_ comprising the Centipedes and their
allies, characterised by their numerous feet.
NATATORES (Lat. _nare_, to swim). The order of the Swimming Birds.
NATATORY (Lat. _nare_, to swim). Formed for swimming.
NAUTILOID. Resembling the shell of the _Nautilus_ in shape.
NERVURES (Lat. _nervus_, a sinew). The ribs which support the
membranous wings of insects.
NEUROPTERA (Gr. _neuron_, a nerve; _pteron_, a wing). An order
of Insects characterised by four membranous wings with numerous
reticulated nervures (_e.g._, Dragon-flies).
NEUROPTERIS (Gr. _neuron_, a nerve; _pteris_, a fern). An extinct
genus of Ferns.
NOTHOSAURUS (Gr. _nothos_, spurious; _saura_, lizard). A genus
of _Plesiosaurian_ Reptiles.
NOTOCHORD (Gr. _notos_, back; _chorde_, string). A cellular rod
which is developed in the embryo of Vertebrates immediately beneath
the spinal cord, and which is usually replaced in the adult by the
vertebral column. Often it is spoken of as the "chorda dorsalis."
NUDIBRANCHIATA (Lat. _nudus_, naked; and Gr. _bragchia_, gill).
An order of the _Gasteropoda_ in which the gills are naked.
NUMMULINA (Lat. _nummus_, a coin). A genus of _Foraminifera_,
comprising the coin-shaped "Nummulites."
OBOLELLA (Lat. dim. of _obolus_, a small coin). An extinct genus
of Brachiopods.
OCCIPITAL. Connected with the _occiput_, or the back part of the
head.
OCEANIC. Applied to animals which inhabit the open ocean (= pelagic).
ODONTOPTERYX (Gr. _oduos_, tooth; _pterux_, wing). An extinct
genus of Birds.
ODONTORNITHES (Gr. _oduos_, tooth; _ornis_, bird). The extinct
order of Birds, comprising forms with distinct teeth in sockets.
OLIGOCENE (Gr. _oligos_, few; _kainos_, new). A name used by
many Continental geologists as synonymous with the Lower Miocene.
OPHIDIA (Gr. _ophis_, a serpent). The order of Reptiles comprising
the Snakes.
OPHIUROIDEA (Gr. _ophis_, snake; _oura_, tail; _eidos_, form).
An order of _Echinodermata_, comprising the Brittle-stars and
Sand-stars.
ORNITHOSCELIDA (Gr. _ornis_, bird; _skelos_, leg). Applied by
Huxley to the Deinosaurian Reptiles, together with the genus
_Compsognathus_, on account of the bird-like character of their
hind-limbs.
ORTHIS (Gr. _orthos_, straight). A genus of Brachiopods, named
in allusion to the straight hinge-line.
ORTHOCERATIDÆ (Gr. _orthos_, straight; _keras_, horn). A family
of the _Nautilidoe_, in which the shell is straight, or nearly
so.
ORTHOPTERA (Gr. _orthos_, straight; _pteron_, wing). An order
of Insects.
OSTEOLEPIS (Gr. _osteon_, bone; _lepis_, scale). An extinct genus
of Ganoid Fishes.
OSTRACODA (Gr. _ostrakon_, a shell). An order of small Crustaceans
which are enclosed in bivalve shells.
OTODUS (Gr. _ota_, ears; _odous_, tooth). An extinct genus of
Sharks.
OUDENODON (Gr. _ouden_, none; _odous_, tooth). A genus of Dicynodont
Reptiles.
OVIBUS (Lat. _ovis_, sheep; _bos_, ox). The genus comprising the
Musk-ox.
PACHYDERMATA (Gr. _pachus_, thick; _derma_, skin). An old Mammalian
order constituted by Cuvier for the reception of the Rhinoceros,
Hippopotamus, Elephant, &c.
PALÆASTER (Gr. _palaios_, ancient; _aster_, star). An extinct
genus of Star-fishes.
PALÆOCARIS (Gr. _palaios_, ancient; _karis_, shrimp). An extinct
genus of Decapod Crustaceans.
PALÆOLITHIC (Gr. _palaios_, ancient; _lithos_, stone). Applied
to the rude stone implements of the earliest known races of men,
to the men who made these implements, or to the period at which
they were made.
PALÆONTOLOGY (Gr. _palaios_, ancient; and _logos_, discourse).
The science of fossil remains or of extinct organised beings.
PALÆOPHIS (Gr. _palaios_, ancient; _ophis_, serpent). An extinct
genus of Snakes.
PALÆOSAURUS (Gr. _palaios_, ancient; _saura_, lizard). A genus
of Thecodont Reptiles.
PALÆOTHERIDÆ. (Gr. _palaios_, ancient; _ther_, beast). A group
of Tertiary Ungulates.
PALÆOZOIC (Gr. _palaios_, ancient; and _zoe_, life). Applied to
the oldest of the great geological epochs.
PARADOXIDES (Lat. _paradoxus_, marvellous). A genus of Trilobites.
PATAGIUM (Lat. the border of a dress). Applied to the expansion
of the integument by which Bats, Flying Squirrels, and other
animals support themselves in the air.
PECOPTERIS (Gr. _peko_, I comb; _pteris_, a fern). An extinct
genus of Ferns.
PECTEN (Lat. a comb). The genus of Bivalve Molluscs comprising
the Scallops.
PECTORAL (Lat. _pectus_, chest). Connected with, or placed upon,
the chest.
PENTACRINUS (Gr. _penta_, five; _krinon_, lily). A genus of Crinoids
in which the column is five-sided.
PENTAMERUS (Gr. _penta_, five; _meros_, part). An extinct genus
of Brachiopods.
PENTREMITES (Gr. _penta_, five; _trema_, aperture). A genus of
_Blastoidea_, so named in allusion to the apertures at the summit
of the calyx.
PERENNIBRANCHIATA (Lat. _perennis_, perpetual; Gr. _bragchia_,
gill). Applied to those Amphibia in which the gills are permanently
retained throughout life.
PERISSODACTYLA (Gr. _perissos_, uneven; _daktulos_, finger).
Applied to those Hoofed Quadrupeds (_Ungulata_) in which the feet
have an uneven number of toes.
PETALOID. Shaped like the petal of a flower.
PHACOPS (Gr. _phaké_, a lentil; _ops_, the eye). A genus of
Trilobites.
PHALANGES (Gr. _phalanx_, a row). The small bones composing the
digits of the higher _Vertebrata_. Normally each digit has three
phalanges.
PHANEROGAMS (Gr. _phaneros_, visible; _gamos_, marriage). Plants
which have the organs of reproduction conspicuous, and which
bear true flowers.
PHARYNGOBRANCHII (Gr. _pharugx_, pharynx; _bragchia_, gill). The
order of Fishes comprising only the Lancelet.
PHASCOLOTHERIUM (Gr. _phaskolos_, a pouch; _therion_, a beast).
A genus of Oolitic Mammals.
PHRAGMACONE (Gr. _phragma_, a partition; and _konos_, a cone).
The chambered portion of the internal shell of a _Belemnite_.
PHYLLOPODA (Gr. _phullon_, leaf; and _pous_, foot). An order of
_Crustacea_.
PINNATE (Lat. _pinna_, a feather). Feather-shaped; or possessing
lateral processes.
PINNIGRADA (Lat. _pinna_, a feather; _gradior_, I walk). The
group of _Carnivora_, comprising the Seals and Walruses, adapted
for an aquatic life. Often called _Pinnipedia_.
PINNULÆ. (Lat. dim. of _pinna_). The lateral processes of the
arms of _Crinoids_.
PISCES (Lat. _piscis_, a fish). The class of Vertebrates comprising
the Fishes.
PLACOID (Gr. _plax_, a plate; _eidos_, form). Applied to the
irregular bony plates, grains, or spines which are found in the
skin of various fishes (_Elasmobranchii_).
PLAGIOSTOMI (Gr. _plagios_, transverse; _stoma_, mouth). The
Sharks and Rays, in which the mouth is transverse, and is placed
on the under surface of the head.
PLATYCERAS (Gr. _platus_, broad; _keras_, horn). A genus of Univalve
Molluscs.
PLATYCRINUS (Gr. _platus_, broad; _krinom_, lily). A genus of
Crinoidea.
PLATYRHINA (Gr. _platus_, broad; _rhines_, nostrils). A group
of the _Quadrumana_.
PLATYSOMUS (Gr. _platus_, wide; _soma_, body). A genus of Ganoid
Fishes.
PLEISTOCENE (Gr. _pleistos_, most; _kainos_, new). Often used
as synonymous with "Post-Pliocene."
PLEUROTOMARIA (Gr. _pleura_, the side; _tomé_, notch). A genus
of Univalve shells.
PLIOCENE (Gr. _pleion_, more; _kainos_, new). The later Tertiary
period.
PLIOPITHECUS (Gr. _pleion_, more; _pithekos_, ape). An extinct
genus of monkeys.
PLIOSAURUS (Gr. _pleion_, more; _saura_, lizard). A genus of
Plesiosaurian Reptiles.
POLYCYSTINA (Gr. _polus_, many; and _kustis_, a cyst). An order
of _Protozoa_ with foraminated siliceous shells.
POLYPARY. The hard chitinous covering secreted by many of the
_Hydrozoa_.
POLYPE (Gr. _polus_, many; _pous_, foot). Restricted to the single
individual of a simple _Actinozoön_, such as a Sea-anemone, or
to the separate zooids of a compound _Actinozoön_. Often applied
indiscriminately to any of the _Coelenterata_, or even to the
Polyzoa.
POLYPORA (Gr. _polus_, many; _poros_, a passage). A genus of
Lace-corals (_Fenestellidoe_).
POLYTHALAMOUS (Gr. _polus_; and _thalamos_, chamber). Having
many chambers; applied to the shells of _Foraminifera_ and
_Cephalopoda_.
POLYZOA (Gr. _polus_; and _zoön_, animal). A division of the
_Molluscoida_ comprising compound animals, such as the
Sea-mat--sometimes called _Bryozoa_.
PORIFERA (Lat. _porus_, pore; and _fero_, I carry). Sometimes
used to designate the _Foraminifera_, or the _Sponges_.
PRÆMOLARS (Lat. _proe_, before; _molares_, the grinders). The
molar teeth of Mammals which succeed the molars of the milk-set
of teeth. In man, the bicuspid teeth.
PROBOSCIDEA (Lat. _proboscis_, the snout). The order of Mammals
comprising the Elephants.
PROCOELOUS (Gr. _pro_, before; _koilos_, hollow). Applied to vertebræ
the bodies of which are hollow or concave in front.
PRODUCTA (Lat. _productus_, drawn out or extended). An extinct
genus of Brachiopods, in which the shell is "eared," or has its
lateral angles drawn out.
PROTICHNITES (Gr. _protos_, first; _ichnos_, footprint). Applied
to certain impressions in the Potsdam sandstone of North America,
believed to have been produced by large Crustaceans.
PROTOPHYTA (Gr. _protos_; and _phuton_, plant). The lowest division
of plants.
PROTOPLASM (Gr. _protos_; and _plasso_ I mould). The elementary
basis of organised tissues. Sometimes used synonymously for the
"sarcode" of the _Protozoa_.
PROTOROSAURUS or PROTEROSAURUS (Gr. _protos_, first; _orao_, I
see or discover; _saura_, lizard: or _proteros_, earlier; _saura_,
lizard). A genus of Permian lizards.
PROTOZOA (Gr. _protos_; and _zoön_, animal). The lowest division
of the animal kingdom.
PSAMMODUS (Gr. _psammos_, sand; _odous_, tooth). An extinct genus
of Cestraciont Sharks.
PSEUDOPODIA (Gr. _pseudos_, falsity; and _pous_, foot). The
extensions of the body-substance which are put forth by the
_Rhizopoda_ at will, and which serve for locomotion and prehension.
PSILOPHYTON (Gr. _psilos_, bare; _phuton_, plant). An extinct
genus of Lycopodiaceous plants.
PTERANODON (Gr. _pteron_, wing; _a_, without; _odous_, tooth).
A genus of Pterosaurian Reptiles.
PTERASPIS (Gr. _pteron_, wing; _aspis_, shield). A genus of Ganoid
Fishes.
PTERICHTHYS (Gr. _pteron_, wing; _ichthus_, fish). A genus of
Ganoid Fishes.
PTERODACTYLUS (Gr. _pteron_, wing; _daktulos_, finger). A genus
of Pterosaurian Reptiles.
PTEROPODA (Gr. _pteron_, wing; and _pous_, foot). A class of the
_Mollusca_ which swim by means of fins attached near the head.
PTEROSAURIA (Gr. _pteron_, wing; _saura_, lizard). An extinct
order of Reptiles.
PTILODICTYA (Gr. _ptilon_, a feather; _diktuon_, a net). An extinct
genus of _Polyzoa_.
PTYCHOCERAS (Gr. _ptucé_, a fold; _keras_, a horn). A genus of
_Ammonitidoe_.
PULMONATE. Possessing lungs.
PYRIFORM (Lat. _pyrus_, a pear; and _forma_, form). Pear-shaped.
QUADRUMANA (Lat. _quatuor_, four; _manus_, hand). The order of
Mammals comprising the Apes, Monkeys, Baboons, Lemurs, &c.
RADIATA (Lat. _radius_, a ray). Formerly applied to a large number
of animals which are now placed in separate sub-kingdoms (e.g., the
_Coelenterata_, the _Echinodermata_, the _Infusoria_, &c.)
RADIOLARIA (Lat. _radius_, a ray). A division of _Protozoa_.
RAMUS (Lat. a branch). Applied to each half or branch of the lower
jaw, or mandible, of Vertebrates.
RAPTORES (Lat. _rapto_, I plunder). The order of the Birds of
Prey.
RASORES (Lat. _rado_, I scratch). The order of the Scratching
Birds (Fowls. Pigeons, &c.)
RECEPTACULITES (Lat. _receptaculum_, a storehouse). An extinct
genus of Protozoa.
REPTILIA (Lat. _repto_, I crawl). The class of the _Vertebrata_
comprising the Tortoises, Snakes, Lizards, Crocodiles, &c.
RETEPORA (Lat. _reté_, a net; _porus_, a pore). A genus of
Lace-corals (_Polyzoa_).
RHAMPHORHYNCHUS (Gr. _rhamphos_, beak; _rhugchos_, nose). A genus
of Pterosaurian Reptiles.
RHINOCEROS (Gr. _rhis_, the nose; _keras_, horn). A genus of Hoofed
Quadrupeds.
RHIZOPODA (Gr. _rhiza_, a root; and _pous_, foot). The division
of _Protozoa_ comprising all those which are capable of emitting
pseudopodia.
RHYNCHOLITES (Gr. _rhugchos_, beak; and _lithos_, stone). Beak-shaped
fossils consisting of the mandibles of _Cephalopoda_.
RHYNCHONELLA (Gr. _rhugchos_, nose or beak). A genus of Brachiopods.
RODENTIA (Lat. _rodo_, I gnaw). An order of the Mammals; often
called _Glires_ (Lat. _glis_, a dormouse).
ROTALIA (Lat. _rota_, a wheel). A genus of _Foraminifera_.
RUGOSA (Lat. _rugosus_, wrinkled). An order of Corals.
RUMINANTIA (Lat. _ruminor_, I chew the cud). The group of Hoofed
Quadrupeds (_Ungulata_) which "ruminate" or chew the cud.
SARCODE (Gr. _sarx_, flesh; _eidos_, form). The jelly-like substance
of which the bodies of the _Protozoa_ are composed. It is an
albuminous body containing oil-granules, and is sometimes called
"animal protoplasm."
SAURIA (Gr. _saura_, a lizard). Any lizard-like Reptile is often
spoken of as a "Saurian;" but the term is sometimes restricted
to the Crocodiles alone, or to the Crocodiles and Lacertilians.
SAUROPTERYGIA (Gr. _sauro_; _pterux_, wing). An extinct order
of Reptiles, called by Huxley _Plesiosauria_, from the typical
genus _Plesiosaurus_.
SAURURÆ (Gr. _saura_; _oura_, tail). The extinct order of Birds
comprising only the _Archoeopteryx_.
SCANSORES (Lat. _scando_, I climb). The order of the Climbing
Birds (Parrots, Woodpeckers, &c.)
SCAPHITES (Lat. _scapha_, a boat). A genus of the _Ammonitidoe_.
SCOLITHUS (Gr. _skolex_, a worm; _lithos_, a stone). The vertical
burrows of sea-worms in rocks.
SCUTA (Lat. _scutum_, a shield). Applied to any shield-like plates;
especially to those which are developed in the integument of
many Reptiles.
SELACHIA or SELACHII (Gr. _selachos_, a cartilaginous fish, probably
a shark). The sub-order of _Elasmobranchii_ comprising the Sharks
and Dog-fishes.
SEPIOSTAIRE. The internal shell of the Sepia, commonly known as
the "cuttle-bone."
SEPTA. Partitions.
SERPENTIFORM. Resembling a serpent in shape.
SERTULARIDA (Lat. _sertum_, a wreath). An order of _Hydrozoa_.
SESSILE (Lat. _sedo_, I sit). Not supported upon a stalk or peduncle;
attached by a base.
SETHÆ (Lat. bristles). Bristles or long stiff hairs.
SIGILLARIOIDS (Lat. _sigilla_, little images). A group of extinct
plants of which _Sigillaria_ is the type, so called from the
seal-like markings on the bark.
SILICEOUS (Lat. _silex_, flint). Composed of flint.
SINISTRAL (Lat. _sinistra_, the left hand). Left-handed; applied
to the direction of the spiral in certain shells, which are said
to be "reversed."
SIPHON (Gr. a tube). Applied to the respiratory tubes in the
_Mollusca_; also to other tubes of different functions.
SIPHONIA (Gr. _siphon_, a tube). A genus of fossil Sponges.
SIPHONOSTOMATA (Gr. _siphon_; and _stoma_, mouth). The division
of _Gasteropodous Molluscs_ in which the aperture of the shell
is not "entire," but possesses a notch or tube for the emission
of the respiratory siphon.
SIPHUNCLE (Lat. _siphunculus_, a little tube). The tube which
connects together the various chambers of the shell of certain
_Cephalopoda_ (_e.g._, the Pearly Nautilus).
SIRENIA (Gr. _seiren_. a mermaid). The order of _Mammalia_ comprising
the Dugongs and Manatees.
SIVATHERIUM (_Siva_, a Hindoo deity; Gr. _therion_, beast). An
extinct genus of Hoofed Quadrupeds.
SOLIDUNGULA (Lat. _solidus_, solid; _ungula_, a hoof). The group
of Hoofed Quadrupeds comprising the Horse, Ass, and Zebra, in
which each foot has only a single solid hoof. Often called
_Solipedia_.
SPHENOPTERIS (Gr. _sphen_, a wedge; _pteris_, a fern). An extinct
genus of ferns.
SPICULA (Lat. _spicidum_, a point). Pointed needle-shaped bodies.
SPIRIFERA (Lat. _spira_, a spire or coil; _fero_, I carry). An
extinct genus of Brachiopods, with large spiral supports for
the "arms."
SPIRORBIS (Lat. _spira_, a spire; _orbis_, a circle). A genus
of tube-inhabiting Annelides, in which the shelly tube is coiled
into a spiral disc.
SPONGIDA (Gr. _spoggos_, a sponge). The division of _Protozoa_
commonly known as sponges.
STALACTITES (Gr. _stalasso_, I drop). Icicle-like encrustations
and deposits of lime, which hang from the roof of caverns in
limestone.
STALAGMITE (Gr. _stalagma_, a drop). Encrustations of lime formed
on the floor of caverns which are hollowed out of limestone.
STIGMARIA (Gr. _stigma_, a mark made with a pointed instrument).
A genus founded on the roots of various species of _Sigillaria_.
STRATUM (Lat. _stratus_, spread out; or _stratum_, a thing spread
out). A layer of rock.
STROMATOPORA (Gr. _stroma_, a thing spread out; _paras_, a passage
or pore). A Palæozoic genus of _Protozoa_.
STROPHOHENA (Gr. _strophao_, I twist; _mené_, moon). An extinct
genus of Brachiopods.
SUB-CALCAREOUS. Somewhat calcareous.
SUB-CENTRAL. Nearly central, but not quite.
SUTURE (Lat. _suo_, I sew). The line of junction of two parts
which are immovably connected together. Applied to the line where
the whorls of a univalve shell join one another; also to the lines
made upon the exterior of the shell of a chambered _Cephalopod_
by the margins of the septa.
SYRINGOPORA (Gr. _surigx_, a pipe; _poros_, a pore). A genus of
Tabulate Corals.
TABULÆ. (Lat. _tabula_, a tablet). Horizontal plates or floors
found in some Corals, extending across the cavity of the "theca"
from side to side.
TEGUMENTARY (Lat. _tegumentum_, a covering). Connected with the
integument or skin.
TELEOSAURUS (Gr. _teleios_, perfect; _saura_, lizard). An extinct
genus of Crocodilian Reptiles.
TELEOSTEI (Gr. _teleios_, perfect; _osteon_, bone). The order
of the "Bony Fishes."
TELSON (Gr. a limit). The last joint in the abdomen of _Crustacea_;
variously regarded as a segment without appendages, or as an
azygous appendage.
TENTACULITES (Lat. _tentaculum_, a feeler). A genus of _Pteropoda_.
TEREBRATULA (Lat. _terebratus_, bored or pierced). A genus of
_Brachiopoda_, so called in allusion to the perforated beak of
the ventral valve.
TEST (Lat. _testa_, shell). The shell of _Mollusca_, which are
for this reason sometimes called "_Testacea_;" also, the calcareous
case of _Echinoderms_; also, the thick leathery outer tunic in
the _Tunicata_.
TESTACEOUS. Provided with a shell or hard covering.
TESTUDINIDÆ (Lat. _testudo_, a tortoise). The family of the
Tortoises.
TETRABRANCHIATA (Gr. _tetra_, four; _bragchia_, gill). The order
of _Cephalopoda_ characterised by the possession of four gills.
TEXTULARIA. (Lat. _textilis_, woven). A genus of _Foraminifera_.
THECA (Gr. _theké_, a sheath). A genus of Pteropods.
THECODONTOSAURUS (Gr. _theké_, a sheath; _odous_, tooth; _saura_,
lizard). A genus of "Thecodont" Reptiles, so named in allusion
to the fact that the teeth are sunk in distinct sockets.
THERIODONT (Gr. _therion_, a beast; _odous_, tooth). A group of
Reptiles so named by Owen in allusion to the Mammalian character
of their teeth.
THORAX (Gr. a breastplate). The region of the chest.
THYLACOLEO (Gr. _thulakos_, a pouch; _leo_, a lion). An extinct
genus of Marsupials.
TRIGONIA (Gr. _treis_, three; _gonia_, angle). A genus of Bivalve
Molluscs.
TRIGONOCARPON (Gr. _treis_, three; _gonia_. angle; _karpos_,
fruit). A genus founded on fossil fruits of a three-angled form.
TRILOBITA (Gr. _treis_, three; _lobos_, a lobe). An extinct order
of _Crustaceans_.
TRINUCLEUS (Lat. _tris_, three; _nucleus_, a kernel). A genus
of Trilobites.
TROGONTHERIUM (Gr. _trogo_, I gnaw; _therion_, beast). An extinct
genus of Beavers.
TUBICOLA (Lat. _tuba_, a tube; and _colo_, I inhabit). The order
of _Annelida_ which construct a tubular case in which they protect
themselves.
TUBICOLOUS. Inhabiting a tube.
TUNICATA (Lat. _tunica_, a cloak). A class of _Molluscoida_ which
are enveloped in a tough leathery case or "test."
TURBINATED (Lat. _turbo_, a top). Top-shaped; conical with a round
base.
TURRILITES (Lat, _turris_, a tower). A genus of the _Ammonitidoe_.
UMBO (Lat. the boss of a shield). The beak of a bivalve shell.
UNGUICULATE (Lat. _unguis_, nail). Furnished with claws.
UNGULATA (Lat. _ungula_, hoof). The order of Mammals comprising
the Hoofed Quadrupeds.
UNGULATE. Furnished with expanded nails constituting hoofs.
UNILOCULAR (Lat. _unus_, one; and _loculus_. a little purse).
Possessing a single cavity or chamber. Applied to the shells
of _Foraminifera_ and _Mollusca_.
UNIVALVE (Lat. _unus_, one; _valvoe_, folding-doors). A shell
composed of a single piece or valve.
URODELA (Gr. _oura_, tail; _delos_, visible). The order of the
Tailed Amphibians (Newts, &c.)
VENTRAL (Lat. _venter_, the stomach). Relating to the inferior
surface of the body.
VENTRICULITES (Lat. _ventriculum_, a little stomach). A genus
of siliceous Sponges.
VERMIFORM (Lat. _vermis_, worm; and _forma_, form). Worm-like.
VERTEBRA (Lat. _verto_, I turn). One of the bony segments of the
vertebral column or backbone.
VERTEBRATA (Lat. _vertebra_, a bone of the back, from _vertere_,
to turn). The division of the Animal Kingdom roughly characterised
by the possession of a backbone.
VESICLE (Lat. _vesica_, a bladder). A little sac or cyst.
WHORL. The spiral turn of a univalve shell.
XIPHOSURA (Gr. _xiphos_, a sworn; and _oura_, tail). An order of
_Crustacea_, comprising the _Limuli_ or King-Crabs, characterised
by their long sword-like tails.
XYLOBIUS (Gr. _xulon_, wood; _bios_, life). An extinct genus of
Myriapods, named in allusion to the fact that the animal lived
on decaying wood.
ZAPHRENTIS (proper name). A genus of Rugose Corals.
ZEUGLODONTIDÆ. (Gr. _zeuglé_, a yoke; _odous_, a tooth). An extinct
family of Cetaceans, in which the molar teeth are two-fanged,
and look as if composed of two parts united by a neck.
ZOOPHYTE (Gr. _zoön_, animal; _phuton_, plant). Loosely applied
to many plant-like animals, such as Sponges, Corals, Sea-anemones,
Sea-mats, &c.
INDEX.
Acadian Group.
_Acer_.
_Acervularia_.
_Acidaspis_.
Acorn-shells.
_Acroculia_.
_Acrodus; nobilis_.
_Acrotreta_.
_Acroura_.
_Actinocrinus_.
_Æglina_.
_Æpiornis_.
_Agnostus; rex_.
_Alces malchis_.
_Alecto_.
_Alethopteris_.
_Algoe_ (_see_ Sea-weeds).
Alligators.
_Alnus_.
_Amblypterus; macropterus_.
_Ambonychia_.
_Ammonites; Humpresianus; bifrons_.
_Ammonitidoe_.
_Amphibia_; of the Carboniferous; of the Permian; of the Trias;
of the Jurassic; of the Miocene.
_Amphicyon_.
_Amphilestes_.
_Amphispongia_.
_Amphistegina_.
_Amphitherium; Prevostii_.
_Amphitragulus_.
_Amplexus; coralloides_.
_Ampyx_.
_Anachytes_.
_Anchitherium_.
_Ancyloceras; Matheronianus_.
_Ancylotherium Pentelici_.
_Andrias Scheuchzeri_.
_Angiosperms_.
Animal Kingdom, divisions of.
_Anisopus_.
_Annelida_, of the Cambrian period; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous.
_Annularia_.
_Anomodontia_.
_Anoplotheridoe_.
_Anoplotherium; commune_.
Ant-eaters.
Antelopes.
_Anthracosaurus Russelli_.
_Anthrapaloemon gracilis_.
_Antilocapra_.
_Antilope quadricornis_.
Antwerp Crag.
Apes.
_Apiocrinus_.
_Apteryx_.
Aqueous rocks.
_Arachnida_ of the Coal-measures.
Aralo-Caspian Beds.
_Araucaria_.
_Araucarioxylon_.
_Arca; antiqua_.
_Archoeocidaris_.
_Archoeocyathus_.
_Archoeopteryx; macrura_.
_Archoeospoerinoe_.
_Archimedes; Wortheni_.
_Archiulus_.
Arctic regions, Miocene flora of.
_Arctocyon_.
Arenaceous rocks.
_Arenicolites; didymus_.
Arenig rocks.
Argillaceous rocks.
Armadillos.
_Artiodactyle Ungulates_.
_Asaphus; tyrannus_.
_Ascoceras_.
_Aspidella_.
_Aspidura loricata_.
_Astarte borealis_.
_Asterophyllites_.
_Asterosteus_.
_Astroeidoe_.
_Astroeospongia_.
_Astylospongia; proemorsa_.
_Athyris; subtilita_.
Atlantic Ooze.
_Atrypa; congesta; hemispoerica; reticularis_.
Auger-shells.
Aurochs.
Aves (_see_ Birds).
_Avicula; cantorta; socialis_.
"Avicula contorta Beds".
_Aviculidoe_.
_Aviculopecten_.
_Axophyllum_.
Aymestry Limestone.
Azoic rocks.
_Baculites; anceps_.
Bagshot and Bracklesham Beds.
_Bakewellia_.
_Baloena_.
Bala Group.
Bala Limestone.
_Balanidoe_.
_Banksia_.
Barbadoes Earth.
Barnacles.
Bath Oolite.
Bats.
Bears.
Beaver.
Beetles.
_Belemnitella mucronata_.
_Beleminites; canaliculatus_.
_Belemnitidoe_.
_Belemnoteuthis_.
_Belinurus_.
_Bellerophon; Argo_.
_Belodon; Carolinensis_.
_Belosepia_.
_Beloteuthis subcostata_.
Bembridge Beds.
_Beryx; Lewesiensis_.
_Beyrichia; complicata_.
Bird's-eye Limestone.
Birds, of the Trias; of the Jurassic; of the Cretaceous; of
the Eocene; of the Post-Pliocene.
_Bison priscus_.
Bituminous Schists of Caithness.
Bivalves (_see_ Lamellibranchiata).
Black-lead (_see_ Graphite).
Black-River Limestone.
_Blastoidea_; of the Devonian; of the Carboniferous.
_Boidoe_.
Bolderberg Beds.
Bone-bed, of the Upper Ludlow; of the Trias.
Bony Fishes (_see_ Teleostean Fishes).
_Bos primigenius; _taurus_.
Boulder-clay.
_Bourgueticrinus_.
Bovey-Tracy Beds.
_Brachiopoda_; of the Cambrian rocks; of the Lower Silurian;
of the Upper Silurian; of the Devonian; of the Carboniferous;
of the Permian; of the Trias; of the Jurassic; of the
Cretaceous; of the Eocene.
_Brachymetopus_.
Brachyurous Crustaceans.
Bradford Clay.
Breaks in the Geological and Palæontological record.
Breccia.
Brick-earths.
Bridlington Crag.
Brittle-stars (_see_ Ophiuroidea).
_Bronteus_.
_Brontotheridoe_.
_Brontotherium ingens_.
_Brontozoum_.
_Buccinum_.
_Bucklandia_.
_Bulimus_.
Bunter Sandstein.
Butterflies.
_Byssoarca_.
Cainozoic (_see_ Kainozoic).
Calamaries.
_Calamites; cannoeformis_.
Calcaire Grossier.
Calcareous rocks; Tufa.
Calciferous Sand-rock.
_Calveria_.
_Calymene; Blumenbachii_.
_Camarophoria globulina_.
Cambrian period; rocks of, in Britain; in Bohemia; in
North America; life of.
_Camelopardalidoe_.
Camels.
_Canis lupus; Parisiensis_.
Caradoc rocks.
Carbon, origin of.
Carboniferous Limestone.
Carboniferous period; rocks of; life of.
Carboniferous Slates of Ireland.
_Carcharias_.
_Carcharodon; productus_.
_Cardinia_.
_Cardiocarpon_.
_Cardiola; fibrosa; interrupta_.
_Cardita; planicosta_.
_Cardium; Rhoeticum_.
Caribou.
_Carnivora_, of the Eocene; of the Miocene; of the Pliocene;
of the Post-Pliocene.
_Caryocaris_.
_Caryocrinus ornatus_.
_Castor fiber_.
_Castoroides Ohioensis_.
Catastrophism, theory of.
_Catopterus_.
Cauda-Galli Grit.
_Caulopteris_.
Cave-bear.
Cave-deposits.
Cave-hyæna.
Cave-lion.
Caves, formation of; deposits in.
_Cavicornia_.
Cement-stones.
_Cephalaspis_.
_Cephalopoda_, of the Cambrian period; of the Lower Silurian;
of the Upper Silurian; of the Devonian; of the Carboniferous;
of the Permian; of the Trias; of the Jurassic; of the Cretaceous;
of the Eocene; of the Miocene.
_Ceratiocaris_.
_Ceratites; nodosus_.
_Ceratodus; altus; Fosteri; serratus_.
_Ceriopora; Hamiltonensis_.
_Cerithium; _hexagonum_.
_Cervidoe_, of the Miocene period; of the Pliocene; of the
Post-Pliocene.
_Cervus; capreolus; elaphus; megaceros; tarandus_.
_Cestracion Philippi_.
Cestracionts, of the Devonian; of the Carboniferous; of the Permian;
of the Trias; of the Jurassic; of the Cretaceous.
_Cetacea_; of the Eocene; of the Miocene.
_Cetiosaurus_.
_Choeropotamus_.
_Choetetes; tumidus_.
Chain-coral.
Chalk; structure of; Foraminifera of; origin of; with flints;
without flints.
_Chama_.
_Chamoerops; Helvetica_.
Chazy Limestone.
_Cheiroptera_, of the Eocene; of the Miocene.
_Cheirotherium_.
_Cheirurus; bimucronatus_.
_Chelichnus Duncani_.
_Chelone Benstedi; planiceps_.
_Chelonia_, of the Permian; of the Jurassic; of the Cretaceous;
of the Eocene; of the Miocene.
_Chemnitzia_.
Chemung Group.
Chert.
Chillesford Beds.
_Chonetes; Hardrensis_.
_Chonophyllum_.
_Cidaris_.
Cincinnati Group.
_Cinnamomum polymorphum_.
Cinnamon-trees.
_Cladodus_.
Claiborne Beds.
_Clathropora; intertexta_.
Clay; Red, origin of.
Clay-ironstone, nodules of.
_Cleidophorus_.
_Cleodora_.
_Climacograptus_.
Clinton Formation.
_Clisiophyllum_.
_Clupeidoe_.
_Clymenia; Sedgwickii_.
Coal; structure of; mode of formation of.
Coal-measures; mineral characters of; mode of formation of;
plants of.
Coccoliths.
_Coccosteus_.
_Cochliodus; cantortus_.
_Coleoptera_.
_Colossochelys Atlas_.
_Columnaria; alveolata_.
_Comatula_.
Conclusions to be drawn from Fossils.
Concretions, calcareous; phosphatic; of clay-ironstone;
of manganese.
Conglomerate.
_Coniferoe_; wood of; of Devonian period; of the Carboniferous;
of the Permian; of the Trias; of the Jurassic period.
Coniston Flags and Grits.
Connecticut Sandstones, footprints of.
_Conocoryphe Mathewi; Sultzeri_.
Conodonts.
_Constellaria_.
Constricting serpents of the Eocene.
Contemporaneity of strata.
Continuity, theory of.
_Conularia; ornata_.
_Conulus_.
_Conus_.
Coomhola Grits.
Coprolites.
Coralline Crag.
Corallines.
_Corallium_.
Coral-rag.
Coral-reefs.
Coral-rock.
Coral-sand.
Corals; of the Lower Silurian; of the Upper Silurian; of the
Devonian; of the Carboniferous; of the Permian; of the Trias;
of the Jurassic; of the Cretaceous; of the Eocene; of the
Miocene.
_Corbula_.
Cornbrash.
Corniferous Limestone.
_Cornulites_.
Cornus.
_Coryphodon_.
Cowries.
Crabs.
Crag, Red; White; Norwich; Antwerp; Bridlington; Coralline.
_Crania; Ignabergensis_.
_Crassatella_.
_Crepidophyllum; Archiaci_.
Cretaceous period; rocks of, in Britain; in North America;
life of.
Crinoidal Limestone.
_Crinoidea_; of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Triss; of the Jurassic; of the Cretaceous;
of the Eocene.
_Crioceras; cristatum_.
_Crocodilia_; of the Trias; of the Jurassic; of the Cretaceous;
of the Eocene.
Cromer Forest-bed.
_Crossozamites_.
_Crotalocrinus_.
_Crustacea_, of the Cambrian; of the Lower Silurian; of the Upper
Silurian; of the Devonian; of the Carboniferous; of the Permian;
of the Trias; of the Jurassic; of the Cretaceous.
Cryptogams.
_Ctenacanthus_.
_Ctenodonta_.
_Cupressus_.
Cursores.
Cuttle-fishes (_see_ Dibranchiate Cephalopods).
_Cyathocrinus_.
_Cyathophyllum_.
_Cycadopteris_.
Cycads; of the Carboniferous; of the Permian; of the Trias;
of the Jurassic; of the Cretaceous.
_Cyclas_.
_Cyclonema_.
_Cyclophthalmus senior_.
_Cyclostoma; Arnoudii_.
_Cynodraco_.
_Cyproea; elegans_.
Cypress.
_Cypridina_.
Cypridina Slates.
_Cyrena_.
_Cyrtina_.
_Cyrtoceras_.
_Cystiphyllum; vesiculosum_.
_Cystoidea_; of the Cambrian; of the Lower Silurian; of
the Upper Silurian.
Dachstein Beds.
_Dadoxylon_.
_Daonella; Lommelli_.
_Dasornis Londinensis_.
Decapod Crustaceans.
Deer.
_Deinosauria_; of the Trias; of the Jurassic; of the Cretaceous.
_Deinotherium; giganteum_.
Denbighshire Flags and Grits.
_Dendrocrinus_.
_Dendrograptus_.
Desmids.
Devonian Formation; origin of name; relation to Old Red Sandstone;
of Devonshire; of North America; life of.
_Diadema_.
Diatoms; of the Devonian; of the Carboniferous; of flints; of
Richmond Earth.
Dibranchiate Cephalopods; of the Trias; of the Jurassic; of
the Cretaceous; of the Eocene; of the Miocene.
_Diceras; arietina_.
Diceras Limestone.
_Dichobune_.
_Dichograptus; octobrachiatus_.
Dicotyledonous plants.
_Dicotyles antiquus_.
_Dicranograptus_.
_Dictyonema; sociale_.
_Dicynodon; lacerticeps_.
_Didelphys; gypsorum_.
_Didus ineptus_.
_Didymograptus; divaricatus_.
_Dikellocephalus Celticus; Minnesotensis_.
_Dimorphodon_.
_Dinichthys; Hertzeri_.
_Ditoceras; mirabilis_.
_Dinocerata_.
_Dinophis_.
_Dinornis; elephantopus; giganteus_.
_Dinosauria_ (see _Deinosauria_).
_Dinotherium_ (see _Deinotherium_).
_Diphyphyllum_.
_Diplograptus; pristis_.
_Dipnoi_.
_Diprotodon; australis_.
_Diptera_.
_Discina_.
_Discoidea; cylindrica_.
_Dithyrocaris; Scouleri_.
Dodo.
Dog whelks.
Dolomite.
Dolomitic Couglomerate of Bristol.
Dolphins.
_Dorcatherium_.
Downton Sandstone.
_Draco volans_.
Dragon-flies.
Drift, Glacial.
_Dremotherium_.
_Dromatherium sylvestre_.
_Dryandra_.
_Dryopithecus_.
Dugougs.
_Echinodermata_, of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Trias; of the Jurassic; of the Cretaceous;
of the Eocene.
_Echinoidea_; of the Upper Silurian; or the Devonian; of the
Carboniferous; of the Permian; of the Jurassic; of the
Cretaceous.
_Edentata_; of the Eocene; of the Miocene; of the Post-Pliocene.
_Edriocrinus_.
Eifel Limostone.
_Elasmobranchii_ (_See_ Placoid Fishes).
_Elasmosaurus_.
Elephants.
_Elphas; Americanus; antiquus; Falconeri; Melitensis; meridionalis;
planifrons; primigenius_.
Elk; Irish.
_Ellipsocephalus Hoffi_.
_Elotherium_.
_Emydidoe_.
_Emys_.
Enaliosaurians.
Encrinital warble.
_Encrinurus_.
_Encrinus liliiformis_.
Endogenous plants.
_Endophyllum_.
_Endothyra; Bailyi_.
Engis skull.
_Entomis_.
_Entomoconchus Scouleri_.
Eocene period; rocks of, in Britain; in France; in North
America; life of.
_Eocidaris_.
_Eophyton; Linneanum_.
Eophyton Sandstone.
_Eosaurus Acadianus_.
Eozoic rocks.
_Eozoön Bavaricum_.
_Eozoön Canadense_; appearance of, in mass; minute structure
of; affinities of, with _Foraminifera_.
_Ephemeridoe_.
_Equisetaceoe_.
_Equisetites_.
_Equidoe_.
_Equus; caballus; excelsus; fossilis_.
_Eridophyllum_.
_Eryon arctiformis_.
_Eschara_.
_Escharidoe_.
_Escharina; Oceani_.
_Estheria; tenella_.
_Eucalyptocrinus; polydactylus_.
_Eucladia_.
_Euomphalus; discors_.
_Euplectella_.
_Euproöps_.
European Bison.
_Eurypterida_; of the Upper Silurian; of the Devonian.
Even-toed Ungulates.
Exogenous plants.
_Exogyra; virgula_.
Extinction of species.
_Fagus_.
Faluns.
Fan-palms.
_Favistella_.
_Favostites; Gothlandica; hemisphoerica_.
Faxöe Limestone.
_Felis angustus; leo; speloea_.
_Fenestella; cribrosa; magnifica; retiformis_.
_Fenestellidoe_.
Ferns, of the Devonian; of the Carboniferous; of the Permian;
of the Trias; of the Jurassic; of the Cretaceous.
Fig-shells.
Fishes; of the Upper Silurian; of the Devonian; of the
Carboniferous; of the Permian; of the Trias; of the
Jurassic; of the Cretaceous; of the Eocene; of the
Miocene.
Flint; structure of; origin of; organisms of; of Chalk.
Human implements associated with bones of extinct Mammals.
Flora (_see_ Plants).
Footprints of _Cheirotherium_; of the Triassic sandstones of
Connecticut.
_Foraminifera_; of the Cambrian; of the Lower Silurian;
of the Carboniferous; of the Permian; of the Trias; of the
Jurassic; of the Cretaceous; of the Eocene; of the Miocene;
of the Post-Pliocene; of Atlantic ooze; as builders of
limestone; as forming green sands.
_Forbesiocrinus_.
Forest-bed of Cromer.
Forest-bugs.
Forest-marble.
Formation, definition of; succession of.
Fossiliferous rocks; chronological succession of.
Fossilisation, processes of.
Fossils, definition of; distinctive, of rock-groups; conclusions
to be drawn from; biological relations of.
Foxes.
Fringe-finned Ganoids.
Fucoidal Sandstone.
Fucoids.
Fuller's Earth.
_Fusulina; cylindrica_.
_Fusus_.
_Galeocerdo_.
_Galerites; albo-galerus_.
_Galestes_.
Ganoid Fishes; of the Upper Silurian; of the Devonian; of the
Carboniferous; of the Permian; of the Trias; of the Jurassic;
of the Cretaceous; of the Eocene.
Gaspé Beds.
_Gasteropoda_, of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Trias; of the Jurassic; of the Cretaceous;
of the Eocene.
_Gastornis Parisiensis_.
Gault.
Gavial.
Genesee Slates.
Geological record, breaks in the.
Giraffes.
Glacial period; deposits of.
_Glandulina_.
Glauconite.
_Glauconome; pulcherrima_.
Globe Crinoids (_see_ Cystoidea).
_Globigerina_.
Glutton.
_Glyptaster_.
_Glyptocrinus_.
_Glyptodon; clavipes_.
_Glyptoloemus_.
Goats.
_Goniatites; Jossoe_.
_Gorgonidoe_.
_Grallatores_.
Graphite; mode of occurrence of; origin of.
_Graptolites_; structure of; of the Lower Silurian; of the
Upper Silurian.
Great Oolite; Upper.
Greenland. Miocene plants of.
Greensand, Lower.
Green sands, origin of.
_Grevillea_.
_Griffithides_.
Grizzly Bear.
Groond Sloths.
_Gryphoea; incurva_.
Guelph Limestone.
_Gulo luscus; speloeus_.
Guttenstein Beds.
Gymnospermous Exogens.
Gypsum.
_Gyracanthus_.
_Gyroceras_.
_Hadrosaurus_.
_Halitherium_.
Hallstadt Beds.
_Halobia_.
_Halysites; agglomerata; catenularia_.
Hamilton formation.
_Hamites; rotundus_.
_Haplophlebium Barnesi_.
Harlech Grits.
_Harpes; ungula_.
Hastings Sands.
Headon and Osborne series.
Heart-urchins.
_Heliolites_.
_Heliophyllum; exiguum_.
_Helix_.
_Helladotherium_.
_Helopora fragilis_.
_Hemicidaris crenularis_.
_Hemiptera_.
_Hemitrochiscus paradoxus_.
Hempstead Beds.
_Hesperornis; regalis_.
_Heteropoda_; of the Lower Silurian; of the Upper Silurian;
of the Devonian; of the Carboniferous.
_Hinnites_.
_Hipparion_.
_Hippopodium_.
_Hippopotamus; amphibus; major; Sivalensis_.
_Hippothoa_.
Hippurite Marble.
_Hippurites; Toucasiana_.
_Hippuritidoe_.
_Histioderma_.
Hollow-horned Ruminants.
_Holocystis elegan_.
_Holopea; Subconica_.
_Holopella; obsoleta_.
_Holoptychius; nobilissimus_.
Holostomatous Univalves.
Holothurians.
_Holtenia_.
_Homacanthus_.
_Homalonotus; armatus_.
_Homo diluvii testis_.
Honeycomb Corals.
Hoofed Quadrupeds.
Hudson River Group.
Huronian Period; rocks of.
_Hyoena crocuta; speloea; Hipparionum_.
_Hyoenictis_.
_Hyoenodon_.
_Hyalea D'Orbignyana_.
_Hybodus_.
_Hydractinia_.
Hydroid Zoophytes.
_Hymenocaris vermicauda_.
_Hymenophyllites_.
_Hymenoptera_.
_Hyopotamus_.
_Hyperodapedon_.
_Hypsiprymnopsis_.
_Hystrix primigenius_.
_Ichthyocrinus loevis_.
_Ichthyornis; dispar_.
_Ichthyosaurus; communis_.
_Ictitherium_.
_Iguana_.
_Iguanodon; Mantelli_.
Ilfracombe Group.
_Illoenus_.
Imperfection of the palæontological record.
Inferior Oolite.
Infusorial Earth.
_Inoceramus; sulcatus_.
_Insectivora_, of the Eocene; of the Miocene.
Insects, of the Devonian; of the Carboniferous; of the Jurassic;
of the Miocene.
Irish Elk.
_Ischadites_.
Isopod Crustaceans.
Jackson Beds.
Jurassic period; rocks of; life of.
_Kaidacarpum_.
Kainozoic period.
Kangaroo.
Kelloway Rock.
Kent's Cavern, deposits in.
Keuper.
Kimmeridge Clay.
King-crabs.
_Koninckia_.
Kössen Beds.
_Labyrinthodon Joegeri_.
_Labyrinthodontia_; of the Carboniferous; of the Permian;
of the Trias.
Lace-corals.
_Lacertilia_; of the Permian; of the Trias; of the Jurassic;
of the Cretaceous.
_Loelaps_.
_Lamellibranchiata_, of the Cambrian; of the Lower Silurian;
of the Upper Silurian; of the Devonian; of the Carboniferous;
of the Permian; of the Trias; of the Jurassic; of the
Cretaceous; of the Eocene.
_Lamna_.
Lamp-shells (see _Brachiopoda_).
Land-tortoises.
_Lauraceoe_.
Laurentian period; rocks of; Lower Laurentian; Upper Laurentian;
areas occupied by Laurentian rocks; limestones of; iron-ores of;
phosphate of lime of; graphite of; life of.
Leaf-beds of the Isle of Mull.
_Leda; truncata_.
_Leguminosites Marcouanus_.
Lemming.
_Lepadidoe_.
_Lepadocrinus Gebhardi_.
_Leperditia; canadensis_.
_Lepidaster_.
_Lepidechinus_.
_Lepidesthes_.
Lepidodendroids.
_Lepidodendron; Sternberg_.
_Lepidoptera_.
_Lepidosiren_.
_Lepidosteus_.
_Lepidostrobus_.
_Lepidotus_.
_Leptoena; Liassica; sericea_.
_Leptocoelia; plano-convexa_.
Lias.
Lichas.
_Licrophycus Ottawaensis_.
Lignitic Formation of North America.
Lily-encrinite.
_Lima_.
Lime, phosphate of.
Limestone; varieties of; origin of; microscopical structure of;
Crinoidal; Foraminiferal; coralline; magnesian; metamorphic;
oolitic; pisolitic; bituminous; Laurentian.
_Limnoea; pyramidalis_.
_Limulus_.
_Lingula; Credneri_.
Lingula Flags.
_Lingulella; Davisii; ferruginea_.
_Liriodendron; Meeki_.
_Lithostrotion; irregulare_.
_Lituites_.
Lizards (see _Lacertilia_).
Llama.
Llanberis Slates.
Llandeilo rocks.
Llandovery rocks; Lower; Upper.
Lobsters.
Loess.
London Clay.
Longmynd rocks.
_Lonsdaleia_.
_Lophiodon_.
_Lophophyllum_.
Lower Cambrian; Chalk; Cretaceous; Devonian; Eocene; Greensand;
Helderberg; Laurentian rocks; Ludlow rock; Miocene; Old Red
Sandstone; Oolites; Silurian period; rocks of, in Britain; in
North America; life of.
_Loxonema_.
Ludlow rock.
_Lycopodiaceoe_.
Lynton Group.
_Lyrodesma_.
Macaques.
_Machoeracanthus major_.
_Machairodus; cultridens_.
_Maclurea; crenulata_.
_Macrocheilus_.
_Macropetalichthys; Sullivanti_.
_Macrotherium giganteum_.
_Macrurous Crustaceans_.
_Mactra_.
Maestricht Chalk.
Magnesian Limestone; nature and structure of; of the Permian
series.
Magnolia.
_Mammalia_, of the Trias; of the Jurassic; of the Eocene; of
the Miocene; of the Pliocene; of the Post-Pliocene.
Mammoth.
Man, remains of, in Post-Pliocene deposits.
Manatee.
_Mantellia; megalophylla_.
Maple.
Marble; encrinital; statuary.
Marcellus Shales.
_Mariacrinus_.
Marmots.
Marsupials; of the Trias; of the Jurassic; of the Eocene; of
the Miocene; of the Post-Pliocene.
_Marsupiocrinus_.
_Marsupites_.
_Mastodon; Americanus, angustidens; Arvenensis; longirostris;
Ohioticus; Sivalensis_.
Medina Sandstone.
_Megalichthys_.
_Megalodon_.
_Megalomus_.
_Megalonyx_.
_Megalosaurus_.
_Megatherium; Cuvieri_.
_Melania_.
_Melonites_.
Menevian Group.
_Menobranchus_.
_Meristella; cylindrica; intermedia; naviformis_.
_Mesopithecus_.
Mesozoic Period.
_Michelinia_.
_Micraster_.
_Microlestes; antiquus_.
Middle Devonian; Eocene; Oolites; Silurian.
Miliolite Limestone.
_Millepora_.
Millstone Grit.
Miocene period; rocks of, in Britain; in France; in Belgium;
in Switzerland; in Austria; in Germany; in Italy; in India;
in North America; life of.
Mitre-shells.
_Mitra_.
Moas of New Zealand.
_Modiolopsis; Solvensis_.
Molasse.
Mole.
Monkeys.
Monocotyledonous plant.
_Monograptus; priodon_.
_Monotis_.
Monte Bolca, fishes of.
_Montlivaltia_.
Mosasauroids.
_Mosasaurus; Camperi; princeps_.
Mountain Limestone.
Mud-fishes.
Mud-turtles.
Mull, Miocene strata of.
_Murchisonia; gracilis_.
_Murex.
Muschelkalk.
Musk-deer.
Musk-ox.
Musk-sheep.
_Myliobatis Edwardsii_.
_Mylodon; robustus_.
_Myophoria; lineata_.
_Myriapoda_ of the Coal.
_Nassa_.
_Natatores_.
_Natica_.
_Nautilus; Danicus; pompilius_.
Neanderthal skull.
Neocomian series.
_Neolimulus_.
_Nerinoea; Goodhallii_.
_Nerita_.
_Neuroptera_.
_Neuropteris_.
Newer Pliocene.
New Red Sandstone.
Newts.
Niagara Limestone.
_Nipadites; ellipticus_.
_Noeggerathia_.
Norwich Crag.
_Nothosaurus; mirabilis_.
_Notidanus_.
_Numenius gypsorum_.
_Nummulina; loevigata; pristina_.
_Nummulitic Limestone_.
Oak.
_Obolella; sagittalis_.
Odd-toed Ungulates.
_Odontaspis_.
_Odontopteris; Schlotheimi_.
_Odontopteryx; toliapicus_.
_Odontornithes_.
_Ogygia; Buchii_.
Older Pliocene.
_Oldhamia; antiqua_; slates of Ireland.
Old Red Sandstone; origin of name; of Scotland; relations of,
to Devonian.
_Olenus; micrurus_.
Oligocene.
_Oligoporus_.
Olive-shells.
_Omphyma_.
_Onchus; tenuistriatus_.
Oneida Conglomerate.
_Onychodus; sigmoides_.
Oolitic limestone, structure of; mode of formation of.
Oolitic rocks (_see_ Jurassic).
Ooze, Atlantic.
_Ophidia_; of the Eocene.
_Ophiuroidea_, of the Lower Silurian; of the Upper Silurian;
of the Carboniferous; of the Trias; of the Jurassic.
Opossum.
_Orbitoides_.
Oriskany Sandstone.
_Ormoxylon_.
_Orohippus_.
_Orthis; biforata; Davidsoni; elegantula; flabellulum; Hicksii;
lenticularis; plicatella; resupinata; subquadrala; testudinaria_.
_Orthoceras; crebriseptum_.
_Orthonota_.
_Orthoptera_.
_Osmeroides; Mantelli_.
_Osmerus_.
_Ostealepis_.
_Ostracode_ Crustaceans of the Cambrian; of the Lower Silurian;
of the Upper Silurian; of the Devonian; of the Carboniferous;
of the Permian; of the Trias; of the Jurassic; of the Cretaceous.
_Ostrea acuminata; Couloni; deltoidea; distorta; expansa, gregarea;
Marshii_.
_Otodus; obtiquus_.
_Otozamites_.
_Otozoum_.
_Oudenodon; Bainii_.
_Ovibos moschatus_.
Oxford Clay.
_Oxyrhina; xiphodon_.
Oysters.
_Pachyphyllum_.
_Paloearca_.
_Paloeaster; Ruthveni_.
_Palasterina; primoeva_.
_Paloechinus; ellipticus_.
_Paloeocaris; typus_.
_Paloeocoma; Colvini_.
_Paloeocoryne_.
Palæolithic man, remains of.
_Paloeomanon_.
_Paloeoniscus_.
_Paloeontina Oolitica_.
Palæontological evidence as to Evolution.
Palæontological record, imperfection of the.
Palæontology, definition of.
_Paloeonyctis_.
_Paloeophis; toliapictus; typhoeus_.
_Paloeoreas_.
_Paloeosaurus; platyodon_.
_Paloeosiren Beinerti_.
_Paloeotherium; magnum_.
_Paloeoxylon_.
Palæozoic period.
Palms.
_Paludina_.
_Pandaneoe_.
_Pandanus_.
_Paradoxides; Bohemicus_.
_Parasmilia_.
_Parkeria_.
Pear Encrinite.
Pearly Nautilus.
Peccaries.
_Pecopteris_.
_Pecten Groenlandicus; Islandicus; Valoniensis_.
Penarth Beds.
_Pennatulidoe_.
_Pentacrinus; caput-medusoe; fasciculosus_.
_Pentamerus; galeatus; Knightii_.
_Pentremites_ (_see_ Blastoidea).
_Pentremites conoideus; pyriformis_.
Perching Birds.
_Percidoe_.
_Periechocrinus_.
_Perissodactyle Ungulates_.
Permian period; rocks of, in Britain; in North America;
life of.
Persistent types of life.
_Petalodus_.
_Petraster_.
Petroleum, origin of.
Pezophaps.
_Phacops; Downingioe; granulatus; loevis; latifrons;
longicaudatus; rana_.
_Phoenopora ensiformis_.
Phalangers.
Phanerogams.
_Phaneropleuron_.
_Phascolotherium_.
_Pheronema_.
_Phillipsastroea_.
_Phillipsia; seminifera_.
_Pholadomya_.
_Phormosoma_.
_Phorus_.
Phosphate of lime, concretions of; disseminated in rocks; origin of.
_Phyllograptus; typus_.
_Phyllopoda_, of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Trias.
_Phyllopora_.
_Physa; columnaris_.
Pigs.
Pilton Group.
_Pinites_.
_Pisces (_see_ Fishes).
_Pisolite_.
Pisolitic Limestone of France.
_Placodus; gigas_.
Placoid Fishes; of the Upper Silurian; of the Devonian; of
the Carboniferous; of the Permian; of the Trias; of the
Jurassic; of the Cretaceous; of the Eocene; of the Miocene.
_Plagiaulax_.
_Planolites; vulgaris_.
_Planorbis_.
Plants, of the Cambrian; of the Lower Silurian; of the Upper
Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Trias; of the Jurassic; of the Cretaceous;
of the Eocene; of the Miocene.
_Plasmopora_.
_Platanus; aceroides_.
_Platephemera antiqua_.
_Platyceras; dumosum; multisinuatum; ventricosum_.
_Platycrinus; tricontadactylus_.
_Platyostoma; Niagarense_.
Platyrhine Monkeys.
_Platyschisma helicites_.
_Platysomus; gibbosus_.
_Platystoma_.
Pleistocene period; climate of.
_Plesiosaurus; dolichodeirus_.
_Pleurocystites squamosus_.
_Pleurotoma_.
_Pleurotomaria_.
_Plicatula_.
Pliocene period; rocks of, in Britain; in Belgium; in
Italy; in North America; life of.
_Pliopithecus; antiquus_.
_Pliosaurus_.
_Podocarya_.
_Podozamites; lanceolatus_.
Polir-schiefer.
_Polycystina_; of Barbadoes-earth.
_Polypora; dendroides_.
_Polypterus_.
_Polystomella_.
_Polytremacis_.
_Polyzoa_, of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous; of the
Permian; of the Trias; of the Cretaceous; of the Miocene.
_Populus_.
_Porcellia_.
Porcupines.
Portage Group.
Port-Jackson Shark.
Portland beds.
Post-Glacial deposits.
Post-Pliocene period.
Post-Tertiary period.
_Poteriocrinus_.
Potsdam Sandstone.
Pre-Glacial deposits.
_Prestwichia; rotundata_.
_Primitia; strangulata_.
Primordial Trilobites.
Primordial zone.
_Proboscidea_, of the Miocene; of the Pliocene; of the
Post-Pliocene.
_Producta; horrida; longispina; semireticulata_.
_Productella_.
_Productidoe_.
_Proëtus_.
Prong-buck.
_Protaster; Sedgwickii_.
_Proteaceoe_.
_Proteus_.
_Protichnites_.
_Protocystites_.
_Protornis Glarisiensis_.
_Protorosaurus; Speneri_.
_Protospongia; fenestrata_.
_Prototaxites; Logani_.
_Psammobia_.
_Psammodus_.
_Psaronius_.
_Pseudocrinus bifasciatus_.
_Psilophyton; princeps_.
_Pteranodon; longiceps_.
_Pteraspis; Banksii_.
_Pterichthys; cornutus_.
_Pterinoea; subfalcata_.
_Pteroceras_.
_Pterodactylus; crassirostris_.
_Pterophyllum; Joegeri_.
_Pteropoda_, of the Cambrian; of the Lower Silurian; of
the Upper Silurian; of the Devonian; of the Carboniferous;
of the Permian; of the Jurassic.
_Pterosauria_; of the Jurassic; of the Cretaceous.
_Pterygotus Anglicus_.
_Ptilodictya; acuta; falciformis; raripora; Schafferi_.
_Ptychoceras; Emericianum_.
_Ptychodus_.
_Pupa vetusta_.
Purbeck Beds; Mammals of.
_Puryuroidea_.
_Pycnodus_.
_Pyrula_.
_Quadrumana_, of the Eocene; of the Miocene; of the
Pliocene; of the Post-Pliocene.
Quadrupeds (_see_ Mammalia).
Quaternary period.
Quebec Group.
_Quercus_.
Rabbits.
_Rana_.
_Raptores_.
_Rasores_.
Recent period.
_Reptaculites_.
Red clays, origin of.
Red Coral.
Red Crag.
Red Deer.
Reindeer.
_Remopleurides_.
Reptiles; of the Permian; of the Trias; of the Jurassic; of
the Cretaceous; of the Eocene.
_Retepora; Ehrenbergi; Phillipsi_.
_Retiolites_.
_Retzia_.
_Rhætic Beds_.
_Rhamphorhynchus; Bucklandi_.
_Rhinoceridoe_.
_Rhinoceros Etruscus; leptorhinus; megarhinus; tichorhinus_.
_Rhinopora verrucosa_.
_Rhizodus_.
_Rhombus minimus_.
Rhyncholites.
_Rhynchonella; cuneata; neglecta; pleurodon; varians.
_Rhynchosaurus; articeps.
Rice-shells.
Richmond Earth.
Ringed Worms (_see_ Annelida).
River-gravels, high-level and low-level.
_Robulina_.
Rocks, definition of; divisions of; igneous; aqueous;
mechanically-formed; chemically-formed; organically-formed;
arenaceous; argillaceous; calcareous; siliceous.
_Rodentia_, of the Eocene; of the Miocene; of the
Post-Pliocene.
Roebuck.
_Rostellaria_.
_Rotalia; Boueana_.
Rugose Corals; of the Lower Silurian; of the Upper Silurian;
of the Devonian; of the Carboniferous; of the Permian; of
the Upper Greensand.
Rupelian Clay.
_Sabal major_.
Sabre-toothed Tiger.
_Saccammina_.
_Saccosoma.
Salamanders.
Salina Group.
_Salix; Meeki_.
_Salmonidoe_.
_Sao hirsuta_.
_Sassafras cretacea_.
_Sauropterygia_.
_Scalaria; Groenlandica_.
_Scaphites; oequalis_.
_Schizodus_.
Schoharie Grit.
_Scolecoderma_.
_Scoliostoma_.
_Scolithus; Canadensis_.
Scorpions of the Coal-measures.
Scorpion-shells.
Screw-pines.
_Scutella; subrotunda_.
Sea-cows (_see_ Sirenia).
Sea-lilies (_see_ Crinoidea).
Sea-lizards (_see_ Enaliosaurians).
Seals.
Sea-mats and Sea-mosses (_see_ Polyzoa).
Sea-shrubs (_see_ Gorgonidæ).
Sea-urchins (_see_ Echinoidea).
Sea-weeds.
Secondary period.
Sedimentary rocks.
_Semnopithecus_.
Septaria.
_Sequoia; Couttsioe; gigantea; Langsdorffii_.
_Serolis_.
Serpents (_see_ Ophidia).
_Serpulites_.
Sewâlik Hills (_see_ Siwâlik Hills).
Sheep.
Shell-sands.
_Sigillaria; Groeseri_.
Sigillarioids.
Silicates, infiltration of the shells of Foraminifera by.
Siliceous rocks.
Siliceous Sponges.
Silicification.
Silurian period (_see_ Lower Silurian and Upper Silurian).
_Simosaurus; Gaillardoti_.
_Siphonia; ficus_.
Siphonostomatous Univalves.
_Siphonotreta_.
_Sirenia_; of the Eocene; of the Miocene.
_Siren lacertina_.
_Sivatherium; giganteum_.
Siwâlik Hills, Miocene strata of.
Skiddaw Slates.
Sloths.
_Smilax_.
_Smithia_.
Snakes (_see_ Ophidia).
Soft Tortoises.
_Solarium_.
Solenhofen Slates.
Solitaire.
_Spalacotherium_.
_Spatangus_.
_Sphoerospongia_.
_Sphagodus_.
_Sphenodon_.
_Sphenopteris_.
Spiders of the Coal-measures.
Spider-shells.
Spindle-shells.
_Spirifera; crispa; disjuncta; hysterica; mucronata; Niagarensis;
rostrata; sculptilis; trigonalis_.
_Spiriferidoe_.
_Spirophyton cauda-Galli_.
_Spirorbis; Arkonensis; Carbonarus; laxus; Lewisii; omphalodes;
spinulifera_.
_Spirulirostra_.
_Spondylus; spinosus_.
Sponges, of the Cambrian; of the Lower Silurian; of the Upper
Silurian; of the Devonian; of the Carboniferous; of the Permian;
of the Trias; of the Jurassic; of the Cretaceous.
_Spongilla_.
_Spongillopsis_.
_Spongophyllum_.
Spore-eases, of Cryptogams in the Ludlow rocks; in the Coal.
Squirrels.
_Stagonolepis_.
Staircase-shell.
Stalactite.
Stalagmite.
Star-corals.
Star-fishes.
St Cassian Beds.
_Stephanophyllia_.
_Stereognathus_.
_Stigmaria; ficoides_.
Stonesfield Slate; Mammals of.
Strata, contemporaneity of.
Stratified rock.
_Streptelasma_.
_Streptorhynchus_.
_Stromatopora; rugosa; tuberculata_.
_Strombodes; pentagonus_.
_Strombus_.
_Strophalosia_.
_Strophodus_.
_Strophomena; alternata; deltoidea; filitexta; rhomboidalis;
Subplana_.
Sub-Apennine Beds.
Sub-Carboniferous rocks.
Succession of life upon the globe.
_Suida_.
Sulphate of lime.
_Sus Erymanthius; scrofa_.
_Synastroea_.
_Synhelia Sharpeana_.
_Synocladia; virgulacea_.
_Syringopora; ramulosa_.
Tabulate Corals; of the Lower Silurian; of the Upper Silurian;
of the Devonian; of the Carboniferous; of the Permian.
_Talpa Europoea_.
_Tapiridoe_.
Tapirs.
_Tapirus Arvernensis_.
_Taxocrinus tuberculatus_.
_Taxodium_.
_Teleosaurus_.
Teleostean Fishes; of the Cretaceous.
_Telerpeton Elginense_.
_Tellina proxima_.
_Tentaculites; ornatus_.
_Terebra_.
_Terebratella; Astleriana_.
_Terebratula; digona; elongata; hastata; quadrifida;
sphoeroidalis_.
_Terebratulina; caput-serpentis; striata_.
Termites.
Terrapins.
Tertiary period.
Tertiary rocks, classification of.
_Testudinidoe_.
Tetrabranchiate Cephalopods; of the Cambrian; of the Lower
Silurian; of the Upper Silurian; of the Devonian; of the
Carboniferous; of the Permian; of the Trias; of the Jurassic;
of the Cretaceous; of the Eocene; of the Miocene.
_Textularia; Meyeriana_.
Thanet Sands.
_Theca_.
_Theca Davidii_.
_Thecidium_.
Thecodont Reptiles.
_Thecodontosaurus; antiquus_.
_Thecosmilia annularis_.
_Thelodus_.
Theriodont Reptiles.
_Thylacoleo_.
Tile-stones.
_Titanotherium_.
Toothed Birds.
Tortoises.
_Tragoceras_.
Travertine.
Tree-Ferns, of the Devonian; of the Coal-measures.
Tremadoc Slates.
_Trematis_.
Trenton Limestone.
_Trianthrus Beckii_.
Triassic period; rocks of, in Britain; in Germany; in the
Austrian Alps; in North America; life of.
_Triconodon_.
_Trigonia_.
_Trigoniadoe_.
_Trigonocarpum; ovatum_.
Trilobites; of the Cambrian; of the Lower Silurian; of the
Upper Silurian; of the Devonian; of the Carboniferous.
_Trimerellidoe_.
_Trinucleus; concentricus_.
_Trionycidoe_.
_Triton_.
_Trochocyathus_.
_Trochonema_.
_Trogontherium; Cuvieri_.
Trumpet-shells.
Tulip-tree.
_Turbinolia sulcata_.
_Turbinolidoe_.
_Turrilites; catenulatus_.
_Turritella_.
Turtles.
_Typhis tubifer_.
_Ullmania selaginoides_.
Unconformability of strata.
Under-clay of coal.
_Ungulata_, of the Eocene; of the Miocene; of the
Pliocene; of the Post-Pliocene.
Uniformity, doctrine of.
_Unio_.
Univalves (_see_ Gasteropoda).
Upper Cambrian; Chalk; Cretaceous; Devonian; Eocene; Greensand;
Helderberg; Laurentian; Llandovery; Ludlow rock; Miocene;
Oolites; Silurian period; rocks of, in Britain; in North
America; life of.
_Ursus arctos; Arvernensis; ferox; speloea_.
_Ursus_.
Valley-gravels, high-level and low-level.
_Vanessa Pluto_.
_Varanidoe_.
Vegetation (_see_ Plants).
_Ventriculites; simplex_.
Venus's Flower-basket.
_Vermilia_.
_Vespertilio Parisiensis_.
Vicksburg Beds.
Vines.
Vitreous Sponges.
_Voltzia; heterophylla_.
_Voluta; elongata_.
Volutes.
_Walchia; piniformis_.
Walrus.
Wealden Beds.
_Wellingtonia_.
Wenlock Beds; Limestone; Shale.
Wentle-traps.
Werfen Beds.
Whalebone Whales.
Whales.
Whelks.
White Chalk; structure of; origin of.
White Crag.
White River Beds.
Wild Boar.
_Williamsonia_.
Winged Lizards (_see_ Pterosauria).
Winged Snails (_see_ Pteropods).
Wing-shells.
Wolf.
Wolverine.
Wombats.
Woolhope Limestone.
Woolly Rhinoceros.
Woolwich and Reading Beds.
Worm-burrows.
_Xanthidia_.
_Xenoneura antiquorum_.
_Xiphodon_.
_Xylobius; Sigillarioe_.
_Zamia spiralis_.
_Zamites_.
_Zaphrentis; cornicula; Stokesi; vermicularis_.
_Zeacrinus_.
Zechstein.
_Zeuglodon; cetoides_.
End of the Project Gutenberg EBook of The Ancient Life History of the Earth
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