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Title: Relics of Primeval Life
Beginning of Life in the Dawn of Geological Time
Author: Sir J. William Dawson
Release Date: January 30, 2022 [eBook #67287]
Language: English
Produced by: Tom Cosmas produced from materials provided at The Internet
Archive and placed in the Public Domain.
*** START OF THE PROJECT GUTENBERG EBOOK RELICS OF PRIMEVAL LIFE ***
Transcriber Note
Text emphasis displayed as _Italics_ and =Bold=.
RELICS OF PRIMEVAL LIFE
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| WORKS BY |
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[Illustration: Cryptozoon Boreale, _Dawson_.]
Two divisions or branches of a large specimen collected by Mr. E. T.
Chambers in the Ordovician of Lake St. John. (See Appendix D.)
[_Frontis._
RELICS OF PRIMEVAL LIFE
BEGINNING OF LIFE IN THE DAWN OF GEOLOGICAL TIME
BY
SIR J. WILLIAM DAWSON LL.D., F.R.S., Etc.
_WITH SIXTY-FIVE ILLUSTRATIONS_
[Illustration]
NEW YORK CHICAGO TORONTO FLEMING H. REVELL COMPANY
1897
_The substance of a Course of Lectures on Pre-Cambrian Fossils
delivered in the Lowell Institute, Boston, in November, 1895._
To
AUGUSTUS LOWELL Esq
_Vice-President of the American Academy of Arts and Sciences
Trustee of the Lowell Institute_
AS THE WISE AND LIBERAL ADMINISTRATOR OF A NOBLE
ENDOWMENT FOR THE ADVANCEMENT AND DIFFUSION
OF KNOWLEDGE
THIS WORK IS DEDICATED
WITH MUCH RESPECT AND ESTEEM
BY THE AUTHOR
PREFACE
IT is now more than thirty-five years since the announcement was made
of the discovery of remains supposed to indicate the existence of
animal life in the oldest rocks known to geologists. It was hailed with
enthusiasm by some as "opening a new era in geological science"; but
was regarded with scepticism by others, in consequence of the condition
and mineral character of the supposed fossil, and because of the great
interval in time between the oldest animal remains previously known and
these new claimants for recognition. Since that time, many new facts
have been learned, and the question has been under almost continuous
discussion and debate, with various fortunes, in different quarters.
The author was associated with the original discovery and description
of these supposed earliest traces of life; and has since, in the
intervals of other work, devoted much time to further exploration and
research, the results of which have been published from time to time in
the form of scientific papers. He has also given attention to the later
discoveries which have tended to fill up the gap between the Laurentian
fossil and its oldest known successors.
In 1875 he endeavoured to sum up in a popular form what was then known,
in a little volume named "The Dawn of Life," which has long been out of
print; and in 1893 the matter was referred to in a chapter of his work
"Salient Points in the Science of the Earth." In 1895 he was invited
to present the subject to a large and intelligent audience in a course
of lectures delivered in the Lowell Institute, Boston; and the success
which attended these lectures has induced him to reproduce them in the
present work, in the hope that inquiries into the Dawn of Life may
prove as fascinating to general readers as to those who prosecute them
as a matter of serious work, and that their presentation in this form
may stimulate further research in a field which is destined in the
coming years to add new and important domains to the knowledge of life
in the early history of the earth.
Hypotheses respecting the introduction and development of life are
sufficiently plentiful; but the most scientific method of dealing
with such questions is that of searching carefully for the earliest
remains of living beings which have been preserved to us in the rocky
storehouses of the earth.
There are many earnest labourers in this difficult field, and it will
be the object of the writer in the following pages to do justice to
their work as far as known to him, as well as to state his own results.
J. W. D.
CONTENTS
I
PAGE
The Chain of Life Traced Backward in Geological Time 3
II
Life in the Early Cambrian 17
III
Pre-Cambrian Life 47
IV
Foundations of the Continents, and their General
Testimony as to Life 79
V
Probabilities as to Laurentian Life, and Conditions
of its Preservation 107
VI
The History of a Discovery 125
VII
The Dawn of Life 147
VIII
Contemporaries of Eozoon 193
IX
Difficulties and Objections 221
X
The Origin of Life 245
XI
Some General Conclusions 281
APPENDIX
A. Geological Relations of Eozoon, etc. 295
B. Organic Remains and Hydrous Silicates 298
C. Affinities of Eozoon, etc. 303
D. Cryptozoon 310
E. Receptaculites and Archæocyathus 315
F. Pre-Geological Evolution 320
G. Controversies respecting Eozoon 324
H. Notes to Appendix, December, 1896 329
LIST OF ILLUSTRATIONS
FIG. PAGE
Cryptozoon Boreale _Frontispiece_
Map xvi
1. Olenellus 20
2. Triarthrus 23
3. Hymenocaris 27
4. Ctenichnites 32
5, 6. Archæocyathus 35
7, 8. Cryptozoon 37, 39
9. Fossils in Lower Cambrian Boulder 41
10. Section Hanford Brook 51
11. Worm Tracks 53
12. Pre-Cambrian Fossils 54
13. Arenicolites and Aspidella 54
14. Cryptozoon 56
15. Worm Burrows 67
16. Casts of Foraminifera 68
17. Tudor Eozoon 69
18. Laurentian America 85
19. Map of Grenville Limestones 88
19A. Attitude of Limestone, Côte St. Pierre 91
20, 21. Disturbed Beds 103
22. Section of Limestone 113
23. Silicification of Coral 113
24. Cast of Polystomella in Glauconite 115
24A. Crinoid and Shell in Glauconite 116
25. Nature-print of Eozoon 121
26, 27. Eozoon from Calumet 130
28, 29. Canals of Eozoon 133
30, 31. Canals and Tubuli 135
32. General Form of Eozoon 149
33, 34. Eozoon with Funnels 152, 153
35. Small Specimen and Structure 155
36. Decalcified Eozoon 157
37. Finest Tubuli filled with Dolomite 158
38. Arrangement of Canals 159
39-41. Finest Tubuli 160-2
42. Canals after Möbius 163
43. Stromatocerium 172
44. Stromatopora 173
45. Cœnostroma 174
46. Recent Protozoa 176
47. Fragmental Eozoon 183
48, 49. Nummulites and Calcarina 186
50, 51. Archæospherinæ 190, 200
52. Acervuline Eozoon 205
53, 54. Archæospherinæ 205, 208
55. Ditto, Finland 212
56. Eozoon Bavaricum 213
57. Archæozoon 215
58. Restoration of Eozoon 230
59. Eozoon in Different States 237
60. Nature-print of Large Specimen _To face_ 296
[Illustration: _Walker & Boutall SCt_
Grenville Series on the Ottawa River (17 miles to an inch).
_From Logan's Original Map of 1865._]
_THE CHAIN OF LIFE TRACED BACKWARD IN GEOLOGICAL TIME_
GEOLOGICAL CHRONOLOGY OF LIFE.
_After Prof. C. A. White._
=Column Key=--_Using First Letter_
----------------------------------------
Invertebrates. Vertebrates. Plants.
-------------- ------------- ---------
Protozoa Ganoid Fishes Algæ
Corals, etc. Telios Fishes Land Cryptogs
Echinoids Batrachians Phænogams
Worms Reptiles
Mollusks Dinosaurs
Arthropods Birds
Insects Marsupials
Land Snails Placentals
Humans
Geological Invertebrates. Vertebrates. Plants.
Systems or
Periods. P C E W M A I L G T B R D B M P H A L P
+------------------------------------------+
Kainozoic. | ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖|
{ Cretaceous ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖|
{ |-‖-‖-‖-‖-‖-‖-‖-‖--‖-‖-‖-‖-‖-‖-‖------‖-‖--|
{ Jurassic ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-‖-‖--‖---‖-‖-‖---‖------‖-‖--|
{ Triassic ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
|-‖-‖-‖-‖-‖-‖-‖-‖--‖---‖-‖------------‖-‖--|
Palæozoic. | ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ Permian ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-‖-‖--‖---‖--------------‖-‖--|
{ Carboniferous ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-‖-‖--‖------------------‖-‖--|
{ Devonian ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-‖----‖------------------‖-‖--|
{ Silurian ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-------------------------‖-‖--|
{ Ordovician ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-------------------------‖----|
{ Cambrian ...| ‖ ‖ ‖ ‖ ‖ ‖ ‖ |
{ |-‖-‖-‖-‖-‖-‖-------------------------‖----|
{ Etcheminian ...| ‖ ‖ ‖ ‖ ‖ ‖ |
|-‖-‖-‖-‖-----------------------------‖----|
Eozoic. | ‖ ‖ ‖ ‖ |
{ Huronian ...| ‖ · |
{ |-‖----------------------------------------|
{ Laurentian. | ‖ |
{ Grenvillian ...| ‖ |
{ |------------------------------------------|
{ Archæan ...| |
| |
+------------------------------------------+
Note.--It is not supposed that the Geological Periods were of equal
lengths, as represented in the diagram.
ERRATA.
Where _Cryptozoon prolificum_ occurs in the text, read _Cryptozoon
proliferum_.
[Transcriber Note: Errata Corrections HAVE BEEN applied to text!]
I
_THE CHAIN OF LIFE TRACED BACKWARD IN GEOLOGICAL TIME_
In infancy we have little conception of the perspective of time. To us
the objects around us and even our seniors in age seem to have always
been, and to have had no origin or childhood. It is only as we advance
in knowledge and experience that we learn to recognise distinctions
of age in beings older than ourselves. In thinking of this, it seems
at first sight an anomaly, or at least contrary to analogy, that the
oldest literature and philosophy deal so much with doctrines as to the
origins of things. In this respect primitive men do not seem to have
resembled children; and the fact that our own sacred records begin with
answers to such questions, and that these appear in the oldest literary
remains of so many ancient nations, and even in the folk-lore of
barbarous tribes, might be used as an additional argument in favour of
an early Divine revelation on such subjects, as a means of awakening
primitive men to the comprehension of their own place in the universe.
However this may be, it is certain that modern science at first took a
different stand.
The constancy of the motions of the heavenly bodies, our great
time-keepers, and of the changes on the earth depending upon them, and
the resolution of apparent perturbations into cycles of greater or less
length, impressed astronomers and physicists with the permanence of the
arrangements of the heavens and their eternal circling round without
any change. In like manner, on the rise of geology, the succession of
changes recorded in the earth seemed interminable, and Hutton could
say that in the geological chronology he could see "no vestige of a
beginning, no prospect of an end."
But the progress of investigation has changed all this, and has brought
physical and natural science back to a position nearer to that of
the old cosmogonies. Physical astronomy has shown that the constant
emission of heat and light from the sun and other stars must have had
a beginning, and is hurrying on toward an end, that the earth and
its satellite the moon are receding from each other, and that even
the spinning of our globe on its axis is diminishing in rapidity.
In summing up these and other changes, Lord Kelvin says: "To hold
the doctrine of the eternity of the universe would be to maintain a
stupendous miracle, and one contrary to the fundamental laws of matter
and force."
So, on our earth itself, we can now assign to their relative ages
those great mountain chains which have been emblems of eternity. We
can transfer ourselves in imagination back to a time when man and his
companion animals of to-day did not exist, when our continents and
seas had not assumed their present forms, and even when the earth was
an incandescent mass with all its volatile materials suspended in its
atmosphere. It is true that in all the changes which our earth has
undergone the same properties of matter and the same natural laws
have prevailed; but the interactions of these properties and laws
have been tending to continuous changes in definite directions, and
not infrequently to accumulations of tension leading to paroxysmal
vicissitudes.
If all this is true of the earth itself, it is especially applicable
to its living inhabitants. Successive dynasties of animals and plants
have occupied the earth in the course of geological time; and as we go
back in the record of the rocks, first man himself and, in succession,
all the higher animals disappear, until at length in the oldest
fossiliferous beds only a portion of the more humble inhabitants of the
sea can be found. In the time of the formation of the oldest of these
rocks, or perhaps somewhat earlier, must have been the first beginning
of life on our planet.
Just as we can trace every individual animal to a microscopic germ in
which all its parts were potentially present, so we can trace species,
genera, and larger groups of animals to their commencement at different
points of the earth's history, and can endeavour to follow the lines
of creation or descent back to the first beings in which vital powers
manifested themselves. All such beginnings must end in mystery, for
as yet we do not know how either a germ or a perfect animal could
originate from inanimate matter; but we may hope at least to make some
approximation to the date of the origin of life and to a knowledge of
the conditions under which it began to exist, confining ourselves for
the present principally to the Animal Kingdom.
As preliminary to the consideration of this subject, we may shortly
notice the grades of animals at present existing, and then the evidence
which we have of their successive appearance in different periods of
geological time, in order that we may eliminate all those of more
recent origin, in so far as the knowledge at present available will
permit, and restrict our consideration to forms which seem to have been
the earliest. In attempting this, we may use for reference the table
of geological periods and animal types presented in the diagram facing
this chapter, which is based on one prepared by Prof. Charles A. White,
of the United States Geological Survey, with modifications to adapt it
to our present purpose. In this table the leading groups of animals are
represented by lines stretching downward in the geological column of
formations as far as they have yet been traced. Such a table, it must
be observed, is always liable to the possibility of one or more of its
lines being extended farther downward by new discoveries.
The broadest general division of the Animal Kingdom is into back-boned
animals (Vertebrates) and those which have no back-bone or equivalent
structure (Invertebrates).[1] The former includes, besides man
himself, the familiar groups of Beasts, Birds, Reptiles, and Fishes.
The latter consists of the great swarms of creatures included under
the terms Insects, Crustaceans, Worms, Cuttle-fishes, Snails, Bivalve
Mollusks, Star-fishes, Sea-urchins, Coral Animals, Sea-jellies.
Sponges, and Animalcules. This mixed multitude of animals, mostly of
low grade and aquatic. Includes a vast variety of forms, which, though
comparatively little known to ordinary observers, are vastly numerous,
of great interest to naturalists, and, as we shall find, greatly older
in geological date than the higher animals.
[Footnote 1: The twofold primary division now sometimes used, into
Metazoa and Protozoa, seems more arbitrary and unequal, and therefore
of less practical value.]
It will be seen by a glance at the diagram that the higher vertebrates
are of most recent origin, man himself coming in as one of the newest
of all. Only the lower reptiles or batrachians and the fishes extend
very far back in geological time. None of the other vertebrate groups
reach, so far as yet known, farther back than the middle of the
geological scale--probably in point of time very much less than this.
Those of the invertebrates that breathe air reach no farther back than
the fishes, possibly not so far. On the other hand, all the leading
groups of marine invertebrates run without interruption back to the
Lower Cambrian, and some of them still farther. Thus it would appear
that for long ages before the introduction of land or air-breathing
animals of any kind, the sea swarmed with animal life, which was almost
as varied as that which now inhabits it. The reasons of this would seem
to be that the better support given by the water makes less demands
upon organs for mechanical strength, that the water preserves a more
uniform temperature than the air, and that arrangements for respiration
in water are less elaborate than those necessary in air. Hence the
conditions of life are, so to speak, easier in water than in air, more
especially for creatures of simple structure and low vital energy.
Besides this, the waters occupy two-thirds of the surface of the earth,
and in earlier periods probably covered a still greater area.
We are now in a position to understand that the Animal Kingdom had
not one but many beginnings, its leading types arriving in succession
throughout geological time. Thus the special beginning of any one line
of life, or those of different lines, might form special subjects
of inquiry; but our present object is to inquire as to the first or
earliest introduction of life in our planet, and in what form or forms
it appeared. We may, therefore, neglect all the vertebrate animals and
the air-breathing invertebrates, and may restrict our inquiries to
marine invertebrates.
In relation to these, six of the larger divisions or provinces of the
Animal Kingdom may suffice to include all the lower inhabitants of the
ocean, whether now or in some of the oldest fossiliferous rocks.[2]
[Footnote 2: Some modern zoologists, having perhaps, like some of the
old Greeks, lost the idea of the unity of nature, or at least that of
one presiding divinity, prefer for the larger divisions of animals
the term _phylum_ or _phylon_, implying merely a stock, race or kind,
without reference to a definite place in an ordered kosmos.]
Looking more in detail at our diagram, we observe that the higher
vertebrates nearest to man in structure extend back but a little
way, or, with a few minor exceptions, only as far as the beginning
of the Kainozoic or Tertiary Period, in the later part of which
we still exist. Other air-breathing vertebrates, the birds and
the true reptiles, extend considerably farther, to the beginning
of the previous or Mesozoic Period. The amphibians, or frog-like
reptiles, reach somewhat farther, and the fishes and the air-breathing
arthropods farther still. On the other hand, our six great groups of
marine invertebrates run back for a vast length of time, without any
companions, to the lowest Palæozoic, and this applies to their higher
types, the cuttles and their allies, and the crustaceans, as well as
to the lower tribes. Turning now again to our table, we find that
these creatures extend in unbroken lines back to the Lower Cambrian,
the oldest beds in which we find any considerable number of organic
remains, and leave all the other members of the Animal Kingdom far
behind.
If now we endeavour to arrange the leading groups of these persistent
invertebrates under a few general names, we may use the following,
beginning with those highest in rank:--
(1) _Insects_ and _Crustaceans_ (Arthropoda).
(2) _Cuttles, univalve and bivalve Shell-fishes_ (Mollusca).
(3) _Worms_ (Annelida).
(4) _Sea-urchins_ and _Sea-stars_ (Echinodermata).
(5) _Coral Animals_, _Sea-anemones_, and _Sea-jellies_ (Cœlenterata).
(6) _Sponges_, _Foraminifera_ and _Animalcules_ of simple organization
(Protozoa).
There are, it is true, some animals allied to the mollusks and worms,
which might be entitled to form separate groups, though of minor
importance The position of the sponges is doubtful, and the great mass
of Protozoa may admit of subdivision; but for our present purpose these
six great groups or provinces of the Animal Kingdom may be held to
include all the humbler forms of aquatic life, and they keep company
with each other as far as the Early Cambrian. If, in accordance with
the previous statements, we choose to divide the earth's history by
the development of animal life rather than by rock formations, and to
regard each period as presided over by dominant animal forms, we shall
thus have an age of man, an age of mammals, an age of reptiles and
birds, an age of amphibians and fishes, and an age of crustaceans and
mollusks.
It is only within recent years that the researches more especially of
Barrande, Hicks, Lapworth, Linarrson, Brögger, and others in Europe,
and of Matthew, Ford and Walcott in America, have enlarged the known
animals of the Lower Cambrian to nearly 200 species, and below this
we know as yet very little of animal life. We may therefore take the
Lower Cambrian, or "Olenellus Zone" as it has been called from one of
its more important crustaceans,[3] as our starting-point for plunging
into the depths below. In doing so, we may remark on the orderly and
symmetrical nature of the chain of life, and on the strange fact that
for so long ages animal life seems to have been confined to the waters,
and to have undergone little development toward its higher forms. It
is like a tree with a tall branchless stem bearing all its leaves and
verdure at the top, or like some obscure tribe of men long living in
isolation and unknown to fame, and then, under some hidden impulse
or opportunity, becoming a great conquering and dominant nation. Or
to compare it with higher things, it is like the Christian religion,
for ages confined to a small and comparatively unimportant people,
and developing slowly its faith and hopes, and then suddenly, under
the personal influence of Christ and His apostles, spreading itself
over the world, and in a few centuries becoming the ruling power in
its greatest empire, surviving the fall of this and permeating all
the great nations that sprang from its ruins. God's plans in nature,
in history, and in grace seem to us very slow in their growth and
maturity, but they are very sure.
[Footnote 3: See figure, p. 20.]
_LIFE IN THE EARLY CAMBRIAN_
II
_LIFE IN THE EARLY CAMBRIAN_
In the old Chaldean fable of the descent of Ishtar into Hades, to
recover her lost Tammuz, at each successive gate of the lower regions
she is stripped of some of her ornaments and garments, till at length
she has to appear naked and unadorned in the presence of the lord of
the Nether World. So in our descent from the surface on which men
live, through the successive rocky layers of the earth's crust, we
leave behind, one by one, all the higher forms of life with which we
are familiar; but there still remain to us our six groups of aquatic
invertebrates, in the guise, it is true, of species and genera now
unknown in a living state, yet well represented as far down as the
lower part of the Cambrian. Let us now suppose that we take our stand
on the shores of the Cambrian sea, or cast our dredge into its waters
in search of these old animals; though we can only actually do so by
painfully hammering and chiselling them out of their rocky tombs, and
this often in fragments which must be put together before we can fully
realize the forms and structures of the animals to which they belonged.
We may pause here, however, to remark that neither the geographical
nor climatal conditions of the earth at this early time were similar
to these with which we are now familiar. The marine animals of the
Cambrian have left their remains in beds of sediment, which now
constitute rocks forming parts of our continents remote from the sea,
and much elevated above its level, showing that large areas, then under
the ocean, are now dry land; while there is no good evidence that
the sea and land have changed places. The facts rather indicate that
the continents have extended their area at the expense of the ocean,
which has, however, probably increased in depth. In evidence of these
statements, I need only mention that some of the oldest rocks in the
Scottish and Welsh hills, in Scandinavia, in Russia and in Bohemia, are
rich in Cambrian marine fossils.
[Illustration: Fig. 1.--_Olenellus Thompsoni_, Hall.
A characteristic Trilobite of the Lower Cambrian in North America.
After Walcott and specimen in Peter Redpath Museum.]
In America, in like manner, such rocks are found on the flanks of the
Appalachians, in New Brunswick, and in Newfoundland, in the table-land
of Colorado and in the Rocky Mountains. In point of fact, a map of
the Northern Hemisphere at this period would show only a limited
circumpolar continent with some outlying islands to the south of it,
and shallows stretching across the northern part of the areas of the
present Atlantic and Pacific Oceans. The great ocean, however, thus
extending over most of the temperate and tropical parts of the Northern
Hemisphere, was probably also more muddy and shallow than that of
modern times. The surface temperature of this vast ocean was also,
it is probable, more uniform than that of the modern sea, while even
its profounder depths or abysses would have more earth-heat than at
present. Thus we may, without hesitation, affirm that in this early
age the conditions for the introduction of swarming marine life of low
grade, and its extension over the whole earth, were at a maximum.
Let us inquire, then, what these old Cambrian seas actually produced,
more especially in the early portions of that ancient and probably
protracted time.
The most highly organized type of which we have any certain evidence
is that of the Crustacea, the group to which our modern lobsters and
crabs belong, and its most prominent representatives are the trilobites
(Figs. 1, 2), so called from the three lobes into which the body is
divided. These creatures are indeed remarkable for the twofold property
of bilateral symmetry, and fore and aft jointed structure, both based
on the number three. From front to rear we have a large head, usually
with well-developed eyes and oral organs, a middle or thoracic part
composed of a series of movable segments, and a tail-piece sometimes
small, sometimes nearly as large as the head. Transversely, the body
is divided into a central and two lateral lobes, which can be seen in
the head, the thorax, and usually in the tail as well. The organization
of these animals must have been as complex as that of most existing
Crustaceans. Their nerve system must have been well developed; a vast
number of muscles were required to move the different parts of the
trunk, and the numerous and complex limbs which have been observed
in some of the species, and no doubt were possessed by all. Their
digestive and circulatory organs must have been in proportion to the
complexity of their locomotive organs.
[Illustration: Fig. 2.--_Triarthrus Becki_, Green.
A Trilobite of primitive type, showing its limbs and antennæ. (After
Beecher.)]
Figure 2, borrowed from Beecher,[4] shows the limbs of a species,
not of the Lower Cambrian, but of a somewhat later formation. There
can be no doubt, however, that those of earlier species were equally
perfect, more especially as Triarthrus is an animal of an old type
approaching to extinction in the age succeeding the Cambrian, and its
representatives in the earlier and palmy days of the family could not
have been inferior in organization. These creatures swarmed in every
sea in the Cambrian period, and were represented by a great number of
species, some of them of large size, others very small; some
many-jointed, others few-jointed, and with a great variety of tubercles,
spines, and other ornamental and protective parts. If we ask for their
affinities and place in the great group of Crustacea, the answer must
be that, while in some points allied to the higher forms, they approach
most nearly to those which occupy a medium position in the class, and
are, in fact, a composite type, presenting points of structure now
distributed among different groups. If we ask for affinities with lower
groups, we have to reply that their nearest allies in this direction
are the bristle-footed marine worms; but there is a vast gap, both
in the Cambrian and Modern seas, between any of these worms and the
Crustacea, which, either as embryos or as adults, have any resemblance
to them.
[Footnote 4: _American Journal of Science_, 1896.]
The Trilobites, after appearing in a great variety of generic and
specific forms, and playing a most important part in their time,
were not destined to continue beyond the Carboniferous period, and
before that time they were beginning to give place to the Limuli,
King-crabs, or Horseshoe-crabs, a few species of which continue on our
coasts until the present time. In this limited duration the Trilobites
present a strange contrast to certain shrimp-like Crustaceans, their
contemporaries (the Phyllopods), which very closely resemble some
still extant, and the same remark applies to swarms of little bivalve
Crustaceans (Ostracods), which are still represented by hosts of modern
species both in the sea and in the fresh waters. There is, however,
a remarkable group of shrimp-like Crustaceans, represented in the
modern world by only a few small species, which in the Cambrian age
attained greater size, and constitute a very generalized type combining
characters now found in lower and higher groups of Crustacea.
_Hymenocaris vermicauda_ of Salter (Fig. 3) may serve to illustrate one
of these primitive forms.
[Illustration: Fig. 3.--_Hymenocaris vermicauda_, Salter.
A Lower Cambrian Shrimp of generalized type. (After Salter.)]
In point of fact, as Dr. Henry Woodward has shown in an able
presidential address delivered to the Geological Society in 1895, at
the base of the Lower Cambrian we still have several distinct groups
of Crustacea; and if with some we were to hold them as traceable to
one original form or to a worm-like ancestor, we must seek for this
far back in those pre-Cambrian rocks in which we find no Crustaceans
whatever. There is, it is true, no good reason to demand this; for
whatever the cause, secondary or final, which produced any form of
Crustacean in the Lower Cambrian, it might just as well have produced
several distinct forms. Evolutionists seem to be somewhat unreasonable
in demands of this kind, for any cause capable of originating a new
form of living being, might have been operative at the same time in
different localities and under somewhat diverse conditions, and may
also have acted at different times. All imaginary lines of descent of
animals are more or less subject to this contingency; and this may
partly account for the great diversity in the lines of affiliation
presented to us by evolutionists, which may in part have a basis in
fact in so far as distinct varietal and racial forms are concerned, but
may just as likely be entirely fallacious in the case of true species.
In any case, in the lowest rocks into which we can trace Crustacea, we
have already probably five of the orders into which their successors
in the modern seas are divided by zoologists; and this is certainly a
singular and suggestive fact, the significance of which we shall be
better prepared to understand at a later stage of our investigation.
Allied in some respects to the Crustacea, though much lower in grade,
are the marine Worms--a great and varied host--usually inhabiting the
shallower parts of the ocean; though the 330 species collected by the
_Challenger_ expedition show that they also abound in those greater
depths to which voyagers have only recently had access. Sea-worms seem
thus to be able to live in all depths, as well as in all climates; and
in accordance with this they abound in the oldest rocks, which are
often riddled with the holes caused by their burrowing, or abundantly
marked on the surfaces of the beds with their trails.
The great province of the Mollusca, in which, for our present purpose,
we may include some aberrant and rudimentary Molluscoids, is now best
known to us by its medium types, the univalve and bivalve Shell-fishes;
the higher group of the Cuttle-fishes and Nautili, though not uncommon,
being much less numerous, and one at least of the lower groups, the
Lamp-shells or Brachiopods, being represented in the modern world
by but few forms. The extension of the Mollusks backwards into the
Cambrian is remarkable as being on the whole meagre in comparison with
that of the Crustaceans, and as presenting only in small numbers the
types most common in later times. One or two shells, and perhaps some
tracks, represent the highest group: some forms resembling the floating
species of Sea-snails, and a very few ordinary bivalves represent
the types best known in the modern seas; while the Brachiopods, and
probably some still simpler forms, are in great comparative excess.
The individual specimens are also of small size, as if these creatures
were but insinuating themselves on the arena of life in insignificant
and humble forms. So far as yet known, the lowest groups supposed
to be allied to the Mollusks, the Ascidians or Sea-squirts, and the
Sea-mosses (Polyzoa), do not appear; but they may have been represented
by species which possessed no hard parts capable of preservation.
This leads us to the consideration that while all the Crustacea
necessarily possess some kind of crust or external skeleton, the
Mollusks are very different in this respect. While some of them have
ponderous shells, others even of the highest forms are quite destitute
of such protective parts. This again leads to a curious question
respecting the armature of the Trilobites. Some of these, even of the
larger species, have strong and formidable spines, like those of the
King-crabs and other modern Crustaceans. Now in the modern species we
know these organs to be intended to defend their possessors against the
attacks of fishes more swift and powerful than themselves. But what
enemies of this kind had the Trilobites to dread? Yet species a foot or
more in length presented great bayonet-like spines.
[Illustration: Fig. 4.--_Ctenichnites ingens_, Matthew.
A slab with markings of aquatic animals. From specimen in Peter Redpath
Museum.]
All that we know on this subject is that on the surfaces of the Lower
Cambrian rocks there are in some places complicated and mysterious
tracks or scratches, which seem to have been produced when the rock
was in the state of soft mud, by large and swiftly swimming animals
possessing some sort of arms or similar appendages (Fig. 4). Matthew
has ingeniously suggested that they may have been large Mollusks allied
to the modern gigantic Squids which still abound in the ocean, that
they may have been sufficiently powerful to prey on the Trilobites,
and, being swift swimmers, would have found them a helpless prey but
for their defensive spines. Yet such large Mollusks might have perished
without leaving any remains recognisable in the rocks, except what
may be termed their hand-writing on clay. A few small examples of the
shell-bearing species of these highest Mollusks, however, appear in
the Cambrian, and in the succeeding ages they become very abundant and
attain to large dimensions, again dwindling toward modern times. It
would thus seem that for some unknown reason the highest and lowest
Mollusks may have been locally plentiful, but the intermediate types
were rare.
The much lower group of Echinoderms, or Sea-urchins and Sea-stars,
curiously enough puts in but a small appearance in the Early Cambrian,
being represented, as far as yet known, by only one embryonic group,
the Cystideans. A little later, however, Feather-stars became greatly
abundant, and a little later still the true Star-fishes and Urchins.
The aberrant group of the Sea-slugs seems, so far as known, to be of
more modern origin; but most of these animals are soft-bodied, and
little likely to have been preserved.
The great group of the coral animals, so marked a feature of later
ages, is scarcely known in the oldest Cambrian, except by some
highly generalized forms[5] (Fig. 5). There are, however, small
Zoophytes referable to the lower type of Hydroids, and markings which
are supposed to be casts of stranded Jelly-fishes. If, with some
naturalists, we regard the Sponges as very humble members of the
coral group (Cœlenterata), then we have a right to add them to its
representatives in the lowest Cambrian; but perhaps they had better be
ranked with the next and lowest group of all--the Protozoa.
[Footnote 5: Dr. G. J. Hinde has carefully studied these forms, and
also similar species occurring in Lower Cambrian beds in different
parts of North America, Spain, Sardinia, and elsewhere. See note in the
Appendix, and _Journal Geol. Society of London_, vol. xlv. p. 125.]
[Illustration: Fig. 5.--_Archæocyathus profundus_, Billings.
Possibly a Coral of generalized type from the Lower Cambrian of L'Anse
à Loup, Labrador. A small specimen.]
[Illustration: Fig. 6.--_Structures of A. profundus (magnified)._
From specimens in Peter Redpath Museum.
(_a_) Lower acervuline portion. (_b_) Upper part, with three of the
radiating laminæ and section of pores, (_c_) Portion of lamina, with
pores, the calcareous skeleton unshaded.]
These are the humblest of all the inhabitants of the sea, presenting
very simple, jelly-like bodies with few organs, but sometimes producing
complex and beautiful calcareous and siliceous coverings or tests.
Animals of this type have been found in the Lower Cambrian, though not
in such vast multitudes as in some later formations. There are also in
the Cambrian some large, laminated, calcareous bodies (Cryptozoon of
Hall), to be noticed more fully below, and which have recently been
traced in still lower deposits even below the lowest Cambrian (Figs.
7, 8). These have some resemblance to the layer-corals or stromatoporæ
of the Silurian and Ordovician, which are by many regarded as the
skeletons of coral animals of a low type; but the microscopic structure
of Cryptozoon rather allies it with some of the larger forms of
Protozoa found higher up in the series of formations. We shall have to
discuss this later in connection with still older fossils.
[Illustration: Fig. 7.--_Cryptozoon proliferum_, Hall.
Portion of slab reduced in size. (After Hall.) See also Fig. 59, p.
237.]
[Illustration: Fig. 7_a_.--_Portion of thin section of Cryptozoon
proliferum (magnified × 50)._]
(_a_) Corneous layers, (_a¹_) One of these dividing, (_b_) Intermediate
stroma with granules of calcite, dolomite and quartz, traversed by
canals.
_From a Micro-photograph by_ Prof. Penhallow.
[_To face p. 39._
If now in imagination we cast our tow-net or dredge into the sea of the
Lower Cambrian, we may hope to take specimens illustrative of all our
six groups of invertebrate animals, and under several of them examples
of more than one subordinate group. Of the Crustaceans we might have
representatives of four or five ordinal groups, and of the Mollusca
as many. These are the two highest and most complicated. In the four
lower groups we would naturally have less variety, though it would seem
strange, were it not for so many examples in later periods, that the
dominant and highest groups should be most developed in regard to the
number of their modifications.
[Illustration: Fig. 8.--_Diagrammatic section of two Laminæ of
Cryptozoon, showing the Canals of the intermediate space, or Stroma
(magnified)._
Specimen in Peter Redpath Museum.]
Of the whole we might perhaps have been able to secure at least 200
species even in one locality. The likelihood is that if there had been
a collecting expedition like that of the _Challenger_ in Early Cambrian
times, it could have secured thousands of specific forms representing
all the above types, more especially as we probably know very little of
the softer and shell-less animals of these old seas, and there is some
reason to believe that these may have been in greater proportion than
in the present ocean.
In illustration of the richness of some parts of the lowest Cambrian
sea, I may refer here to the large and beautifully illustrated Memoir
of Walcott on the Lower Cambrian, containing fifty folio plates of
species collected in a few districts of North America; and, as a minor
example, to the contents of a loose boulder of limestone of that age,
found at Little Metis on the Lower St. Lawrence, under the following
circumstances (Fig. 9):--
[Illustration: Fig. 9.--_Lower Cambrian Fossils found in a few cubic
inches of limestone in a conglomerate at Little Metis; viz., Trilobites
of genera Olenellus, Ptychoparia, Solenopleura, Protypus; Brachiopod
of genus Iphidea; Pteropod of genus Hyolithes; Gastropod, genus
Stenotheca; Sponge, undetermined._]
Along what is now the valley of the Lower St. Lawrence and the gulf
of the same name, there seem to have been deposited in the oldest
Cambrian or Olenellus period beds of limestone rich in shells of marine
animals and fragments of these. These can be seen in place in some
parts of Newfoundland, and here and there on the hills bounding the
St Lawrence River; but for the most part they have been swept away
by the sea when these districts were being elevated to form parts
of the American land. Their ruins appear as boulders and pebbles in
thick beds of conglomerate or pudding-stone, constituting portions of
the Upper Cambrian and Lower Ordovician series, which now occupy the
south coast of the Lower St. Lawrence. In one of these boulders, less
than a foot in diameter, removed from its hard matrix and carefully
broken up, I found fragments representing eleven different species,
of which no less than eight were trilobites, one a gastropod, one a
brachiopod, and one probably a sponge--and this forms an interesting
illustration of the number of species sometimes to be found in a
limited space, and also of the great prevalence of the Trilobites in
these beds. The statistics of these groups for North America, as given
by Walcott, show 165 species belonging to all the groups enumerated
above, and of these the Trilobita constitute one-third of the whole;
so that the Olenellus Zone, as it has been called from one genus of
these Crustaceans, might well be named the reign of Trilobites, unless,
indeed, as the indications already referred to seem to show, giant
cuttle-fishes, destitute of shells, were then the tyrants of the sea,
but are represented only by the markings of their long and muscular
arms on the soft sea mud while dashing after their Crustacean prey.
What I desire, however, chiefly to emphasize is, that in the lowest
beds of the Cambrian we have evidence of sea-bottoms swarming with
representatives of all the leading types of marine invertebrate life,
and therefore seem to be still far from the beginning of living things,
if that was a slow and gradual process, rather than a sudden or rapid
series of events.
_PRE-CAMBRIAN LIFE_
III
_PRE-CAMBRIAN LIFE_
Having traced the chain of life through the long geological ages, from
the present day back to the Cambrian Period, we may now take our stand
on the fauna of the lowest Cambrian or Olenellus Zone, as a platform
whence we may dive into still deeper abysses of past time. Here,
however, we seem to have arrived at a limit beyond which few remains
of living things have yet been discovered, though there still remain
pre-Cambrian deposits of vast thickness and occupying large areas of
our continents. These pre-Cambrian formations are as yet among those
least known to geologists. The absence of fossils, the disturbances and
alterations which the rocks themselves have undergone, and which make
their relative ages and arrangement difficult to unravel, have acted
as deterrents to amateur geologists, and have to some extent baffled
the efforts of official explorers. In addition to this, workers in
different regions have adopted different methods of arrangement and
nomenclature; and in a very recent address, the Director-General of the
Geological Survey of Great Britain expresses his inability to satisfy
himself of the equivalency of the different pre-Cambrian groups on the
opposite sides of the Atlantic, and in consequence prefers to retain
for those of Britain merely local names.
On the other hand, those who hold the modern theories of gradual
evolution repudiate the idea that the Lower Cambrian fauna can be
primitive, and demand a vast series of changes in previous time to
prepare the way for it. In any case this comparatively unexplored
portion of geological time holds out the inducement of mystery and the
possibility of great discoveries to the hardy adventurers who may enter
into it. It must now be our effort to explore this dim and mysterious
dawn of life, and to ascertain what forms, if any, are visible amid its
fogs and mists.
The Kewenian or Etcheminian.
In certain basal Cambrian or infra-Cambrian beds, found by Matthew in
Southern New Brunswick, by Walcott in Colorado, and by Scandinavian
and English geologists in their respective countries, we find a
few remains referred to Algæ, or seaweeds; small tests or shells of
Protozoa; burrows and trails similar to those of modern sea-worms;
a few bivalve shells allied to modern Lingulæ, but presenting some
remarkable generalized characters; some bivalve and shrimp-like
Crustaceans, spicules of sponges, and large laminated forms
(Cryptozoon) similar to those already referred to as occurring in the
Upper Cambrian; also certain mysterious markings that are supposed to
have been produced by the arms or tentacles of free-swimming animals
of various kinds. In these lower beds the Trilobites have nearly or
quite disappeared, being represented only by doubtful fragments. The
beds of rock, originally sandy or muddy sediments, contain fossils very
sparingly, and only in certain layers separated by great thicknesses
of barren material, as if earthy matters were being deposited very
rapidly, or as if animal life was rare on the sea-bottom except at
intervals. It has, however, been suggested as possible[6] that much
of the marine population in those early times consisted of pelagic or
swimming animals destitute of any hard parts that could be preserved.
In addition to biological arguments in favour of this view, there is
the fact that some of the beds are stained with carbonaceous or coaly
matter, as if the sediment had been mixed with decomposed remains of
plants or animals retaining no determinate forms. Future discoveries
may increase our knowledge of the life of this period preceding the
Cambrian, but it is evident that so far as these rocks have been
examined, they indicate a great step downward in regard to the variety
and complexity of marine life.
[Footnote 6: By Prof. Brookes, of Johns Hopkins University.]
Still we must bear in mind that in later periods there have been times
of rapid deposition, in which, in certain localities at least, great
thicknesses of rock with few organic remains were formed. We have
instances of this in the later Cambrian, in the Ordovician, and still
later in the Permian and Trias. Thus in the beds immediately underlying
the lowest Cambrian we may be passing through a tract of comparative
barrenness to find more fertile ground below.
It is also to be observed that there is evidence of disturbance
occurring in the interval between the lowest Cambrian and the highest
pre-Cambrian, which may involve the lapse of much time not recorded in
the localities hitherto explored, but of which monuments may be found
elsewhere.
We may now, taking some North American localities as our best available
guides, inquire as to the nature and contents of the beds next below
the Lower Cambrian.
[Illustration: Fig. 10.--_Section at Hanford Brook._ (After Matthew.)
Showing St. John group resting on Etcheminian, and this on Coldbrook
(Huronian).]
In Southern New Brunswick, Matthew indicated, several years ago, the
occurrence of certain conglomerates and sandy and slaty beds over the
rocks, mostly of igneous origin, constituting a great thickness of
beds under the Cambrian, and known locally as the "Coldbrook" series,
which is probably equivalent to the Huronian of Northern and Western
Canada, to be noticed later. These beds were at first regarded as an
upper member of the Huronian, but subsequently it was thought better
to unite them with the overlying Cambrian as basal Cambrian. The fact
that these problematical beds were ascertained to be unconformable to
the Cambrian, and the peculiarity of their fossils, led to their being
constituted a separate group under the name _Etcheminian_, which seems
to represent a time and conditions introductory to the Cambrian (Fig.
10). The fossils in these beds are few and hard to find. Matthew has
kindly furnished me with the following list.[7] The Trilobites are
conspicuous by their absence. Sea-worms have left burrows, trails, and
casts, which probably represent several species (Fig. 11). A single
little shell (Volborthella) is supposed to be a precursor of the
straight chambered shells allied to the modern nautilus, which become
so large and numerous in succeeding periods. There are a few univalve
shell-fishes allied to modern sea-snails, a brachiopod of the antique
genus Obolus, some fragments supposed to represent Cystideans, a
rudimentary type of the stalked sea-stars so abundant later, spicules
of sponges and minute Protozoa, with shells not unlike those of their
modern successors. This meagre list sums up the forms of life known
in the Etcheminian of this district, one in which the Cambrian beds
exhibit the rich and varied fauna of Trilobites and other animals
described and figured by Matthew in several successive volumes of the
"Transactions of the Royal Society of Canada" (Fig. 12).
[Footnote 7: "Transactions Royal Society of Canada," vol. vii.]
[Illustration: Fig. 11.--_Trails of Worms of two types (Psammchnites
and Planilites)._]
Beds in Newfoundland (the Signal Hill and Random Sound series),
underlying the Lower Cambrian, have afforded to Murray and Billings
some well-characterized worm-castings of spiral form, and a few
problematical forms known as Aspidella, which may be Crustaceans or
Mollusks allied to the limpets (Fig. 13).
[Illustration: Fig. 12.--_Group of pre-Cambrian (Etcheminian) Animals
from the Etcheminian._ (After Matthew.)]
The name "Etcheminian" is derived from that of an ancient Indian tribe
of New Brunswick.
(_a_) Volborthella, supposed to be a Cephalopod shell. (_b_)
Pelagiella. (_c_) Orthotheca, supposed to be Pteropods. (_d_) Primitia,
an Ostracod Crustacean, (_e_) Obolus, a Brachiopod shell. (_f_)
Platysolenites, probably fragment of a Cystidean. (_g_) Globigerinæ,
casts of Foraminiferal shells, Etcheminian, New Brunswick.
[Illustration: Fig. 13.--_Arenicolites (Spiroscolex) spirales_
(Billings) _and Aspidella tenanovica_ (Billings), _Signal Hill Series,
Newfoundland._]
[Illustration: Fig. 14.--_Fragment of Cryptozoon, Grand Cañon, Arizona._
Photograph from a specimen presented by Dr Walcott to the Peter Redpath
Museum.]
In a thick series of pre-Cambrian beds in the Colorado Cañon in the
Western United States, Walcott has found a small roundish shell of
uncertain affinities,[8] a species of Hyolithes, probably a swimming
sea-snail or Pteropod, a small fragment which may possibly have
belonged to a Trilobite, and some laminated forms which, if organic,
are related to the Cryptozoon already mentioned (Fig. 14).
[Footnote 8: Discinoid or Patelloid.]
The Kewenian series of Lake Superior has yielded no fossils, but the
pipestone beds of Minnesota, supposed to be about the same age, have
afforded a small bivalve shell allied to Lingula;[9] and the black
shales of the head of Lake Superior contain some impressions supposed
to be trails of animals.[10]
[Footnote 9: Winchell.]
[Footnote 10: Selwyn and Matthew.]
It has been a question whether the beds above referred to should be
regarded as a downward continuation of the Cambrian, or as the upper
part of an older system. Matthew, whose opinion on such a subject is
of the highest authority, regards them as a distinct system, but as
belonging, with the Cambrian, to the great Palæozoic Period. Van
Hise, and some other United States authorities, would separate them
even from the Palæozoic, and unite them with the underlying Huronian,
as representing a "Proterozoic" or "Algonkian" Period. This is merely
a matter of classification, necessarily more or less arbitrary; but I
believe the facts to be stated subsequently show that it will be best
to unite the Etcheminian and its equivalents with the Palæozoic, and to
place the groups lower than this in one great division, equivalent to
Palæozoic, and for which many years ago I proposed the name "Eozoic,"
or that of the Dawn of Life.
Having thus hastily glanced at the slender fauna of the rocks
immediately below the Cambrian, we may now proceed to inquire a little
more in detail into its true value and import as leading toward the
beginning of life. I have already referred to the apparently sudden
drop in the number of groups and of species below the base of the
Cambrian, and have hinted that this may be an effect of temporary
local conditions of deposit or of defective information. Another fact
that strikes us is the diverse and miscellaneous character of the
fossils that remain to us; and this would suggest that we are either
dealing with a mere handful picked at random, as it were out of a
richer fauna, or that in the beginning of things the gaps and missing
links between different forms of life were even more pronounced than
at present. This, however, would be likely to occur if the plan of
creation was to represent at first different types, with few forms in
each; to produce, in short, a sort of type collection representing the
whole range of organization by a few characteristic things rather than
to give a complete series, with all the intermediate connections. Such
a mode of introduction of life is not _à priori_ improbable, however at
variance with some prevalent hypotheses.
Beginning with the higher Invertebrates, we must not conclude that
we have altogether lost the Trilobites. The fragments referred to
this group may represent at least a few species, and it would be very
interesting to know more of these as to their relations to their
successors, and whether they are tending to lower or more embryonic
forms. The bivalve Crustaceans (Ostracods) may be regarded as inferior
in rank to the Trilobites, but are still very complex, and specialized
animals and a specimen silicified in such a manner as to show the
interior organs testified that, as far back as the Carboniferous at
least, these creatures were as highly organized as at present,[11]
while their generally larger size in the earlier formations tends to
show that they have rather been degenerating in the lapse of geological
time.
[Footnote 11: _Palæocypris Edwardsi_, Brougniart, Coal Formation of St.
Etienne, France.]
In regard to the Sea-worms, the burrows, castings, and trails found
in the pre-Cambrian beds are scarcely, if at all, different from
those now seen on sandy and muddy shores, and would seem to indicate
that these highly organized and very sensitive and active creatures
swarmed in the muddy bottom of the pre-Cambrian Sea, and lived in the
same way as at present. It is impossible, however, to know anything
of the internal structures of these creatures, but the marks left by
their bristle-bearing feet seem to indicate that some of them at least
belong to the higher group of Sea-centipedes, creatures rivalling the
Crustaceans in complexity of organization, and near to them in plan
of structure, though at present usually widely separated from them in
current systems of classification. In the Ordovician system, next above
the Cambrian, Hinde has found many curiously formed jaws of animals of
this kind, which show at least that their alimentary arrangements were
similar to those now in force. If any of the problematical "Conodonts"
discovered by Pander in the Cambrian of Russia belonged to marine
worms, this inference would be extended back to the Lower Cambrian,
so that if the evidence of structure anywhere remains we may hope
to find that the pre-Cambrian worms were not inferior to their more
modern successors, perhaps even that in this early period, when they
probably played a more important part in nature, they were of higher
organization than in later times.
The evidence as to pre-Cambrian mollusks, so far as it goes, is
even more curious. The little shell called Volborthella, so far as
can be judged from its form and internal structure, is a miniature
representative of these straight Nautili, the Orthoceratites of
the Ordovician and later Palæozoic rocks; and no one doubts that
these latter belong to the highest class of the Mollusks, a class
approaching in the development of nerve system and sensory organs to
the Vertebrates themselves. This tiny member of the great class of
Cuttle-fishes may perhaps have been more nearly allied to the modern
Spirula than to the Nautilus. In any case, if, as seems altogether
probable it was, a mollusk, it must have been one of advanced type, and
with a highly complex structure, as well as the singular apparatus for
flotation implied in a chambered shell with a siphuncle.
Next to this among these primitive Mollusks are straight and spiral
shells representing those delicate and beautiful animals of the modern
seas, the Pteropods, or wing-footed Sea-snails, beautiful and graceful
creatures, the butterflies of the sea, and moving in the water with
the greatest ease and beauty by the aid of membranous fins, or wings,
sometimes brightly coloured. These creatures abound in all latitudes
in the modern ocean, and their delicate shells sometimes accumulate in
beds of "Pteropod sand." They very early entered on the arena of marine
life, and have continued to this day.
We miss here the two great Molluscan groups of the creeping Sea-snails
like the limpet and whelk, and of the ordinary bivalves like the
oyster and cockle. Both are present in the lowest Cambrian, though in
small numbers compared with their present abundance. Possibly they had
not yet appeared in the Etcheminian Sea, though the muddy and sandy
bottoms, evidenced by its slates and sandstones, would seem to have
afforded favourable habitats, and warrant the expectation that species
may yet be found.
The case was different with the little group of the Lamp-shells, or
Brachiopods. These creatures, somewhat resembling the ordinary bivalves
in their shelly coverings, were very dissimilar in their internal
structure, and once settled on the bottom they were attached for life,
not having even the limited means of locomotion possessed by the
Sea-snails and common bivalves. They collected their food wholly by
means of currents of water produced by cilia, or movable threads, on
arms or processes within their shells. In this they resembled the young
or embryo stages of some of the more ordinary Mollusks, though they are
so remote from these in their adult condition that they have usually
been placed in a distinct class, and some naturalists have thought
it best to separate them from the Mollusks altogether. Their history
is peculiar. Coming into existence at a very early date, they became
very abundant in early Palæozoic times, then gradually gave place to
the ordinary bivalves, and in the modern seas are represented by very
few species. Yet while in the middle period of their history they are
represented by very many peculiar specific and generic forms. Some of
the earliest types, like Obolus and Lingula, persist very long, and
the latter has continued without change from the Early Cambrian to the
Modern period.
The great group of the Sea-stars and Sea-urchins appears only in a
few of its lower forms, and seems to be the only class represented by
embryonic types. The coral animals are absent, so far as known. The
Jelly-fishes and their allies cannot be preserved as fossils, but some
peculiar markings, at one time regarded as plants, are now supposed to
be trails made by the tentacles of creatures of this kind moving over
muddy bottoms. A few spicules indicate Sponges, and the ubiquitous
groups of the marine Protozoa, the Foraminifera and the Radiolaunus,
are represented by shells scarcely distinguishable from those of modern
species. The great and peculiar forms represented at this early time by
Cryptozoon and its allies seem long ago to have perished, and we shall
have to return to them in a later stage of our inquiry.
To sum up the little that we know of this earliest Palæozoic life:--It
was perfect of its kind, equally pregnant with evidences of design, and
of the nicest and most delicate contrivance as the animal life of any
later time, and it presupposed vegetable life and multitudes of minute
organic beings altogether unknown to us to nourish the creatures we do
know. As an example of this, a little Brachiopod or sponge nourished
by the currents produced by its cilia, or a Jelly-fish gathering
food by its thread-like tentacles, or a Globigerina selecting its
nourishment by its delicate gelatinous pseudopods, required an ocean
swarming with minute forms of life, which probably can never be known
to us, but every one of which must have been an inscrutable miracle of
organization and vital function.
Lastly, with reference to our present subject, the Etcheminian fossils
carry life backward one whole great period earlier than the Lower
Cambrian, and appear to indicate that we are approaching a beginning
of living things in the Palæozoic world. Much no doubt remains to be
discovered, but it would seem that any future discoveries must fail to
negative this conclusion.
The Huronian.
In whatever way the rocks immediately below the Cambrian may be
classified, it is certain that the next system in descending order
is that to which Logan long ago gave the name Huronian, from its
development on Lake Huron[12]--a name to which it is still entitled,
though there may, perhaps, be some grounds for dividing it into an
upper and lower member.[13] To this sub-division, however, we need
not for the present give any special attention. In the typical area
of Lake Huron the Huronian consists of quartzites, which are merely
hardened sandstones, of slates which are muddy or volcanic-ash beds,
of conglomerates or pebble-rocks, and of coarse earthy limestone.
With these rocks are deposits of igneous material which represent
contemporary volcanic eruptions. In other districts, as in New
Brunswick, Newfoundland, etc., the beds have been considerably altered,
and are locally more mixed with igneous products. The physical picture
presented to us by the Huronian is that of a shore deposit, formed
under circumstances in which beds of pebbles and sand were intermixed
with the products of neighbouring volcanoes.
[Footnote 12: Dr. G. M. Dawson, F.R.S., the present Director of the
Geological Survey of Canada, whose judgment in this matter should be of
the highest value, holds that the original simple arrangement of Logan
still holds, notwithstanding the multitude of new names proposed by the
Western Geologists of the United States.]
[Footnote 13: Van Hise, "Pre-Cambrian Rocks of North America." _Comptes
Rendus_, 5th Session International Geol. Congress 1891, p. 134. Also
"Report U.S. Geol. Survey, 1895."]
[Illustration: Fig. 15.--_Annelid Burrows, Hastings Series, Madoc._
1. _Transverse section of Worm-burrow_--magnified, as a transparent
object. (_a_) Calcareo-silicious rock. (_b_) Space filled with
calcareous spar, (_c_) Sand agglutinated and stained black. (_d_) Sand
less agglutinated and uncoloured. 2. Transverse section of Worm-burrow
on weathered surface, natural size. 3. The same, magnified.]
Such a formation is not likely to afford fossils in any considerable
number and variety, even if deposited at a time of abundant marine
life. It is therefore not wonderful that we find little evidence of
living beings in the Huronian. In Canada I can point to nothing of this
kind, except a few cylindrical burrows, probably of worms (Fig. 15),
and spicules possibly of silicious sponges, which occur in nodules of
chert in the limestones, traces of laminated forms like Cryptozoon
or Eozoon (Fig. 17), and minute carbonaceous fragments which may be
debris of sea-weeds or Zoophytes. In rocks of similar age in the United
States, Gresley has recently discovered worm-burrows, and in Brittany
there are quartzite beds in which Barrois and Cayeux believe that they
have found tests of Radiolarians, Foraminifera and spicules of sponges,
but their organic nature has been denied by Rauff, of Bonn. The casts
of Foraminifera, however, at least appear to be organic (Fig. 16), and
it is quite likely that Cayeux may be able to verify his Radiolarians
and sponges as well. Matthew's observations in New Brunswick in any
case establish their probability. Gümbel also recognises a species of
Eozoon in the equivalent rocks of Bavaria (see p. 213).
[Illustration: Fig. 16.--_Casts of Foraminifera, from the Huronian of
Brittany._ (After Cayeux.)
Compare with Globigerinæ on Fig. 12 and Archæospherinæ, Figs. 50-54.]
[Illustration: Fig. 17.--_Cryptozoon or Eozoon from the Hastings
Series, Tudor, Ontario_ (natural size).
From a specimen collected by the late Mr. Vennor, and now in the
collection of the Geological Survey, Ottawa. (See also Frontispiece and
figure of _Eozoon Bavaricum_, p. 213.)]
It is evident that here we have approached the limit of the higher
forms of marine invertebrate life, having as yet nothing to show except
worms and Protozoa. It is to be observed, however, that there may be
somewhere Huronian deposits formed in deep and quiet waters, which may
give better results, and that the unconformity between the Huronian and
overlying Kewenian may indicate a lapse of time, of which monuments may
yet be found.
The Laurentian.
Last of all we have the widely distributed Laurentian system of
Logan, the oldest known to geologists, and which with the Huronian
constitutes the great Archæan group of formations of Dana and others.
In its lowest part this consists entirely of the stratified granitic
rock known as gneiss, inter-bedded in some places with dark-coloured
crystalline rocks or schists. This may be a part of the first-formed
crust of our globe, produced under conditions different from those
of any later rocks, and incompatible with the existence of life. The
upper part of the Laurentian system, however, known in Canada as the
"Grenville Series," shows evidence of ordinary marine deposition in
quiet waters, which may have been not unfavourable to the lower forms
of marine life; and though its beds have been greatly changed by heat
and pressure, we can still to some extent realize the conditions of a
time of comparative quiescence intervening between the underlying Lower
Laurentian and the succeeding Huronian. This part of the system still
contains gneisses, bedded diorites, and other rocks which may have been
volcanic; but it has also quartzites and quartzose gneisses which must
have been sandstones or shales, thick limestones, beds of carbon now
in the state of graphite or plumbago, and large beds of iron ore. Such
rocks were in all succeeding formations produced under water and by
accumulations of the remains of plants and the hard parts of animals,
in strictly sedimentary beds, usually formed slowly and without
mechanical disturbance. Hence we may infer that aquatic life at least
existed in this early period, and as there must have been land and
water, shallows and deep seas, there may have been scope for various
kinds of living beings. The Grenville period is, however, separated
from the succeeding Huronian by a great interval, occupied mainly by
volcanic ejections and earth-movements; so that our Grenville series,
if it contains organic remains, may be supposed to afford species
differing from those of the Huronian, and to form a sort of oasis in
the desert of the early pre-Cambrian world. We find that the limestones
of this age actually contain remains supposed to be of animal origin.
They were first found in Canada, which contains the largest and best
exposed area of these rocks in the world, and were brought under the
notice of geologists by the late Sir William E. Logan, the first
director of the Geological Survey of that country.
In anticipation of details to be given later, the story of this
discovery and its announcement may here be given in brief
As early as 1858, Sir William Logan had begun to suspect that certain
laminated bodies found in the Laurentian limestones of the Grenville
series might be of organic origin. The points which struck him were
these: They differed from any known laminated concretions; they
resembled the "Stromatoporæ" or layer-corals of the lower Palæozoic
rocks next in succession to the Laurentian and Huronian; the forms were
similar in all the specimens, while the mineralizing substances were
different; they were found only in the limestone, and specially in one
of the three great beds known in the formation, the upper limestone
of the Grenville system. He exhibited specimens, and mentioned these
probabilities at the meeting of the American Association in 1859. In
1862 it was suggested to Logan that the microscopic structure of some
of the best preserved examples should be studied, and slices were
accordingly prepared and submitted to the writer for examination.
They revealed in the calcareous laminæ of the specimens complicated
systems of canals or tubes filled with mineral matter, which appeared
to be similar to those that Carpenter had recognised in the thickened
parts of the shells of modern Foraminifera. This clew being followed,
large numbers of slices of the supposed fossils and of the containing
limestone and of similar limestones from other parts of the world were
examined.
The writer also visited the localities of "Eozoon," and studied its
mode of occurrence _in situ_. The facts ascertained were communicated
to the Geological Society of London, the name "Eozoon Canadense"
being proposed for the species. Its description was accompanied by a
paper on the geological conditions by Logan, and one on the chemical
conditions by Sterry Hunt, while supplementary notes were added by
the late Dr. Carpenter and Professor T. Rupert Jones. Thus launched
on the scientific world, "Eozoon" at once became a fertile subject
of discussion, and volumes of more or less controversial literature
have appeared respecting it. It still has its friends and opponents,
and this may long continue, as so few scientific men are sufficiently
acquainted on the one hand with the possibilities and conditions of the
preservation of fossils in crystalline rocks, and on the other hand
with the structures of modern "Protozoa." Thus, few are in a position
to form an independent judgment, and "Eozoon" has met with some
scepticism on the part both of biological and mineralogical specialists.
To aid us in forming an opinion, it will be necessary to consider the
oldest known strata of the earth's crust, and the evidence which they
afford of the condition of the world when they were deposited. As
preliminary to this, we may look at the following table of pre-Cambrian
formations in Canada.
SUCCESSION OF PRE-CAMBRIAN ROCKS IN CANADA, AS UNDERSTOOD UP TO 1896.
(_In descending order._)
----------------------------------------------------
PALÆOZOIC.
{ Etcheminian in New Brunswick, _Kewenian_ or _Upper
{ Copper-bearing Series_ of Lake Superior, _Signal Hill
{ Series_ of Newfoundland. _Chuar_, and _Grand Cañon_
{ rocks of Colorado, etc.
{
{ Red and greenish Sandstones and Shales, Conglomerates,
{ Igneous Outflows and Ash-rocks. Bivalve
{ Crustacea, Mollusks, Worms, Sponges, Cystideans,
{ Zoophytes, Protozoa, Cryptozoon.
{ ----------------------------------------------------
(_Unconformity._)
----------------------------------------------------
EOZOIC.
{ Huronian, including _Hastings_ of Ontario, _Coldbrook_
{ and _Coastal_ of New Brunswick, _Algonkian_ (in part).
{ Conglomerates, Hard Sandstones, Shales and Schists,
{ Iron Ores, Coarse Limestones, Igneous Outflows, and
{ Ash-rocks. Worms, Sponges, Zoophytes, and Protozoa
{ (Cryptozoon or Eozoon).
----------------------------------------------------
(_Unconformity [?]_)
----------------------------------------------------
EOZOIC.
{ Grenvillian or Upper Laurentian.
{ Gneiss, Hornblendic and Micaceous Schists, Limestones,
{ Quartzite, Iron Ores, Graphite. Eozoon, Archæozoon,
{ Archæospherinæ, Archæophyton.
----------------------------------------------------
_Unconformity._
----------------------------------------------------
AZOIC
{ Archæan or Lower Laurentian.
{ Gneiss, Hornblende Schists, with many igneous or
{ igneo-aqueous intrusions.
_THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE_
IV
_THE FOUNDATIONS OF THE CONTINENTS, AND
THEIR GENERAL TESTIMONY AS TO LIFE_
That the reader may be enabled better to understand the relation of
the old foundations or pillars of the earth to the beginning of life,
and the preservation of the remains of the earliest animals, it may be
well to reverse the method we have hitherto followed, and to present
a theoretical or ideal historical sketch of the early history of the
earth, beginning with that stage in which it may be supposed to have
been a liquid mass, considerably larger than it is at present, and
intensely heated, and surrounded by a vast vaporous envelope composed
of all the substances capable of being resolved by its heat into a
gaseous condition--a smooth and shining spheroid, invested with an
enormous atmosphere.
In such a condition its denser materials, such as the heavier metals,
would settle toward the centre, and the surface would consist of
lighter material composed of the less dense and more oxidizable
substances combined with oxygen, and similar in character and
appearance to the slag which forms on the surface of some ores in the
process of smelting. Of this slaggy material there might, however, be
different layers more or less dense in proceeding from the interior to
the surface. This molten surface would, of course, radiate heat into
space; and as it would naturally consist of the least fusible matters,
these would begin to form a solid crust. We may imagine this crust at
first to be smooth and unbroken, though such a condition could scarcely
exist for any length of time, as the hardened crust would certainly be
disturbed by ascending currents from within, and by tidal movements
without. Still, it might remain for ages as a spheroidal crust,
presenting little difference of elevation or depression in comparison
with its extent. When it became sufficiently thick and cool to allow
water to lie on its surface, new changes would begin. The water so
condensed would be charged with acid substances which would begin to
corrode the rocky surface. Penetrating into crevices and flashing into
steam as it reached the heated interior, it would blow up masses and
fragments of stone, and would perhaps force out and cause to flow over
the surface beds of molten material from below the crust, and differing
somewhat from it in their composition. All this aqueous work would
accelerate the cooling and thickening of the crust, and at length a
universal or almost universal heated ocean would envelope the globe,
and so far as its surface was concerned, the reign of water would
replace that of fire. We may pause here to consider the probable nature
of the earth's crust in this condition.
The substance most likely to predominate would be silica or quartz,
one of the lighter and most infusible materials of the crust; but
which, heated in contact with alumina, lime, potash, and other earths
and alkalis, forms fusible slags, enamels and glasses. One of these,
composed of silica, alumina, and potash, or soda, was long ago named
by the German miners felspar, a name which it still retains, though
now several distinct kinds of it are distinguished by different names.
Another is a compound of silica with magnesia and lime, forming the
mineral known as Amphibole or Hornblende, and by several other names,
according to its colour and crystalline form. In many deep-seated
rocks these minerals are formed together, and having crystallized
out separately give a spotted and granular character to the mass.
Naturally colourless, all these minerals, and especially the felspar
and hornblende, are liable to be coloured with different oxides of
iron, the felspar usually taking a reddish, and the hornblende a
greenish or blackish hue. Now, if we examine a fragment of the oldest
or fundamental gneiss or granite, we shall see glassy grains of quartz,
reddish or white flat-surfaced crystals of felspar, and dark-coloured
prisms of hornblende. When destitute of any arrangement in layers, the
rock is granite; when arranged more or less in flakes or laminæ, it is
gneiss, the structure of which may arise either from its having been
formed in successive beds, or from its having been flattened or drawn
out by pressure. These structures can be seen more or less distinctly
in any ordinary coarse-grained granite, or with the lens or microscope
in finer varieties.
The Lower Laurentian rocks of our section consist essentially of the
materials above described, with a vast variety in the proportions
and arrangements of the constituent minerals. There is, there-fore,
nothing to prevent us from supposing that these rocks are really
remains of the lower portions of the original crust which first formed
on the surface of our cooling planet, though the details of their
consolidation and the possible interactions of heat and heated water
may admit of much discussion and difference of opinion.
But after the formation of a crust and its covering in whole or in
part with heated water, other changes must occur, in order to fit the
earth for the abode of life. These proceeded from the tensions set
up by the contraction and expansion of the interior heated nucleus
and the solid crust--a complicated and difficult question, when we
consider its laws and their mode of operation, but which resulted in
the folding and fracturing of the crust along long lines which are
parts of great circles of the earth, running in N.E. and S.W. and N.W.
and S.E. directions; and these ridges, which in the earliest Archæan
period must have attained to great height and very rugged outlines,
formed the first rudiments of our mountain chains and continents. Those
constituting the Laurentian nucleus of North America--a very simply
outlined continent--form a case in point (Fig. 18).
The elevation of these mountain ridges forced the waters to recede into
the lower levels. As the old psalm of creation has it,--
"The mountains ascend,
the valleys descend into
the place Thou hast founded
for them,"
and so sea-basins and land were produced.
Milton merely paraphrases this when he says,--
"The mountains huge appear
Emergent, and their broad, bare backs upheave
Into the clouds; their tops ascend the sky.
So high as heaved the tumid hills, so low
Down sunk a hollow bottom wide and deep.
Capacious bed of waters."
Englishmen have been accused of taking their ideas of creation from
Milton rather than from nature or the Bible. Milton had not the
guidance of modern geology. His cosmology is entirely that of a close
student of the Biblical narrative of creation. He is in many respects
the best commentator on the early chapters of Genesis, because he
had a very clear conception of the mind of the writer, and the power
of expressing the ideas he derived from the old record. For the same
reason he is the greatest bard of creation and primitive man, and
surprisingly accurate and true to nature.
[Illustration: Fig. 18.--_Map of Laurentian, North America._
Showing the protaxis or nucleus of the continent.]
Then began the great processes of denudation and sedimentation to which
we owe the succeeding rock formations. The rains descended on the
mountain steeps, and washed the decaying rocks as sand, gravel and mud
into the rivers and the sea. The sea itself raged against the coasts,
and cut deeply into their softer parts; and all the detritus thus
produced by atmospheric and marine denudation was spread out by the
tides and currents in the bed of the ocean, and its gulfs and seas,
forming the first aqueous deposits, while the original land must have
been correspondingly reduced.
The sea might still be warm, and it held in solution or suspension
somewhat different substances from those now present in it, and the
land was at first a mere chaos of rocky crags and pinnacles. But so
soon as the temperature of the waters fell somewhat below the boiling
point, and as even a little soil formed in the valleys and hollows of
the land, there was scope for life, provided that its germs could be
introduced.
On a small scale there was something of this same kind in the sea
and land of Java, after the great eruption of Krakatoa, in 1883. The
bare and arid mountain left after the eruption, began, in the course
of a year, to be occupied by low forms of vegetable life, gradually
followed by others, and verdure was soon restored. The once thickly
peopled sea-bottom, so prolific of life in these warm seas, but
buried under many feet of volcanic ashes and stones, soon began to be
re-peopled, and is now probably as populous as before. But in this
case there were plenty of spores of lichens, mosses, and other humble
plants to be wafted to the desolate cone, and multitudes of eggs and
free-swimming germs of hundreds of kinds of marine animals to re-people
the sea-bottom. Whence were such things to come from to occupy the
old Archæan hills and sea-basins? and all our knowledge of nature
gives us no answer to the question, except that a creative power must
have intervened; but in what manner we know not. That this actually
occurred, we can, however, be assured by the next succeeding geological
formation. We have seen that the granitic and gneissic ridges could
furnish pebbles, sand, and clay, and these once deposited in the
sea-bottom could be hardened into conglomerate, sandstone and slate.
But beside these we have in the next succeeding or Upper Laurentian
formation rocks of a very different character. We have great beds of
limestone and iron ore, and deposits, of carbon or coaly matter, now
in the peculiar state of graphite or plumbago, and it is necessary
for us to inquire how these could originate independently of life. In
modern seas limestone is forming in coral reefs, in shell beds, and in
oceanic chalky ooze composed of minute microscopic shells; but only in
rare and exceptional instances is it formed in any other way; and when
we interrogate the old limestones and marbles which form parts of the
land, they give us evidence that they also are made up of calcareous
skeletons of marine animals or fragments of these.
[Illustration: Fig. 19.--_Distribution of Grenville Limestone in
the district north of Papineauville, with section showing supposed
arrangement of the beds._]
Scale of Map 7 miles to one inch. See also Dr. Bonney's paper, _Geol.
Mag._, July, 1895.
_Dotted area:_ Limestone. _Horizontal lines:_ Upper gneiss (fourth
gneiss of Logan). _Vertical lines:_ Lower gneiss (third gneiss of
Logan). _Diagonal lines:_ Overlying Cambrian and Cambro-Silurian
(Ordovician). (See also Fig. 19A.)
Now when we find in the Grenvillian series, the first oceanic group of
beds known to us, great and widely extended limestones, thousands of
feet in thickness, and rivalling in magnitude those of any succeeding
period, we naturally infer that marine life was at work. No doubt
the primitive sea contained more lime and magnesia than the present
ocean holds in solution; but while this might locally favour the
accumulation of inorganic limestones, it cannot account for so great
and extensive deposits. On the other hand, a sea rich in lime would
have afforded the greatest facilities for the growth of those marine
plants which accumulate lime, and through these for the nutrition of
animals forming calcareous shells or corals. Thus we have presumptive
evidence that there must have been in the Upper Laurentian sea
something corresponding to our coral reefs and shell-beds, whatever
this something may have been.
These limestones, however, demand more particular notice (Fig. 19).
One of the beds measured by the officers of the Geological Survey is
stated to be 1,500 feet in thickness, another is 1,250 feet thick,
and a third 750 feet; making an aggregate of 3,500 feet.[14] These
beds may be traced, with more or less interruption, for hundreds of
miles. Whatever the origin of such limestones, it is plain that they
indicate causes equal in extent, and comparable in power and duration,
with those which have produced the greatest limestones of the later
geological periods. Now, in later formations, limestone is usually an
organic rock, accumulated by the slow gathering from the sea-water,
or its plants, of calcareous matter, by corals, foraminifera, or
shell-fish, and the deposition of their skeletons, either entire or
in fragments on the sea-bottom. The most friable chalk and the most
crystalline limestones have alike been formed in this way. We know of
no reason why it should be different in the Laurentian period. When,
therefore, we find great and conformable beds of limestone, such as
those described by Sir William Logan in the Laurentian of Canada, we
naturally imagine a quiet sea-bottom, in which multitudes of animals of
humble organization were accumulating limestone in their hard parts,
and depositing this in gradually increasing thickness from age to age.
Any attempts to account otherwise for these thick and greatly extended
beds, regularly interstratified with other deposits, have so far been
failures, and have arisen either from a want of comprehension of the
nature and magnitude of the appearances to be explained, or from the
error of mistaking the true bedded limestones for veins of calcareous
spar.
[Footnote 14: Logan: "Geology of Canada," p. 45.]
[Illustration: Fig. 19A.--_Attitude of Limestone at Côte St. Pierre_
(see Map, p. 88).
(_a_) Gneiss band in the Limestone, (_b_) Limestone with Eozoon. (_c_)
Diorite and Gneiss.]
Again, in the original molten world, it seems likely that most of
the carbon present--at least, at the surface--was in the atmosphere
in the gaseous form of carbon dioxide. This might be dissolved by
the rain and other waters; but we know in the modern world no agency
which can decompose this compound and reduce it to ordinary carbon
or coal, except that of living plants, which are always carrying on
this function to an enormous extent. We know that all our great beds
of coal and peaty matter are composed of the remains of plants which
took their carbon from the air and the waters in past times. We also
know that this coaly vegetable matter may, under the influence of heat
and pressure, when buried in the earth, be converted into anthracite
and into graphite, and even into diamond. It is true that an eminent
French chemist[15] has shown that graphite and hydrocarbons may be
produced from some of the metallic compounds of carbon which may have
been formed under intense heat in the interior of the earth, by the
subsequent action of water on such compounds; but there is nothing to
show that this can have occurred naturally, unless in very exceptional
cases. Now in the Grenvillian system in Canada there is not only a
vast quantity of carbon diffused through the limestones, and filling
fissures in other rocks, into which it seems to have been originally
introduced as liquid bitumen, but also in definite beds associated with
earthy matter, and sometimes ten to twelve feet thick. The occurrence
of this large amount of carbon warrants us in supposing that it
represents a vast vegetable growth, either on the land or in the sea,
or both.
[Footnote 15: Henri Moissan, "Proceedings Royal Society," June, 1896,]
In like manner, in later geological periods, beds of iron ore are
generally accumulated as a consequence of the solvent action of
acids produced by vegetable decay, as in the clay ironstones of the
coal formation and the bog iron ores of later times. Thus the beds
of magnetic iron occurring in the Upper Laurentian may be taken as
evidences, not of vegetable accumulation, but of vegetable decay.
May not also the great quantity of calcium phosphate mined in the
Grenville series in Canada, indicate, as similar accumulations do in
later formations, the presence of organisms having skeletons of bone
earth?
With reference to the carbon and iron ore of the Grenville series, I
may quote the following from a paper published in the _Journal of the
Geological Society of London_ in 1870:--
"The quantity of graphite in the Upper Laurentian series is enormous.
In a recent visit to the township of Buckingham, on the Ottawa River,
I examined a band of limestone believed to be a continuation of that
described by Sir W. E. Logan as the Green Lake Limestone. It was
estimated to amount, with some thin interstratified bands of gneiss,
to a thickness of 600 feet or more, and was found to be filled with
disseminated crystals of graphite and veins of the mineral to such
an extent as to constitute in some places one-fourth of the whole;
and making every allowance for the poorer portions, this band cannot
contain in all a less vertical thickness of pure graphite than from
twenty to thirty feet. In the adjoining township of Lochaber Sir W. E.
Logan notices a band from twenty-five to thirty feet thick, reticulated
with graphite veins to such an extent as to be mined with profit for
the mineral. At another place in the same district a bed of graphite
from ten to twelve feet thick, and yielding twenty per cent, of the
pure material, is worked. When it is considered that graphite occurs in
similar abundance at several other horizons, in beds of limestone which
have been ascertained by Sir W. E. Logan to have an aggregate thickness
of 3,500 feet, it is scarcely an exaggeration to maintain that the
quantity of carbon in the Laurentian is equal to that in similar areas
of the Carboniferous system. It is also to be observed that an immense
area in Canada appears to be occupied by these graphitic and Eozoon
limestones, and that rich graphitic deposits exist in the continuation
of this system in the State of New York; while in rocks believed to be
of this age near St. John, New Brunswick, there is a very thick bed
of graphitic limestone, and associated with it three regular beds of
graphite, having an aggregate thickness of about five feet.[16]
[Footnote 16: Matthew, in _Quart. Journ. Geol. Soc._, vol. xxi. p. 423.
"Acadian Geology," p. 662.]
"It may fairly be assumed that in the present world, and in those
geological periods with whose organic remains we are more familiar than
with those of the Laurentian, there is no other source of unoxidized
carbon in rocks than that furnished by organic matter, and that this
has obtained its carbon in all cases, in the first instance, from the
deoxidation of carbonic acid by living plants. No other source of
carbon can, I believe, be imagined in the Laurentian period. We may,
however, suppose either that the graphitic matter of the Laurentian
has been accumulated in beds like those of coal, or that it has
consisted of diffused bituminous matter similar to that in more
modern bituminous shales and bituminous and oil-bearing limestones.
The beds of graphite near St. John, some of those in the gneiss at
Ticonderoga in New York, and at Lochaber and Buckingham and elsewhere
in Canada, are so pure and regular that one might fairly compare them
with the graphitic coal of Rhode Island. These instances, however, are
exceptional, and the greater part of the disseminated and vein graphite
might rather be compared in its mode of occurrence to the bituminous
matter in bituminous shales and limestones.
"We may compare the disseminated graphite to that which we find in
those districts of Canada in which Silurian and Devonian bituminous
shales and limestones have been metamorphosed and converted into
graphitic rocks not dissimilar to those in the less altered portions of
the Laurentian.[17] In like manner it seems probable that the numerous
reticulating veins of graphite may have been formed by the segregation
of bituminous matter into fissures and planes of least resistance, in
the manner in which such veins occur in modern bituminous limestones
and shales. Such bituminous veins occur in the Lower Carboniferous
limestone and shale of Dorchester and Hillsborough, New Brunswick, with
an arrangement very similar to that of the veins of graphite; and in
the Quebec rocks of Point Levi, veins attaining to a thickness of more
than a foot are filled with a coaly matter having a transverse columnar
structure, and regarded by Logan and Hunt as an altered bitumen.
These Palæozoic analogies would lead us to infer that the larger part
of the Laurentian graphite falls under the second class of deposits
above mentioned, and that, if of vegetable origin, the organic matter
must have been thoroughly disintegrated and bituminized before it was
changed into graphite. This would also give a probability that the
vegetation implied was aquatic, or at least that it was accumulated
under water.
[Footnote 17: Granby, Melbourne, Owl's Head, etc., "Geology of Canada,"
1863, p. 599.]
"Dr. Hunt has, however, observed an indication of terrestrial
vegetation, or at least of subaërial decay, in the great beds of
Laurentian iron ore. These, if formed in the same manner as more modern
deposits of this kind, would imply the reducing and solvent action of
substances produced in the decay of plants. In this case such great
ore beds as that of Hull, on the Ottawa, 70 feet thick, or that near
Newborough, 200 feet thick,[18] must represent a corresponding quantity
of vegetable matter which has totally disappeared. It may be added that
similar demands on vegetable matter as a deoxidizing agent are made
by the beds and veins of metallic sulphides of the Laurentian, though
some of the latter are no doubt of later date than the Laurentian rocks
themselves.
[Footnote 18: "Geology of Canada," 1863.]
"It would be very desirable to confirm such conclusions as those above
deduced by the evidence of actual microscopic structure. It is to be
observed, however, that when, in more modern sediments, algæ have
been converted into bituminous matter, we cannot ordinarily obtain
any structural evidence of the origin of such bitumen, and in the
graphitic slates and limestones derived from the metamorphosis of
such rocks no organic structure remains. It is true that, in certain
bituminous shales and limestones of the Silurian system, shreds of
organic tissue can sometimes be detected, and in some cases, as in
the Lower Silurian limestone of the La Cloche mountains in Canada,
the pores of brachiopodous shells and the cells of corals have been
penetrated by black bituminous matter, forming what may be regarded as
natural injections, sometimes of much beauty. In correspondence with
this, while in some Laurentian graphitic rocks,--as, for instance,
in the compact graphite of Clarendon,--the carbon presents a curdled
appearance due to segregation, and precisely similar to that of the
bitumen in more modern bituminous rocks, I can detect in the graphitic
limestones occasional fibrous structures which may be remains of
plants, and in some specimens vermicular lines, which I believe to be
tubes of Eozoon penetrated by matter once bituminous, but now in the
state of graphite.
"When Palæozoic land-plants have been converted into graphite, they
sometimes perfectly retain their structure. Mineral charcoal, with
structure, exists in the graphitic coal of Rhode Island. The fronds of
ferns, with their minutest veins perfect, are preserved in the Devonian
shales of St. John, in the state of graphite; and in the same formation
there are trunks of Conifers (_Dadoxylon ouangondianum_) in which the
material of the cell-walls has been converted into graphite, while
their cavities have been filled with calcareous spar and quartz, the
finest structures being preserved quite as well as in comparatively
unaltered specimens from the coal-formation.[19] No structures so
perfect have as yet been detected in the Laurentian, though in the
largest of the three graphitic beds at St. John there appear to be
fibrous structures which I believe may indicate the existence of
land-plants. This graphite is composed of contorted and slicken-sided
laminæ, much like those of some bituminous shales and coarse coals; and
in these there are occasional small pyritous masses which show hollow
carbonaceous fibres, in some cases presenting obscure indications of
lateral pores. I regard these indications, however, as uncertain; and
it is not as yet fully ascertained that these beds at St. John are
on the same geological horizon with the Grenville series of Canada,
though they certainly underlie the Cambrian series of the St. John or
Acadian group, and are separated from it by beds having the character
of the Huronian, and thus come, approximately at least, into the same
geological position.
[Footnote 19: "Acadian Geology," p. 535. In calcified specimens the
structures remain in the graphite after decalcification by an acid.]
"There is thus no absolute impossibility that distinct organic tissues
may be found in the Laurentian graphite, if formed from land-plants,
more especially if any plants existed at that time having true woody
or vascular tissues; but it cannot with certainty be affirmed that
such tissues have been found. It is possible, however, that in the
Laurentian period the vegetation of the land may have consisted wholly
of cellular plants, as, for example, mosses and lichens; and if so,
there would be comparatively little hope of the distinct preservation
of their forms or tissues, or of our being able to distinguish the
remains of land-plants from those of Algæ. The only apparent plant
of the Laurentian to which a name has been given, _Archæophyton_ of
Britton, from New Jersey, consists of ribbon-like strips, destitute
of apparent structure, and which, if they are of vegetable origin,
may have belonged to either of the leading divisions of the vegetable
kingdom. I have found similar flat frond-like objects in the limestone
of the Grenville series, at Lachute, in Canada.
"We may sum up these facts and considerations in the following
statements:--First, that somewhat obscure traces of organic structure
can be detected in the Laurentian graphite; secondly, that the general
arrangement and microscopic structure of the substance corresponds with
that of the carbonaceous and bituminous matters in marine formations
of more modern date; thirdly, that if the Laurentian graphite has been
derived from vegetable matter, it has only undergone a metamorphosis
similar in kind to that which organic matter in metamorphosed sediment
of later age has experienced; fourthly, that the association of the
graphitic matter with organic limestone, beds of iron ore, and metallic
sulphides, greatly strengthens the probability of its vegetable origin;
fifthly, that when we consider the immense thickness and extent of
the Eozoonal and graphitic limestones and iron ore deposits of the
Laurentian, if we admit the organic origin of the limestone and
graphite, we must be prepared to believe that the life of that early
period, though it may have existed under low forms, was most copiously
developed, and that it equalled, perhaps surpassed, in its results, in
the way of geological accumulation, that of any subsequent period."
[Illustration: Figs. 20 _and_ 21.--_Bent and dislocated Quartzite,
in contorted schists interstratified with Grenville Limestone, near
Montebello._
The Quartzites have been broken and displaced, while the schists have
been bent and twisted. In the immediate vicinity the same beds may be
seen slightly inclined and undisturbed.]
Let us take, in connection with all this, the fact that we are dealing
with the deposits of the earliest ocean known to us--an ocean warm and
abounding in the mineral matters suitable for the skeletons of humble
animals, and fitted to nourish aquatic plants. The conditions were
certainly favourable to an exuberant development of the lower forms
of marine life; and in later times, when such conditions prevail, we
generally find that life has been introduced to take advantage of them.
The prudent farmer does not usually allow his best pasture to remain
untenanted with flocks and herds, and the Great Husbandman of nature
has, so far as we know, been similarly careful.
I add two sections showing the local disturbances of beds of quartzite
and schist associated with the Grenville limestones (Figs. 20 and 21,
page 103).
_PROBABILITIES AS TO LAURENTIAN LIFE, AND
CONDITIONS OF ITS PRESERVATION_
V
_PROBABILITIES AS TO LAURENTIAN LIFE, AND
CONDITIONS OF ITS PRESERVATION_
We have seen that the mineral constitution of the Upper Laurentian
affords evidence that in this age there were already land and water,
and that the processes by which the land is being worn down, and its
materials deposited on the sea-bottom, were in full operation; while
the absence of any evidence of violent wave-action, and the presence of
thick deposits of limestone, coaly matter, iron ore, and fine-grained
beds of sediment, indicates a time of rest and quiescence. All these
conditions were favourable to the presence of life, and we should
expect to find in such a period some sign of its commencement.
But here we are met by a formidable difficulty. If the beds of the
Grenville series were originally deposits in a quiet sea, they are, as
now existing in the old Laurentian hills and valleys, very much changed
from their original condition. They have, in short, experienced the
changes known to geologists by the formidable word metamorphism,
whereby they have lost the more obvious characters of ordinary aqueous
deposits, and have assumed new and strange forms. Dr. Adams, of
Montreal, has taken the pains to collect a number of chemical analyses
of the gneisses and schists or crystalline slates of the Grenville
series, and finds that, however unlike to more modern shales and clays,
they have substantially the same chemical composition. Now if they were
originally such shales and clays, it has happened to them that the
ingredients of the clays have rearranged themselves in new forms and
become crystalline. We are familiar in a small way with such changes
when brick clay, over-heated in the kiln, becomes fused into slag
or vitrified; and if such slag were allowed to cool very slowly, it
would present different kinds of crystalline minerals. We actually see
changes of this kind in the substance of bricks which have been long
exposed to intense heat in the walls of furnaces. Now in the crust of
the earth, very old rocks, buried under newer deposits, and exposed
to the heat of the interior molten rocks, experience such changes on
a great scale; and there is one kind of influence present in the
bowels of the earth which we in our experiments cannot easily imitate
or understand, namely, the action of superheated water prevented by
pressure from escaping as steam, and permeating the whole substance of
deposits, which are thus baked at a high temperature in presence of
water, instead of being exposed to mere dry heat, as in our kilns and
furnaces. The study of the partial changes which have passed on later
sediments where in contact with volcanic masses once intensely heated,
enables us to understand the greater and more extensive metamorphism
of the oldest rocks. Thus a mere mud becomes glorified by metamorphic
crystallization into a micaceous schist. We have taken ordinary clay
as an example; but under the same processes sand has been converted
into a compact quartzite, ordinary limestone into crystalline marble,
clay-ironstone into magnetic iron ore, coal into graphite, and lavas or
volcanic ashes into hard crystalline granites, gneisses, or pyroxene
rocks or hornblendic schists, according to their original composition.
There may exist portions of these old rocks which have been exempt
from such alteration, but hitherto we have not been able to find them,
and they are probably under the ocean bed, or deeply burled beneath
later rocks, while the parts exposed are precisely those which have
by their crumpling and pressure, and the influence of internal heat,
become most hardened and altered, and have therefore best resisted
denudation. We need not therefore be astonished if any organic remains
originally present in such rocks should have perished, or should have
been subjected to such changes of composition and form as to have
altogether lost their original characters. The searcher for fossils
in such rocks has to expect that these can have been preserved only
under very rare and exceptional circumstances. We have now to consider
what these circumstances are, and for simplicity may suppose that we
are endeavouring to discover in a crystalline limestone the remains
of animals having a skeleton of limestone, as is the case with most
shell-fishes and corals, and with many Protozoa and marine worms. In
regard to these, we have to consider what may happen to them when they
are imbedded in calcareous marl or ooze, or the limestone which results
from the hardening of such materials; and we have to bear in mind that
such organisms usually consist of hard, stony walls or partitions,
enclosing cavities originally filled with the soft parts of the animal
which may be supposed to have disappeared by decay before or during the
mineralization of its skeleton.
So long as the imbedding mass continues soft and incoherent, shells,
corals, etc., can be recovered in a condition similar to that of recent
specimens, except that they may have become bleached in colour and
brittle in texture, owing to the removal of organic matter intimately
associated with the lime, and that their cavities may have been filled
with sand or silt washed into them, or with calcite or calcareous spar
introduced in solution in water. But if the containing mass has become
a hard stone, the material filling the interior of our shell or coral
has experienced a similar change; and when we break open the stone,
we may obtain the specimen, now hard, solid, and heavy, but still
showing more or less of its outer surface and markings, and possibly to
some extent also its internal structure when it is sliced and studied
under the microscope. But if the whole mass has been metamorphosed,
and has become crystalline, the contained fossil and its contents may
have experienced a similar change, and may have so coalesced with the
containing matrix that it is no longer separable from it. Even in this
case, however, if the whole is reduced to a thin transparent slice
and examined microscopically, some traces may be found of the external
and internal limiting lines of the fossil, and even of its minute
structures, which often cause it to present an appearance granular,
cellular, or otherwise different from that of the enclosing matrix. It
requires, however, both skill and care to detect organic remains in
such circumstances, and they may often escape observation, except when,
as in many old crystalline limestones, the fossils are darkened in
whole or in part with coaly matter derived from the decay of their own
organic substance. The crystalline Trenton limestone of Montreal, used
there as a building stone, is an excellent example (Fig. 22).
[Illustration: Fig. 22.--_Section of "Trenton Limestone" (magnified)._
Showing its composition of fragments of calcareous fossils.]
[Illustration: Fig. 23.--_Diagram of different States of Fossilization
of the Cell of a Tubulate Coral._
(_a_) Natural condition, (_b_) Cell filled with calcite. (_c_) Walls
calcite, filling silica. (_d_) Walls silica, filling calcite. (_e_)
Both walls and calcite silica. All these conditions are found in the
fossil corals of the corniferous Limestone of Canada--Middle Permian.]
It is otherwise, however, when the calcareous fossils have been filled
or injected with some mineral matter different from the matrix, as, for
example, silica or some silicate, oxide or sulphide of iron. In this
case the texture, colour, or hardness of the filling appear different
from those of the limestone, and may be seen in a fresh fracture or
polished slice; or when the rock is weathered, the hard mineralizing
substance may project from the surface of the specimens, or may be
disclosed by treating the surface with a weak acid. The figures here
given may suffice to show some of these conditions of mineralization
in ordinary limestones, and the effects which they produce (Fig. 23).
The mineral matters which thus aid in preserving fossils are of various
kinds, and the whole subject is a very curious one; but for the present
we may content ourselves with two kinds of mineralization--that by
silicates and that by magnesian limestone or dolomite.
From the bottom of modern seas the dredge often brings up multitudes
of minute shells, especially those of the simple gelatinous Protozoa,
known as Foraminifera, whose internal cavities and pores have been
filled with a greenish mineral composed of silica, iron and potash,
combined with water (or, chemically speaking, a hydrous silicate of
iron and potassium), which is named _glauconite_ from its bluish-green
colour--a name which we shall do well to remember. In such compounds,
bases of similar chemical properties often replace one another, so
that various glauconites differ somewhat in composition, the iron
being in part often replaced by alumina or magnesia, and the potash by
soda. The combined water also differs somewhat in its percentage. When
minute shells fossilized in this way are treated with an acid so as to
remove the calcareous shell itself, the enclosed silicate remains as a
beautiful cast or core, representing all the forms of the interior,
and any pores that may have penetrated the walls, and also perfectly
representing the soft gelatinous body of the animal which once tenanted
the shells (Fig. 24). (See also Fig. 25 at end of chapter.)
[Illustration: Fig. 24.--_Cast of Cavities of Polystomella in
Glauconite (magnified)._
After a photograph from Dr. Carpenter, and mounted specimens from his
collection.]
When we examine oceanic sediments of older date, we find similar
fillings in limestones, chalks, and sandstones of various ages, some
of the latter containing glauconite so abundantly as to bear the name
of green-sands, from their colour; and in these older examples we more
frequently find alumina and magnesia occupying a large place in the
mineralizing silicate. Fig. 24A gives two illustrations of this--one
a crinoidal stem from the Silurian of New Brunswick, injected with a
silicate of alumina, iron, magnesia and potash; the other a spiral
shell from more ancient perhaps Cambrian rocks in Wales, filled with a
silicate apparently more nearly related to serpentine. Further examples
will be referred to in an appended note.
[Illustration: Fig. 24A.--(_a_) _Joint of Crinoid injected with a
Hydrous Silicate, Silurian, Pole Hill, New Brunswick._ (× 25.)
(_b_) _Spiral Shell injected with a Hydrous Silicate allied to
Serpentine, near Llangwyllog, North Wales,_ (× 25.)]
We may now consider shortly the relation of dolomite, or the mixed
carbonates of lime and magnesia, to the preservation of fossils. The
presence of dolomite or magnesian limestone in these beds does not
affect the conclusion as to their probable organic origin. This form of
limestone occurs abundantly in later formations, and is even forming in
connection with coral deposits in the modern ocean.
Dana has shown this by his observations on the occurrence of dolomite
in the elevated coral island of Matea in Polynesia,[20] under
circumstances which show that it was formed in the lagoon of an ancient
coral atoll, or ring-shaped island, while he finds that coral and
coral sands of the same elevated reef contain very little magnesia.
He concludes that the introduction of magnesia into the consolidating
under-water coral sand or mud has apparently taken place--"(1) In
sea-water at the ordinary temperature; and (2) without the agency of
any other mineral water except that of the ocean"; but the sand and
mud were those of a lagoon in which the saline matter was in process
of concentration by evaporation under the solar heat. Klement has
more recently taken up this fact in the way of experiment, and finds
that, while in the case of ordinary calcite this action is slow
and imperfect, with the aragonite which constitutes the calcareous
framework of certain corals,[21] and at temperatures of 60° or over,
it is very rapid and complete, producing a mixture of calcium and
magnesium carbonates, from which a pure dolomite more or less mixed
with calcite may subsequently result.[22]
[Footnote 20: "Corals and Coral Islands," p. 356, etc.]
[Footnote 21: Aragonite, like ordinary limestone, is calcium carbonate,
but its atoms seem to be differently arranged, so as to make it a
less stable compound, and it has a different crystalline form. Some
calcareous organisms are composed of aragonite, others of ordinary
calcite.]
[Footnote 22:"Bulletin Geol. Soc. Belgium," vol. ix. (1895, p. 3). Also
notice in _Geol. Mag._, July, 1895, p. 329.]
I regard these observations as of the utmost importance in reference to
the relations of dolomite with fossiliferous limestones, and especially
with those of the Grenville series. The waters of the Laurentian ocean
must have been much richer in salts of magnesium than those of the
present seas, and the temperature was probably higher, so that chemical
changes now proceeding in limited lagoons might have occurred over
much larger areas. If at that time there were, as in later periods,
calcareous organisms composed of aragonite, these may have been
destroyed by conversion into dolomite, while others more resisting were
preserved, just as a modern _Polytrema_ or _Balanus_ might remain, when
a coral to which it might be attached would be dolomitized, or might
even be removed altogether by sea-water containing carbonic acid. There
is reason to believe that this last change sometimes takes place in
the deeper parts of the ocean at present. This would account for the
persistence of Eozoon and its fragments, when other organisms may have
perished, and also for the frequent filling of the canals and tubuli
with the magnesian carbonate.
The main point here, however, for our present purpose is that, when a
calcareous shell or skeleton has been thus infiltrated with a silicate,
it becomes imperishable, so that any amount of alteration of the
containing limestone short of its absolute fusion would not suffice
to destroy an organism once injected with silicious matter. Thus the
occasional persistence of silicified fossils in highly metamorphosed
limestones is in no respect contradictory to the general fact, that
when not preserved by silicious infiltration, they have perished, and
this more especially in the case of those whose skeletons are composed
of aragonite.
Carrying these facts with us, the next question is, What manner of
fossil remains should we expect to find in the Upper Laurentian rocks,
supposing that any such are therein preserved? The answer to this
question follows at once from the facts as to the succession of life
noticed above. Only the marine invertebrates have been traced as far
back as the oldest Cambrian, and only Worms, Sponges, and Protozoa
into the Huronian. We should therefore have no expectation of finding
remains of any vertebrate animals or of any of the land invertebrates;
and even allowing for the more favourable conditions, as compared
with the Huronian, evidenced by the great limestones and the abundant
carbon, we could scarcely expect anything higher than some of the
lower types of invertebrate life, such as Worms, Hydroids, Corals and
Protozoa. We have next to inquire what forms, possibly organic, have
actually been found, and what information we can derive from them as to
the beginnings of life. Since, however, such discoveries as have been
made have been the result of much labour and scientific skill brought
to bear on these old rocks, and are connected with the reputations of
several eminent men, now deceased, we may first refer shortly to the
history of the discovery of supposed fossils in the Laurentian rocks of
Canada.
[Illustration: Fig. 25.--_Nature-print of an etched Specimen of Eozoon._
Showing the laminæ, a part of the natural margin, near which passes a
diagonal calcite vein, and at the upper right-hand corner, fragmental
material with casts of Archæospherinæ. The dark lines represent the
chambers filled with serpentine, the white the calcite wall.]
_THE HISTORY OF A DISCOVERY_
VI
_THE HISTORY OF A DISCOVERY_
When Mr. Logan, afterwards Sir William Logan, entered on the Geological
Survey of Canada, in 1840, he found that vast and little-explored
regions in the northern part of that country were occupied with
gneissic rocks, similar to the oldest gneisses of Scotland and
Scandinavia, and to which the name Azoic had been given by Murchison,
as rocks destitute of fossils, while they had been the "fundamental
granite" or ur-gneiss of most European geologists. They were
unquestionably below and more ancient than the oldest fossiliferous
Cambrian rocks both in Europe and North America, and geologists had for
the most part contented themselves with regarding them as primitive
rocks, destitute of any geological interest, much as some United States
geologists of the present day call them the "Archæan complex," a name
which the late Prof Dana has well characterized as a "term of despair."
Logan was, however, a man not to be daunted by an unsolved problem,
even though the facts for its solution must be sought in a wilderness
known to few except adventurous trappers, hunters, and lumbermen; and
he soon learned that this ancient gneissic formation contained other
rocks beside gneiss, more especially thick and extensive limestones,
and that its beds seemed to have a definite arrangement, and could
be traced over great areas. He addressed himself, therefore, to
the problem of unravelling the tangled "complex," and with a few
hardy assistants, spent years in laboriously tracing its beds along
river courses and over mountains, and in mapping, in a manner never
previously attempted, its several members, designating at the same time
the whole by the term "Laurentian," because it constituted the mass
of the hills lying north of the St. Lawrence, called by old French
geographers the Laurentides, and separating the St. Lawrence Valley and
the region of the great lakes from Hudson's Bay and the Arctic Sea. In
this manner he laid a foundation, which still remains unshaken, for the
geology of the oldest rocks, and prepared the way for the discovery
of the forms afterward named Eozoon Canadense. At the same time Dr.
Sterry Hunt, the chemist of the Survey, was examining chemically the
rocks and minerals collected, and all Sir William's assistants were
instructed to search, more especially in the limestones, for anything
bearing the aspect of fossils. On the other hand. Dr. Carpenter was
independently pursuing his studies of the humbler inhabitants of the
modern ocean, and of the manner in which the pores of their skeletons
became infiltrated with mineral matter, and had kindly contributed
specimens to the collections of the writer in Canada. The discovery
of this most ancient fossil was thus not the chance picking up of a
rare and curious specimen, but the result of several combined lines of
laborious and skilful research.
The following notice of the persons and incidents connected with its
discovery is taken from a previous publication of the writer, with only
a little alteration in terms to suit it to the present date.
The first specimens of Eozoon ever procured, in so far as known, were
collected at Burgess, in Ontario, by a veteran Canadian mineralogist.
Dr. Wilson of Perth, and were sent to Sir William Logan as mineral
specimens. Their chief interest at that time lay in the fact that
certain laminæ of a dark green mineral present in the specimens
were found, on analysis by Dr. Hunt, to be composed of a new hydrous
silicate, allied to serpentine, and which he named loganite, but
which seems to be a mixture of different silicates. The form of this
mineral was not suspected to be of organic origin. Some years after,
in 1858, other specimens, differently mineralized with the minerals
serpentine and pyroxene, were found by Mr. J. McMullen, an explorer in
the service of the Geological Survey, in the limestone of the Grand
Calumet on the river Ottawa. These seem to have at once struck Sir W.
E. Logan as resembling the Silurian fossils known as _Stromatoporæ_,
or layer-corals, and at that time of quite uncertain nature, though
supposed to be allied to some kinds of modern corals. He showed them
to Mr. Billings, the palæontologist of the Survey, and to the writer,
with this suggestion, confirming it with the sagacious consideration
that inasmuch as the Ottawa and Burgess specimens were mineralized
by different substances, yet were alike in form, there was little
probability that they were merely mineral or concretionary. Mr.
Billings was naturally unwilling to risk his reputation in affirming
the organic nature of such specimens; and my own suggestion was that
they should be sliced, and examined microscopically; and that if
fossils, as they presented merely concentric laminæ and no cells, they
would probably prove to be protozoa rather than corals. A few slices
were accordingly made, but no definite structure could be detected.
Nevertheless, Sir William Logan took some of the specimens to the
meeting of the American Association at Springfield, in 1859, and
exhibited them as possibly Laurentian fossils; but the announcement was
evidently received with some incredulity. In 1862 they were exhibited
by Sir William to some geological friends in London, but he remarks
that "few seemed disposed to believe in their organic character, with
the exception of my friend Professor Ramsay." In 1863 the General
Report of the Geological Survey, summing up its work to that time, was
published, under the name of the "Geology of Canada," and in this, at
page 49, will be found two figures of one of the Calumet specimens,
here reproduced, and which, though unaccompanied with any specific
name or technical description, were referred to as probably Laurentian
fossils (Figs. 26 and 27).
[Illustration: Fig. 26.--_Weathered Specimen of Eozoon from the Grand
Calumet._ (Collected by Mr. McMullen.)]
[Illustration: Fig. 27.--_Cross Section of the Specimen represented in
Fig. 26._
The dark parts are the laminæ of calcareous matter converging to the
outer surface.]
About this time Dr. Hunt happened to mention to me, in connection with
a paper on the mineralization of fossils which he was preparing, that
he proposed to notice the mode of preservation of certain fossil woods
and other things with which I was familiar, and that he would show me
the paper in proof, in order that he might have any suggestions that
occurred to me. On reading it, I observed, among other things, that
he alluded to the supposed Laurentian fossils, under the impression
that the organic part was represented by the serpentine or loganite,
and that the calcareous matter was the filling of the chambers. I took
exception to this, stating that though in the slices before examined
no structure was apparent, still my impression was that the calcareous
matter was the fossil, and the serpentine or loganite the filling. He
said: "In that case, would it not be well to re-examine the specimens,
and to try to discover which view is correct?" He mentioned at the same
time that Sir William had recently shown him some new and beautiful
specimens collected by Mr. Lowe, one of the explorers on the staff
of the Survey, from a third locality, at Grenville, on the Ottawa.
It was supposed that these might throw further light on the subject;
and accordingly Dr. Hunt suggested to Sir William to have additional
slices of these new specimens made by Mr. Weston, of the Survey,
whose skill as a preparer of these and other fossils has often done
good service to science. A few days thereafter, some slices were sent
to me, and were at once put under the microscope. I was delighted to
find in one of the first specimens examined, which happened to be cut
parallel to the laminæ, a beautiful group of tubuli penetrating one of
the calcite layers. Here was evidence, not only that the calcite layers
represented the true skeleton of the fossil, but also of its affinities
with the Foraminifera, whose tubulated supplemental skeleton, as
described and figured by Dr. Carpenter, and represented in specimens
in my collection presented by him, was evidently of the same type with
that preserved in the canals of these ancient fossils. Fig. 28 is an
accurate representation of the first seen group of canals penetrated by
serpentine.
On showing the structures discovered to Sir William Logan, he entered
into the matter with enthusiasm, and had a great number of slices and
afterwards of decalcified specimens prepared, which were placed in my
hands for examination.
[Illustration: Fig. 28.--_Group of Canals in the Supplemental Skeleton
of Eozoon._
Taken from the specimen in which they were first recognised.
(Magnified.)]
[Illustration: Fig. 29.--_Canals of Eozoon, from same specimen,_
(Highly magnified.)]
Feeling that the discovery was most important, but that it would be
met with determined scepticism on the part both of geologists and
biologists, I was not content with examining the typical specimens of
Eozoon, but had slices prepared of
every variety of Laurentian limestone, of altered limestones from the
Cambrian and Silurian, and of serpentine marbles of all the varieties
furnished by our collections. These were examined with ordinary and
polarized light, and with every variety of illumination. Dr. Hunt,
on his part, undertook the chemical investigation of the various
associated minerals. An extensive series of notes and camera tracings
were made of all the appearances observed; and of some of the more
important structures beautiful drawings were executed by the late
Mr. H. S. Smith, the then palæontological draughtsman of the Survey.
The result of the whole investigation was a firm conviction that the
structure was organic and probably foraminiferal, and that it could be
distinguished from any merely mineral or crystalline forms occurring in
these or other limestones.
At this stage of the matter, and after exhibiting to Sir William all
the characteristic appearances in comparison with such concretionary,
dendritic, and crystalline structures as most resembled them, and also
with the structure of recent and fossil Foraminifera, I suggested that
the further prosecution of the matter should be handed over to Mr.
Billings, as palæontologist of the Survey, and as our highest authority
on the fossils of the older rocks.
[Illustration: Fig. 30.--_Casts of Canals of Eozoon, in Serpentine._
Decalcified and highly magnified.]
[Illustration: Fig. 31.--_Group of finest Tubuli._
Highly magnified, from a micro-photograph.]
I was engaged in other researches, and knew that no little labour
must be devoted to the work and to its publication, and that some
controversy might be expected. Mr. Billings, however, with his
characteristic caution and modesty, declined. His hands, he said, were
full of other work, and he had not specially studied the microscopic
appearances of Foraminifera or of mineral substances. It was finally
arranged that I should prepare a description of the fossil, which
Sir William would take to London, along with Dr. Hunt's notes, the
more important specimens, and lists of the structures observed in
each. Sir William was to submit the manuscript and specimens to Dr.
Carpenter, and also to Prof T. Rupert Jones, in the hope that these
eminent authorities would confirm our conclusions, and bring forward
new facts which I might have overlooked or been ignorant of Sir William
saw both gentlemen, who gave their testimony in favour of the organic
and foraminiferal character of the specimens; and Dr. Carpenter in
particular gave much attention to the subject, and worked out the
structure of the delicate tubulation of the surfaces of the laminæ or
cell-walls, which I had not distinguished previously, through a curious
accident as to specimens. Mr. Lowe had been sent back to the Ottawa
to explore, and just before Sir William's departure had sent in some
specimens from a new locality at Petite Nation, similar in general
appearance to those from Grenville, which Sir William took with him
unsliced to England. These showed in a perfect manner the tubuli of
the primary cell-wall, which I had in vain tried to resolve in the
Grenville specimens, and which I did not see until after they had been
detected by Dr. Carpenter in London. Dr. Carpenter thus contributed in
a very important manner to the perfecting of the investigations begun
in Canada, and on him fell the greater part of their illustration and
defence,[23] in so far as Great Britain is concerned.
[Footnote 23: In papers by Dr. Carpenter, subsequently referred to.
Prof. Jones published an able exposition of the facts in the _Popular
Science Monthly_.]
The immediate result was a composite paper in the _Proceedings of the
Geological Society_, by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and
myself, in which the geology, palæontology, and mineralogy of _Eozoon
Canadense_ and its containing rocks were first given to the world.[24]
It cannot be wondered at that when geologists and palæontologists
were thus required to believe in the existence of organic remains in
rocks regarded as altogether Azoic and hopelessly barren of fossils,
and to carry back the dawn of life as far before those Cambrian rocks,
which were supposed to contain its first traces, as these are before
the middle period of the earth's life-history, some hesitation should
be felt. Further, the accurate appreciation of the evidence for such a
fossil as Eozoon required an amount of knowledge of minerals, of the
more humble types of animals, and of the conditions of mineralization
of organic remains, possessed by few even of professional geologists.
Thus Eozoon has met with some negative scepticism and positive
opposition--though the latter has been smaller in amount than might
have been anticipated, when we consider the novel and startling
character of the facts adduced. The most annoying element in the
discussion has consisted in the liability of observers, only partially
informed, to confound our specimens with things of very different
character, from which we had taken pains to distinguish them.
[Footnote 24: In _Quarterly Journal of Geological Society_, vol. xxii.;
_Proc. Royal Society_, vol. xv.; _Intellectual Observer_, 1865; _Annals
and Magazine of Natural History_, 1874; and other papers and notices.]
"The united thickness," says Sir William Logan, "of these three great
series, the Lower and Upper Laurentian and Huronian, may possibly far
surpass that of all succeeding rocks, from the base of the Palæozoic to
the present time. We are thus carried back to a period so far remote
that the appearance of the so-called Primordial fauna may be considered
a comparatively modern event."[25] So great a revolution of thought,
and this based on one fossil, of a character little recognisable by
geologists generally, might well tax the faith of a class of men
usually regarded as somewhat faithless and sceptical. Yet this new
extension of life has been very generally received, and has found
its way into text-books and popular treatises. Its opponents have
been under the necessity of inventing the most strange and incredible
pseudomorphoses of mineral substances to account for the facts. As
might have been expected, after the publication of the original paper,
other facts developed themselves. Mr. Vennor found other and scarcely
altered specimens closely allied to the Laurentian forms in the
Hastings series of Tudor, probably of Huronian age. Gümbel recognised
the organism in Laurentian rocks in Bavaria and elsewhere in Europe,
and discovered a new species in the Huronian of Bavaria.[26] Eozoon was
recognised in Laurentian limestones in Massachusetts[27] and New York,
and there has been a rapid growth of new facts increasing our knowledge
of Foraminifera and other humble animals in the succeeding Eozoic and
Palæozoic rocks. Special interest attaches to the discovery by Mr.
Vennor, and by Walcott and Matthew, to be mentioned in the sequel,
and tending to bridge over the interval between the Laurentian fossil
and those of the Lower Cambrian. Another fact, whose significance is
not to be over-estimated, is the recognition both by Dr. Carpenter
and myself of specimens in which the canals are occupied by dolomite
or by calcite like that of the organism itself I have made several
visits to the locality at Petite Nation originally discovered by
Mr. Lowe, in company with Dr. Carpenter, Dr. Bonney,[28] and other
skilled observers, and have very carefully studied all the facts with
reference to the mode of occurrence of the forms in the beds, and their
association with layers of fragmental Eozoon, and have found that these
are strictly in accordance with the theory that these old Laurentian
limestones are truly marine deposits, holding the remains of the sea
animals of their time.
[Footnote 25: _Journal Geological Society_, February, 1865.]
[Footnote 26: _Ueber das Vorkommen von Eozoon_, 1866.]
[Footnote 27: By Mr. Bicknell at Newbury, and Mr. Burbank at
Chelmsford. The latter gentleman has since maintained that the
limestones at the latter place are not true beds; but his own
descriptions and figures lead to the belief that this is an error
of observation on his part. The Eozoon in the Chelmsford specimens
and in those of Warren, New York, is in small and rare fragments in
serpentinous limestone.]
[Footnote 28: See an excellent account of one of these visits by Dr.
Bonney, _Geological Magazine_, 1895.]
Eozoon is not, however, the only witness to the great fact of
Laurentian life, of which it is the most conspicuous exponent. In many
of the Laurentian limestones, mixed with innumerable fragments of
Eozoon, there are other fragments with traces of organic structure of
a different character. There are also casts in silicious matter which
seem to indicate smaller species of Foraminifera; and large laminated
forms, apparently organic, yet distinct from Eozoon. Some of these must
be noticed in the following pages.
Other discoveries also are foreshadowed here. The microscope may
yet detect the true nature and affinities of some of the fragments
associated with Eozoon. Less altered portions of the Laurentian rocks
may be found, where even the vegetable matter may retain its organic
forms, and where fossils may be recognised by their external outlines
as well as by their internal structure. Thus the time may come when
the rocks now called Primordial shall not be held to be so in any
strict sense, and when swarming dynasties of Protozoa and other low
forms of life may be known as inhabitants of oceans vastly ancient as
compared with even the old Primordial seas. Who knows whether even the
land of the Laurentian time may not have been clothed with plants,
perhaps as much more strange and weird than those of the Devonian and
Carboniferous, as those of the latter are when compared with modern
forests?
_THE DAWN OF LIFE_
VII
_THE DAWN OF LIFE_
In the Grenvillian system, as represented in the vicinity of the
Ottawa River, perfect specimens of Eozoon are found in one only of
the principal limestones there exposed, and in certain layers of that
limestone, and they are associated with concretions and grains of the
greenish mineral serpentine, which, as we shall see, has much to do
with their preservation. As exposed on broken surfaces, the specimens
consist of concentric layers of greenish serpentine and white calcite,
not, however, even or uniform, as in ordinary concretions having
concentric structure, but often approaching and uniting with each
other, so as to constitute wide flat chambers, and forming patches from
an inch to nearly a foot in diameter, while some of the larger patches
seem to coalesce or to become confluent. On weathered surfaces the
serpentine laminæ often become brown, owing to the rusting of the iron
contained in them, and project above the general surface, in this case
resembling very much the appearance of the layer-corals so plentiful in
some limestones of later date.
The external forms of Eozoon are at first sight not very obvious,
as they adhere very closely to the containing rock; but the smaller
specimens, when entirely weathered out or disengaged by the solution of
the limestone in an acid, usually present the form of a broad inverted
cone, like some modern sponges or the broader turbinate fossil corals
(Fig. 32). The limestone having, like the other beds of the formation,
been much compressed and folded, the specimens of Eozoon are sometimes
crumpled in these folds or broken across by small cracks or faults,
which shift the laminæ slightly out of their places. The cracks thus
formed are also sometimes filled with a fibrous variety of serpentine,
known to mineralogists as chrysotile and popularly as "rock cotton"
or "asbestus." It is finely fibrous, and of a silky lustre, and must
have been deposited by water in the cracks and fissures formed by the
fracturing of the rock and the contained fossils, by movements taking
place after the whole was hardened. Accordingly these veins often cross
not only the rock, but also the serpentine and calcite layers of the
contained masses of Eozoon, without regard to the direction of their
laminæ, though sometimes they run parallel to the structure, the rock
having broken more easily in that direction.
[Illustration: Fig. 32.--_Entire specimen of Eozoon, disengaged from
the matrix and showing its turbinate form, enclosed in the outline of a
larger specimen of similar form._
Both natural size, Côte St. Pierre. (Specimens in Peter Redpath
Museum.)]
Bearing in mind these general points of material form and appearance,
we may now proceed to inquire as to the following points: (1) _The
structures visible in the specimens_; (2) _The manner in which they are
represented by different mineral substances, and how these are to be
accounted for_; (3) _The explanation of the whole on the supposition
that we are dealing with an animal fossil_.
(1) In regard to the first of these questions, I may quote here, with
some slight alteration, from a recent memoir of my own[29]:--
[Footnote 29: _London Geological Magazine_, 1895.]
In recent years I have been disposed to attach more importance than
formerly to the general form of Eozoon. The earlier examples studied
were, for the most part, imbedded in the limestone in such a manner
as to give little definite information as to external form; and at a
later date, when Sir William Logan employed one of his assistants, Mr.
Lowe, to quarry large specimens at Grenville and Côte St. Pierre, the
attempt was made to secure the most massive blocks possible, in order
to provide large slabs for showy museum specimens.
[Illustration: Fig. 33.--_Weathered surface of Eozoon._ Showing
sections of two funnels or tubes with limiting walls, Côte St. Pierre.]
More recently, when collections have been made from the eroded and
crumbling surfaces of the limestone in its wider exposures, it was
found that specimens of moderate size had been weathered out, and
could, either naturally or by treatment with acid, be entirely
separated from the matrix. Such specimens sometimes showed, either on
the surfaces or on the sides of "funnels" and tubes penetrating the
mass (Figs. 33, 34), a confluence of the laminæ, constituting a porous
cortex or limiting structure. Specimens of this kind were figured in
1888, and I was enabled to add to the characters of the species that
the original and proper form was "broadly turbinate with a depression
or cavity above, and occasionally with oscula or pits penetrating the
mass." The great flattened masses thus seemed to represent confluent or
overgrown individuals, often contorted by the folding of the enclosing
beds.
[Illustration: Fig. 34.--_Section of the Base of a specimen of Eozoon._]
This specimen shows an oscuilform, cylindrical funnel, cut in such
a manner as to show its _reticulated wall_ and the descent of the
laminæ toward it. Two-thirds of natural size. From a photograph. Col.
Carpenter, also in Redpath Museum.
[This illustration (from Prof. Prestwich's "Geology," vol. ii. p. 21)
has been courteously lent by the Clarendon Press, Oxford.]
There are also in well-preserved specimens certain constant properties
of the calcite and serpentine layers. The former are continuous,
and connected at intervals, so that if the silicious filling of
the chambers could be removed, the calcareous portion would form a
continuous skeleton, while the serpentine filling the chambers, when
the calcareous plates are dissolved out by an acid, forms a continuous
cast of the animal matter filling the chambers (Fig. 36). This cast
of the sarcodous material, when thus separated, is very uniformly
and beautifully mammillated on the surfaces of the laminæ, and this
tuberculation gradually passes upward into smaller chambers having
amœboid outlines, and finally into rounded chamberlets. It is also
a very constant point of structure that the lower laminæ of calcite
are thicker than those above, and have the canal-systems larger and
coarser. There is thus in the more perfect specimens a definite plan of
macroscopical structure (Fig. 35).
[Illustration: Fig. 35.--_Structure of small specimen of Eozoon,
calcareous matter removed._]
1. Natural size. 2. Acervuline cells of upper part. 3. Group of the
same coalescing into a lamina with tuberculated surface. 4. Laminæ with
tuberculated surfaces in section. (See also Fig. 36.)
[Illustration: Fig. 36.--_Decalcified Eozoon, in section, slightly
enlarged._ Showing the character of the sarcodous laminæ now replaced
by Serpentine.]
The normal mode of mineralization at Côte St. Pierre and Grenville is
that the laminæ of the test remain as calcite, while the chambers and
larger canals are filled with serpentine of a light green or olive
colour, and the finer tubuli are injected with dolomite. It may also
be observed that the serpentine in the larger cavities often shows a
banded structure, as if it had been deposited in successive coats, and
the canals are sometimes lined with a tubular film of serpentine, with
a core or axis of dolomite, which also extends into the finer tubuli of
the surfaces of the laminæ. This, on the theory of animal origin, is
the most perfect state of preservation, and it equals anything I have
seen in calcareous organisms of later periods. This state of perfection
is, however, naturally of infrequent occurrence.
[Illustration: Fig. 37.--_Finest Tubuli filled with Dolomite
(magnified)._]
The finer tubuli are rarely perfect or fully infiltrated. Even the
coarser canals are not infrequently imperfect, while the laminæ
themselves are sometimes crumpled, crushed, faulted, or penetrated with
veins of chrysotile or of calcite. In some instances the calcareous
laminæ are replaced by dolomite, in which case the canal-systems
are always imperfect or obsolete. The laminæ of the test itself are
also in some cases replaced by serpentine in a flocculent form. At
the opposite extreme are specimens, or portions of specimens, in
which the chambers are obliterated by pressure, or occupied only
with calcite. In such cases the general structure is entirely lost
to view, and scarcely appears in weathering. It can be detected only
by microscopic examination of slices, in parts where the granular
structure or the tubulation of the calcite layers has been preserved.
All palæontologists who have studied silicified fossils in the older
rocks are familiar with such appearances.
[Illustration: Fig. 38.--_Plan of arrangement of Canals in Lamina of
Eozoon._]
It has been alleged by Möbius and others that the canal-systems and
tubes present no organic regularity. This difficulty, however, arises
solely from imperfect specimens or inattention to the necessary results
of slicing any system of ramifying canals. In Eozoon the canals form
ramifying groups in the middle planes of the laminæ, and proceed at
first almost horizontally, dividing into smaller branches, which
ultimately give off brushes of minute tubuli running nearly at right
angles to the surfaces of the lamina, and forming the extremely fine
tubulation which Dr. Carpenter regarded as the proper wall (Figs. 38,
39).
[Illustration: Fig. 39.--_Cross section of minute Tubuli, about 5
microms in diameter (magnified)._]
In my earlier description I did not distinguish this from the
canal-system, with which its tubuli are inwardly continuous. Dr.
Carpenter, however, understood this arrangement, and has represented
it in his figures[30] (see also Fig. 28). It is evident that in a
structure like this a transverse or oblique section will show truncated
portions of the larger tubes apparently intermixed with others much
finer and not continuous with them, except very rarely. Good specimens
and many slices and decalcified portions are necessary to understand
the arrangement This consideration alone, I think, entirely invalidates
the criticisms of Möbius, and renders his large and costly figures of
little value, though his memoir is, as I have elsewhere shown, liable
to other and fatal objections.[31]
[Footnote 30: "Ann. and Mag. Nat. Hist.," ser. 4, xiii., p. 456, figs.
3, 4.]
[Footnote 31: "Museum Memoir," pp. 50 _et seq._]
It has been pretended that the veins of chrysotile, when parallel
to the laminæ, cannot be distinguished from the minute tubuli
terminating on the surfaces of the laminæ. I feel confident, however,
that no microscopist who has seen both, under proper conditions of
preservation and study, could confound them. The fibres of chrysotile
are closely appressed parallel prisms, with the optical properties of
serpentine. The best preserved specimens of the "proper wall" contain
no serpentine, but are composed of calcite with extremely minute
parallel cylinders of dolomite about five to ten microms. in diameter,
and separated by spaces greater than their own diameter (Figs. 40, 41).
In the rare cases where the cylinders are filled with serpentine, they
are, of course, still more distinct and beautiful. At the same time,
I do not doubt that observers who have not seen the true tubulation
may have been misled by chrysotile veins when these fringe the laminæ.
Möbius, for instance, figures the true and false structure as if they
were the same.
[Illustration: Fig. 40.--_Cross section of similar Tubuli to those in
Fig. 39, more highly magnified, and showing granular character of the
test._
(From camera tracings.)]
[Illustration: Fig. 41.--_Comparison of Tubulate Wall and Prisms of
Chrysotile in perspective._]
[Illustration: _Canals of Eozoon._ (After Möbius.)]
[Illustration: _Finer Canals of Eozoon._ (After Möbius.)]
[Illustration: _Canals of modern Calcarina._ (After Carpenter.)]
[Illustration: _Canals and Tubule of Tertiary Nummulina._ (After
Möbius.)]
Fig. 42.
Figures selected from Möbius, to show the resemblance of structures of
Eozoon to those of modern Foraminifera.
Protest should here be made against that mode of treating ancient
fossils which regards the most obscure or defaced specimens as typical,
and those better preserved as mere accidents, of mineral structure. In
Tertiary Nummulites injected with glauconite it is rare to find the
tubuli perfectly filled, except in tufts here and there; yet no one
doubts that these patches represent a continuous structure.
I have remarked on previous occasions that the calcite constituting the
laminæ of Eozoon often has a minutely granular appearance, different
from that of the surrounding limestone. Under a high power it resolves
itself into extremely minute dots or flocculi, somewhat uniformly
diffused. Whether these dots are particles of carbon, iron, apatite, or
silicious matter, or the remains of a porous structure, I do not know;
but similar appearances occur in the calcareous fossils contained in
altered limestones of later date. Wherever they occur in crystalline
limestones, supposed to be organic, the microscopist should examine
them with care. I have sometimes by this appearance detected fragments
of Eozoon which afterward revealed their canals.
(2) The second question requires us to consider the nature and
origin of the substances constituting the specimens. Reference has
already been made to these in our fifth chapter, but they may be
more particularly noticed here in connection with the forms as above
described.
The calcareous laminæ are usually composed of clear translucent
calcite or calcium carbonate, though, as in the case of many later
fossils, sometimes replaced by dolomite. It often has the fine granular
appearance above referred to, but is nearly always crystalline, and
traversed by cleavage planes visible under the microscope.[32] This
crystalline structure, as every student of fossils knows, is very
common in calcareous fossils of all geological ages. In the thicker
laminæ the canals traversing them and branching out in their substance
are usually visible under a low power, except when they are filled with
calcite similar to that of the laminæ themselves. In this case they
can be seen only by very careful management of an oblique and subdued
light. When occupied with serpentine, this presents, in a thin slice
under transmitted light, a yellowish or brownish colour, and in a
specimen decalcified with an acid an opaque white appearance. In some
of the larger threads of serpentine, as already stated, this mineral
forms a thin outer cylinder with a core of calcite or dolomite within;
but this appearance is not common. Here and there, especially in the
lower layers, a portion of a tube is filled with the harder mineral
pyroxene, which is in some respects similar to serpentine, except
that it contains lime as well as magnesia, and is destitute of water
as an ingredient The finer tubuli into which the canals ramify are
most usually filled with dolomite or magnesian limestone, which has
a glossy appearance and higher lustre than the surrounding calcite,
and so may be distinguished even in a transparent slice; but these
fine dolomite threads are best seen when the surface of a slice is
treated with a dilute acid in the cold, in which circumstances the
calcite is dissolved, while the dolomite remains as tufts of delicate
cylindrical hairs, presenting often a very beautiful appearance under
the microscope. Thus, as in many other fossils, what are supposed to
have been tubes and tubuli are found not empty, but filled with matter
even harder and more resisting than the shell itself.
[Footnote 32: Especially when the specimen has been heated or jarred in
the process of grinding or polishing.]
Serpentine is a mineral which has been produced in different ways.
Some igneous or volcanic rocks consist largely of compounds of silica
and magnesia (olivine, etc.). When these rocks have become cold and
are exposed to the action of water, they sometimes absorb this and
become hydrated, thus passing into a kind of serpentine. When such
rocks are pulverized and dispersed as volcanic ash, this falling into
the sea may be there hydrated, and may form serpentinous layers, or in
a fine paste or in solution may pass into the pores and cavities of
shells and other organic things, acting, as we have seen, in the same
manner with ordinary glauconite. In like manner serpentine of this
origin may form nodules or grains in limestones, in consequence of its
particles being aggregated together by concretionary attraction. We
have already seen that some comparatively modern so-called glauconites
are essentially of the nature of serpentine, and we know that in the
old Laurentian sea, salts of magnesia and magnesian minerals were
abundant, so that serpentinous minerals might play a greater part than
they do in the modern seas. Loganite, the mineralizing substance of
the Burgess Eozoon, is different from serpentine, yet closely allied
to the glauconites. The presence of pyroxene may be explained in a
similar way. It is a frequent constituent of bedded volcanic rocks
and of volcanic ashes, and beds of it occur in the Grenville series
which once, no doubt, were ash-beds. Layers of it also occasionally
occur from a similar cause in the limestone, and crystals of it have
been deposited by water in the veins passing through the limestones
and schists. Dr. Johnston-Lavis has described in the July number of
the _Geological Magazine_ for 1895 the aqueous deposition at ordinary
temperature of crystals of pyroxene and hornblende, in cavities and
crevices of bones included in an ash-bed of recent date, and in
presence of calcite, apatite, and fluoride of calcium, as in the
Grenville series. This is a modern instance analogous to that suggested
above. Hence all these minerals filling the cavities and canals of
Eozoon may have been deposited by water at ordinary temperatures, and
have no connection with the alteration to which the beds have been
subsequently subjected.
I may add here that a Tertiary glauconite from the Calcaire Grossier
of Paris analysed by Berthier[33] is essentially a serpentine composed
of silicate of iron and magnesia, that Loganite as analysed by Hunt
contains thirty-one per cent, of magnesia, and that Hoskins has
shown[34] that modern glauconites often contain large proportions of
magnesia and equivalent bases.
[Footnote 33: Beudant, _Mineralogie_, xi. 178.]
[Footnote 34: _Geological Magazine_, July, 1895.]
It is also to be observed that independently of volcanic debris the
reports of the _Challenger_ expedition show that in the deep seas
the decay of organic matter causes an alkaline condition of the
sediments leading to the formation of alkaline silicates, while the
presence of decaying volcanic dust furnishes the basis, whether of
iron, alumina, or magnesia, necessary for the making up of glauconite.
I have also suggested that the assimilation by Protozoa making
calcareous skeletons, of the matter of Diatoms or humble plants having
soluble silica in their organization or of silicious Protozoa, and
sponge germs, must set free much soluble silica as a rejected or
excrementitious matter which may contribute to the same result.
It is much more likely that the serpentine of the Laurentian limestones
was produced in these ways than that it resulted from the hydration
of magnesian minerals after the rock was consolidated. In the former
case it would be in the most favourable conditions for mineralizing
organisms as glauconites do in the modern seas. In the latter it would
cause disturbances and changes of volume of which we have no evidence.
We thus find that the chemistry of the modern seas and that relating to
the preservation of fossils of various ages by silicious infiltrations
lends great probability to the belief that serpentine played this
role in the oldest seas, though it would seem that dolomite was more
suitable to the filling of the extremities of the minute tubes and
their finer terminations.[35]
[Footnote 35: I have shown also that in the limestone containing Eozoon
we find layers holding concretions of serpentine alternating with
others holding crystals of dolomite, as if there were at some times
conditions favourable to the deposition of silicate of magnesia, and at
others to that of the carbonate.]
[Illustration: Fig. 43.--Stromatocerium rugosum, Hall, Ordovician.]
(3) Our third question leads to the inquiry in what modern or ancient
marine animals we can find structures akin to those of our supposed
Laurentian fossil. The first analogy which suggested itself to Sir W.
Logan, and a very natural one, was that to the so-called layer-corals
(Figs. 43 to 45) that abound in the Silurian, Ordovician, and Cambrian
rocks, and which though undoubtedly fossil animals, have proved very
difficult to interpret or to assign to any known group. At first
vaguely associated with the true corals, they were subsequently
regarded as probably of more simple character, and as gigantic
Protozoa; and later strong reasons have been assigned for giving them
an intermediate place, as allied to those curious communities of humble
animals possessing simple stomachs and prehensile tentacles (Hydroids)
which form some of the simpler corals (Millepores, etc.), and the
crusts (Hydractiniæ) which cover dead shells and other bodies in the
sea. When examined microscopically, however, they differ very much
among themselves, and it may be that some of them were Hydroids and
some Protozoa.
[Illustration: Fig. 44.--_Structures of Stromatopora._
(_a_) Portion of oblique section, (_b_) Wall with pores, and coated
with crystals of quartz, (_c_) Thickened portion of wall with canals,
(_d_) Laminæ and pillars.]
[Illustration: Fig. 45.--_Tubular Structure of Cœnostroma, Silurian._]
The oldest that we at present know, and consequently the nearest in
time to Eozoon, impress us rather with the latter affinity. They
are the fossils of the genus Cryptozoon of Hall (Fig. 7[36]), which
form great masses filling certain beds of Upper Cambrian age, and
which, when sliced and studied microscopically, are found to consist
of concentric thin laminæ filled in between with a porous mass of
calcareous matter penetrated by an infinity of tortuous tubes. Forms of
this kind have been traced downward into pre-Cambrian beds in Colorado,
and as we shall find in New Brunswick, into the Upper Laurentian itself.
[Footnote 36: See Figs. 7 and 7a, pp. 37, 38; also Fig. 8 and
Microscopic slice, Fig. 59, at end.]
They present, however, structural differences from Eozoon, which
rather conforms to the arrangements found in some Protozoa of smaller
size, and which, under the name of Foraminifera, have abounded in all
geological periods, and are excessively abundant in the modern ocean.
They may be defined as animals composed of a soft and apparently
homogeneous animal jelly known as protoplasm or sarcode. When carefully
examined, however, it is found to have a granular texture and to be
divisible into two layers, an outer and an inner, while it possesses
a little hollow vessel capable of expanding and absorbing the liquid
matter of the enclosing protoplasm, and of contracting so as to expel
its contents. This seems to be the only organ of circulation and
excretion. There are, however, small cells or reproductive bodies in
the interior, varying in number, size, and development in different
forms. The most remarkable property of these creatures is that of
stretching out from the surface of the body threads or projections of
the protoplasm,[37] often of considerable length, and which serve at
once as organs of locomotion and prehension.
[Footnote 37: Known as Pseudopodia.]
[Illustration: _Amœba._]
[Illustration: _Actinophrys._]
From original sketches.
[Illustration: _Biloculina._ A many-chambered Foraminifer. Magnified as
a transparent object.]
[Illustration: _Polystomella._ A spiral Foraminifer. Magnified as an
opaque object.]
Fig. 46.--Recent Protozoa.
These creatures are in some respects the simplest of animals, yet
in other respects they present strange complexities. This is more
especially evident in their tests or coverings, made for the most part
of limestone or calcium carbonate, but sometimes of grains of fine
sand cemented together. These coverings are always perforated with at
least one orifice for the emission of the thread-like processes or
pseudopods, and often with a vast number of small pores for the same
purpose. Sometimes the test or shell is smooth, sometimes beautifully
sculptured externally. Sometimes it consists of a single chamber like
a ball or vase. More often, as the animals increase in size, they
form additional chambers, and the body thus becomes divided into
lobes connected with each other by necks passing through orifices in
the partitions. The chambers are arranged in rows or in spirals, and
in other ways, giving a vast variety of forms, often presenting the
most beautiful patterns executed in the purest white marble, and the
ornamental parts constitute thickenings of the walls giving greater
strength, and are penetrated with microscopic canals communicating with
the soft substance of the animal.
These creatures abound in all parts of the ocean, from the surface
to the greatest depths. The Foraminifera have also existed from
the earliest geological times, and in all the long ages of the
earth's history seem to have retained the same structures and even
ornamentation; so that species from very old geological formations
are often scarcely distinguishable from those now living, and must
have played precisely the same parts in the system of nature. One of
these functions is that of accumulating great thicknesses of calcareous
matter in the sea-bottom.
The manner in which such accumulation takes place we learn from what
is now going on in the ocean, more especially from the result of the
recent deep-sea dredging expeditions. The Foraminifera are vastly
numerous, both near the surface and at the bottom of the sea, and
multiply rapidly; and as successive generations die, their shells
accumulate on the ocean bed, or are swept by currents into banks, and
thus in process of time constitute thick beds of white chalky material,
which may eventually be hardened into limestone. This process is now
depositing a great thickness of white ooze in the bottom of the ocean;
and in times past it has produced such vast thicknesses of calcareous
matter as the chalk and the nummulitic limestone of Europe and the
orbitoidal limestone of America. The chalk, which alone attains a
maximum thickness of 1,000 feet, and, according to Lyell, can be traced
across Europe for 1,100 geographical miles, may be said to be entirely
composed of shells of Foraminifera imbedded in a paste of still more
minute calcareous bodies, the Coccoliths, which are probably products
of marine vegetable life, if not of some animal organism still simpler
than the Foraminifera.
There are, however, some sessile examples of these animals which
attain to larger dimensions than the free and locomotive forms. As an
example of these we may take the _Polytrema_, which forms little hard
red lumps on West Indian corals. Such a creature, beginning life as a
little round spot of protoplasm, almost invisible, and protected with a
little dome of carbonate of lime for the extension of its pseudopods as
it grows in size, adds chamber to chamber in successive tiers till it
assumes an appreciable size, all the chambers communicating with each
other, while the outer ones are perforated with pores for extension of
the pseudopods. In one form (_Carpenteria_) the same end is secured by
leaving an open space in the middle of the conical mass like the crater
of a small volcano. It is with these larger and sessile forms that
we must compare Eozoon, though some of its minute structures rather
resemble those of some smaller types.
All the creatures referred to above, notwithstanding the differences
in their skeletons, resemble each other very closely in their soft
parts, and come under the general name of Foraminifera, a name
having reference to the openings by which the animal matter within
communicates with the water without, for nutrition and respiration.
Such creatures may be regarded as the simplest and most ready media
for the conversion of vegetable matter into animal tissues, and their
functions are almost entirely limited to those of nutrition. Hence it
is likely that they will be able to appear in the most gigantic forms
under such conditions as afford them the greatest amount of pabulum
for the nourishment of their soft parts and for their skeletons. There
is reason to believe, for example, that the occurrence, both in the
chalk and the deep-sea mud, of immense quantities of the minute oval
bodies known as Coccoliths along with Foraminifera, is not accidental.
The Coccoliths appear to be grains of calcareous matter formed in
minute plants adapted to a deep-sea habitat; and these, along with
the vegetable and animal debris constantly being derived from the
death of the living things at the surface, and falling to the bottom,
afford the material both of sarcode and shell. Now if the Laurentian
graphite represents an exuberance of vegetable growth in those old seas
proportionate to the great supplies of carbonic acid in the atmosphere
and in the waters, and if the Eozoic ocean was even better supplied
with carbonate of lime than those Silurian seas whose vast limestones
bear testimony to their richness in such material, we can easily
imagine that the conditions may have been more favourable to a creature
like Eozoon than those of any other period of geological time.
Growing, as Eozoon may be supposed to have done, on the floor of the
ocean, and covering wide patches with more or less irregular masses,
it must have thrown up from its whole surface its pseudopods to seize
whatever floating particles of food the waters carried over it There
is also reason to believe, from the outline of certain specimens, that
it often grew upward in inverted, conical, or club-shaped forms, and
that only the broader patches were penetrated by the tubes or oscula
already mentioned, admitting the sea-water deeply into the substance of
the masses. In this way its growth might be rapid and continuous; but
it does not seem to have possessed the power of growing indefinitely
by new and living layers covering those that had died, in the manner
of some corals. Its life seems to have had a definite termination, and
when that was reached, an entirely new colony had to be commenced.
In this it had more affinity with the Foraminifera, as we now know
them, than with the corals, though practically it had the same power
with the coral polyps of accumulating limestone in the sea-bottom, a
power indeed still possessed by its foraminiferal successors. In the
case of coral limestones, we know that a large proportion of these
consist, not of continuous reefs, but of fragments of coral mixed with
other calcareous organisms, spread usually by waves and currents in
continuous beds over the sea-bottom. In like manner we find in the
limestones containing Eozoon, layers of fragmental matter which shows
in places the characteristic structures, and which evidently represents
the debris swept from the Eozoon masses and reefs by the action of
the waves. With this fragmental matter small rounded organisms to be
noticed in the sequel occur; and while they may be distinct animals
resembling the smaller modern species, they may also be the fry of
Eozoon, or small portions of its acervuline upper surface floated off
in a living state, and possibly capable of living independently and of
founding new colonies.
[Illustration: Fig. 47.--_Slice of Limestone (magnified),_
(_a_) Fragment of Eozoon with canals, (_b_) Fragments of granular
calcite, probably organic, (_c_) Structureless calcite with cleavage
lines (Côte St. Pierre).]
It is only by a somewhat wild poetical licence that Eozoon has been
represented as a "kind of enormous composite animal stretching from the
shores of Labrador to Lake Superior, and thence northward and southward
to an unknown distance, and forming masses 1,500 feet in depth." We may
discuss by-and-by the question of the composite nature of masses of
Eozoon, and we see in the corals evidence of the great size to which
composite animals of a higher grade can attain. In the case of Eozoon
we must imagine an ocean floor more uniform and level than that now
existing. On this the organism would establish itself in spots and
patches. These might finally become confluent over large areas, just
as massive corals do. As individual masses attained maturity and died,
their pores would be filled up with limestone or silicious deposits,
and thus could form a solid basis for new generations, and in this way
limestone to an indefinite extent might be produced. Further, wherever
such masses were high enough to be attacked by the breakers, or where
portions of the sea-bottom were elevated, the more fragile parts of the
surface would be broken up and scattered widely in beds of fragments
over the bottom of the sea, while here and there beds of mud or sand
or of volcanic debris would be deposited over the living or dead
organic mass, and would form the layers of gneiss and other schistose
rocks interstratified with the Laurentian limestone. In this way, in
short, Eozoon would perform a function combining that which corals and
Foraminifera perform in the modern seas; forming both reef limestones
and extensive chalky beds, and probably living both in the shallow and
the deeper parts of the ocean. If in connection with this we consider
the rapidity with which the soft, simple, and almost structureless
sarcode of these Protozoa can be built up, and the probability that
they were more abundantly supplied with food, both for nourishing their
soft parts and skeletons, than any similar creatures in later times, we
can readily understand the great volume and extent of the Laurentian
limestones which they aided in producing. I say aided in producing,
because I would not desire to commit myself to the doctrine that the
Laurentian limestones are wholly of this origin. There may have been
other animal limestone-builders than Eozoon, and there may have been
limestones formed by plants like the modern Nullipores or by merely
mineral deposition.
Its relations to modern animals of its type have been very clearly
defined by Dr. Carpenter. In the structure of its proper wall and its
fine parallel perforations, it resembles the _Nummulites_ and their
allies (Figs. 48, 49); and the organism may therefore be regarded as
an aberrant member of the Nummuline group, which affords some of the
largest and most widely distributed of the fossil Foraminifera. This
resemblance may be seen in Fig. 48.
[Illustration: Fig. 48.--_Section of a Nummulite, from Eocene Limestone
of Syria._
Showing chambers, tubuli, and canals. Compare this and Fig. 49 with
Figs. 28 and 29.]
[Illustration: Fig. 49.--_Portion of Shell of Calcarina._
Magnified, after Carpenter, (_a_) Cells. (_b_) Original cell-wall with
tubuli. (_c_) Supplementary skeleton with canals.]
To the Nummulites it also conforms in its tendency to form a
supplemental or intermediate skeleton with canals, though the canals
themselves in their arrangement more nearly resemble Calcarina, which
is represented in Fig. 49. In its superposition of many layers, and in
its tendency to a heaped-up or acervuline irregular growth it resembles
_Carpenteria_, _Polytrema_ and _Tinoporus_, forms of a different group
in so far as shell-structure is concerned. The large and curious sandy
Foraminifer from the Pacific dredged by Alexander Agassiz, and named
by Goës, _Neusina Agassizi_, may also be mentioned as presenting some
points of resemblance.[38] It may thus be regarded as a composite
type, combining peculiarities now observed in two groups, or it may be
regarded as a representative in the Nummuline series of Polytrema and
Tinoporus in the Rotaline series. At the time when Dr. Carpenter stated
these affinities, it might be objected that Foraminifera of these
families are in the main found in the Modern and Tertiary periods. Dr.
Carpenter has since shown that the curious oval Foraminifer called
_Fusulina_, found in the coal formation, is in like manner allied to
both Nummulites and Rotalines; and still more recently Mr. Brady has
discovered a true Nummulite in the Lower Carboniferous of Belgium. This
group being now fairly brought down to the Palæozoic, we may hope
finally to trace it back to the Primordial, and thus to bring it still
nearer to Eozoon in time.
[Footnote 38: _Bulletin Mus. Comp. Zoology_, vol. xxiii., No. 5, Dec.,
1892.]
Though Eozoon was probably not the only animal of the Laurentian seas,
yet it was in all likelihood the most conspicuous and important as
a collector of calcareous matter, filling the same place afterwards
occupied by the reef-building corals. Though probably less efficient
than these as a constructor of solid limestones, from its less
permanent and continuous growth, it formed wide floors and patches
on the sea-bottom, and when these were broken up vast quantities of
limestone were formed from their debris. It must also be borne in
mind that Eozoon was not everywhere infiltrated with serpentine or
other silicious minerals; quantities of its substance were merely
filled with carbonate of lime, resembling the chamber-wall so closely
that it is nearly impossible to make out the difference, and thus is
likely to pass altogether unobserved by collectors, and to baffle
even the microscopist. Although therefore the layers which contain
well-characterized Eozoon are few and far between, there is reason to
believe that in the composition of the limestones of the Laurentian it
bore no small part; and as these limestones are some of them several
hundreds of feet in thickness, and extend over vast areas, Eozoon
may be supposed to have been as efficient a world-builder as the
Stromatoporæ of the Silurian and Devonian, the Globigerinæ and their
allies in the chalk, or the Nummulites and Miliolites in the Eocene. It
is a remarkable illustration of the constancy of natural causes and of
the persistence of animal types, that these humble Protozoans, which
began to secrete calcareous matter in the Laurentian period, have been
continuing their work in the ocean through all the geological ages,
and are still busy in accumulating those chalky muds with which recent
dredging operations in the deep sea have made us so familiar.
[Illustration: Fig. 50.--_Figures of Archæospherinæ._
(1) Specimen with tubulated wall. (2 to 5) Casts in serpentine, Côte
St. Pierre and Long Lake]
_CONTEMPORARIES OF EOZOON_
VIII
_CONTEMPORARIES OF EOZOON_
The name Eozoon, or Dawn-animal, raises the question whether we
shall ever know any earlier representative of animal life. Here I
think it necessary to explain that in suggesting the name Eozoon for
the earliest fossil, and Eozoic for the formation in which it is
contained, I had no intention to affirm that there may not have been
precursors of the Dawn-animal. By the similar term. Eocene, Lyell
did not mean to affirm that there may not have been modern types in
the preceding geological periods: and so the dawn of animal life may
have had its grey or rosy breaking at a time long anterior to that in
which Eozoon built its marble reefs. When the fossils of this early
auroral time shall be found, it will not be hard to invent appropriate
names for them. There are, however, two reasons that give propriety
to the name in the present state of our knowledge. One is, that the
Laurentian rocks are absolutely the oldest that have yet come under
the notice of geologists, and at the present moment it seems extremely
improbable that any older sediments exist, at least in a condition to
be recognised as such. The other is that Eozoon, as a member of the
group Protozoa, of gigantic size and comprehensive type, and oceanic in
its habitat, is as likely as any other creature that can be imagined
to have been the first representative of animal life on our planet.
Vegetable life may have preceded it, nay probably did so by at least
one great creative æon, and may have accumulated previous stores of
organic matter; but if any older forms of animal life existed, it is
certain at least that they cannot have belonged to much simpler or more
comprehensive types. It is also to be observed that such forms of life,
if they did exist, may have been naked protozoa, which may have left no
sign of their existence except a minute trace of carbonaceous matter,
and perhaps not even this.
But if we do not know, and perhaps are not likely to know, any
animals older than Eozoon, may we not find traces of some of its
contemporaries, either in the Eozoon limestones themselves, or other
rocks associated with them? Here we must admit that a deep-sea
Foraminiferal limestone may give a very imperfect indication of the
fauna of its time. A dredger who should have no other information as
to the existing population of the world, except what he could gather
from the deposits formed under several hundred fathoms of water,
would necessarily have very inadequate conceptions of the matter. In
like manner a geologist who should have no other information as to
the animal life of the Mesozoic ages than that furnished by some of
the thick beds of white chalk, might imagine that he had reached a
period when the simplest kinds of protozoa predominated over all other
forms of life; but this impression would at once be corrected by the
examination of other deposits of the same age: so our inferences as to
the life of the Laurentian from the contents of its oceanic limestones
may be very imperfect, and it may yet yield other and various fossils.
Its possibilities are, however, limited by the fact that before we
reach this great depth in the earth's crust, we have already left
behind in much newer formations all traces of animal life except a
few of the lower forms of aquatic invertebrates; so that we are not
surprised to find only a limited number of living things, and those of
very low type. Do we then know in the Laurentian even a few distinct
species, or is our view limited altogether to Eozoon Canadense? In
answering this question, we must bear in mind that the Laurentian
itself was of vast duration, and that important changes of life may
have taken place even between the deposition of the Eozoon limestones
and that of those rocks in which we find the comparatively rich fauna
of the Primordial age. This subject was discussed by the writer as
early as 1865, and I may repeat here what could be said in relation to
it at that time:--
"In connection with these remarkable remains, it appeared desirable to
ascertain, if possible, what share these or other organic structures
may have had in the accumulation of the limestones of the Laurentian
series. Specimens were therefore selected by Sir W. E. Logan, and
slices were prepared under his direction. On microscopic examination,
a number of these were found to exhibit merely a granular aggregation
of crystals, occasionally with particles of graphite and other foreign
minerals, or a laminated mixture of calcareous and other matters, in
the manner of some more modern sedimentary limestones. Others, however,
were evidently made up almost entirely of fragments of Eozoon, or of
mixtures of these with other calcareous and carbonaceous fragments
which afford more or less evidence of organic origin. The contents of
these organic limestones may be considered under the following heads:--
1. Remains of Eozoon.
2. Other calcareous bodies, probably organic.
3. Objects imbedded in the serpentine.
4. Carbonaceous matters.
"(1) The more perfect individuals of Eozoon do not constitute the mass
of any of the larger specimens in our collections; but considerable
portions of some of them are made up of material of similar minute
structure, destitute of lamination, and irregularly arranged. Some of
this material gives the impression that there may have been organisms
similar to Eozoon, but growing in an irregular or acervuline manner
without lamination. Of this, however, I cannot be certain; and, on the
other hand, there is distinct evidence of the aggregation of fragments
of Eozoon in some of these specimens. In some they constitute the
greater part of the mass. In others they are imbedded in calcareous
matter of a different character, or in serpentine or granular pyroxene.
In most of the specimens the cells of the fossils are more or less
filled with these minerals; and in some instances it would appear that
the calcareous matter of fragments of Eozoon has been in part replaced
by serpentine."
[I may add here that in the limestone at Côte St. Pierre there are in
some of the beds successive laminæ with grains of serpentine and others
with crystals of dolomite, and that both contain fragments of Eozoon.
It thus seems as if the magnesia associated with the limestone, at some
stages of deposition took the form of silicate, and in others that of
carbonate. I may also observe here that I have detected fragments of
Eozoon in Laurentian limestone from New Brunswick, from Chelmsford in
Massachusetts, from Warren County, New York, from Brazil, and from the
Alps.]
"(2) Intermixed with the fragments of Eozoon above referred to are
other calcareous matters apparently fragmentary. They are of various
angular and rounded forms, and present several kinds of structure. The
most frequent of these is a strong lamination varying in direction
according to the position of the fragments, but corresponding, as
far as can be ascertained, with the diagonal of the rhombohedral
cleavage. This structure, though crystalline, is highly characteristic
of crinoidal remains when preserved in altered limestones. The more
dense parts of Eozoon, destitute of tubuli, also sometimes show
this structure, though less distinctly. Other fragments are compact
and structureless, or show only a fine granular appearance; and
these sometimes include grains, patches, or fibres of graphite. In
Cambro-Silurian limestones, fragments of corals and shells which have
been partially infiltrated with bituminous matter, show a structure
like this. On comparison with altered organic limestones of the
Cambro-Silurian system, these appearances would indicate that, in
addition to the debris of Eozoon, other calcareous structures, more
like those of crinoids, corals, and shells, have contributed to the
formation of the Laurentian limestones.
"(3) In the hydrous silicate (Loganite) filling the chambers of a
large specimen of Eozoon from Burgess, there are numerous small pieces
of foreign matter; and the silicate itself is laminated, indicating
its sedimentary nature. Some of the included fragments appear to be
carbonaceous, others calcareous; but no distinct organic structure
can be detected in them. There are, however, in the Loganite, many
minute silicious grains of a bright green colour, resembling green-sand
concretions; and the manner In which these are occasionally arranged
in lines and groups suggests the supposition that they may possibly
be casts of the interior of minute Foraminiferal shells. They may,
however, be concretionary in their origin (Fig. 51).
[Illustration: Fig. 51.--Archæospherinæ from Burgess Eozoon. Grains
included in Loganite.
(Magnified.)]
"(4) In some of the Laurentian limestones submitted to me by Sir W. E.
Logan, and in others from Arnprior on the Ottawa, there are fibres and
granules of carbonaceous matter which do not conform to the crystalline
structure, and present appearances quite similar to those which in
more modern limestones result from the decomposition of the algæ, etc.
Though retaining mere traces of organic structure, little doubt would
be entertained as to their vegetable origin if they were found in
fossiliferous limestones. In limestones of Upper Laurentian age, near
St. John, New Brunswick, more distinct fibres occur, and associated
with these beds Matthew has found what seem to be spicules of sponges,
some simple and others hexactinelled like those of Protospongia of the
Cambrian.
Though the abundance and wide distribution of Eozoon, and the important
part it seems to have acted in the accumulation of limestone, indicate
that it was one of the most prevalent forms of animal existence
in the seas of the Laurentian period, the non-existence of other
organic beings is not implied. On the contrary, independently of the
indications afforded by the limestones themselves, it is evident that
in order to the existence and growth of these large Rhizopods, the
waters must have swarmed with more minute animal or vegetable organisms
on which they could subsist. On the other hand, though this is a less
certain inference, the dense calcareous skeleton of Eozoon may indicate
that it also was liable to the attacks of animal enemies. It is also
possible that the growth of Eozoon or the deposition of the serpentine
and pyroxene in which its remains have been preserved, or both, may
have been connected with certain oceanic depths and conditions, and
that we have as yet revealed to us the life of only certain stations in
the Laurentian seas. Whatever conjectures we may form on these more
problematic points, the observations above detailed appear to establish
the following conclusions:--
First, that in the Laurentian period, as in subsequent geological
epochs, the Rhizopods were important agents in the accumulation of
beds of limestone; and secondly, that in this early period these low
forms of animal life attained to a development, in point of magnitude
and complexity, unexampled, in so far as yet known, in the succeeding
ages of the earth's history. This early culmination of the Rhizopods is
in accordance with one of the great laws of the succession of living
beings, ascertained from the study of the introduction and progress of
other groups; and, should it prove that these great Protozoans were
really the dominant type of animals in the Laurentian period, this fact
might be regarded as an indication that in these ancient rocks we may
actually have the records of the first appearance of animal life on our
planet.
With reference to the first of the above heads, I have now to state
that it seems quite certain that the upper and younger portions of
the masses of Eozoon often passed into the acervuline form, and the
period in which this change took place seems to have depended on
circumstances. In some specimens there are only a few regular layers,
and then a heap of irregular cells. In other cases a hundred or more
regular layers were formed; but even in this case little groups of
irregular cells occurred at certain points near the surface. I have
also found some masses clearly not fragmental which consist altogether
of acervuline cells. A specimen of this kind is represented in Fig. 52.
It is oval in outline, enclosed in a nodule of serpentine, about three
inches in length, wholly made up of rounded or cylindrical cells, the
walls of which have a beautiful tubular structure, but there is little
or no supplemental skeleton. Whether this is a portion accidentally
broken off from the top of a mass of Eozoon, or a peculiar varietal
form, or a distinct species, it would be difficult to determine. In
the meantime I have described it as a variety, "_acervulina_" of the
species Eozoon Canadense. It admits of comparison with a fragment
figured by Dr. Carpenter, which he compares with the chamberlets and
tubes of _Nummulites lævigata_ of the Eocene.[39] Another variety
also, from Petite Nation, shows extremely thin laminæ, closely placed
together and very massive, and with little supplemental skeleton. This
may be allied to the last, and may be named variety "_minor_."[40]
[Footnote 39: _Proceedings of Geological Society_, 1875.]
[Footnote 40: _Annals and Magazine of Natural History_, Sen 4, vol.
xiii. p. 457.]
All this, however, has nothing to do with the layers of fragments of
Eozoon which are scattered through the Laurentian limestones. In these
the fossil is sometimes preserved in the ordinary manner, with its
cavities filled with serpentine, and the thicker parts of the skeleton
having their canals filled with this substance. In this case the
chambers may have been occupied with serpentine before it was broken
up. At St. Pierre there are distinct layers of this kind, from half an
inch to several inches in thickness, regularly interstratified with
the ordinary limestone. In other layers no serpentine occurs, but the
interstices of the fragments are filled with crystalline dolomite or
magnesian limestone, which has also penetrated the canals; and there
are indications, though less manifest, that some at least of the layers
of pure limestone are composed of fragmental Eozoon.
[Illustration: Fig. 52.--_Acervuline Variety of Eozoon, Côte St.
Pierre._
(_a_) General form, half natural size. (_b_) Portion of cellular
interior, magnified, showing the course of the tubuli.]
[Illustration: Fig. 53.--_Archæospherinæ from Côte St. Pierre._
(_a_) Specimens dissolved out by acid, the lower one showing interior
septa. (_b_) Specimens seen in section.]
In the Laurentian limestone of Wentworth, belonging apparently to the
same band with that of St. Pierre, there are many small rounded pieces
of limestone, evidently the debris of some older rock, broken up and
rounded by attrition. In some of these fragments the structure of
Eozoon may be plainly perceived. This shows that still older limestones
composed of Eozoon were at that time undergoing waste, and carries our
view of the existence of this fossil back to the very beginning of the
Grenville series of the Laurentian.
With respect to organic fragments not showing the structure of Eozoon,
I have not as yet been able to refer these to any definite origin. Some
of them may be simply thick portions of the shell of Eozoon with their
pores filled with calcite, so as to present a homogeneous appearance.
Others have much the appearance of fragments of such Primordial forms
as _Archæocyathus_, now usually regarded as corals or sponges; but
after much careful search, I have thus far been unable to say more than
I could say in 1865.
It is different, however, with the round cells infiltrated with
serpentine and with the silicious grains included in the loganite.
Fig. 53 shows such bodies found mixed with fragmental Eozoon and in
separate thin layers at Côte St. Pierre. In Fig. 51, I have shown
some of the singular grains found in the loganite occupying the
chambers of Eozoon from Burgess, and in Fig. 54 some remarkable forms
of this kind found in the limestones of Long Lake and Wentworth. All
these, I think, are essentially of the same nature, namely, chambers
originally invested with a tubulated wall like Eozoon, and aggregated
in groups, sometimes in a linear manner, sometimes spirally, like those
Globigerinæ which constitute the mass of modern deep-sea dredgings and
also of the chalk.
[Illustration: Fig. 54.--_Archæospherinæ from Long Lake Limestone._]
(Magnified.)
(_a_) Single cell, showing tubulated wall. (_b, c_) Portions of same
more highly magnified, (_d_) Casts decalcified, and showing casts of
tubules.
These bodies occur dispersed in the limestone, arranged in thin layers
parallel to the bedding or sometimes in the large chamber-cavities of
Eozoon. They are so variable in size and form that it is not unlikely
they may be of different origins. The most probable of these may be
thus stated. First, they may in some cases be the looser superficial
parts of the surface of Eozoon broken up into little groups of cells.
Secondly, they may be few-celled germs or buds given off from Eozoon.
This would correspond with what Carpenter, and more recently Brady and
Lester, have observed in the case of some of the larger of the modern
Foraminifera. Thirdly, they may be smaller Foraminifera, structurally
allied to Eozoon, but in habit of growth resembling those little
globe-shaped forms which, as already stated, abound in chalk and in the
modern ocean. The latter view I should regard as highly probable in the
case of many of them; and I have proposed for them, in consequence, and
as a convenient name, _Archæospherinæ_ or ancient spherical animals.
Carbonaceous matter is rare in the true Eozoon limestones, and, as
already stated, I would refer the Laurentian graphite or plumbago
mainly to plants.
Dr. Gümbel, the Director of the Geological Survey of Bavaria, is one of
the most active and widely informed of European geologists, combining
European knowledge with an extensive acquaintance with the larger and
in some respects more typical areas of the older rocks in America, and
stratigraphical geology with enthusiastic interest in the microscopic
structures of fossils. He at once, and in a most able manner, took up
the question of the application of the discoveries in Canada to the
rocks of Bavaria. The spirit in which he did so may be inferred from
the following extract:--
"The discovery of organic remains in the crystalline limestones of the
ancient gneiss of Canada, for which we are indebted to the researches
of Sir William Logan and his colleagues, and to the careful microscopic
investigations of Drs. Dawson and Carpenter, must be regarded as
opening a new era in geological science.
"This discovery overturns at once the notions hitherto commonly
entertained with regard to the origin of the stratified primary
limestones, and their accompanying gneissic and quartzose strata,
included under the general name of primitive crystalline schists. It
shows us that these crystalline stratified rocks, of the so-called
primary system, are only a backward prolongation of the chain of
fossiliferous strata; the elements of which were deposited as oceanic
sediment, like the clay-slates, limestones, and sandstones of the
Palæozoic formations, and under similar conditions, though at a time
far more remote, and more favourable to the generation of crystalline
mineral compounds.
"In this discovery of organic remains in the primary rocks, we hail
with joy the dawn of a new epoch in the critical history of these
earlier formations. Already in its light, the primeval geological time
is seen to be everywhere animated, and peopled with new animal forms
of whose very existence we had previously no suspicion. Life, which
had hitherto been supposed to have first appeared in the Primordial
division of the Silurian period, is now seen to be immeasurably
lengthened beyond its former limit, and to embrace in its domain the
most ancient known portions of the earth's crust. It would almost
seem as if organic life had been awakened simultaneously with the
solidification of the earth's crust."
Gümbel has described from limestones of Laurentian age in various parts
of Europe forms referable to Eozoon or to Archæospherinæ, and I have
found fragmental Eozoon in specimens collected by Favre in the supposed
Archæan nucleus of the Alps.
Gümbel also found in the Finnish and Bavarian limestones knotted
chambers, like those of Wentworth above mentioned (Fig. 55), which he
regards as belonging to some other organism than Eozoon; and flocculi
having tubes, pores, and reticulations which would seem to point to the
presence of structures akin to sponges or possibly remains of seaweeds.
These observations Gümbel has extended into other localities in Bavaria
and Bohemia, and also in Silesia and Sweden, establishing the existence
of Eozoon fossils in all the Laurentian limestones of the middle and
north of Europe.
[Illustration: Fig. 55.--_Archæospherinæ from Pargas in Finland._
(After Gümbel.)
(Magnified.)]
Gümbel has further found in beds overlying the older Eozoic series,
and probably of the same age with the Canadian Huronian, a different
species of Eozoon, with smaller and more contracted chambers, and
still finer and more crowded canals. This, which is to be regarded as
a distinct species, or at least a well-marked varietal form, he has
named _Eozoon Bavaricum_ (Fig. 56). Thus this early introduction of
life is not peculiar to that old continent which we sometimes call the
New World, but applies to Europe as well, and Europe has furnished a
successor to Eozoon in the later Eozoic or Huronian period.
[Illustration: Fig. 56.--_Section of Eozoon Bavaricum, with Serpentine,
from the Crystalline Limestone of the Hercynian primitive Clay-slate
Formation at Hohenberg; 25 diameters (probably Huronian)._
(_a_) Sparry carbonate of lime, (_b_) Cellular carbonate of lime, (_c_)
System of tubuli. (_d_) Serpentine replacing the coarser ordinary
variety, (_e_) Serpentine and hornblende replacing the finer variety,
in the very much contorted portions.]
In rocks of this age in America, after long search and much slicing of
limestones, I have hitherto failed to find any decided foraminiferal
remains other than the Tudor and Madoc specimens, which may be of this
age. They are laminated forms resembling Eozoon, but I have reason to
believe that their minute structure more closely resembles that of
Cryptozoon, though it is somewhat obscure. If these are really Huronian
and not Laurentian, the Eozoon from this horizon does not sensibly
differ from that of the Lower Laurentian.
We are indebted to Mr. Matthew, of St. John, New Brunswick, who has so
greatly distinguished himself by his discoveries in the Cambrian of
that region, for some remarkable additions to the contemporaries of
Eozoon. One of these is a laminated body, like Eozoon in its general
appearance, but growing in crowded masses which by mutual pressure
become columnar (Fig. 57). In the best preserved specimens each layer
seems to consist of a thin lamina separated from its neighbours by
a finely granular mass, traversed by innumerable irregular tubes.
This recalls the structure of Cryptozoon of Hall, which, as we have
seen, is found in pre-Cambrian rocks in Colorado, and abounds in the
Upper Cambrian in New York, in Minnesota, and in different parts of
Canada, but Archæozoon differs in its form and habit of growth. If
the Stromatoporæ of the Ordovician and Silurian are hydroids, this
may also be the case with Cryptozoon; but so far as its own structure
is concerned, it approaches most nearly to the fossils known as
Loftusia in the Carboniferous and later formations, and these are
generally regarded as Foraminiferal. We may thus have another giant
Foraminiferal organism which contributed to the building up of rocks in
the Laurentian seas.
[Illustration: Fig. 57.--_Archæozoon Acadiense_, Matthew. _Diagrammatic
transverse and longitudinal sections of a small specimen._
Specimen in Peter Redpath Museum.]
_Pre-Palæozoic Rocks of Southern New Brunswick, as tabulated by
Matthew:--"_
+--+--+------------------------------------------------------------+
| | | Thickness |
| | | Feet. |
| | | Coastal series (or system), 1872.-- |
| | | Grits, hydromicaschists, agillities, etc. |
| | | resembling the Pebidian rocks of Dr. H. |
| | | Hicks 10,000 |
| | | |
| |E | Coldbrook Series (or System), 1865.-- |
| |O | Diorites, felsites, petrosilex, etc.; |
| |Z | resembling the Arvonian rocks of Dr. |
| |O | Hicks. Thickness more than 15,000 |
| |I | |
| |C | Upper series (or system) of Laurentian, 1872. |
|A | | Upper division.--Argillites, |
|R | | limestones, graphitic shales. Fossils. In |
|C | | upper part of the upper limestones of the |
|H | | South basin, fragmental _Eozoon_, observed |
|Æ | | by Sir J. W. Dawson in specimens sent him. In |
|A | | middle of upper limestones in Middle basin, |
|N | | spicules of sponges. In graphitic shale |
| | | of South basin, spicules of _Halichondrites |
| | | graphitiferus_. In lowest limestone of |
| | | the Middle basin, the reef of columnar |
| | | fossils described as Archæozoon 740 |
| | | Middle division.--Quartzites, |
| | | silicious schists, Fossils _Cyathospongia (?) |
| | | eozoica_ near the top of this division 450 |
| | | Lower division.--Limestones and |
| |__| gneisses. No Fossils known 260[41]|
| | | Lower series of Laurentian.-- |
| | | Gneisses, Micaschists, etc ? |
+--+--+------------------------------------------------------------+
[Footnote 41: The above thicknesses are on the authority of Dr. L.
W. Bailey. _Report Progress Geological Survey Canada_, 1879, pp. 10,
D. D., and 21, D. D. Dr. R. W. Ells in the same Report, p. 6, D.,
describes these rocks, sixty miles east of St. John, as one system,
with a thickness of 14,000 feet.]
[Illustration: Fig. 57A.--_Archæozoon Acadiense_, Matthew.
_Horizontal and vertical sections of a group of specimens, reduced._
(From Photographs.)]
This discovery is also of importance as connecting Eozoon through
Cryptozoon with large organisms, probably Protozoa, extending upward to
the top of the Cambrian, and thus forming a link of connection between
the life of the Eozoic and that of the Palæozoic period. Matthew has
also described forms which he regards as spicules of sponges from
the Laurentian of New Brunswick.[42] One of these seems to present
cruciform needles forming square areas, like the Protospongia of
Salter, from the Cambrian. The other has simple elongate needle-like
spicules arranged in bundles. Matthew summarizes the rocks containing
these fossils as in the table on p, 216, in descending order, the
highest bed being below the Etcheminian.[43] The first and second
groups, it will be observed, are equivalent to the Huronian; the third
corresponds to the Grenvillian, and the fourth to the Lower Laurentian.
[Footnote 42: Fuller descriptions of these rocks may be found in _Rep.
Prog. Geol. Surv. of Canada_, 1872, pp. 30, 34, etc.]
[Footnote 43: _Bulletin Nat. Hist. Society of New Brunswick_, 1890
where further details are given as to the fossils.]
_DIFFICULTIES AND OBJECTIONS_
IX
_DIFFICULTIES AND OBJECTIONS_
The active objectors to the animal nature of Eozoon have been few,
though some of them have returned to the attack with a pertinacity and
determination which would lead one to believe that they think the most
sacred interests of science to be dependent on the annihilation of this
proto-foraminifer. I do not propose here to treat of the objections in
detail. I have presented the case of Eozoon on its own merits, and on
these it must stand. I may merely state that the objectors strive to
account for the existence of Eozoon by purely mineral deposition, and
that the complicated changes which they require to suppose are perhaps
the strongest indirect evidence for the necessity of regarding the
structures as organic. The reader who desires to appreciate this may
consult my memoir of 1888.[44]
[Footnote 44: Also Rowney and King's papers in _Journal Geological
Society_, August, 1866; and _Proceedings Irish Academy_, 1870 and
1871.]
I confess that I feel disposed to treat very tenderly the position
of objectors. The facts I have stated make large demands on the
faith of the greater part even of naturalists. Very few geologists
or naturalists have much knowledge of the structure of foraminiferal
shells, or would be able under the microscope to recognise them with
certainty. Nor have they any distinct ideas of the appearances of such
structures under different kinds of preservation and mineralization.
Further, they have long been accustomed to regard the so-called Azoic
or Archæan rocks as not only destitute of organic remains, but as
being in such a state of metamorphism that these could not have been
preserved had they existed. Few, therefore, are able intelligently
to decide for themselves, and so they are called on to trust to the
investigations of others, and on their testimony to modify in a marked
degree their previous beliefs as to the duration of life on our planet.
In these circumstances it is rather wonderful that the researches made
with reference to Eozoon have met with so general acceptance, and
that the resurrection of this ancient inhabitant of the earth has not
aroused more of the sceptical tendency of our age.
It must not be lost sight of, however, that in such cases there may
exist a large amount of undeveloped and even unconscious scepticism,
which shows itself not in active opposition, but merely in quietly
ignoring this great discovery, or regarding it with doubt, as an
uncertain or unestablished point in science. Such scepticism is
especially to be expected on the part of the many enthusiastic students
of petrography who are accustomed to regard rocks merely as mineral
aggregates, and even to have their slices prepared in a manner which
scarcely permits organic remains of present to be distinguished.
Such students should consider that the discovery of Eozoon brings
the rocks of the Laurentian system into more full harmony with the
other geological formations. It explains the origin of the Laurentian
limestones in consistency with that of similar rocks in the later
periods, and in like manner it helps us to account for the graphite
and sulphides and iron ores of these old rocks. It shows us that no
time was lost in the introduction of life on the earth. Otherwise there
would have been a vast lapse of time in which, while the conditions
suitable to life were probably present, no living thing existed to
take advantage of these conditions. Further, it gives a more simple
beginning of life than that afforded by the more complex fauna of the
Cambrian age; and this is more in accordance with what we know of the
slow and gradual introduction of new forms of living things during the
vast periods of Palæozoic time. In connection with this, it opens a
new and promising field of observation in the older rocks; and if this
should prove fertile, its exploration may afford a vast harvest of new
forms to the geologists of the present and coming time. This result
will be in entire accordance with what has taken place before in the
history of geological discovery. I can myself remember a time when the
old and semi-metamorphic sediments constituting the great Cambrian
system were massed together in geological classifications as primitive
or primary rocks, destitute or nearly destitute of organic remains.
The brilliant discoveries of Sedgwick, Murchison, Barrande, and a
host of others, have peopled these once barren regions; and they now
stretch before our wondering gaze in the long vistas of early Palæozoic
life. So we now look out from the Cambrian shore upon the ocean of the
Etcheminian, the Huronian, and the Laurentian--all to us yet almost
tenantless, except for the few organisms which, like stray shells cast
upon the beach, or a far-off land dimly seen in the distance, incite
to further researches, and to the exploration of the unknown treasures
that still lie undiscovered. It would be a suitable culmination of
the geological work of the last half-century, and one within reach at
least of our immediate successors, to fill up this great blank, and to
trace back the Primordial life to the stage of Eozoon, and perhaps even
beyond this, to predecessors which may have existed at the beginning
of the Laurentian, when the earliest sediments of that great formation
were laid down. Vast unexplored areas of Laurentian and Huronian rocks
exist in the Old World and the New. The most ample facilities for
microscopic examination of rocks may now be obtained; and I could wish
that one result of the publication of these pages may be to direct the
attention of some of the younger and more active geologists to these
fields of investigation. It is to be observed also that such regions
are among the richest in useful minerals, and there is no reason why
search for these fossils should not be connected with other and more
practically useful researches. On this subject it will not be out of
place to quote the remarks which I made in one of my earlier papers on
the Laurentian fossils:--
"This subject opens up several interesting fields of chemical,
biological, and geological inquiry. One of these relates to the
conclusions stated by Dr. Hunt as to the probable existence of a
large amount of carbonic acid in the Laurentian atmosphere, and of
much carbonate of lime in the seas of that period, and the possible
relation of this to the abundance of certain low forms of plants and
animals. Another is the comparison already instituted by Professor
Huxley and Dr. Carpenter, between the conditions of the Laurentian and
those of the deeper parts of the modern ocean. Another is the possible
occurrence of other forms of animal life than Protozoa, which I have
stated in my paper of 1864, after extensive microscopic study of the
Laurentian limestones, to be indicated by the occurrence of calcareous
fragments, differing in structure from Eozoon, but at present of
unknown nature. Another is the effort to bridge over, by further
discoveries [similar to those of Cryptozoon and Archæozoon], the gap
now existing between the life of the Lower Laurentian and that of the
Cambrian period. It is scarcely too much to say that these inquiries
open up a new world of thought and investigation, and hold out the
hope of bringing us into the presence of the actual origin of organic
life on our planet, though this may perhaps be found to have been
pre-Laurentian. I would here take the opportunity of repeating that,
in proposing the name Eozoon for the first fossil of the Laurentian,
and in suggesting for the period the name 'Eozoic,' I have by no means
desired to exclude the possibility of forms of life which may have been
precursors of what is now to us the dawn of organic existence. Should
remains of still older organisms be found in those rocks now known to
us only by pebbles in the Laurentian, these names will at least serve
to mark an important stage in geological investigation."
But what if the result of such investigations should be to produce more
sceptics, or to bring to light mineral structures so resembling Eozoon
as to throw doubt upon the whole of the results detailed in these
chapters? I can fancy that this might be the first consequence, more
especially if the investigations were those of persons more conversant
with rocks and minerals than with fossils; but I see no reason to
fear the ultimate results. In any case, no doubt, the value of the
researches hitherto made may be diminished. It is always the fate of
discoverers in Natural Science, either to be followed by opponents who
temporarily or permanently impugn or destroy the value of their new
facts, or by other investigators who push on the knowledge of facts and
principles so far beyond their standpoint that the original discoveries
are cast into the shade. This is a fatality incident to the progress of
scientific work, from which no man can be free; and in so far as such
matters are concerned, we must all be content to share the fate of the
old fossils whose history we investigate, and, having served our day
and generation, to give place to others. If any part of our work should
stand the fire of discussion, let us be thankful. One thing at least
is certain, that such careful surveys as those in the Laurentian rocks
of Canada which led to the discovery of Eozoon, and such microscopic
examinations as those by which it has been worked up and presented to
the public, cannot fail to yield good results of one kind or another.
Already the attention excited by the controversies about Eozoon,
by attracting investigators to the study of various microscopic and
imitative forms in rocks, has promoted the advancement of knowledge,
and must do so still more. For my own part, though I am not content to
base all my reputation on such work as I have done with respect to this
old fossil--which, indeed, was merely an interlude into which I was led
by the urgency of my friend Logan--I am willing at least to take the
responsibility of the results I have announced, whatever conclusions
may be finally reached; and in the consciousness of an honest effort
to extend the knowledge of nature, to look forward to a better fame
than any that could result from the most successful and permanent
vindication of every detail of our scientific discoveries, even if they
could be pushed to a point which no subsequent investigation in the
same difficult line of research would be able to overpass.
Contenting myself with these general remarks, I shall close this
chapter with a short summary of the reasons which may be adduced
in support of the animal nature of Eozoon, prefaced by an ideal
restoration of it in the supposition that it was a rhizopod (Fig. 58).
[Illustration: Fig. 58.--_Restoration of Eozoon as a generalized
Foraminiferal Organism (enlarged)._
Showing endosarc, exosarc, and pseudopods, and the calcareous skeleton
with its canals.]
In doing so, I shall merely sum up the evidence as it has been
presented by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and the author,
in a short and intelligible form; and I shall do so under a few brief
heads, with some explanatory remarks:--
1. The Upper Laurentian of Canada, a rock formation whose distribution,
age, and structure have been carefully worked out in several extensive
districts by the Canadian Survey, is found to contain thick and widely
distributed beds of limestone, related to the other beds in the same
way in which limestones occur in the sediments of other geological
formations. There also occur in the same formation, graphite, iron
ores, and metallic sulphides, in such relations as to suggest the idea
that the limestones as well as these other minerals are of organic
origin.
2. In the limestones are found laminated bodies of definite form and
structure, composed of calcite alternating with serpentine and other
minerals. The forms of these bodies suggested a resemblance to the
Silurian Stromatoporæ, and the different mineral substances associated
with the calcite in the production of similar forms showed that these
were not accidental or concretionary.
3. On microscopic examination, it proved that the calcareous laminæ
of these forms were similar in structure to the shells of modern
and fossil Foraminifera, more especially those of the Rotaline and
Nummuline types, and that the finer structures, though usually filled
with serpentine and other hydrous silicates, were sometimes occupied
with calcite, pyroxene, or dolomite, showing that they must when recent
have been empty canals and tubes.
4. The mode of filling thus suggested for the chambers and tubes of
Eozoon is precisely that which takes place in modern Foraminifera
filled with glauconite, and in Palæozoic crinoids and corals filled
with other hydrous silicates, all more or less chemically allied to
serpentine.
5. The type of growth and structure predicated of Eozoon from the
observed appearances, in its great size, its laminated and acervuline
forms, and in its canal system and tubulation, are not only in
conformity with those of other Foraminifera, but such as might be
expected in a very ancient form of that group.
6. Indications exist of other organic bodies in the limestones
containing Eozoon, and also of the Eozoon being preserved not only in
reefs but in drifted fragmental beds as in the case of modern corals.
7. Similar organic structures have been found in the Laurentian
limestones of Massachusetts, New York, Brazil,[45] and also in those
of various parts of Europe, and Dr. Gümbel has found an additional
species in rocks succeeding the Laurentian.
[Footnote 45: Fragmental; specimens from J. A. Derby, Esq.]
8. The manner in which the structures of Eozoon are effected by the
faulting, development of crystals, mineral veins, and other effects of
disturbance and metamorphism in the containing rocks, is precisely that
which might be expected on the supposition that it is of organic origin.
9. The exertions of several active and able opponents have failed to
show how, otherwise than by organic agency, such structures as those
of Eozoon can be formed, except on the supposition of pseudo-morphism
and replacement, which must be regarded as chemically extravagant,
and which would equally impugn the validity of all fossils determined
by microscopic structure. In like manner all comparisons of these
structures with dendritic and other imitative forms have signally
failed, in the opinion of those best qualified to judge.
Another and perhaps simpler way of putting the case is the
following:--Only four general modes of accounting for the existence
of Eozoon have been proposed. The first is that of Professors King
and Rowney, who regard the chambers and canals filled with serpentine
as arising from the erosion or partial dissolving away of serpentine
and its replacement by calcite. The objections to this are conclusive.
It does not explain the fine tubulation, which has to be separately
accounted for by confounding it, contrary to the observed facts,
with the veins of fibrous serpentine which actually pass through
cracks in the fossil. Such replacement is in the highest degree
unlikely on chemical grounds, and there is no evidence of it in the
numerous serpentine grains, nodules, and bands in the Laurentian
limestones. On the other hand, the opposite replacement, that of
limestone by serpentine, seems to have occurred. The mechanical
difficulties in accounting for the delicate canals on this theory are
also insurmountable. Finally, it does not account for the specimens
preserved in pyroxene and other silicates, and in dolomite and calcite.
A second mode of accounting for the facts is that the Eozoon forms are
merely peculiar concretions. But this fails to account for their great
difference from the other serpentine concretions in the same beds, and
for their regularity of plan and the delicacy of their structure, and
also for minerals of different kinds entering into their composition,
and still presenting precisely the same forms and structures. The third
is that first suggested, I think, by Jullien, and later by Gregory and
Lavis, that the forms are merely banded alternations of calcite with
silicious minerals similar to those observed at the junction of igneous
rocks and limestones. To this it may be replied that there is really
only an apparent resemblance, which, on careful examination, proves
to be illusory; that it does not account for the canals and tubuli,
and that studies of such banded rocks from several regions have been
made by competent observers, who have distinguished these from the
Laurentian Eozoon. The only remaining theory is that of the filling
of cavities by infiltration with serpentine. This accords with the
fact that such infiltration by minerals akin to serpentine exists in
fossils in later rocks. It also accords with the known aqueous origin
of the serpentine nodules and bands, the veins of fibrous serpentine,
and the other minerals found filling the cavities of Eozoon. Even the
pyroxene has been shown by Hunt to exist in the Laurentian in veins
of aqueous origin. The only difficulty existing on this view is how
a calcite skeleton with such chambers, canals, and tubuli could be
formed; and this is solved by the discovery that all these facts
correspond precisely with those to be found in the shells of modern
oceanic Foraminifera. The existence, then, of Eozoon, its structure,
and its relations to the containing rocks and minerals being admitted,
no rational explanation of its origin seems at present possible other
than that advocated in the preceding pages.
If the reader will now turn to the figures in the illustration on the
opposite page (Fig. 59), he will find a selection of examples bearing
on the above arguments and objections. Fig. 1 represents a portion of a
very thin slice of a specimen traversed by veins of fibrous serpentine
or chrysotile, and having the calcite of the walls more broken by
cleavage planes than usual. The portion selected shows a part of one
of the chambers filled with serpentine, which presents the usual
curdled aspect almost impossible to represent in a drawing (_s_). It
is traversed by a branching vein of chrysotile (_s′_), which, where
cut precisely parallel to its fibres, shows clear fine cross lines,
indicating the sides of its constituent prisms, and where the plane of
section has passed obliquely to its fibres, has a curiously stippled or
frowsy appearance.
[Illustration: Fig. 59.--_Figures of various Structures and States of
Preservation._
Fig. 1.--Portion of two laminæ and intervening serpentine, with
chrysotile vein. (_a_) Proper wall tubulated. (_b_) Intermediate
skeleton, with large canals. (_c_) Openings of small chamberlets
filled with serpentine. (_s_) Serpentine filling chamber. (_s¹_)
Vein of chrysotile, showing its difference from the proper wall.
Fig. 2.--Junction of a canal and the proper wall. Lettering as in
Fig. 1.
Fig. 3.--Proper wall shifted by a fault, and more recent chrysotile
vein not faulted. Lettering as in Fig. 1.
Fig. 4.--Large and small canals filled with dolomite.
Fig. 5.--Abnormally thick portion of intermediate skeleton, with
large tubes and small canals filled with dolomite.
]
On either side of the serpentine band is the nummuline or proper wall,
showing under a low power a milky appearance, which, with a higher
power, becomes resolved into a tissue of the most beautiful parallel
threads, representing the filling of its tubuli. Nothing can be more
distinct than the appearances presented by this wall and a chrysotile
vein, under every variety of magnifying power and illumination; and all
who have had an opportunity of examining my specimens have expressed
astonishment that appearances so dissimilar should have been confounded
with each other. On the lower side two indentations are seen in the
proper wall (_c_). These are connected with the openings into small
subordinate chamberlets, one of which is in part included in the
thickness of the slice. At the upper and lower parts of the figure
are seen portions of the intermediate skeleton traversed by canals,
which in the lower part are very large, though from the analogy of
other specimens it is probable that they have in their interstices,
and at their branching extremities, minute canaliculi not visible in
this slice. Fig. 2, from the same specimen, shows the termination of
one of the canals against the proper wall, its end expanding into a
wide disc of sarcode on the surface of the wall, as may be seen in
similar structures in modern Foraminifera. In this specimen the canals
are beautifully smooth and cylindrical, but they sometimes present a
knotted or jointed appearance, especially in specimens decalcified
by acids, in which perhaps some erosion has taken place. They are
also occasionally fringed with minute crystals, especially in those
specimens in which the calcite has been partially replaced with other
minerals. Fig. 3 shows an example of faulting of the proper wall, an
appearance not infrequently observed; and it also shows a vein of
chrysotile crossing the line of fault, and not itself affected by it--a
clear evidence of its posterior origin. Figs. 4 and 5 are examples of
specimens having the canals filled with dolomite, and showing extremely
fine canals in the interstices of the others: an appearance observed
only in the thicker parts of the skeleton, and when these are very well
preserved. These dolomitized portions require some precautions for
their observation, either in slices or decalcified specimens, but when
properly managed they show the structures in very great perfection. The
specimen in Fig. 5 is from an abnormally thick portion of intermediate
skeleton, having unusually thick canals, and referred to in a previous
chapter. Such additional peculiarities and specialties might be
multiplied to any extent from the numerous prepared specimens now in
our collections.
One object which I have in view in thus minutely directing attention
to these illustrations, is to show the nature of the misapprehensions
which may occur in examining specimens of this kind, and at the same
time the certainty which may be attained when proper precautions are
taken. I may add that such structures as those referred to are best
seen in extremely thin slices, and that the observer must not expect
that every specimen will exhibit them equally well. It is only by
preparing and examining many specimens that the best results can be
obtained. It often happens that one specimen is required to show well
one part of the structures, and a different one to show another; and
previous to actual trial, it is not easy to say which portion of the
structures any particular fragment will show most clearly. This renders
it somewhat difficult to supply one's friends with specimens. Really
good slices can be prepared only from the best material and by skilled
manipulators; imperfect slices may only mislead; and rough specimens
may not be properly prepared by persons unaccustomed to the work, or
if so prepared, may not turn out satisfactory, or may not be skilfully
examined. One slice heated in the grinding may show nothing but
cleavage in the calcite layers, while an adjoining one more carefully
prepared may show beautiful canals. These difficulties, however, Eozoon
shares with other specimens in micro-geology, and I have experienced
similar disappointments in the case of fossil wood.
In conclusion of this part of the subject, and referring to the notes
appended to this work for some further details, I would express the
hope that those who have hitherto opposed the interpretation of Eozoon
as organic, and to whose ability and honesty of purpose I willingly
bear testimony, will find themselves enabled to acknowledge at least
the reasonable probability of that interpretation of these remarkable
forms and structures.
_THE ORIGIN OF LIFE_
X
_THE ORIGIN OF LIFE_
The thoughts suggested to the philosophical naturalist by the
contemplation of the dawn of life on our planet are necessarily many
and exciting, and the subject has in it the materials for enabling the
general reader better to judge of some of the theories of the origin of
life agitated in our time. Let us then put Eozoon into the witness-box,
and try to elicit its testimony as to the beginnings of life; supposing
for the moment that it is really an animal, and not a mere pretender;
though even in that case, it might serve to represent the first animal,
whatever it may have been.
Looking down from the elevation of our physiological and mental
superiority, it is difficult to realize the exact conditions in which
life exists in creatures so simple as the Protozoa. There may perhaps
be higher intelligences that find it equally difficult to realize how
life and reason can manifest themselves in such poor houses of clay
as those we inhabit. But placing ourselves near to these creatures,
and entering as it were into sympathy with them, we can understand
something of their powers and feelings. In the first place, it is
plain that they can vigorously, if roughly, exercise those mechanical,
chemical, and vegetative powers of life which are characteristic of
the animal. They can seize, swallow, digest, and assimilate food; and,
employing its albuminous parts in nourishing their tissues, can burn
away the rest in processes akin to our respiration, or reject it from
their system. Like us, they can subsist only on food which the plant
has previously produced; for in this world, from the beginning of time,
the plant has been the only organism which could use the solar light
and heat as forces to enable it to turn the dead elements of matter
into living, growing tissues, and into organic compounds capable of
nourishing the animal. Like us, the Protozoa expend the food which
they have assimilated in the production of animal force, and in doing
so cause it to be oxidized, or burnt away, and resolved again into
dead matter. It is true that we have much more complicated apparatus
for performing these functions, but it does not follow that this gives
us much real superiority, except relatively to the more difficult
conditions of our existence. The gourmand who enjoys his dinner may
have no more pleasure in the act than the Amœba which swallows a
Diatom; and for all that the man knows of the subsequent processes to
which the food is subjected, his interior might be a mass of jelly,
with extemporised vacuoles, like that of his humble fellow-animal. The
workman or the athlete has bones and muscles of vastly complicated
structure, but to him the muscular act is as simple and unconscious a
process as the sending out of a pseudopod to a Protozoon. The clay is
after all the same, and there may be as much credit to the artist in
making a simple organism with varied powers, as a more complex frame
for doing nicer work. It is a weakness of humanity to plume itself on
advantages not of its own making, and to treat its superior gifts as
if they were the result of its own endeavours. The truculent traveller
who illustrated his boast of superiority over the Indian by comparing
his rifle with the bow and arrows of the savage, was well answered by
the question, "Can you make a rifle?" and when he had to answer, "No,"
by the rejoinder, "Then I am at least better than you, for I can make
my bow and arrows." The Amœba or the Eozoon is probably no more than
we its own creator; but if it could produce itself out of vegetable
matter, or out of inorganic substances, it might claim in so far a
higher place in the scale of being than we; and as it is, it can assert
equal powers of digestion, assimilation, and motion, with much less of
bodily mechanism.
In order that we may feel, a complicated apparatus of nerves and
brain-cells has to be constructed and set to work; but the Protozoon,
without any distinct brain, is all brain, and its sensation is simply
direct. Thus vision in these creatures is probably performed in a rough
way by any part of their transparent bodies, and taste and smell are
no doubt in the same case. Whether they have any perception of sound
as distinct from the mere vibrations ascertained by touch, we do not
know. Here also we are not far removed above the Protozoa, especially
those of us to whom touch, seeing, and hearing are mere feelings,
without thought or knowledge of the apparatus employed. We might so far
as well be Amœbas. As we rise higher we meet with more differences.
Yet it is evident that our gelatinous fellow-being can feel pain,
dread danger, desire possessions, enjoy pleasure, and in a simple,
unconscious way entertain many of the appetites and passions that
affect ourselves. The wonder is that with so little of organization it
can do so much. Yet, perhaps, life can manifest itself in a broader
and more intense way where there is little organization; and a highly
strung and complex organism is not so much a necessary condition of
a higher life as a mere means of better adapting it to its present
surroundings. Those philosophies which identify the thinking mind with
the material organism, must seem outrageous blunders to an Amœba on
the one hand, or to an angel on the other, could either be enabled to
understand them; which, however, is not very probable, as they are too
intimately bound up with the mere prejudices incident to the present
condition of our humanity. In any case, the Protozoa teach us how much
of animal function may be fulfilled by a very simple organism, and warn
us against the fallacy that creatures of this simple structure are
necessarily nearer to inorganic matter, and more easily developed from
it than beings of more complex mould.
A similar lesson is taught by the complexity of their skeletons. We
speak in a crude, unscientific way of these animals accumulating
calcareous matter, and building up reefs of limestone. We must,
however, bear in mind that they are as dependent on their food for
the materials of their skeletons as we are, and that their crusts
grow in the interior of the sarcode just as our bones do within our
bodies. The provision even for nourishing the interior of the skeleton
by tubuli and canals is in principle similar to that involved in the
Haversian canals, cells, and canalicules of bone. The Protozoon of
course knows neither more nor less of this than the average Englishman.
It is altogether a matter of unconscious growth. The process in
the Protozoa strikes some minds, however, as the more wonderful of
the two. It is, says an eminent modern physiologist, a matter of
"profound significance" that this "particle of jelly [the sarcode
of a Foramlnifer] is capable of guiding physical forces in such a
manner as to give rise to these exquisite and almost mathematically
arranged structures." Respecting the structures themselves, there is
no exaggeration in this. No arch or dome framed by human skill is more
perfect in beauty or in the realization of mechanical ideas than the
tests of some Foraminifera, and none is so complete and wonderful in
its internal structure. The particle of jelly, however, is a figure of
speech. The body of the humblest Foramlnifer is much more than this.
It is an organism with divers parts, as we have already seen in a
previous chapter, and It is endowed with the mysterious forces of life
which in it guide the physical forces, just as they do in building
up phosphate of lime in our bones, or indeed just as the will of the
architect does in building a palace. The profound significance which
this has, reaches beyond the domain of the physical and vital, even to
the spiritual. It clings to all our conceptions of living things: quite
as much, for example, to the evolution of an animal, with all its parts
from a one-celled germ, or to the connection of brain-cells with the
manifestations of intelligence. Viewed in this way, we may share with
the author of the sentence I have quoted his feeling of veneration in
the presence of this great wonder of animal life, "burning, and not
consumed," nay, building up, and that in many and beautiful forms. We
may realize it most of all in the presence of the organism which was
perhaps the first to manifest on our planet these marvellous powers.
We must, however, here, also, beware of that credulity which makes too
many thinkers limit their conceptions altogether to physical force
in matters of this kind. The merely materialistic physiologist is
really in no better position than the savage who quails before the
thunderstorm, or rejoices in the solar warmth, and seeing no force or
power beyond, fancies himself in the immediate presence of his God. In
Eozoon we must discern not only a mass of jelly, but a being endowed
with that higher vital force which surpasses vegetable life and also
physical and chemical forces; and in this animal energy we must see an
emanation from a Will higher than our own, ruling vitality itself; and
this not merely to the end of constructing the skeleton of a Protozoon,
but of elaborating all the wonderful developments of life that were to
follow in succeeding ages, and with reference to which the production
and growth of this creature were initial steps. It is this mystery of
design which really constitutes the "profound significance" of the
foraminiferal skeleton.
Another phenomenon of animality forced upon our notice by the Protozoa
is that of the conditions of life in animals not individual, as we
are, but aggregative and accumulative in indefinite masses. What, for
instance, the relations to each other of the Polyps, growing together
in a coral mass, of the separate parts of a Sponge, or the separate
cells of a Foraminifer, or of the sarcode mass of an indefinitely
spread out Cryptozoon. In the case of the Polyps, we may believe that
there is special sensation in the tentacles and oral opening of each
individual, and that each may experience hunger when in want, or
satisfaction when it is filled with food, and that injuries to one part
of the mass may indirectly affect other parts, but that the nutrition
of the whole mass may be as much unfelt by the individual Polyps as
the processes going on in our own bones are by us. So in the case of
a large Sponge or Foraminifer, there may be some special sensation in
individual cells, pseudopods, or segments, and the general sensation
may be very limited, while unconscious living powers pervade the whole.
In this matter of aggregation of animals we have thus various grades.
The Foraminifers and Sponges present us with the simplest of all, and
that which most resembles the aggregation of buds in the plant. The
Polyps and complex Bryozoons present a higher and more specialized
type; and though the bilateral symmetry which obtains in the higher
animals is of a different nature, it still at least reminds us of that
multiplication of similar parts which we see in the lower grades of
being. It is worthy of notice here that the lower animals which show
aggregative tendencies present but imperfect indications, or none
at all, of bilateral symmetry. Their bodies, like those of plants,
are for the most part built up around a central axis, or they show
tendencies to spiral modes of growth.
It is this composite sort of life which is connected with the main
geological function of the Foraminifer. While active sensation,
appetite, and enjoyment pervade the pseudopods and external sarcode
of the mass, the hard skeleton common to the whole is growing within;
and in this way the calcareous matter is gradually removed from
the sea-water, and built up in solid reefs, or in piles of loose
foraminiferal shells. Thus it is the aggregative or common life,
alike in Foraminifers as in Corals, that tends most powerfully to the
accumulation of calcareous matter; and those creatures whose life is
of this complex character are best suited to be world-builders, since
the result of their growth is not merely a cemetery of their osseous
remains, but a huge communistic edifice, to which multitudes of lives
have contributed, and in which successive generations take up their
abode on the remains of their ancestors. This process, so potent in the
progress of the earth's geological history, began, as far as we know,
with Eozoon.
Whether, then, in questioning our proto-foraminifer, we have reference
to the vital functions of its gelatinous sarcode, to the complexity and
beauty of its calcareous test, or to its capacity for effecting great
material results through the union of individuals, we perceive that we
have to do, not with a low condition of those powers which we designate
life, but with the manifestation of those powers through the means of a
simple organism; and this in a degree of perfection which we, from our
point of view, would have in the first instance supposed impossible.
If we imagine a world altogether destitute of life, we still might
have geological formations in progress. Not only would volcanoes belch
forth their liquid lavas and their stones and ashes, but the waves and
currents of the ocean and the rains and streams on the land, with the
ceaseless decomposing action of the carbonic acid of the atmosphere,
would be piling up mud, sand, and pebbles in the sea. There might even
be some formation of limestone taking place where springs charged
with bicarbonate of lime were oozing out on the land or the bottom of
the waters. But in such a world all the carbon would be in the state
of carbonic acid, and all the limestone would either be diffused in
small quantities through various rocks or in limited local beds, or
in solution, perhaps as chloride of calcium, in the sea. Dr. Hunt has
given chemical grounds for supposing that the most ancient seas were
largely supplied with this very soluble salt, instead of the chloride
of sodium, or common salt, which now prevails in the sea-water.
Where in such a world would life be introduced? on the land or in the
waters? All scientific probability would say in the latter. The ocean
is now vastly more populous than the land. The waters alone afford
the conditions necessary at once for the most minute and the grandest
organisms, at once for the simplest and for others of the most complex
character. Especially do they afford the best conditions for those
animals which subsist in complex communities, and which aggregate large
quantities of mineral matter in their skeletons. So true is this that
up to the present time all the species of Protozoa and of the animals
most nearly allied to them are aquatic. Even in the waters, however,
plant life, though possibly in very simple forms, must precede the
animal.
Let humble plants, then, be introduced in the waters, and they would
at once begin to use the solar light for the purpose of decomposing
carbonic acid, and forming carbon compounds which had not before
existed, and which independently of vegetable life would never have
existed. At the same time lime and other mineral substances present in
the sea-water would be fixed in the tissues of these plants, either
in a minute state of division, as little grains or Coccoliths, or in
more solid masses like those of the Corallines and Nullipores. In this
way a beginning of limestone formation might be made, and quantities
of carbonaceous and bituminous matter, resulting from the decay of
marine plants, might accumulate in the sea-bottom. The plants have
collected stores of organic matter, and their minute germs, along
with microscopic species, are floating everywhere in the sea. Nay,
there may be abundant examples of those Amœba-like germs of aquatic
plants, simulating for a time the life of the animal, and then
returning into the circle of vegetable life. In these some might see
precursors of the Protozoa, though they are probably rather prophetic
analogues than blood relations. The plant has fulfilled its function
as far as the waters are concerned, and now arises the opportunity
for the animal. In what form shall it appear? Many of its higher
forms, those which depend upon animal food or on the more complex
plants for subsistence, would obviously be unsuitable. Further, the
sea-water is still too much saturated with saline matter to be fit
for the higher animals of the waters. Still further, there may be a
residue of internal heat forbidding coolness, and that solution of free
oxygen which is an essential condition of existence to most of the
modern animals.[46] Something must be found suitable for this saline,
imperfectly oxygenated, tepid sea. Something too is wanted that can aid
in introducing conditions more favourable to higher life in the future.
Our experience of the modern world shows us that all these conditions
can be better fulfilled by the Protozoa than by any other creatures.
They can live now equally in those great depths of ocean where the
conditions are most unfavourable to other forms of life, and in tepid
unhealthy pools overstocked with vegetable matter in a state of
putridity. They form a most suitable basis for higher forms of life.
They have remarkable powers of removing mineral matters from the waters
and of fixing them in solid forms. So in the fitness of things Eozoon
is just what we need, and after it has spread itself over the mud and
rock of the primeval seas, and built up extensive reefs therein, other
animals may be introduced capable of feeding on it, or of sheltering
themselves in its stony masses, and thus we have the appropriate dawn
of animal life.
[Footnote 46: It has been assumed that any temperature over 120°
Fahrenheit would be incompatible with ordinary aquatic life. Still such
life is at least possible in some form up to 200°.]
But what are we to say of the cause of this new series of facts, so
wonderfully superimposed upon the merely vegetable and mineral? Must
it remain to us as an act of creation, or was it derived from some
pre-existing matter in which it had been potentially present ? Science
fails to inform us, but conjectural "phylogeny" steps in and takes its
place. Haeckel, one of the prophets of this new philosophy, waves his
magic wand, and simple masses of sarcode spring from inorganic matter,
and form diffused sheets of sea-slime, from which are in time separated
distinct Amœboid and Foraminiferal forms. Experience, however, gives us
no facts whereon to build this supposition, and it remains neither more
nor less scientific or certain than that old fancy of the Egyptians,
which derived animals from the fertile mud of the Nile.
If we fail to learn anything of the origin of Eozoon, and if its
life-processes are just as inscrutable as those of higher creatures,
we can at least inquire as to its history in geological time. In this
respect we find in the first place that the Protozoa have not had
a monopoly in their profession of accumulators of calcareous rock.
Originated by Eozoon in the old Laurentian time, this process has
been proceeding throughout the geological ages; and while Protozoa,
equally simple with the great prototype of the race, have been and
are continuing its function, and producing new limestones in every
geological period, and so adding to the volume of the successive
formations, new workers of higher grades have been introduced, capable
of enjoying higher forms of animal activity, and equally of labouring
at the great task of continent-building; of existing, too, in seas
less rich in mineral substances than those of the Eozoic time, and for
that very reason better suited to higher and more skilled artists.
It is to be observed in connection with this, that as the work of
the Foraminifers has thus been assumed by others, their size and
importance have diminished, and the grander forms of more recent times
have some of them been fain to build up their hard parts of cemented
sand instead of limestone.
But we further find that, while the first though not the only organic
gatherers of limestone from the ocean waters, they have had to do, not
merely with the formation of calcareous sediments, but also with that
of silicious deposits. The greenish silicate called glauconite, or
green-sand, is found to be associated with much of the foraminiferal
slime now accumulating in the ocean, and also with the older deposits
of this kind now consolidated in chalks and similar rocks. This name
glauconite is, as Dr. Hunt has shown, employed to designate not only
the hydrous silicate of iron and potash, which perhaps has the best
right to it, but also compounds which contain in addition large
percentages of alumina, or magnesia, or both; and one glauconite from
the Tertiary limestones near Paris is said to be a true serpentine,
or hydrous silicate of magnesia.[47] Now the association of such
substances with Foraminifera is not purely accidental. Just as a
fragment of decaying wood, imbedded in sediment, has the power of
decomposing soluble silicates carried to it by water, and parting with
its carbon in the form of carbonic acid, in exchange for the silica,
and thus replacing, particle by particle, the carbon of the wood with
silicon, so that at length it becomes petrified into a flinty mass, so
the sarcode of a Foraminifer can in like manner abstract silica from
the surrounding water or water-soaked sediment. From some peculiarity
in the conditions of the case, however, our Protozoon usually becomes
petrified with a hydrous silicate instead of with pure silica. The
favourable conditions presented by the deep sea for the combination
of silica with bases, as indicated in the reports of the _Challenger_
already referred to, may perhaps account in part for this. But whatever
the cause, it is usual to find fossil Foraminifera with their sarcode
replaced by such material. We also find beds of glauconite retaining
the forms of Foraminifera, while the calcareous tests of these have
been removed, apparently by acid waters.
[Footnote 47: Berthier, quoted by Hunt.]
One consideration which, though conjectural, deserves notice, is
connected with the food of these humble animals. They are known to feed
to a large extent on minute plants, the Diatoms, and other organisms
having silica in their skeletons or cell-walls, and consequently
soluble silicates in their juices. The silicious matter contained
in these organisms is not wanted by the Foraminifera for their own
skeletons, and will therefore be voided by them as an excrementitious
matter. In this way, where Foraminifera greatly abound, there may be
a large production of soluble silica and silicates, in a condition
ready to enter into new and insoluble compounds, and to fill the
cavities and pores of dead shells. Thus glauconite and even serpentine
may, in a certain sense, be a sort of foraminiferal coprolitic matter
or excrement. Of course it is not necessary to suppose that this is
the only source of such materials. They may be formed in other ways,
and especially by the disintegration of volcanic ashes and lapilli
in the sea-bottom; but I suggest this as at least a possible link of
connection.
Whether or not the conjecture last mentioned has any validity, there is
another and most curious bond of connection between oceanic Protozoa
and silicious deposits. Professor Wyville Thompson reports from the
_Challenger_ soundings, that in certain areas of the South Pacific
the ordinary foraminiferal ooze is replaced by a peculiar red clay,
which he attributes to the action of water laden with carbonic
acid, in removing all the lime, and leaving this red mud as a sort
of ash, composed of silica, alumina, and iron oxide. Now this is in
all probability a product of the decomposition and oxidation of the
glauconitic matter contained in the ooze. Thus we learn that when
areas on which calcareous deposits have been accumulated by Protozoa
are invaded by cold arctic or antarctic waters charged with carbonic
acid, the carbonate of lime may be removed, and the glauconite left, or
even the latter may be decomposed, leaving silicious, aluminous, and
other deposits, which may be quite destitute of any organic structures,
or retain only such remnants of them as have been accidentally or by
their more resisting character protected from destruction.[48] In this
way it may be possible that many silicious rocks of the Laurentian
and Primordial ages, which now show no trace of organization, may be
indirectly products of the action of life. In any case it seems plain
that beds of green-sand and similar hydrous silicates may be the
residue of thick deposits of foraminiferal limestone or chalky matter,
and that these silicates may in their turn be oxidized and decomposed,
leaving beds of apparently inorganic clay. Such beds may finally be
consolidated and rendered crystalline by metamorphism, and thus a
great variety of silicated rocks may result, retaining little or no
indication of any connection with the agency of life. We can scarcely
yet conjecture the amount of light which these new facts may eventually
throw on the serpentine and other rocks of the Eozoic age. In the
meantime they open up a noble field to chemists and microscopists.
[Footnote 48: The "red chalk" of Antrim, and that of Speeton, contain
arenaceous Foraminifera and silicious casts of their shells, apparently
different from typical glauconite, and the extremely fine ferruginous
and argillaceous sediment of these chalks may well be decomposed
glauconitic matter like that of the South Pacific. I have found these
beds, the hard limestones of the French Neocomian, and the altered
green-sands of the Alps, very instructive for comparison with the
Laurentian limestones; and they well deserve study by all interested in
such subjects.]
When the marvellous results of recent deep-sea dredgings were first
made known, and it was found that chalky foraminiferal earth is yet
accumulating in the Atlantic, with sponges and sea-urchins resembling
in many respects those whose remains exist in the chalk, the fact was
expressed by the statement that we still live in the chalk period.
Thus stated, the conclusion is scarcely correct. We do not live in the
chalk period, but the conditions of the chalk period still exist in the
deep sea. We may say more than this. To some extent the conditions of
the Laurentian period still exist in the sea, except in so far as they
have been removed by the action of the Foraminifera and other limestone
builders. To those who can realize the enormous lapse of time involved
in the geological history of the earth, this conveys an impression
almost of eternity in the existence of this oldest of all the families
of the animal kingdom.
We are still more deeply impressed with this when we bring into view
the great physical changes which have occurred since the dawn of life.
When we consider that the skeletons of Eozoon contribute to form the
oldest hills of our continents; that they have been sealed up in solid
marble, and that they are associated with hard crystalline rocks
contorted in the most fantastic manner; that these rocks have, almost
from the beginning of geological time, been undergoing waste to supply
the material of new formations; that they have witnessed innumerable
subsidences and elevations of the continents; and that the greatest
mountain chains of the earth have been built up from the sea since
Eozoon began to exist,--we acquire a most profound impression of the
persistence of the lower forms of animal life, and know that mountains
may be removed and continents swept away and replaced, before the least
of the humble gelatinous Protozoa can finally perish. Life may be a
fleeting thing in the individual, but as handed down through successive
generations of beings, and as a constant animating power in successive
organisms, it appears, like its Creator, eternal.
This leads to another and very serious question. How long did lineal
descendants of Eozoon exist, and do they still exist ? We may for
the present consider this question apart from ideas of derivation
and elevation into higher planes of existence of which, in point of
fact, we have no actual evidence. Eozoon as a species and even as a
genus may cease to exist with the Eozoic age, and we have no proof
that any succeeding forms of Protozoa are its modified descendants.
Whatever the causes which produced the earliest Protozoan, they may
have continued more or less to be operative in succeeding ages. As far
as their structures inform us, they may as much claim to be original
creations as Eozoon itself. Still descendants of Eozoon may have
continued to exist, though we have not yet met with them. I should not
be surprised to hear of a veritable specimen being some day dredged
alive in the Atlantic or the Pacific. It is also to be observed that
in animals so simple as Eozoon many varieties may appear, widely
different from the original. In these the general form and habit of
life are the most likely things to change, the minute structures much
less so. We need not, therefore, be surprised to find its descendants
diminishing in size or altering in general form, while the characters
of the fine tubulation and of the canal system would remain. We need
not wonder if any sessile Foraminifer of the Nummuline group should
prove to be a descendant of Eozoon. It would be less likely that a
Sponge or a Foraminifer of the Rotaline type should originate from
it. If one could only secure a succession of deep-sea limestones
with Foraminifers, extending all the way from the Laurentian to the
present time, I can imagine nothing more interesting than to compare
the whole series, with the view of ascertaining the limits of descent
with variation, and the points where new forms are introduced. We have
not yet such a series, but it may be obtained; and as Foraminifera
are eminently cosmopolitan, occurring over vastly wide areas of
sea-bottom, and are very variable, they would afford a better test of
theories of derivation than any that can be obtained from the more
locally distributed and less variable animals of higher grade. I was
much struck with this recently, in examining a series of Foraminifera
from the Cretaceous of Manitoba, and comparing them with the varietal
forms of the same species in the interior of Nebraska, 500 miles to
the south, and with those of the English chalk and of the modern seas.
In all these different times and places we had the same species. In
all they existed under so many varietal forms passing into each other,
that in former times every species had been multiplied into several.
Yet in all, the identical varietal forms were repeated with the most
minute markings alike. Here were at once constancy the most remarkable
and variations the most extensive. If we dwell on the one to the
exclusion of the other, we reach only one-sided conclusions, imperfect
and unsatisfactory. By taking both in connection we can alone realize
the full significance of the facts. We cannot yet obtain such series
for all geological time; but it may even now be worth while to inquire,
What do we know as to any modification in the case of the primeval
Foraminifers, whether with reference to the derivation from them of
other Protozoa or of higher forms of life?
There is no link whatever in geological fact to connect Eozoon with any
of the Mollusks, Radiates, or Crustaceans of the succeeding Palæozoic.
What may be discovered in the future we cannot conjecture; but at
present these stand before us as distinct creations. It would, of
course, be more probable that Eozoon should be the ancestor of some
of the Foraminifera of the Primordial age, but strangely enough it is
very dissimilar from all these except Cryptozoon; and here, as already
stated, the evidence of minute structure fails to a great extent, and
Eozoon Bavaricum of the Huronian age scarcely helps to bridge over the
gap which yawns in our imperfect geological record. Of actual facts,
therefore, we have none; and those evolutionists who have regarded the
dawn-animal as an evidence in their favour, have been obliged to have
recourse to supposition and assumption.
Taking the ground of the derivationist, it is convenient to assume
(1) that Eozoon was either the first or nearly the first of animals,
and that, being a Protozoan of simple structure, it constitutes an
appropriate beginning of life; (2) that it originated from some
unexplained change in the protoplasmic or albuminous matter of some
humble plant, or directly from inorganic matter, or at least was
descended from some creature only a little more simple which had
being in this way; (3) that it had in itself unlimited capacities
for variation and also for extension in time; (4) that it tended to
multiply rapidly, and at last so to occupy the ocean that a struggle
for existence arose; (5) that though at first, from the very nature
of its origin, adapted to the conditions of the world, yet as these
conditions became altered by physical changes, it was induced to
accommodate itself to them, and so to pass into new species and genera,
until at last it appeared in entirely new types in the Cambrian fauna.
These assumptions are, with the exception of the first two, merely
the application to Eozoon of what have been called the Darwinian laws
of multiplication, of limited population, of variation, of change
of physical conditions, and of equilibrium of nature. If otherwise
proved, and shown to be applicable to creatures like Eozoon, of course
we must apply them to it; but in so far as that creature itself is
concerned they are incapable of proof, and some of them contrary to
such evidence as we have. We have, for example, no connecting link
between Eozoon and any form of vegetable life. Its structures are such
as to enable us at once to assign it to the animal kingdom, and if we
seek for connecting links between the lower animals and plants, we have
to look for them in the modern waters. We have no reason to conclude
that Eozoon could multiply so rapidly as to fill all the stations
suitable for it, and to commence a struggle for existence. On the
contrary, after the lapse of untold ages the conditions for the life of
Foraminifers still exist over two-thirds of the surface of the earth.
In regard to variation, we have, it is true, evidence of the wide range
of varieties of species in Protozoa, within the limits of the group,
but none whatever of any tendency to pass into other groups. Nor can
it be proved that the conditions of the ocean were so different in
Cambrian or Silurian times as to preclude the continued and comfortable
existence of Eozoon. New creatures came in which superseded it, and
new conditions more favourable in proportion to these new creatures;
but neither the new creatures nor the new conditions were necessarily
or probably connected with Eozoon, any farther than that it may
have served newer tribes of animals for food, and may have rid the
sea of some of its superfluous lime in their interest. In short, the
hypothesis of evolution will explain the derivation of other animals
from Eozoon if we adopt its assumptions, just as it will in that case
explain anything else; but the assumptions are improbable, and contrary
to such facts as we know.
Eozoon itself, however, bears some negative though damaging testimony
against evolution, and I take the liberty of repeating here a summary
of its imaginary autobiography:--"I, Eozoon Canadense, being a creature
of low organization and intelligence, and of practical turn, am no
theorist, but have a lively appreciation of such facts as I am able
to perceive. I found myself growing upon the sea-bottom, and know not
whence I came. I grew and flourished for ages, and found no let or
hindrance to my expansion, and abundance of food was always floated
to me without my having to go in search of it. At length a change
came. Certain creatures with hard snouts and jaws began to prey on
me. Whence they came I know not; I cannot think that they came from
the germs which I had dispersed so abundantly throughout the ocean.
Unfortunately, just at the same time lime became a little less abundant
in the waters, perhaps because of the great demands I myself had made,
and thus it was not so easy as before to produce a thick supplemental
skeleton for defence. So I had to give way. I have done my best to
avoid extinction; but it is clear that I must at length be overcome,
and must either disappear or subside into a humbler condition, and that
other creatures better provided for the new conditions of the world
must take my place." In such terms we may suppose that this patriarch
of the seas might tell his history, and mourn his destiny, though he
might also congratulate himself on having in an honest way done his
duty and fulfilled his function in the world, leaving it to other and
perhaps wiser creatures to dispute as to his origin and fate, while,
much less perfectly fulfilling the ends of their own existence.
Thus our dawn-animal has positively no story to tell as to his own
introduction or his transmutation into other forms of existence. He
leaves the mystery of creation where it was; but in connection with
the subsequent history of life we can learn from him a little as to
the laws which have governed the succession of animals in geological
time. First, we may learn that the plan of creation has been
progressive, that there has been an advance from the few, low, and
generalized types of the primeval ocean to the more numerous, higher,
and more specialized types of more recent times. Secondly, we learn
that the lower types, when first introduced, and before they were
subordinated to higher forms of life, existed in some of their grandest
modifications as to form and complexity, and occupied very important
places in the economy of the world, and that in succeeding ages, when
higher types were replacing them they were subjected to decay and
degeneracy. Thirdly, we learn that while the species has a limited term
of existence in geological time, any grand type of animal existence,
like that of the Foraminifera or of the Sponges, once introduced,
continues and finds throughout all the vicissitudes of the earth some
appropriate residence. Fourthly, as to the mode of introduction of new
types, or whether such creatures as Eozoon had any direct connection
with the subsequent introduction of mollusks, worms, or crustaceans, it
is altogether silent, nor can it predict anything as to the order or
manner of their introduction.
Had we been permitted to visit the Laurentian seas, and to study
Eozoon and its contemporary Protozoa when alive, it is plain that we
could not have foreseen or predicted from the consideration of such
organisms the future development of life. No amount of study of the
prototypal Foraminifer could have led us distinctly to the conception
of even a Sponge or a Polyp, much less of any of the higher animals.
Why is this? The answer is that the improvement into such higher types
does not take place by any change of the elementary sarcode, either in
those chemical, mechanical, or vital properties which we can study, but
in the adding to it of new structures. In the Sponge, which is perhaps
the nearest type of all, we have the movable pulsating cilium and true
animal cellular tissue, and along with this the spicular or fibrous
skeleton, these structures leading to an entire change in the mode of
life and subsistence. In the higher types of animals it is the same.
Even in the highest we have white blood-corpuscles and germinal matter,
which, in so far as we know, carry on no higher functions of life than
those of an Amœba; but they are now made subordinate to other kinds of
tissue, of great variety and complexity, which never have been observed
to arise out of the growth of any Protozoon. There would be only a
very few conceivable inferences which the highest finite intelligence
could deduce as to the development of future and higher animals. He
might infer that the foraminiferal sarcode, once introduced, might be
the substratum or foundation of other but unknown tissues in the higher
animals, and that the Protozoan type might continue to subsist side
by side with higher forms of living things as they were successively
introduced. He might also infer that the elevation of the animal
kingdom would take place with reference to those new properties of
sensation and voluntary motion in which the humblest animals diverge
from the life of the plant.
It is important that these points should be clearly before our minds,
because there has been current of late among naturalists a loose way
of writing with reference to them, which seems to have imposed on many
who are not naturalists. It has been said, for example, that such an
organism as Eozoon may include potentially all the structures and
functions of the higher animals, and that it is possible that we might
be able to infer or calculate all these with as much certainty as we
can calculate an eclipse or any other physical phenomenon. Now, there
is not only no foundation in fact for these assertions, but it is from
our present standpoint not conceivable that they can ever be realized.
The laws of inorganic matter give no data whence any _à priori_
deductions or calculations could be made as to the structure and
vital forces of the plant. The plant gives no data from which we can
calculate the functions of the animal. The Protozoon gives no data from
which we can calculate the specialties of the Mollusc, the Articulate,
or the Vertebrate. Nor unhappily do the present conditions of life of
themselves give us any sure grounds for predicting the new creations
that may be in store for our old planet. Those who think to build a
philosophy and even a religion on such data are mere dreamers, and have
no scientific basis for their dogmas. They are more blind guides than
our primeval Protozoon himself would be, in matters whose real solution
lies in the harmony of our own higher and immaterial nature with the
Being who is the author of all life--the Father "from whom every family
in heaven and earth is named."
_SOME GENERAL CONCLUSIONS_
XI
_SOME GENERAL CONCLUSIONS_
It may very properly be said that many elements of uncertainty
accompany the questions discussed in the previous chapters, and that
in any case our information is too scanty to warrant any positive
conclusions respecting the origin and earliest history of living
beings. On the other hand, it is well to take stock of what we do know,
and even of what we may reasonably suppose; keeping always in view
the fact that some parts of the problem of the origin of life are at
present insoluble, and may possibly ever continue in that condition. I
may, therefore, profitably close with a summary of what at present seem
to be ultimate facts and principles in this matter, which, if we have
not yet fully attained to, we may at least keep in view as objective
points.
If we admit that Eozoon was an animal, we may either assume that it
was the first introduced on the earth, or that there were earlier and
possibly even simpler creatures. In either case we begin the chain of
animal life with a Protozoan belonging to one of the simpler or more
generalized types of that group, and entitled to the name, both because
of its place in order of time and of rank in the development of the
animal kingdom. If we deny the claims of Eozoon, then the base of our
animal system must for the present be found in the Sponges, Worms,
Foraminifera, and Radiolarians of the Huronian, with the problematical
laminated forms allied to Cryptozoon which seem to occur even in the
Upper Laurentian. Thus in this case the miracle of creation stands
before us in a somewhat more complex form, though greatly less so than
if we had to accept the fauna of the Lower Cambrian as the oldest known.
Under any supposition we cannot hope to get beyond a Protozoan or a
few Protozoa, and we must assume that these could perform perfectly
in their simple way those functions of assimilation, organic
growth, reproduction, sensation, and spontaneous motion, which are
characteristic of these lowest forms of life in the present world.
It is plain, finally, that however simple we imagine this first
possessor of animal life to be, we can have no scientific evidence
of its origination either as an embryo or as an adult. If it had no
living ancestors, we are thus face to face with the problem of the
origin of animal life, either by what has been termed "Abiogenesis" of
a merely physical and fortuitous kind, or by creation. This implies
the previous production of the complex organic compound known as
"Protoplasm," which can, so far as we know, be produced only through
the agency of previously living "Protoplasm" formed by living plants.
We have, therefore, to presuppose the "Abiogenesis" or creation of
plants as predecessors of the animal; but here the same difficulty
meets us. We have next to imagine the spontaneous origin of the
structures of the "Protozoon"--its outer and inner substance, its
nucleus, its pulsating vesicle, and its pseudopods, with its protective
test, and its endowment with vital powers of locomotion, sensation,
assimilation, nutrition, and reproduction. Can we suppose that all this
could come of the chance interaction of physical causes?
At present the production of the living from the non-living seems to
be an impossibility, and the suggestion that at some vastly distant
point of past time physical conditions may have been so different
from those at present existing as to permit spontaneous generation
is of no scientific value. But if the existence of one primitive
Protozoon be granted, what reason have we to believe that it contains
potentially the germ of all the succeeding creatures in the great chain
of life, and the power of co-ordinating these with the successive
physical changes of the geological ages, and so producing the vast and
complicated system of the animal kingdom, extending up to the present
time? In doing so, we either elevate a low form of animal life into
the role of Creator, or fall back on indefinite chance, with infinite
probabilities against us. Reason, in short, requires us to believe in
a First Cause, self-existent, omnipotent and all-wise, designing from
the first a great and homogeneous plan, of which as yet but little
has been discovered by us. Thus any rational scheme of development of
the earth's population in geological time must be, not an agnostic
evolution, but a reverent inquiry into the mode by which it pleased the
Creator to proceed in His great work.
Regarding the matter in this way, there is legitimate scope for science
in tracing the long lines of the different types of ancient animals to
the modern period, and endeavouring to discover which of our so-called
species are original types and which are mere derivative varieties or
races.
It is evident that nothing is gained here by assuming that the whole
geological record is but one of innumerable vast æons of æons, which
have gone on in endless succession. If the world is made to stand
on an elephant, and this on a tortoise, and this on lower forms, it
helps us not at all if the last supporter must stand on nothing. The
difficulty thus postponed only becomes greater; and at the end we have
to imagine, not only life and organization, but even matter and energy
as fortuitously originating or creating themselves, unless produced by
an Almighty Eternal Will.
In pursuing studies of this kind, it is best for the present to content
ourselves with tracing the continuous chains of similar creatures
throughout their extension in geological time, rather than to seek for
connecting links between different lines of being. I endeavoured some
years ago to give a popular outline of this method in a little work
entitled "The Chain of Life in Geological Time."[49]
[Footnote 49: Religious Tract Society, London; Revell Publishing Co.,
New York, Chicago, and Toronto.]
Taking, for example, the earliest Protozoa--the Foraminifera and
Radiolaria--we find two lines of being that in endless varieties, but
with little material change, extend from the earliest periods to the
present time. In successive ages they are represented by families,
genera, and species, which are regarded as distinct, and known by
different names. But these humble animals are very variable, and what
seem to us to be new types may be merely varieties of ancestral forms.
We might even affirm that, for all we know, these two great groups,
as they exist in the present ocean, are lineal descendants of those
that flourished in the Eozoic. We could not prove this, unless we were
to find somewhere a continuous succession of deep-sea deposits that
would show the gradual changes that had occurred. On the other hand, it
is hard to believe that one individual life, so to speak, could have
continued unimpaired to animate successive and increasing masses of
matter in all the vast time extending from the Eozoic to the modern.
It is also at least equally possible that the causes and conditions,
whatever they were, that produced the earliest Protozoa may have acted
again and again in later times, originating new lines of descent with
renewed vitality.
Still, the tracing of these almost incredibly long lines of descent,
if they are such, is a proper, though difficult, subject of scientific
research, whatever may be the result. Something has been attempted in
this direction over limited portions of time; but a vast amount of
patient labour is required before certainty can be attained even in
this department of investigation.
When, on the other hand, we turn to the question whether such lines
of creation or descent have given off branches leading to new types,
as, for instance, from Protozoa to various Crustaceans or Mollusks,
we are entirely destitute of facts, and the statement lately made
by a leading agnostic evolutionist, that "if there is any truth in
the doctrine of evolution, every class of the animal kingdom must be
vastly older than the past records of its appearance on the surface of
the globe," shows us that all the attempts to construct genealogical
trees of the descent of animals are, so far as at present known, quite
visionary. It seems, indeed, that each leading line, as we trace it
back, ends in a blind alley, just where we might suppose that it was
about to pass into another path. This is one reason of the frequent
complaints as to the imperfection of the geological record, and of the
occurrence of "missing links" between different types of being. The
only feasible explanations of this are as yet the suppositions that
the times of introduction of new types may have been unfavourable to
the preservation of their remains, or that the first representatives
of each new group were soft-bodied animals incapable of preservation,
or that they happened to be introduced in regions yet unexplored. But
such accidents could scarcely have been the rule in every case. Even in
relation to man himself, he is still man in all the deposits in which
we can find his remains, and as remote from the apes of his time, in so
far as we know, as he is from those now his contemporaries. It would
seem, in short, as if, ashamed of his humble origin, he had carefully
obliterated his tracks in ascending from his lowly parentage to the
dignity of humanity. But in this he is only following the example of
other animals, his predecessors. We may, as is now constantly done
by evolutionists, fill up these gaps by plausible conjectures; but
this is not a scientific mode of procedure, unless we are content to
regard these conjectures as working hypotheses in aid of researches yet
without result.
It is important that general truths of this kind, impressed upon us by
our descent to the ascertained beginnings of life, should be generally
known, as counteractive to the confident statements so frequently put
forth by enthusiastic speculators and caterers of sensational popular
science. In point of fact, we still occupy the position so long ago
defined by the Apostle Paul, that "God's invisible things from the
creation of the world are clearly seen, being understood by the things
that are made, even His eternal power and divinity"; and the rational
student of nature must still be a pupil in the school of the Almighty
Maker of all things.
Realizing this, we can learn something both as to the dignity and the
humility of our own position. On the one hand we perceive that, in
the whole chain of life, man is the only being in the likeness of the
Maker, fitted to be His deputy in the world, to understand His great
work, and to be the heir of the whole. To man alone He has proclaimed,
"I have said ye are gods, and all of you children of the Most High." To
man alone has He given that "inspiration of the Almighty" which makes
Him the interpreter of nature. On the other hand, when we consider the
long extent in time of the great chain of life before man, and along
with this the vast oceanic area inaccessible to us, yet ever since the
dawn of life teeming with living things innumerable, we find that man
is not even in this little world the only object of Divine care, and we
learn a lesson of humility and of the obligations which rest on us not
only in relation to our fellow-men, but toward our humbler companions
who share with us the care of their Father and ours.
Finally, it is plain that scientific investigation can never bring us
within reach of the absolute origin of life, otherwise than by the
action of a creative Will. Had we stood on the earliest shore, and had
we seen living things appear in the waters where before had been merely
inorganic sand or rock, we should have known as little as we know
to-day of even the proximate causes of this new departure in nature.
If agnostics, we might have said, "this is spontaneous generation";
but such an expression would convey no distinct idea of the nature
of the change which had occurred. It would be merely a cloak for our
ignorance. If theists, we might say, "this is creation"; but we would
have heard no audible fiat, nor seen any process or manipulation, nor
known by what subordinate agency, if any, the result was produced. We
could have given no further explanation than that of the ancient writer
who tells us that God said, "Let the waters swarm with swarmers." We
are told that when these great creative changes occurred, they were
witnessed by higher intelligences than man. "Then the morning stars
sang together, and all the sons of God shouted for joy"[50]; but
even they could perhaps know little more than we, though they might
be better able to trace the future development of the wonderful plan
commenced in the humble Protozoa and culminating in man and immortality.
[Footnote 50: Job xxxviii. 7.]
_APPENDIX_
_APPENDIX_
* * * * *
A. Geological Relations of Eozoon, Archæozoon, etc.
IN the text I have given the arrangement of the pre-Cambrian
rock-formations of Canada, as understood by me at the time of the
delivery of the lectures on which this work is based--an arrangement
which I believe will, in the main, be sustained by the work of the
future, but which cannot as yet be received as final. The work of
Logan and Murray, so far as I have had opportunity to go over their
ground, was admirable; but since their time the progress in the
settlement of the country, the extension of railways, and other means
of communication, and the opening up of mineral deposits have greatly
increased the means of obtaining information, and detailed explorations
have been in progress under the Geological Survey of Canada. At this
moment, under the new Director of the Survey, Dr. G. M. Dawson, much
work is being done in this difficult field, more especially by Dr.
Ells, Dr. Adams, and Mr. Barlow, which it may be hoped will go far
to settle finally the arrangement and distribution of pre-Cambrian
rocks in the Northern part of the American Continent. The maps and
detailed reports representing these explorations are not yet before
the public, but from some preliminary notices which have appeared in
scientific periodicals, it may be inferred that the distinction between
the fundamental gneiss, with its associated igneous products, and the
Upper Laurentian, will become greater than was supposed by Logan. The
Lowest Laurentian or Trembling Mountain series of Logan now represents
a very widely extended basement formation, not so far as can be
ascertained, composed of sedimentary rocks in a metamorphosed state,
but rather of peculiar aqueo-igneous materials, different from the
greater part of those which succeeded them, and associated with varied
and extensive igneous intrusions and _in-meltings_ like those which
Keilhau ascertained long ago in the case of similar rocks in Norway.
The Grenville series, on the other hand, may prove to be a remnant of
an overlying system, originally less extensive or bordering the older
group, and greatly attenuated by the enormous denudation which the
whole region has undergone.
[Illustration: Fig. 60.--_Eozoon Canadense._
Portion of a large specimen. Nature-printed. Showing the laminæ, and
irregular cavities filled with serpentine, perhaps corresponding to the
funnels.]
[_To face p. 296._
It may also be found that the beds of limestone are fewer and their
repetitions more numerous than had been supposed, and that the
Grenville series may be closely associated locally, at least, with
beds hitherto of uncertain age, or associated with the Lower Huronian.
The Huronian proper, on the other hand, may be considerably extended,
and the Kewenian and Animiké series overlying it have already been
ascertained by the Canadian Geological Survey to overlap the Huronian
and Laurentian over vast areas between the great lakes and the Arctic
sea, evidencing much submergence at the close of the Huronian age, and
opening of the Palæozoic. I have noticed in the text the apparently
wide development of deposits of this age over the area of the Rocky
Mountains of Canada, and the corresponding territories in the United
States. There would seem to be in these regions a great thickness of
unaltered sediments between the Lower Cambrian and the crystalline
rocks below, representing the Huronian and Laurentian. In these very
few fossils have yet been found, but they afford perhaps the most
promising field, next to their representatives in Newfoundland and
New Brunswick, for the discovery of the predecessors of the Olenellus
fauna, and the forms of life connecting these with those known in the
Huronian and Laurentian. [For summaries of facts on the last-mentioned
subject, see Report of Dr. G. M. Dawson on the Kamloops map-sheet, in
"Reports of Geological Survey of Canada," vol. vii. B, new series,
pp. 29 _et seq._; also Reports of Dr. C. D. Walcott, U. S. Geological
Survey, vol. xiv., Part I., pp. 103 _et seq._, and Part II., pp. 503
_et seq._]
* * * * *
B. Preservation of Organic Remains by Injection with Hydrous Silicates.
The late Dr. T. Sterry Hunt contributed to the original paper on
Eozoon in the Journal of the Geological Society, a valuable essay on
the mineralization of fossils by serpentine, glauconite, and allied
hydrous silicates. This was in part reprinted in the notes appended
to one of the chapters of "The Dawn of Life," and the subject was
further discussed by Hunt in his invaluable work, "Chemical and
Geological Essays," and more especially in the chapter on the "Origin
of Crystalline Rocks," a chapter which every geologist deserving the
name should study with care.
I give here some of the more important facts referred to by Hunt, and
may add that subsequent microscopic studies have familiarized me with
the occurrence of serpentine and other hydrous silicates as fillings
of the cavities of fossils of various geological ages, insomuch that I
have come to regard the occurrence of these rocks in association with
fossiliferous limestones as among the best available means to enable us
to ascertain the minute structures of shells, Foraminifera, corals, etc.
The following remarks and analyses further illustrate Hunt's views on
the relations of these minerals, with some of the facts on which they
are based:--
"In connection with the Eozoon it is interesting to examine more
carefully into the nature of the matters which have been called
glauconite or green-sand. These names have been given to substances of
unlike composition, which, however, occur under similar conditions,
and appear to be chemical deposits from water, filling cavities in
minute fossils, or forming grains in sedimentary rocks of various ages.
Although greenish in colour, and soft and earthy in texture, it will
be seen that the various glauconites differ widely in composition.
The variety best known, and commonly regarded as the type of the
glauconites, is that found in the green-sand of Cretaceous age in
New Jersey, and in the Tertiary of Alabama; the glauconite from the
Lower Silurian rocks of the Upper Mississippi is identical with it
in composition. Analysis shows these glauconites to be essentially
hydrous silicates of protoxyd of iron, with more or less alumina, and
small but variable quantities of magnesia, besides a notable amount of
potash. This alkali is, however, sometimes wanting, as appears from
the analysis of a green-sand from Kent, in England, by that careful
chemist, the late Dr. Edward Turner, and in another examined by
Berthier, from the calcaire grassier, near Paris, which is essentially
a serpentine in composition, being a hydrous silicate of magnesia and
protoxyd of iron. A comparison of these last two will show that the
loganite, which fills the ancient Foraminifer of Burgess, is a silicate
nearly related in composition.
I. Green-sand from the _calcaire grossier_, near Paris. Berthier (cited
by Beudant, "Mineralogie," ii., 178).
II. Green-sand from Kent, England. Dr. Edward Turner (cited by Rogers,
Final Report, Geol. N. Jersey, page 206).
III. Loganite from the Eozoon of Burgess.
IV. Green-sand, Lower Silurian; Red Bird, Minnesota.
V. Green-sand, Cretaceous, New Jersey.
VI. Green-sand, Lower Silurian, Orleans Island.
The last four analyses are by myself."
I. II. III. IV. V. VI.
Silica 40·0 48·5 35·14 46·58 50·70 50·7
Protoxyd of iron 24·7 22·0 8·60 20·61 22·50 8·6
Magnesia 16·6 3·8 31·47 1·27 2·16 3·7
Lime 3·3 2·49 1·11
Alumina 1·7 17·0 10·15 11·45 8·03 19·8
Potash traces 6·96 5·80 8·2
Soda ·98 ·75 ·5
Water 12·6 7·0 14·64 9·66 8·95 8·5
---- ---- ------ ----- ------ -----
98·9 98·3 100·00 100·00 100·00 100·0
An eminent example is the Silurian limestone of Pole Hill, in New
Brunswick, collected by the late Mr. Robb, of the Geological Survey,
and referred to in the text. I cannot doubt that the silicate injecting
Crinoids and other fossils in this limestone must have been introduced
into these when still recent, and the same remark applies to the
serpentine filling a coral at Lake Chebogamong, and fragments of
corals at Melbourne, in Eastern Canada, and to the similar mineral
filling fossils in a limestone from Llangwyllog, in Wales, and in that
of Maxville, Ohio. Hunt regarded all these as coming essentially into
the same category as regard to general composition and properties. His
analysis of the minerals from Pole Hill and Llangwyllog is as follows:--
Pole Hill. Llangwyllog.
Silica 38·93 35·32
Alumina 28·88 22·66
Protoxyd of iron 18·86 } 24·12 }
Magnesia 4·25 } 6·96 }
Potash 1·69 } 1·40 }
Soda ·48 } 0·67 }
Water 6·91 11·46
Insoluble, quartz
------ -----
100·00 99·89
These minerals approach in composition to the jollyte of Von Kobell,
from which they differ in containing a portion of alkalies, and only
one half as much water. In these respects they agree nearly with the
silicate found by Robert Hoffman, at Raspenau, in Bohemia, where it
occurs in thin layers alternating with picrosmine, and surrounding
masses of Eozoon in the Laurentian limestones of that region;[51]
the Eozoon itself being there injected with a hydrous silicate which
may be described as intermediate between glauconite and chlorite in
composition."
[Footnote 51: _Journ. fur Prakt. Chemie_, Bd., 106 (1869), p. 356.]
In the Welsh specimen the silicate is of a deep green colour, except
where oxidized, and though only 3 per cent, of the whole, is sufficient
to give it an olive colour and slight serpentinous lustre. In the Pole
Hill material, the silicate amounts to 5 per cent, of the whole, and
is of a greyish colour. For some further particulars, see my Paper on
"Fossils Mineralized with Silicates" (_Journal Geological Society_,
February, 1879).
* * * * *
C. Affinities of Eozoon, etc., with more Modern Forms.
Dr. Carpenter, who in admirable papers, which I need not quote
here,[52] has illustrated in detail the structures of Eozoon, and
shown its resemblance to modern forms, places Eozoon as a generalized
type between the Nummuline and Rotaline groups of Foraminifera. It
resembles the former in its fine and complicated tubulations, and some
of the larger sessile forms of the latter in its habit of growth.
More especially, this is near to that of the genera Carpenteria and
Polytrema. In the former, more especially, there are a number of
somewhat flattened calcareous cells with perforated walls, and built
up in a conical form around a central pipe or funnel into which the
apertures of the cells open. A specimen of Carpenteria, enlarged and
having the walls of its cells thickened by a supplemental tubulated
deposit like that of Calcarina, would approach very near to Eozoon.
[Footnote 52: I may specially refer to the following:--
W. B. Carpenter on _Eozoon Canadense_. _Intellectual Observer_, No.
xl., p. 300, 1865. Supplemental notes on the structure and affinities
of _Eozoon Canadense_, _Quart. Journ. Geol. Soc._, Lond. Vol. xxii.,
pp. 219-228, 1866. Notes on the structures and affinities of _Eozoon
Canadense_. _Canad. Nat._, new ser., vol. ii., pp. 111-119, wood-cut,
1865. A reprint from _Quart. Journ. Geol. Soc._, Lond., 1865. Further
observations on the structure and affinities of _Eozoon Canadense_.
In a letter to the President. _Proc. Roy. Soc._, Lond., vol, xxv.,
pp. 503-508, 1867. New observations on _Eozoon Canadense_. _Ann._ and
_Mag. Nat. Hist._, sen 4, vol. xiii., pp. 456-470, one plate, 1874.
Final note on _Eozoon Canadense_. _Ann._ and _Mag. Nat. Hist._, ser.
4, vol. xiv., pp. 371-372, 1874. Remarks on Mr. H. J. Carter's letter
to Prof. King on the structure of the so-called _Eozoon Canadense_.
_Ann._ and _Mag. Nat. Hist._, ser. 4, vol. xiii., pp. 277-284, with two
engravings, 1874.]
The question of the general relation of an organism like Eozoon to
creatures known to us in the modern seas may be answered in either of
two ways:--(1) Functionally or in relation to the position of such
an animal in nature: or (2) Zoologically, or with reference to its
affinities to other animals. With reference to the first consideration,
the answer is plain. The geological function of Eozoon was that of
a collector of calcareous matter from the surrounding waters, then
probably very rich in calcium carbonate, and its role was the same with
that of the Stromatoporæ and calcareous Sponges, smaller Foraminifera
and Corals in latter times. The answer to the second aspect of the
question is less easy. An ordinary observer would at once place
Eozoon with the Stromatoporidæ or Layer-corals, which fill or even
constitute whole beds of limestone in the Cambro-Silurian, Silurian
and Devonian Periods. While, however, Eozoon has been claimed on
the highest authority for the Rhizopods, the Stromatoporæ and their
allies have been regarded as Sponges, or more recently as Hydroids
allied to the Hydractiniæ and Millepores.[53] I confess that I am not
satisfied with these interpretations. I have in my collections large
numbers of encrusting spinous forms, usually called Stromatoporæ, but
which I have long set aside as probably Hydractiniæ. There are other
forms with large vertical tubes which I have regarded as corals,
but some Stromatoporæ seem to be different from either, and I am
still disposed to regard many of them as Protozoa. Bearing in mind,
however, that the Silurian is as remote from the Laurentian on the
one hand as from the Tertiary on the other, we might be prepared to
expect that if the Layer-corals of the Silurian are divisible into
different groups, somewhat widely separated, and we have in the lower
Palæozoic the peculiar type of Cryptozoon, we may be prepared to
expect in the Laurentian much more generalized forms, less susceptible
of classification in our modern systems. If, therefore, Eozoon were
accessible to us in a living state, I should not be surprised to find
that--while perhaps more akin to the calcareous-shelled Rhizopods than
to any other modern group--it may have presented points of resemblance
to Sponges or even to Hydroids, in its skeleton and mode of growth, and
even in the arrangement of its soft parts.
[Footnote 53: See Nicholson and Murie's able memoirs, Publications of
Pal. Soc, 1885.]
Taking this view of its nature and relations, the genus and the
Laurentian species may be characterized as follows:--
_Genus_ Eozoon, _Dawson_.
Foraminiferal skeletons, with irregular and often confluent cells,
arranged in concentric and horizontal laminæ, or sometimes piled in an
acervuline manner. Septal orifices irregularly disposed. Proper wall
finely tubulated. Intermediate skeleton with branching canals.
Eozoon Canadense, _Dawson_.
In inverted conical or rounded masses or thick encrusting sheets,
frequently of large dimensions. Typical structure stromatoporoid, or
with concentric calcareous walls, frequently uniting with each other,
and separating flat chambers, more or less mammillated, and spreading
into horizontal lobes and small chamberlets; chambers often confluent
and crossed by irregular calcareous pillars connecting the opposite
walls. Upper part often composed of acervuline chambers of rounded
forms. Proper wall tubulated very finely. Intermediate skeleton
largely developed, especially at the lower part, and traversed by large
branching canals, often with smaller canals in their interstices. Lower
laminæ and chambers often three millimetres in thickness. Upper laminæ
and chambers one millimetre or less. Age Upper Laurentian and perhaps
Huronian.
_Var._ minor.--Supplemental skeleton wanting, except near the base, and
with very fine canals. Laminæ of sarcode much mammillated, thin, and
separated by very thin walls. Probably a depauperated variety.
_Var._ acervulina.--In oval or rounded masses, wholly acervuline. Cells
rounded; intermediate skeleton absent or much reduced; cell-walls
tubulated. This may be a distinct species, but it closely resembles the
acervuline parts of the ordinary form.
Assuming the Archæospherinæ so abundantly found in the Eozoon
limestones to be distinct organisms, and not mere germs or buds of
Eozoon, they may be thus defined:--
_Genus_ Archæospherina, _Dawson_.
A provisional genus, to include rounded solitary chambers, or
globigerine assemblages of such chambers, with the cell-wall
surrounding them tubulated as in Eozoon, or perhaps in some cases with
simple pores like those of Rotalines. They may be distinct organisms,
or gemmæ, or detached fragments of Eozoon. Some of them much resemble
the bodies figured by Dr. Carpenter, as gemmæ or ova and primitive
chambers of Orbitolites. They are very abundant on some of the strata
surfaces of the limestones at Côte St. Pierre. Age Upper Laurentian.
I may add here the characters of Matthew's new genus, Archæozoon, as
given by him:--
_Genus_ Archæospherina, _Matthew_.
Skeleton composed of thin concentric laminæ convex upward, and having
between them a granular layer filled with minute branching canals.
Archæospherina Acadiense, Matthew.
Habit of growth cylindrical in masses or groups, budding upward. The
microscopic characters are thus given by Matthew[54]:--
"The structures appear to be allied more closely to Cryptozoon than to
Eozoon. The microscopic structure is most easily recognised in the
earthy (as distinguished from the calcareous) layers, and consists
of minute branching canals. Under a one-inch objective the smaller
canals have the appearance of minute threads, which run sometimes for a
distance of two millimetres without branching. The larger canals branch
more frequently and are more sinuous. The canals cross and anastomose
with each other; they run chiefly at right angles to the axis of the
fossil, and appear to branch most in going outward from the centre.
More rarely they ascend from the earthy to the calcareous layer,
branching upward."
[Footnote 54: Bulletin No. ix., Nat. Hist. Soc of New Brunswick, 1890.]
In limestone of the Upper Laurentian, near St. John, New Brunswick.
* * * * *
D. Cryptozoon.
The description above given of Archæozoon very naturally leads us to
consider the allied Cambrian and pre-Cambrian forms known as Cryptozoon.
This remarkable and problematical type was first described by Prof.
James Hall in the Appendix to his Annual Report of 1882 (No. 26). It
is a large massive organism, occurring abundantly on the surface of a
limestone of Calciferous (Upper Cambrian) age at Greenfield, Saratoga
County, New York. The individuals sometimes attain a diameter of two
feet, and are often surrounded by smaller specimens apparently budding
off from them. Like Stromatoporæ, they consist of concentric laminæ,
but these are concave upward, giving a bowl-shaped form to the summits
of the individuals. Prof Hall describes them as "made up of irregular
concentric laminæ of greater or less density, and of very unequal
thickness. The substance between the concentric lines in well-preserved
specimens is traversed by numerous minute irregular canaliculi which
branch and anastomose without regularity. The central portion of
the masses is usually filled with crystalline granular and Oolitic
material, and many specimens show the intrusion of these extraneous and
inorganic substances between the laminæ."
Professor Hall having kindly presented some good specimens to the Peter
Redpath Museum, I have had sections made, and have thus been able to
verify his description, and to compare the structures with those of
some of the more ancient Stromatoporoid specimens in our collections,
including the Archæozoon from New Brunswick, of which Mr. Matthew
has presented a fine slab to the Museum. I have also, through the
kindness of Professor Winchell, been enabled to compare these with his
_Cryptozoon Minnesotense_, and Dr. Walcott has added specimens of his
Stromatoporoid forms from the pre-Cambrian beds of Arizona. It would
appear from these and other specimens in our collections from the
Cambrian and older Ordovician beds, that we have here an ancient type
of Stromatoporoid organism in which the original laminæ seem to have
been thin and coriaceous, without apparent pores or pillars connecting
them with each other, but having between them relatively-thick layers
of fine fragmental matter penetrated by numerous irregularly tortuous
and branching tubes. The laminæ often present a carbonaceous or
chitinous appearance, though frequently replaced by mineral matter,
and the intervening layers show both a calcareous and carbonaceous
substance, with much fine silicious sand often as rounded grains,
and apparently some dolomitic granules. The tubules seem destitute
of any distinct wall, otherwise the whole would resemble on a large
scale the nodular and laminated masses of _Girvanella_, which Wethered
has described as surrounding organic fragments in Silurian and
Carboniferous and Jurassic limestones in England.[55]
[Footnote 55: British Association, Liverpool meeting, 1896.]
The _Streptochetus_ of Seely from the Chazy limestone[56] is evidently
very near to Girvanella, if not generically identical, and I have a
similar species from the Lower Cambrian pebbles in the conglomerates
of the Quebec group. In all these forms, however, the thicker or
intermediate laminæ seem to consist wholly of definite convoluted
tubes, whereas in Cryptozoon the tubes, or tubular perforations, are
separated by a mass of material which in the best preserved specimens
seems to consist of a fibrous stroma including calcareous and silicious
particles. It seems doubtful to what class of beings such a structure
should be referred; but whatever its nature, it evidently had great
powers of growth, and seems to be a very ancient form of life.
[Footnote 56: _Amer. Journ. of Science_, 1885. See Nicholson, "Manual
of Palæontology," ed. of 1889.]
One of the species similar in structure to Hall's type, but budding
out into turbinate branches, was discovered by Mr. E. T. Chambers, of
Montreal, in the Ordovician limestone of Lake St. John, and has been
named _C. boreale_. It differs in structure from Hall's species in
having the tubes less tortuous and more nearly parallel to the laminæ.
In its outline it reminds one of the problematical Eozoon from the
Hastings group at Tudor, Ontario, referred to in the text.
Should time permit, I hope to have all the specimens in our collections
illustrating this interesting and primitive type examined and
described. In the meantime I may merely remark that a near modern
analogue would seem to be the gigantic arenaceous Foraminifer _Neusina
Agassizi_, Goës, dredged by Alexander Agassiz in the Pacific, and
described in the Bulletin of the Museum of Comparative Zoology (Vol.
xxiii., No. 5, 1892). The modern form, it is true, is flat and
foliaceous; but some of the old species approach to this shape, and
if we suppose the little cells of Neusina to represent the tubes of
Cryptozoon, and the carbonaceous matter of the latter to be the remains
of the chitinous stroma seen in some specimens, the general resemblance
will be very close.
The whole subject of these peculiar Stromatoporoid forms extending
from the Upper Cambrian to the Laurentian, deserves a full and careful
investigation, for which I am endeavouring to collect material.
* * * * *
E. Receptaculites and Archæocyathus.
In "The Dawn of Life" (1875), reference was made to the singular and
complicated organisms of the Upper Cambrian and Ordovician systems
known as Receptaculites, which at that time was generally regarded as
foraminiferal, and is still placed by Zittel, in his great work on
Palæontology, among forms doubtfully referable to that group. It has
also been referred to Sponges, though on very uncertain grounds. It has
not, however, so far as I am informed, been traced any farther back
than the Upper Cambrian (Calciferous), and no structural links are
known to connect it with either Eozoon or Archæozoon. For this reason
it was omitted in the text; but I think it well to mention it here, and
to direct attention to it as possibly one of the complex Protozoa which
may be traced far back toward the beginnings of life.[57]
[Footnote 57: Billings, "Palæozoic Times."]
Another primitive and generalized genus mentioned in the text is
_Archæocyathus_ of Billings, whose headquarters seem to be in the Lower
Cambrian, and which may probably be traced farther back.
Mr. Billings described the genus in his "Report on Canadian Fossils"
(1861-64), taking _A. profundus_, from the Lower Cambrian of L'Anse à
Loup, on the Labrador coast, in the first instance, as the type.
A few years later, my attention was attracted to this species by
specimens presented to me by Mr. Carpenter, a missionary on the
Labrador coast, and which Mr. Billings kindly permitted me to compare
with his specimens in the Museum of the Geological Survey, collected
by the late Mr. Richardson, at L'Anse à Loup, in Labrador, in what
were then called Lower Potsdam rocks. Slices of the specimens were
made for the microscope, when it appeared that, though they had
the general aspect of turbinate corals, like Petraia, etc., they
were quite dissimilar in structure, more especially in their porous
outer and inner walls and septa (see Fig. 5, p. 35). Yet they could
scarcely be referred to the group of porous corals known in much later
formations and in the modern seas. Nor could they be referred with
much probability to Sponges, as they were composed of solid calcareous
plates, which, as was evident from their textures, could not have been
originally spicular. One seemed thus shut up to the conclusion that
their nearest alliance was with Foraminifera, and if so, they were
very large and complex forms of that group, consisting of perforated
chambers arranged around a central cavity. I accordingly mentioned them
in this connection in 1875, not as closely related to Eozoon, but as
apparently showing the existence of very complex foraminiferal forms in
the Lower Cambrian.
The specimens thus noticed were altogether calcareous, and were of
the species named _A. profundus_ by Mr. Billings. He had, however,
referred to the same genus silicified specimens from a later formation,
the Calciferous (Upper Cambrian) at Mingan, under the name _A.
Minganensis_, which were subsequently found to be associated with
spicules resembling those of lithistid sponges, and which proved to
be very different from the Lower Cambrian form, and are now referred
to a different genus. The subject had thus become involved in some
confusion, and was left in this state by Mr. Billings on his death.
I therefore asked my friend, Dr. Hinde, of London, to re-examine my
specimens, and at the same time those of the Geological Survey were
placed in his hands by Mr. Whiteaves. Hinde also obtained specimens
from Lower Cambrian rocks in Sardinia, where they seem to be abundant,
and from Spain. He states the results of his examinations very fully
in a paper in the Journal of the _Geological Society of London_.[58] He
retains the original name for the older and calcareous form from L'Anse
à Loup, separating from it, however, another form, _A. Atlanticus_
of Billings's, which is destitute of distinct radiating septa and
acervuline, like the lower part of _A. profundus_. This he names
_Spirocyathus_. The Mingan species he places with Sponges under the
generic name, _Archæoscyphia_. In this Walcott substantially agrees
with Hinde in his "Memoir on the Lower Cambrian Fauna." Both seem to
refer Archæocyathus to corals, though admitting its very exceptional
and anomalous structure. I think, however, we may still be allowed to
entertain some doubts as to the reference to corals, more especially
as the skeleton does not seem to have consisted of aragonite, but of
ordinary calcite, like that of the Foraminifera. It is in any case a
primitive form which seems to be dying out in the Lower Cambrian, and
we may hope that it may be traced into the pre-Cambrian, and may form a
link connecting the Palæozoic with the Eozoic faunas. In my description
of it in "The Dawn of Life" in 1875, I used the following terms:--"To
understand Archæocyathus, let us imagine an inverted cone of carbonate
of lime from an inch or two to a foot in length, with its point planted
in the mud in the bottom of the sea, while its open cup extends upward
into the clear water. The lower part buried in the bottom is composed
of an irregular network of thick calcareous plates, enclosing chambers
communicating with one another. Above this, where the cup expands, its
walls are made up of inner and outer plates, perforated with numerous
round pores in vertical rows, and connected with each other by vertical
partitions also perforated, so as to establish a free communication
of the enclosed radiating chambers with each other, as well as with
the water within and without. Such a structure might no doubt serve as
a skeleton for a coral of somewhat peculiar internal structure, but
it might just as well accommodate a protozoan with chambers for its
sarcode, and pores for emission of pseudopods, both outwardly and by
means of the interior cup, which in that case would represent a funnel
like that of Carpenteria, or one of the tubes of Eozoon."
[Footnote 58: Vol. xlv., 1889, pp. 125 _et seq._]
On the whole, when we consider the magnitude and synthetic character
of such forms as Cryptozoon, Receptaculites, and Archæocyathus,
and their association with generalized types of Crustaceans and
Brachiopods, we can scarcely fail to perceive that at the base of the
Palæozoic we are leaving the reign of the higher marine invertebrates,
and entering on a domain where lower and probably Protozoan forms must
be dominant, and so are getting at least within calculable distance of
the beginnings of life.
* * * * *
F. Pre-Geological Evolution.
Reference is incidentally made in the text to the doctrine implied in
the old notion of successive cataclysms and renewals of the earth,
held by some ancient mythologies and philosophies, and revived in a
slightly different form by Mr. Herbert Spencer, in connection with the
requirements of the Darwinian evolution by natural selection. This
primitive idea was illustrated at considerable length by Professor
Poulton in his address as President of the Zoological Section of the
British Association at its meeting in Liverpool (September, 1896). In
this new and ably presented form, it deserves some notice as excluding
the hope of our finding the beginnings of life in any geological
formations at present known.
Professor Poulton refers to the argument used by Lord Salisbury,
in his address at the Oxford meeting, on the insufficiency of time
for the requirements of the Darwinian evolution. He then discusses
the estimates based by Lord Kelvin and Professor Tait on physical
considerations, and dismisses them as altogether inadequate, though
he admits that Professor George Darwin agrees with Lord Kelvin in
regarding 500 millions of years as the maximum duration of the life of
the sun.
He next takes up the estimates of geologists, and rather blames as too
modest those who ask for the longest time, say 400 millions of years,
for the duration of the habitable earth. He evidently scarcely deems
worthy of notice the more moderate demands of many eminent students of
the earth, who have based far lower estimates on more or less reliable
data of denudation and deposition, and on the thickness of deposits in
connection with their probable geographical extent.
He then proceeds to consider the biological evidence, and dwells on
the number of distinct types represented as far back as the Lower
Cambrian. Independently of the interpretations and explanations
of this great fact, the numerous types there represented, and the
persistence of some of them to the present day, give an almost
overwhelming impression of the vast duration of organisms in time. In
connection with the supposed slow and gradual process of evolution,
this naturally leads to the conclusion that "the whole period in which
the fossiliferous rocks were laid down must be multiplied several times
for this later history (that of the higher groups of animals alone).
The period thus obtained requires to be again increased, and perhaps
doubled for the earlier history." Ordinary geologists naturally stand
aghast at such demands, and inquire if they are seriously put forth,
and if it would not be wise to hesitate before accepting a theory on
behalf of which such drafts on time must be made. The late Edward
Forbes once humorously defined a geologist to be "an amiable enthusiast
who is happy and content if you will give him any quantity of that
which other men least value, namely, past time." But had this great
naturalist lived to "post-Darwinian" times, he might have defined a
Darwinian biologist to be an insatiable enthusiast, who feels himself
aggrieved if not supplied with infinity itself, wherein to carry on
the processes of his science. Seriously however, the necessity for
indefinitely protracted time does not arise from the facts, but from
the attempt to explain the facts without any adequate cause, and to
appeal to an infinite series of chance interactions apart from a
designed plan, and without regard to the consideration, that we know of
no way in which, with any conceivable amount of time, the first living
and organized beings could be spontaneously produced from dead matter.
It is this last difficulty which really blocks the way, and leads to
the wish to protract indefinitely an imaginary process, which must end
at last in an insuperable difficulty.
Were Evolutionists content to require a reasonable time for the
development of life, and to assign this to an adequate cause, they
might see in the reduction of living things in the pre-Cambrian ages to
few and generalized or synthetic types, evidence of an actual approach
to the beginnings of life, and beyond this to a condition of the earth
in which life would be impossible.
* * * * *
G. Controversies Respecting Eozoon.
In the text (Chapter IX.) I have referred in a cursory manner to these,
but have felt that it would be unprofitable to fight the old battles
over again, except in so far as the objections raised have suggested
new lines of study and investigation. The old objections of Messrs.
Rowney, King and Carter were conclusively replied to by the late Dr.
Carpenter. The later criticisms of Möbius in his elaborated memoir
in "Palæontographica" were in appearance more formidable; but he had
evidently entered on the question with imperfect material, and a very
defective conception of its extent and meaning. His treatment of it was
also marked by unfairness to those who had previously worked at the
subject, and by that narrow specialism and captious spirit for which
German naturalists are too deservedly celebrated. The difficulties he
raised were met at the time, more especially in articles by the present
writer in the American _Journal of Science_, and in the Canadian
Naturalist. Möbius, I have no doubt, did his best from his special
and limited point of view; but it was a crime which science should
not readily pardon or forget, on the part of editors of the German
periodical, to publish and illustrate as scientific material a paper
which was so very far from being either fair or adequate.
The later objections of Gregory and Lavis are open to similar criticism
as imperfect and partial, and as confounding Eozoon with mineral
structures which previous writers had carefully distinguished from it.
I have stated these points in letters to _Nature_ and to the Council
of the Dublin Academy, and have also re-stated the evidence bearing on
the animal nature of Eozoon in a series of papers in the Geological
Magazine for 1895. I may add here, as apposite to the present condition
of the matter, a few remarks referring to the appearance of Eozoon
in Dr. Dallinger's new edition of Carpenter's great work on the
Microscope,[59] and more especially to his retaining unchanged the
description of _Eozoon Canadense_, as a monument of an important
research up to a certain date, while adding a note with reference to
the later criticisms of Mr. Gregory.
[Footnote 59: _Nature_, March 17, 1892.]
Dr. Carpenter devoted much time to the study of Eozoon, and brought
to bear on it his great experience of foraminiferal forms, and his
wonderful powers of manipulating and unravelling difficult structures.
After having spent years in studying microscopic slices of Eozoon and
the limestones in which it occurs, I have ever felt new astonishment
when I saw the manner in which, by various processes of slicing and
etching, and by dexterous management of light, he could bring out
the structure of specimens often very imperfect. Not long before Dr.
Carpenter's death, I had an opportunity to appreciate this in spending
a few days with him in studying his more recently acquired specimens,
some of them from my own collections, and discussing the new points
which they exhibited, and which unhappily he did not live to publish.
Some of these new facts, in so far as they related to specimens in our
cabinet here, have since that time been noticed in my _résumé_ of the
question in the "Memoirs of the Peter Redpath Museum," 1888.
Those who know Dr. Carpenter's powers of investigation will not be
astonished that later observers, without his previous preparation
and rare insight, and often with only few and imperfect specimens,
should have failed to appreciate his results. One is rather surprised
that some of them have ventured to state with so great confidence
their own negative conclusions in a matter of so much difficulty,
and requiring so much knowledge of organic structures in various
states of mineralization. For myself, after working fifty years at
the microscopic examination of fossils and organic rocks, I feel more
strongly than ever the uncertainties and liabilities to error which
beset such inquiries.
As an illustration in the case of Eozoon: since the publication of my
memoir of 1888, which I had intended to be final and exhaustive as
to the main points in so far as I am concerned, I have had occasion
to have prepared and to examine about 200 slices of Eozoon from new
material; and while most of these have either failed to show the minute
structures or have presented nothing new, a few have exhibited certain
parts in altogether unexpected perfection, and have shown a prevalence
of injection of the canal system by dolomite not previously suspected.
I have also observed that unsuitable modes of preparation, notably some
of those employed in the preparation of ordinary petrological slices,
may fail to disclose organic structures in crystalline limestones when
actually present. Since that publication also, the discoveries of Mr.
Matthew in the Laurentian of New Brunswick, and the further study of
the singular Cambrian forms of the type of Cryptozoon, have opened up
new fields of inquiry.
I think it proper to state, in reference to Dr. Dallinger's footnote
on the recent paper of Mr. Gregory, that it must not be inferred from
it that Mr. Gregory had access to my specimens from Madoc and Tudor,
though he no doubt had excellent material from the collections of
the Canadian Geological Survey. It might also be inferred from this
note that I have regarded the Madoc and Tudor specimens as "Lower
Laurentian." The fact is, that I was originally induced in 1865, by
the belief of Sir W. E. Logan at that time that these rocks were
representatives in a less altered state of the middle part of the
Laurentian, to spend some time at Madoc and its vicinity in searching
for fossils, but discovered only worm-burrows, spicules, and fragments
of Eozoon, which were noticed in the _Journal of the Geological
Society_ for 1866. (The more complete specimen from Tudor was found by
Vennor in 1866.) On that occasion I satisfied myself fully that the
beds are much older than the Cambro-Silurian strata resting on them,
unconformably; but I felt disposed to regard them as more probably
of the age of some parts of the Huronian of Georgian Bay, which I had
explored with a similar purpose under Logan's guidance in 1856.
[In my subsequent notice of the Tudor specimens in "The Dawn of Life,"
in 1875, I referred to their age as "Upper Laurentian or Huronian";
and I may add, that while it is certain that the beds containing them
are pre-Palæozoic, their place in the Eozoic period is still not
precisely determined. Work is, however, now in progress which it is
hoped may finally settle the age of the "Hastings group" and the old
rocks associated with it. I may add that the specimen of Cryptozoon
discovered by Mr. Chambers, and of which a portion is represented
in the Frontispiece, seems to me to throw a new light on the Tudor
specimen. It shows in any case the survival of Cryptozoa similar
in form and general appearance to that specimen, as late as the
Cambro-Silurian or Ordovician.]
* * * * *
H. Notes to Appendix, December, 1896.
While this work was going through the press, I have received the Report
of the U.S. Geological Survey for 1894-95, containing the elaborate
Memoir of C. R. Van Hise on the pre-Cambrian Geology of North America.
It is a very valuable contribution to the literature of this difficult
subject, and will constitute a standard book of reference: though I
think the use of the term "Algonkian" for groups of beds which are in
part basal Palæozoic and in part Eozoic or Archæan is to be deprecated,
and scarcely sufficient importance is attached to the labours of the
early Canadian explorers in this field.
In the past summer I was enabled to spend a few days, with the
assistance of my friend Mr. H. Tweeddale Atkin, of Egerton Park, Rock
Ferry, in examining the supposed pre-Cambrian rocks of Holyhead Island
and Anglesey. Fossils are very rare in these beds. As Sir A. Geikie
has shown, the quartzite of Holyhead is in some places perforated with
cylindrical worm-burrows, and in the micaceous shales there are long
cylindrical cords, which may be algæ of the genus _Palæochorda_, and
also bifurcating fronds resembling _Chondrites_; but I saw no animal
fossils. I have so far been unable to discover organic structure in
the layers of limestone associated with apparently bedded serpentine
in the southern part of Holyhead Island. In central Anglesey there
are lenticular beds of limestone and dolomite associated with
pre-Cambrian rocks, which Dr. Callaway regards as probably equivalent
to the Pebidian of Hicks. In these there are obscure traces of organic
fragments; and in one bed near Bodwrog Church I found a rounded
laminated body, which may be an imperfectly preserved specimen of
Cryptozoon, or some allied organism. The specimens collected have not,
however, been yet thoroughly examined. These and other pre-Cambrian
deposits in Great Britain correspond in their testimony, with the
Eozoic rocks of North America, as to the small number and rarity of
fossil remains in the formations below the base of the Palæozoic, and
the consequent probability that in these formations we are approaching
to the beginning of life on our planet; though there is still reason
to hope that additional oases of life may be found in these deserts
of the pre-Palæozoic. Such rare intervals of fertility should be the
more valued when the labours of so many skilled observers have proved
so meagre in their results in comparison with the great extent and
thickness of the beds which have been explored.
INDEX
PAGE
Adams on composition of Laurentian schists 108
---- his work on Laurentian stratigraphy 296
Animals, Cambrian, classes of 7, 11
---- pre-Cambrian 53
---- Huronian 67
---- Grenvillian 73, 303
Antiquity, relative 6
Aquatic animals, permanence of 13
Aragonite in fossils 117
Archæocyathus 35, 315
Archæozoon 214, 309
Barlow, his explorations 296
Bavaria, Eozoon of 71
Beecher on limbs of Trilobites 25
Bicknell on Eozoon 141
Billings on Eozoon 137
---- on Receptaculites 315
---- on Archæocyathus 316
---- on Signal Hill fossils 54
Bonney on Côte St. Pierre 142
Burbank on Chelmsford Eozoon 141
Calcarina 186
Calumet, Grand, Eozoon of 130
Canals of Eozoon 133
Cambrian, life of Early 17
---- geography of the 18
Carbon in Laurentian limestone 93
Carpenter, Dr., on Eozoon 137, 303, 324
Cayeux on Huronian fossils 68
Chambers, Mr. E. T. 313
Chrysotile, veins of 161, 239
Cœnostroma 174
Colorado cañon 56
Controversies respecting Eozoon 324
Corals, history of 32
Côte St. Pierre 88, 91
Cryptozoon 36, 56, 310
Dallinger, note on Eozoon 325
Dawson, Dr. G. M. 66, 295
Ells, Dr. 217, 296
Eozoon, its discovery 73, 125
---- its general form 149
---- its mode of occurrence 90
---- its state of preservation 111
---- its laminæ and chambers 152, 157
---- its canals and tubuli 133, 138, 158, 160
---- its funnels 152
---- its minute granular structure 133
---- its characters and affinities 307
---- objections to its animal nature 221
---- acervuline specimens 203
---- in various places 141, 233
---- Bavarian species 71, 213
---- Tudor specimens 68
---- fragments of, in limestones 183
Eozoon, restoration of 327
Eozoic time as a geological age 76
Etcheminian system 48
---- fossils of 54
Evolution, pre-geological 320
Foraminifera, notice of modern 175
---- Etcheminian 59
---- Huronian 71
---- Laurentian, etc. 303
Fossils, how mineralized 111
Glauconite, mineralizing fossils 217, 298
Granular structure in Eozoon 165
Graphite of the Laurentian 93
Gregory on Eozoon 235, 325
Grenvillian series 39
Gresley on Huronian worms 68
Gümbel on European Eozoon 71, 213
Hall, Dr. James, on Cryptozoon 36, 310
Hanford Brook, section at 51
Hastings series (Huronian ?) 67
Hinde on Archæocyathus 34, 317
Hunt, Dr. Sterry, on indications of life 97
---- on silicates in fossils 298
Huronian system 65
Hymenocaris 27
Jones, T. Rupert, on Eozoon 75, 137
Jullien on Eozoon 235
Kewenian or Kewenawan series 48
King, Prof, on Eozoon 221
Laurentian system 71
---- its limestones 92
Lavis, Dr. Johnson, on Eozoon 235, 325
Life in Early Cambrian 17
---- in pre-Cambrian 50
---- in Huronian 65
---- in Laurentian 71
Limestones of Laurentian 92
Logan, Sir W., on Eozoon 129
Loganite in Eozoon 128
Long Lake, Specimens from 190, 208
Lowe as explorer 131, 141
Map of Laurentian America 85
---- Grenville limestone 88
Matthew, Dr., on Archæozoon 214, 309
---- on Etcheminian 48, 51, 54
McMullen as explorer 128
Möbius on Eozoon 161, 162
Murray on Signal Hill beds 53
Nummulite 163, 186
Objections 221
Ocean of Cambrian 18, 21
---- of Laurentian 85
Olenellus zone 20
Petite Nation 141
Pole Hill, specimen from 118
Pre-Cambrian life 47
Pre-Cambrian rocks in Canada 76
Pre-geological evolution 320
Pre-Palæozoic life 216
Pyroxene in Eozoon 167, 169
Receptaculites 315
Robb, Pole Hill specimens 301
Serpentine, mineralizing fossils 147
---- different origins of 167, 171
Signal Hill series 53
Silicates, mineralizing fossils 217, 298
Spines, use of 30
Stromatoporæ 173
St. Pierre, Côte 88, 91
Table of the history of life 2
---- of pre-Cambrian formations 76
Triarthrus 25
Tubuli of Eozoon 60, 61, 159
Van Hise on pre-Cambrian 66, 329
Varieties of Eozoon 107, 202
Vennor referred to 69
Walcott on Lower Cambrian 40, 62
---- on fossils, Colorado Cañon 57
Weston, Mr., referred to 131
White, Prof. C. A., on chronology of life 7
Wilson, Dr., referred to 127
Worm-burrows in Huronian 67
Worm-trails in Lower Cambrian, etc. 40, 43
* * * * *
Transcriber Note
In order to accommodate placement of illustrations and footnotes, many
paragraphs were split where it seemed reasonable. Minor typos were
corrected. A web search shows that the anchorless Footnote on page
139 appears to reference the quoted text on page 140. Therefore, the
Footnote was placed after the quoted text.
On page 174, Footnote 36 referred twice to Figure 8 and to a
"Microscopic slice" as Figure 61 (which does not exist). It is assumed
the intent was to refer to Figures 7, 7a, 8 and 59 and has been altered
to point to those figures. The caption for Fig. 7 also refers to "Fig.
61, p. 310" and has been updated to "Fig. 59, p. 237".
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