The Project Gutenberg EBook of Sea-Weeds, Shells and Fossils, by
Peter Gray and B. B. Woodward
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Title: Sea-Weeds, Shells and Fossils
Author: Peter Gray
B. B. Woodward
Release Date: August 18, 2011 [EBook #37119]
Language: English
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SEA-WEEDS, SHELLS AND FOSSILS.
BY
PETER GRAY, A.B.S. EDIN.;
AND
B. B. WOODWARD,
_Of the British Museum (Natural History), South Kensington._
[Illustration]
LONDON:
SWAN SONNENSCHEIN, LE BAS & LOWREY,
PATERNOSTER SQUARE.
BUTLER & TANNER,
THE SELWOOD PRINTING WORKS
FROME, AND LONDON.
SEA-WEEDS.
BY PETER GRAY.
Algæ, popularly known as sea-weeds, although many species are
inhabitants of fresh water, or grow on moist ground, may be briefly
described as cellular, flowerless plants, having no proper roots, but
imbibing nutriment by their whole surface from the medium in which
they grow. As far as has been ascertained, the total number of species
is about 9000 or 10,000. Many of them are microscopic, as the Desmids
and Diatoms, others, as Lessonia, and some of the larger Laminariæ
(oarweeds), are arborescent, covering the bed of the sea around the
coast with a submarine forest; while in the Pacific, off the
northwestern shores of America, Nereocystis, a genus allied to
Laminaria, has a stem over 300 feet in length, which, although not
thicker than whipcord, is stout enough to moor a bladder,
barrel-shaped, six or seven feet long, and crowned with a tuft of
fifty leaves or more, each from thirty to forty feet in length. This
vegetable buoy is a favourite resting place of the sea otter; and
where the plant exists in any quantity, the surface of the sea is
rendered impassable to boats. The stem of Macrocystis, which "girds
the globe in the southern temperate zone," is stated to extend
sometimes to the enormous length of 1500 feet. It is no thicker than
the finger anywhere, and the upper branches are as slender as
pack-thread; but at the base of each leaf there is placed a buoy, in
the shape of a vesicle filled with air.
Although the worthlessness of Algæ has been proverbial, as in the
"alga inutile" of Horace and Virgil's "projecta vilior alga," they are
not without importance in botanical economics. A dozen or more species
found in the British seas are made use of, raw or prepared in several
ways, as food for man. Of these edible Algæ, Dr. Harvey considers the
two species of Porphyra, or laver, the most valuable. Berkeley says,
"The best way of preparing this vegetable or condiment, which is
extremely wholesome, is to heat it thoroughly with a little strong
gravy or broth, adding, before it is served on toast, a small quantity
of butter and lemon juice." A species of Nostoc is largely consumed in
China as an ingredient in soup. A similar use is made of Enteromorpha
intestinalis in Japan. Many species of fish and other animals, turtle
included, live upon sea-weed. Fucus vesiculosus is a grateful food for
cattle. In Norway, cattle, horses, sheep, and pigs are largely fed
upon it, and on our own coasts cattle eagerly browse on that and
kindred species at low water. In some northern countries, Fucus
serratus sprinkled with meal is used as winter fodder.
[Illustration: Fig. 1. Group of Sea-weeds (chiefly Laminariæ)]
All the marine Algæ contain iodine; and even before the value of that
substance in glandular complaints had been ascertained, stems of a
sea-weed were chewed as a remedy by the inhabitants of certain
districts of South America where goître is prevalent. Chondrus crispus
and (Gigartina) mamillosa constitute the Irish moss of commerce, which
dissolves into a nutritious and delicate jelly, and the restorative
value of which in consumption doubtless depends in some degree on the
presence of iodine. The freshwater Algæ not only furnish abundant and
nourishing food to the fish and other animals living in ponds and
streams, but by their action in the decomposition of carburetted
hydrogen and other noxious gases purify the element in which they
live, thus becoming important sanitary agents. The value of aquatic
plants in the aquarium is well known. A Chinese species of Gigartina
is much employed as a glue and varnish; and also much used in China in
the manufacture of lanterns and transparencies, and in that country
and Japan for glazing windows. Handles for table knives and forks,
tools, and other implements have been made from the thick stems of
oarweeds, and fishing lines from Chorda filum. Tripoli powder,
extensively used for polishing, consists mainly of the silicious
shells of Diatoms. On various parts of our coast, the coarser species
of sea-weed, now used as a valuable manure, were formerly extensively
burnt for kelp, an impure carbonate of soda. This industry, when
carried on upon a large scale, became a fruitful source of income to
some of the poorest districts in the kingdom, bringing, in the last
decade of last century, nearly £30,000 per annum into Orkney alone.
Since the production of soda from rock salt has become general, kelp
is now only burnt for the extraction of iodine, this being the easiest
way of obtaining that substance.
Although the vegetable structure and mode of reproduction are
essentially the same in all Algæ, as regards the former they vary from
the simple cell, through cells arranged in threads, to a stem and
leaves simulating the vegetation of higher tribes. And although the
simpler kinds are obviously formed of threads, most of the more
compound may also be resolved into the same structure by maceration in
hot water or diluted muriatic acid. In substance some are mere masses
of slime or jelly, others are silky to the feel, horny, cartilaginous
or leather-like, and even apparently woody. A few species secrete
carbonate of lime from the water, laying it up in their tissues;
others cover themselves completely with that mineral, while some coat
themselves with silex or flint. Many Algæ are beautifully coloured,
even when growing at depths to which very little light penetrates. As
in their vegetative organs, so in their reproductive, Algæ exhibit
many modifications of structure without much real difference. In the
green sea-weeds reproduction is effected by simple cell division in
the unicellular species, and by spores resulting from the union of the
contents of two cells in the others. The red sea-weeds have a double
system of reproduction, a distinctly sexual one, by spores and
antheridia, and another by tetraspores, which by some are considered
to be of the nature of gemmæ, or buds. The spores are generally
situated in distinct hollow conceptacles (favellæ, ceramidium,
coccidium). The tetraspore is also sometimes contained in a
conceptacle. It consists of a more or less globular, transparent cell,
which when mature contains within it four (rarely three) sporules.
Reproduction in the olive sea-weeds is also double, by zoospores,
generally considered gemmæ, and by spores and antherozoids, which is a
sexual process.
[Illustration: Fig. 2. A, Species of Gleocapsa, one of the
Palmelleæ, in various stages. A becomes B, C, D, and E by
repeated division. Magnified 300 diameters.]
Following the classification adopted by Professor Harvey, which is
that generally employed in English systematic manuals, we divide the
order into three sub-orders, named from the prevailing colour of their
spores. 1. Chlorospermeæ, with green spores; 2. Rhodospermeæ, with red
spores; and 3. Melanospermeæ, with olive-coloured spores. The entire
plant in the first group is usually grass-green, but occasionally
olive, purple, blue, and sometimes almost black; in the second it is
some shade or other of red, very seldom green; and in the third, while
generally olive green, it is occasionally brown olive or yellow.
The Chlorospermeæ are extremely varied in form, often threadlike, and
are propagated either by the simple division of the contents of their
cells (endochrome), by the transformation of particular joints, or by
the change of the contents of the cells into zoospores, which are
cells moving freely in water by means of hairlike appendages. In their
lower forms they are among the most rudimentary of all plants, and
thus of special interest physiologically, as representing the
component parts of which higher plants are formed. They are subdivided
into twelve groups, as follows:
The first group, Palmelleæ, are unicellular plants, the cells of which
are either free or surrounded by a gelatinous mass, and they are
propagated by the division of the endochrome. One of the most
remarkable of the species of this family is Protococcus cruentus,
which is found at the foot of walls having a northern aspect, looking
as if blood had been poured out on the ground or on stones.
Protococcus nivalis, again, is the cause of the red snow, of which
early arctic navigators used to give such marvellous accounts.
(Fig. 2.)
[Illustration: Fig. 3. A, Fragment of a Filament of Zygnema,
one of the Conjugateæ; B, Closterium; C, Euastrium; two
desmids.]
The Desmideaceæ, together with the plants of the next succeeding
group, are favourite subjects of investigation or observation by the
possessors of microscopes, an attention they merit from the beauty and
variety of their forms. They are minute plants of a green colour,
consisting of cells generally independent of each other, but sometimes
forming brittle threads or minute fronds, and are reproduced by spores
generated by the conjugation of two distinct individuals. The process
of conjugation in Desmids and Diatoms consists in the union of the
endochrome of two individuals, each of which in these families is
composed of a single cell. This ultimately forms a rounded body or
resting spore, which afterwards germinates, the resulting plant not
however acquiring the normal form until the third generation. (Fig.
3.)
The Diatomaceæ, closely allied to the preceding group in structure and
reproduction, are however distinguished from them by their flinty
shells, which are often beautifully sculptured. Their endochrome is a
golden brown, instead of green as in the Desmideaceæ. The latter,
also, are confined to fresh water, while the Diatomaceæ are found,
though not exclusively, in the sea, where their shells sometimes,
microscopically minute as they are individually, form banks extending
several hundred miles. It is stated that in the collection made by Sir
Joseph Hooker in the Himalayas the species closely resemble our own.
In the next group, Confervaceæ, we are introduced to forms more like
the general notion of what a plant should be. The individuals of which
it consists are composed of threads, jointed, either simple or
branched, mostly of a grass-green colour, and propagating either by
minute zoospores or by metamorphosed joints. They are found both in
fresh and salt water, and in damp situations. The number of species is
very great. A considerable number consist of unbranched threads; the
branched forms grow sometimes so densely as to assume the form of
solid balls. After floods, when the water stands for several days,
they sometimes increase to such an extent, as to form on its
subsidence a uniform paper-like stratum, which while decomposing is
extremely disagreeable. The name Conferva has been almost discontinued
as a generic title, the majority of British species being now ranged
under Clado- and Chæto-phora. The latter are branched, and require
great care and attention in order to distinguish them, on account of
their general resemblance to each other. Good characters are however
to be found in their mode of branching and the form and comparative
size of the terminal joints.
The Batrachospermeæ constitute a small but very beautiful group,
consisting of gelatinous threads variously woven into a branched
cylindrical frond. The branches are sometimes arranged, as in the
British species, so that the plants appear like necklaces. In colour
they pass from green, through intermediate shades of olive and purple,
to black. In common with some of the higher Algæ, the threads of the
superficial branches send joints down the stem, changing it from
simple to compound. The native species are all fluviatile.
The Hydrodicteæ are among the most remarkable of Algæ. Hydrodictyon
utriculatum, the solitary British species, is found in the large pond
at Hampton Court, and in similar situations in various parts of the
country, but not very generally. It resembles a green purse or net,
from four to six inches in length, with delicate and regular meshes,
the reticulations being about four lines long. Its method of
reproduction is no less than its form. Each of the cells
forms within itself an enormous mass of small elliptic grains. These
become attached by the extremities so as to form a network inside the
cell, and, its walls being dissolved, a new plant is set free to grow
to the size of the parent Hydrodictyon.
The Nostochineæ grow in fresh water, or attached to moist soil. They
consist of slender, beaded threads surrounded by a firm jelly, and
often spreading into large, wavy fronds. The larger beads on the
inclosed threads are reproductive spores. (Fig. 4, A.)
[Illustration: Fig. 4. A, Fragment of a Filament of Nostoc. B,
End of a Filament of Oscillatoria.]
The Oscillatoreæ are another remarkable group, on account of the
peculiar animal-like motions they exhibit. They occur both in salt and
fresh water, and on almost every kind of site in which there is
sufficient moisture. The threads of which they are composed are
jointed, and generally unbranched; they are of various tints of blue,
red, and green, and, where their fructification has been ascertained,
are propagated by cell division. The most curious point about them is,
however, the movements of their fronds. According to Dr. Harvey, these
are of three kinds--a pendulum-like movement from side to side,
performed by one end, whilst the other remains fixed, so as to form a
pivot; a movement of flexure of the filament itself, the oscillating
extremity bending over from one side to the other, like the head of a
worm or caterpillar seeking something on its line of march; and
lastly, a simple onward movement of progression, the whole phenomenon
being, Dr. Harvey thinks, resolvable into a spiral onward movement of
the filament. Whatever is the cause of this motion, it is not, as used
to be supposed, of an animal nature; for the individuals of this group
are undoubted plants. (Fig. 4, B.) Several species of Rivularia,
belonging to the Oscillatoreæ, are found both in the sea and in fresh
water. They are gelatinous, and have something of the appearance of
Nostoc, in aspect as well as in minute structure.
The Conjugatæ are freshwater articulated Algæ, which reproduce
themselves by the union of two endochromes. They are very interesting
objects under the microscope, owing to the spiral or zigzag
arrangement of the endochrome of many of them, and the delicacy of
all.
The Bulbochæteæ constitute a small group, some half-a-dozen species
being British. They are freshwater plants, composed of articulate
branched filaments, with fertile bulbshaped branchlets. The endochrome
is believed to be fertilized by bodies developed in antheridia, the
contents of each fertilized cell dividing into four ovate zoospores.
The last two groups of green sea-weeds consist chiefly of marine
plants. Of these the first, Siphoneæ, is so called because the plant,
however complicated, is composed invariably of a single cell. It
propagates by minute zoospores, by large quiescent spores, or by large
active spores clothed with cilia. It includes the remarkable genus
Codium, three species of which inhabit the British seas. In Codium
Bursa the filamentous frond is spherical and hollow, presenting more
the appearance of a round sponge or puff-ball than a sea-weed, and is
somewhat rare. Another species greatly resembles a branched sponge,
and the third forms a velvety crust on the surface of rocks. Another
genus, Vaucheria, is of a beautiful green colour, forming a velvety
surface on moist soil, on mud-covered rocks overflowed by the tide, or
parasitic on other sea-weeds. The most attractive plants of this
family are however those of the genus Bryopsis, two of which are found
on the British shores. The most common one is B. plumosa, the fronds
of which grow usually in the shady and sheltered sides of rock pools.
The fronds of the last of the green-weed groups, the Ulvaceæ, are
membranous, and either flat or tubular. Two of them, Ulva latissima,
the green, and Porphyra laciniata, the purple laver, are among the
most common sea-weeds, growing well up from low-water mark. The
propagation in all of them is by zoospores. An allied genus,
Enteromorpha, is protean in its forms, which have been classed under
many species. They may, however, be reduced to half a dozen. Some of
them are very slender, so as almost to be mistaken for confervoid
plants.
With the Rhodospermeæ we enter a sub-order of Algæ, exclusively
marine, the plants in which have always held out great attractions to
the collector. In structure they are expanded or filamentous, nearly
always rose-coloured or purple in colour. Of the fourteen groups into
which they are divided by Harvey, the first is Ceramiaceæ, articulate
Algæ, constituting a large proportion of the marine plants of our
shores. Of the genus Ceramium, C. rubrum is the most frequent, and it
is found in every latitude, almost from pole to pole. It is very
variable in aspect, but can always be recognized by its fruit. C.
diaphanum is a very handsome species, growing often in rock pools
along with the other. There are about fifteen native species
altogether, some of them rare, and all very beautiful, both as
displayed on paper and seen under the microscope. Crouania attenuata
is a beautiful plant, parasitic upon a Cladostephus or Corallina
officinalis. It is however extremely rare, being only found in England
about Land's End. A more common and conspicuous, but equally handsome
plant is Ptilota plumosa (Fig. 9), which is mostly confined to our
northern coasts; although P. sericea, a smaller species, or variety,
is common in the south, and easily distinguished from its congener,
which it otherwise greatly resembles, by its jointed branchlets and
pinnules. Callithamnion, Halurus and Griffithsia, articulate like
Ceramium, furnish also several handsome species. (Fig. 5.)
[Illustration: Fig. 5. Species of Callithamnion.]
The group Spyridiaceæ contains only one English plant, Spyridia
filamentosa, which is curiously and irregularly branched, the branches
being articulate and of a pinky red. One of its kinds of fruit,
consisting of crimson spores, is contained in a transparent network
basket, formed by the favellæ, or short branches, whence its name.
[Illustration: Fig. 6. Chondrus crispus.]
The Cryptonemiaceæ are very numerous in genera and species. They all
have inarticulate branches, some are thread-like. Grateloupia filicina
is a neat little plant, met with rarely on the south and west coasts.
Gigartina mamillosa, a common plant everywhere, is the plant sold,
along with Chondrus crispus, as Irish or Carrageen moss. A handsome
little plant, Stenogramme interrupta, is very rare, but it has been
gathered both on the Irish and English coasts. The Phyllophoræ, one
species of which is frequent on all our shores, may be recognised by
the way in which the points and surfaces of their fronds throw out
proliferous leaves. Gymnogongrus has two British species, one much
resembling Chondrus crispus, already named, of which it was formerly
considered a congener. Their fructification is however very different.
Ahnfeltia plicata is a curiouswiry, entangled plant, almost black in
colour, and like horse-hair when dry, and can scarcely be mistaken.
Cystoclonium purpurascens is very commonly cast up by the tide on most
of our coasts. It varies in colour, but is easily distinguished by the
spore-bearing tubercles imbedded in its slender branches. Callophyllis
laciniata is a handsome species, of a rich crimson colour, and
sometimes a foot square. It can scarcely have escaped the notice of
the sea-side visitor, for it is widely distributed and often thrown
out in great abundance; one writer describes the shore near Tynemouth
as having been red for upwards of a mile with this superb sea-weed.
Kalymenia reniformis is another of the broad, flat Algæ, but it is
scarcer, and of a colour not so conspicuous. Among the most frequent
of our sea-weeds, both as growing in the rock pools and cast ashore,
is Chondrus crispus, already twice referred to in connexion with its
officinal uses. It is very variable in form, one author figuring as
many as thirty-six different varieties. (Fig. 6.) Chylocladia
clavellosa, which is sometimes cast ashore a foot and a half long, is
closely set with branches, and these again clothed with branchlets in
one or two series. The whole plant is fleshy, of a rose-red or
brilliant pink colour, turning to golden yellow in decay. There is
another small species, confined to the extreme north of Britain.
Halymenia ligulata is another flat red weed, but sometimes very narrow
in its ramifications. Furcellaria fastigiata has a round, branched,
taper stem, swollen at the summit, which contains the fruit,
consisting of masses of tetraspores in a pod-like receptacle.
Schizymenia edulis, better known perhaps by its old name Iridea, is a
flat, inversely egg-shaped leaf with scarcely any stem. It is one of
the edible Algæ, and pretty frequent in shady rock pools.
Gloiosiphonia capillaris is a remarkably beautiful plant, and not
common, being confined to certain parts of the southern coasts. The
stem is very soft and gelatinous; the spores are produced in red
globular masses imbedded in the marginal filaments, which have a fine
appearance under the microscope when fresh.
[Illustration: Fig. 7. Rhodomenia palmata.]
[Illustration: Fig. 8. Wormskioldia sanguinea.]
The Rhodomeniaceæ are purplish or blood-red sea-weeds, inarticulate,
membranaceous, and cellular. Among the dark-coloured is Rhodomenia
palmata, better known as dulse, a common and edible species. (Fig. 7.)
Wormskioldia sanguinea is not only the most beautiful sea-weed, but
the finest of all leaves or fronds. It is usually about six inches
long, but sometimes nearly double that length and six inches broad,
with a distinct midrib and branching veins, and a delicate wavy
lamina, pink or deep red. The fruit is produced in winter from small
leaflets growing upon the bare midrib. (Fig. 8.) The commonest of all
red sea-weeds on our coast, one of the most elegant, and much sought
after by sea-weed picture makers, Plocamium coccineum, belongs to this
group. Calliblepharis ciliata and jubata are coarser plants, the
latter being the more frequent. They were formerly included in the
genus Rhodymenia, from which they were removed when their fruit was
better understood.
[Illustration: Fig. 9. Ptilota plumosa.]
Wrangelia and Naccaria are the only British genera in Wrangeliaceæ.
There is only one native species in each, both being rare, the latter
especially.
The Helminthocladiæ are also a limited group, of a gelatinous
structure; so much so that on being gathered they feel like a bunch of
slimy worms, whence the name of the family. Helminthora purpurea and
divaricata with Nemaleon multifidum and Scinaia furcellata represent
them in Britain. They are nearly all very rare, pretty plants, and
very effective as microscopic objects.
The Squamariæ, formerly included in the Corallinaceæ, are a small
group of inconspicuous plants resembling lichens, of a leathery
texture, and growing on rocks and shells attached by their lower
surface.
A single genus only, Polyides, represents the Spongiocarpeæ. Polyides
rotundus resembles Furcellaria fastigiata very closely, but differs
widely in the fruit, which consists of spongy warts surrounding the
frond, composed of spores and articulated threads.
Of the next group represented in Britain, Gelidiaceæ, we have only one
plant, Gelidium corneum, very common on our shores, and perhaps the
most variable of all vegetable species.
The Sphærococcidæ include both membranaceous and cartilaginous
species. Of the latter is Sphærococcus coronopifolius, which cannot
easily be mistaken, owing to the numerous berry-like fruits that tip
its branchlets. It is rather rare on the northern, but often thrown
ashore in large quantities on the southern coasts. The genus
Delesseria has four British species, the largest being the well-known
D. sinuosa, the fronds of which resemble an oak leaf in outline. The
handsomest are D. ruscifolia and D. hypoglossum, which are more
delicate and of a finer colour than sinuosa. There are three British
species of Gracillaria, in two of which the branches are cylindrical,
and in the other flat. G. compressa makes an excellent preserve and
pickle, but unfortunately it is the rarest of the three. Nitophyllum
is one of the greatest ornaments of this tribe. There are six British
species, which are amongst the most delicate and beautiful of our
native Algæ.
The Corallinaceæ are remarkable for the property they possess of
absorbing carbonate of lime into their tissues, so that they appear as
a succession of chalky articulations or incrustations. The most common
is Corallina officinalis. There are two British species of Corallina,
and two also of the nearly allied genus, Jania. Of the foliaceous
group there are likewise two British genera, Melobesia and
Hildenbrantia.
The next group, the Laurenciaceæ, are cartilaginous and cylindrical or
compressed, the frond in the greater portion of them being
inarticulate and solid. They contain several species valued by
collectors, although some of them are amongst our commonest plants.
Their colour is, when perfect, a dull purple or brownish red, but they
change under the influence of light and air, while fresh water is
rapidly destructive to their tints. (Fig. 10.)
[Illustration: Fig. 10. Laurencia pinnatifida.]
The Chylocladiæ are curiously jointed plants, removed by Agardh to a
new genus, Lomentaria, and a new order Chondriæ. Bonnemaisonia
asparagoides is the most rare and beautiful of the tribe.
The last tribe of red weeds, Rhodomelaceæ, varies greatly in the
structure of the frond, but the fruit is more uniform. Polysiphonia
and Dasya contain the finest of the filiform division; the leafy one,
Odonthalia, a northern form, is a very beautiful sea-weed both as
respects form and colour. Well-grown specimens are not unlike a
hawthorn twig, and of a blood red colour.
The plants of the sub-order Melanospermeæ, are, like the red
sea-weeds, exclusively marine. They are usually large and coarse, and
confined mostly to comparatively shallow water. In the Laminariaceæ we
find the gigantic oarweeds already briefly referred to. Lessonia,
which encircles in submarine forests the antarctic coasts, is an
erect, tree-like plant, with a trunk from five to ten feet high,
forked branches, and drooping leaves, one to three feet in length, and
has been compared to a weeping willow. Sir Joseph Hooker says, that
from a boat there may on a calm day be witnessed in the antarctic
regions, over these submarine groves, "as busy a scene as is presented
by the coral reefs of the tropics. The leaves of the Lessoniæ are
crowded with Sertulariæ and Mollusca, or encircled with Flustra; on
the trunks parasitic Algæ abound, together with chitons, limpets, and
other shells; at the base and among the tangled roots swarm thousands
of Crustaceæ and Radiata, while fish of several species dart among the
leaves and branches." Of these and other gigantic melanosperms, flung
ashore by the waves, a belt of decaying vegetable matter is formed,
miles in extent, some yards broad, and three feet in depth; and Sir J.
Hooker adds that the trunks of Lessonia so much resemble driftwood
that no persuasion could prevent an ignorant shipmaster from employing
his crew, during two bitterly cold days, in collecting this
incombustible material for fuel. Macrocystis and Nereocystis are also
giant members of this sub-order. Some of the Laminariæ which form a
belt around our own coasts not seldom attain a length of from eight to
twelve feet. The common bladder-wrack (Fucus vesiculosus) sometimes
grows in Jutland to a height of ten feet, and in clusters several feet
in diameter. The colour of most of the plants in this sub-order is
some shade of olive, but several of them turn to green in drying.
The first group, Ectocarpeæ, is composed of thread-like jointed
plants, the fructification of which consists of external spores,
sometimes formed by the swelling of a branchlet. The typical genus,
Ectocarpus, abounds in species, a dozen or so of which, very nearly
allied plants, being found around our own shores. One or two of them
are very handsome. There are also some very beautiful plants in the
genus Sphacelaria, belonging to this group, several of them resembling
miniature ferns. All the Sphacelariæ are easily recognized by the
withered appearance of the tips of the fruiting branches. Myriotrichia
is a genus of small parasitical plants, the two British species of
which grow chiefly on the sea thongs (Chorda).
The Chordariæ are sometimes gelatinous in structure, in other cases
cartilaginous. The fruit is contained in the substance of the frond.
The genus Chordaria consists of plants which have the appearance of
dark coloured twine. There are two British species, one being rather
common. Chorda filum, sea-rope, another string-like sea-weed, grows in
tufts from a few inches to many feet in length, and tapering at the
roots to about the thickness of a pig's bristle. In quiet land-locked
bays with a sandy or muddy bottom, it sometimes extends to forty feet
in length, forming extensive meadows, obstructing the passage of
boats, and endangering the lives of swimmers entangled in its slimy
cords, whence probably its other name of "dead men's lines."
[Illustration: Fig. 11. Padina pavonia.]
The Mesogloieæ in a fresh state resemble bundles of green, slimy
worms. There are three British species, two of which are not uncommon.
Although so unattractive in external aspect, they, like many others of
the same description, prove very interesting under the microscope. One
of the cartilaginous species, Leathsia tuberiformis, has the
appearance, when growing, of a mass of distorted tubers.
The species of Elachista, composed of minute parasites, are, as well
as unattractive like the Mesogloieæ, inconspicuous, but are beautiful
objects when placed under the microscope. Myrionemæ are also
parasitic, and even smaller than the plants of the preceding genus.
In the Dictyoteæ the frond is mostly flat, with a reticulated surface,
which is sprinkled when in fruit with groups of naked spores or spore
cysts. This tribe includes not a few of the most elegant among the
Algæ. In structure they are coriaceous, and include plants both with
broad and narrow, branched and unbranched fronds. In Haliseris there
is a distinct midrib. The largest of the British Dictyoteæ is Cutleria
multifida, sometimes found a foot and a half long; and the best known
is doubtless Padina pavonia, much sought after by seaside visitors
where it grows. Its segments are fan-shaped, variegated with lighter
curved lines, and fringed with golden tinted filaments. (Fig. 11.)
Owing to its power of decomposing light, its fronds, when growing
under water, suggest the train of the peacock, whence its specific
name. Taonia atomaria somewhat resembles Cutleria, but exhibits also
the wavy lines of Padina. The plant of this group most often cast
ashore is Dictyota dichotoma. It makes a handsome specimen when well
dried, and is interesting on account of the manner in which it varies
in the breadth of its divisions. The variety intricata is curiously
curled and entangled. Dictyosiphon foeniculaceus, the solitary
British example of its genus, is a bushy filiform plant, remarkable
for the beautiful net-like markings of its surface. The Punctariæ have
flattened fronds, marked with dots, which sufficiently distinguish
them from all the others. A small form is often found parasitic on
Chorda filum, spreading out horizontally like the hairs of a bottle
brush. Asperococcus derives its name from its roughened surface,
occasioned by the thickly scattered spots of fructification.
The Laminariaceæ are inarticulate, mostly flat, often strap-shaped.
Their spores occur in superficial patches, or covering the whole
frond. The plants of this order, as we have already seen, include the
giants of submarine vegetation. In point of mass they constitute the
larger part of our native Algæ, although they number only a few
species. They are popularly known as tangle or oarweeds, and the stems
of Laminaria saccharina and the midrib of Alaria esculenta are used as
food.
The Sporochnaceæ are a small but beautiful tribe, inarticulate, and
producing their spores in jointed filaments or knob-like masses, and
remarkable for their property of turning from olive brown to a
verdigris green when exposed to the atmosphere.
[Illustration: Fig. 12. Fucus serratus, showing a transverse
section of the Conceptacle, and Antheridium with Antherozoids
escaping.]
They are deep sea plants, or at least grow about low water mark. The
largest of the group is Desmarestia ligulata, which, with the other
British species, D. aculeata, is often cast ashore. The latter
species, at an early period of its existence, is clothed with tufts of
slender hairs, springing from the margin of the frond. Desmarestia
viridis is the most delicate and also the rarest of the three. Nothing
like fruit has been discovered on any of them. Arthocladia villosa and
Sporochnus pedunculatus are branched sea-weeds, covered also with
tufts of closely set hairs. Carpomitra Cabreræ, a rare species, bears,
in common with the two preceding species, its spores in a special
receptacle. In the first the receptacle is pod-like; in the second
knotted; and in the last mitriform.
The concluding group of Algæ is the Fucaceæ, including the universally
known sea wrack (Fucus). The frond in all of them is jointless. They
are reproduced by means of antheridia and oogonia developed in
conceptacles, clustered together at the apex of the branches. Both
from their bulk and their decided sexual distinctions, they deserve to
rank at the head of the order. Of all sea-weeds they are also perhaps
of the greatest use to man. One of the most interesting among them is
the Gulfweed (Sargassum bacciferum), occupying a tract of the Atlantic
extending over many degrees of latitude. Pieces of it, and of its
congener, S. vulgare, are occasionally drifted to our shores, and they
consequently find a place in works on British Algæ, although they have
no claim to be considered native plants. On rocky coasts the various
species of Fucus occupy the greater part of the space between
tide-marks, the most plentiful being Fucus vesiculosus. F. serratus
(Fig. 12) is the handsomest of the genus, the other species being F.
nodosus, said to be the most useful for making kelp, and F.
canaliculatus. Halidrys siliquosa is remarkable for its spore
receptacles, which have quite the appearance of the seed vessel of a
flowering plant. The species of Cystoseira, chiefly confined to the
southern coasts, are also very interesting. Their submerged fronds are
beautifully iridescent, and the stems, of the largest species at
least, are generally covered with a great variety of parasites, animal
and vegetable, the former consisting of Hydrozoa and Polyzoa, and
other curious forms. Himanthalia lorea is another remarkable plant. It
has conspicuous forked fruit-bearing receptacles; but the real plants
are the small cones at the base of these, and from which they are shed
when ripe.
As to conditions of site and geographical distribution, Algæ do not
differ from land plants. Latitude, depth of water, and currents
influence them in the same way as latitude, elevation, and station
operate on the latter; and the analogy is maintained in the almost
cosmopolitan range of some, and the restricted habitat of others. Not
many extra-European species of Desmids are known, but those of Diatoms
are far more widely diffused, and extend beyond the limits of all
other vegetation, existing wherever there is water sufficient to allow
of their production; and they are found not only in water, but also
on the moist surface of the ground and on other plants, in hot springs
and amid polar ice. They are said to occur in such countless myriads
in the South Polar Sea as to stain the berg and pack ice wherever
these are washed by the surge. A deposit of mud, chiefly consisting of
the shells of Diatoms, 400 miles long, 120 miles broad, and of unknown
thickness, was found at a depth of between 200 and 400 feet on the
flanks of Victoria Land in 70° south latitude. Such is their abundance
in some rivers and estuaries that Professor Ehrenberg goes the length
of affirming that they have exercised an important influence in
blocking up harbours and diminishing the depth of channels. The trade
and other winds distribute large quantities over the earth, which may
account for the universality of their specific distribution; for Sir
Joseph Hooker found the Himalayan species to closely resemble our own.
Common British species also occur in Ceylon, Italy, Virginia, and
Peru. The typical species of the Confervaceæ are also distributed over
the whole surface of the globe. They inhabit both fresh and salt
water, and are found alike in the polar seas and in the boiling
springs of Iceland, in mineral waters and in chemical solutions. Some
of the tropical ones are exceedingly large and dense. Batrachospermum
vagum, in the next tribe, a native of England, is also found in New
Zealand. An edible species of Nostochineæ, produced on the boggy
slopes bordering the Arctic Ocean, is blown about by the winds
sometimes ten miles from land, where it is found lying in small
depressions in the snow upon the ice. The common Nostoc of moist
ground in England occurs also in Kerguelen's Land, high in the
southern hemisphere. Floating masses of Monormia are often the cause
of the green hue assumed by the water of ponds and lakes. Certain
species of Oscillatoria of a deep red colour live in hot springs in
India, and the Red Sea is supposed to have derived its name from a
species of this tribe, which covers it with a scum for many miles,
according to the direction of the wind. The lake of Glaslough in
County Monaghan, Ireland, owes its colour and its name to Oscillatoria
ærugescens, and large masses of water in Scotland and Switzerland are
tinted green or purple by a similar agency. A few species of Siphoneæ
have a very wide range, two British species of Codium occurring in New
Zealand. The Ulvaceæ abound principally in the colder latitudes.
Enteromorpha intestinalis, a common British species, is as frequent in
Japan, where it is used, when dried, in soup. The Rhodosperms are
found in every sea, although the geographical boundaries of genera are
often well-marked. Gloiosiphonia, one of our rarest and most
beautiful Algæ, is widely diffused. Of Melanosperms the Laminariæ
affect the higher northern latitudes, Sargassa abound in the warmer
seas, while Durvillæa, Lessonia, and Macrocystis characterize the
marine flora of the Southern Ocean. The Fucaceæ are most abundant
towards the poles, where they attain their greatest size. The marine
meadows of Sargassum, conceived by some naturalists to mark the site
of the lost Atlantis, and which give its name to the Sargasso Sea,
extending between 20° and 25° north latitude, in 40° west longitude,
occupy now the same position as when the early navigators, with
considerable trepidation, forced through their masses on the way to
the New World. Sargassum is drifted into this tract of ocean by
currents, the plants being all detached; and they do not produce fruit
in that state, being propagated by buds, which originate new branches
and leaves. (Fig. 13.)
[Illustration: Fig. 13. The Gulf-weed (Sargassum bacciforum).]
Owing to their soft, cellular structure, Algæ are not likely to be
preserved in a fossil state; but what have been considered such have
been found as low down as the Silurian formation, although their
identity has been disputed, and several of them, it is more than
probable, belong to other orders, and some even to the animal kingdom.
Freshwater forms, all of existing genera and species, are believed to
have been detected in the carboniferous rocks of Britain and France;
others also of the green-coloured division are said to occur from the
Silurian to the Eocene, and the Florideæ to be represented from the
Lias to the Miocene. The indestructible nature of the shells of the
Diatomaceæ has enabled them to survive where the less protected
species may have perished. Tripoli stone, a Tertiary rock, is entirely
composed of the remains of microscopic plants of this tribe. It is
from their silicious shells that mineral acquires its use in the arts,
as powder for polishing stones and metals. Ehrenberg estimates that in
every cubic inch of the tripoli of Bilin, in Bohemia, there are
41,000,000 of Gaillonella distans. Districts recovered from the sea
frequently contain myriads of Diatoms, forming strata of considerable
thickness; and similar deposits occur in the ancient sites of lakes in
this and other countries.
* * * * *
Before setting out in search of Algæ the collector ought to provide
himself with a pair of stout boots to guard his feet from the
sharp-pointed rocks, as well as a staff or pole to balance himself in
rock-climbing, which ought to have a hook for drawing floating weed
ashore. A stout table-knife tied to the other end will be found very
useful. A basket--a fishing-basket does very well--or a waterproof
bag, for stowing away his plants, is also necessary. It is advisable
to carry a few bottles for the very small and delicate plants, and
care should be taken to keep apart, and in sea-water, any specimens of
the Sporochnaceæ; for they are not only apt to decay themselves but to
become a cause of corruption in the other weeds with which they come
in contact. These bottles should always be carried in the bag or
pocket, never in the hand.
Sea-weeds, as every visitor to the coast knows, are torn up in great
numbers by the waves, especially during storms, and afterwards left on
the shore by the retiring tide. Many shallow-growing species are also
to be found attached to the rocks, and in the rock pools, between high
and low water mark. There are three points on the beach where the
greatest accumulations of floating Algæ are found: high water mark,
mid-tide level, and low water mark. Low water occurs about five or
five and a half hours after high water. The best time for the
collector to commence is half an hour or so before dead low water. He
can then work to the lowest point safely, and, retiring before the
approaching tide, examine the higher part of the beach up to high
water mark. If the coarse weeds in the rock pools and chinks are
turned back, many rare and delicate Algæ will be found growing under
them, especially at the lowest level. The most effective method of
collecting the plants of deeper water is by dredging, or going round
with a boat at the extreme ebb, and taking them from the rocks and
from the Laminaria stems, on which a great number have their station.
Stems of Laminaria thrown out by the waves should also be carefully
examined. In all cases the weed should be well rinsed in a clear rock
pool before being put away in the bag or other receptacle.
The next thing to be considered is the laying out and preserving of
the specimens selected for the herbarium. Wherever possible these
should be laid out on paper, and put under pressure as soon as
gathered, or on the same day at all events. When this is
impracticable, they may be spread between the folds of soft and thick
towels and rolled up. Thus treated the most delicate plants will keep
fresh until next day. Another way is to pack the plants in layers of
salt, like herrings; but the most usual method of roughly preserving
sea-weeds collected during an unprepared visit to the shore is by
moderately drying them in an airy room out of the direct rays of the
sun. They are then to be placed lightly in bags, and afterwards
relaxed by immersion and prepared in the usual way. The finer plants,
however, suffer more or less by this delay. If carried directly home
from the sea the plants should be emptied into a vessel of sea-water.
A flat dish, about fourteen inches square and three deep, is then to
be filled with clean water. For most plants this may be fresh, for
some it is essential that it should be salt. Some of the Polysiphonias
and others begin to decompose at once if placed in fresh water. The
Griffithsias burst and let out their colouring matter, and a good many
change their colour. The appliances required are some fine white
paper--good printing demy, thirty-six pounds or so in weight per ream,
does very well,--an ample supply of smooth blotting paper, the coarse
paper used by grocers and called "sugar royal," or, best of all,
Bentall's botanical drying paper, pieces of well-washed book muslin, a
camel's hair brush, a bodkin for assisting to spread out the plants, a
pair of scissors, and a pair of forceps. The mounting paper may be cut
in three sizes: 5 in. by 4 in., 7½ in. by 5¼ in., and 10 in. by
7½ in. Then having selected a specimen, place it in the flat dish
referred to above, and prune it if necessary. Next take a piece of
the mounting paper of suitable size, and slip it into the water
underneath the plant, keeping hold of it with the thumb of the left
hand. Having arranged the plant in a natural manner on the paper,
brush it gently with the camel's hair brush to remove any dirt or
fragments, draw out paper and plant gently and carefully in an oblique
direction, and set them on end for a short time to drain. Having in
this way transferred as many specimens as will cover a sheet of drying
paper, lay them upon it neatly side by side, and cover them with a
piece of old muslin. Four sheets of drying paper are then to be placed
upon this, then another layer of plants and muslin and four more
sheets of drying paper, until a heap, it may be six or eight inches
thick, is built up. Place this between two flat boards, weighted with
stones, bricks, or other weights; but the pressure should be moderate
at first, otherwise the texture of the muslin may be stamped on both
paper and plant. The papers must be changed in about three hours'
time, and afterwards every twelve hours. In three or four days,
according to the state of the weather, the muslin may be removed, the
plants again transferred to dry paper, and subjected to rather severe
pressure for several days.
The very gelatinous plants require particular treatment. One way is to
put them in drying paper and under a board but to apply no other
pressure, change the drying paper at least twice during the first half
hour, and after the second change of dryers apply very gentle
pressure, increasing it until the specimens are fully dry. A safer and
less troublesome way, for the efficacy of which we can vouch, is to
lay down the plants and dry them without any pressure, afterwards
damping the back of the mounting papers and placing them in the drying
press. Some Algæ will scarcely adhere to paper. These should be
pressed until tolerably dry, then be immersed in skim-milk for a
quarter of an hour, and pressed and dried as before. A slight
application of isinglass, dissolved in alcohol, to the under side of
the specimen is sometimes necessary. Before mounting, or at all events
before transference to the herbarium, care should be taken to write in
pencil on the back of the paper the name of the plant, if known, the
place where gathered, and the date. The coarse olive weeds, such as
the bladder-wrack, Halidrys, and the like, may in the case of a short
visit to the coast be allowed to dry in an airy place, and taken home
in the rough. Before pressing, in any case, they should be steeped in
boiling water for about half an hour to extract the salt, then washed
in clean fresh water, dried between coarse towels, and pressed and
dried in the same way as flowering plants. A collection of Algæ may be
fastened on sheets of paper of the usual herbarium size and kept in a
cabinet or portfolios, or attached to the leaves of an album. For
scientific purposes, however, the latter is the least convenient way.
There are few objects more beautiful than many of the sea-weeds when
well preserved; but the filiform species, especially those of the
first sub-order, do not retain their distinguishing characters when
pressed as has been described. Portions of these, however, as well as
sections of stems and fruit, may be usefully dried on small squares of
thin mica, for subsequent microscopic examination, or they may be
mounted on the ordinary microscope slides. This is the only course
possible with Desmids and Diatoms. The former are to be sought in
shallow pools, especially in open boggy moors. The larger species
commonly lie in a thin gelatinous stratum at the bottom of the pools,
and by gently passing the fingers under them they will be caused to
rise towards the surface, when they can be lifted with a scoop. Other
species form a greenish or dirty cloud on the stems and leaves of
other aquatic plants, and by stripping the plant between the fingers
these also may be similarly detached and secured. If they are much
diffused through the water, they may be separated by straining through
linen; and this is a very common way of procuring them. Living Diatoms
are found on aquatic plants, on rocks and stones, under water or on
mud, presenting themselves as coloured fringes, cushion-like tufts, or
filmy strata. In colour the masses vary from a yellowish brown to
almost black. They are difficult, both when living and dead, to
separate from foreign matter; but repeated washings are effectual in
both cases, and, for the living ones, their tendency to move towards
the light may also be taken advantage of. When only the shells are
wanted for mounting, the cell contents are removed by means of
hydrochloric and nitric acid. The most satisfactory medium for
preserving fresh Desmids and Diatoms is distilled water, and if the
water is saturated with camphor, or has dissolved in it a grain of
alum and a grain of bay salt to an ounce of water, confervoid growths
will be prevented. For larger preparations of Algæ, Thwaites' fluid is
strongly recommended. This is made by adding to one part of rectified
spirit as many drops of creasote as will saturate it, and then
gradually mixing with it in a pestle and mortar some prepared chalk,
with sixteen parts of water; an equal quantity of water saturated with
camphor is then to be added, and the mixture, after standing for a
few days, to be carefully filtered.
For authorities on the morphology and classification of the Algæ,
students may be referred to Sachs' "Text Book" and Le Maout's "System
of Botany," of which there are good translations, and the
"Introduction to Cryptogamic Botany," by the Rev. M. J. Berkeley; for
descriptions and the identification of species, to the text and
figures of Harvey's "Phycologia Britannica," and "Nature-Printed
Sea-weeds." Both of these are however costly. Among the cheaper works
are "British Sea-weeds," by S. O. Gray (Lovell, Reeve & Co.),
"Harvey's Manual" and an abridgment by Mrs. A. Gatty, with reduced but
well executed copies of the figures, of the Phycologia. This synopsis
can often be picked up cheap at second-hand book-stalls; and there is
a very excellent low-priced work suitable for amateurs, Grattann's
"British Marine Algæ," containing recognizable figures of nearly all
our native species. Landsborough's "Popular History of British
Sea-weeds," and Mrs. Lane Clarke's "Common Sea-weeds," are also cheap
and useful manuals on the subject.
[Illustration: Floral design]
SHELLS.
BY
B. B. WOODWARD.
[Illustration: POND SNAILS.]
SHELLS.
INTRODUCTORY.
In the very earliest times, long before there was any attempt at the
scientific classification and arrangement of shells, they appear to
have been objects of admiration, and to have been valued on account of
their beauty, for we find that the pre-historic men, who, in company
with the mammoth, or hairy elephant, and other animals now extinct,
inhabited Southern France in days long gone by, used to bore holes in
them, and, like the savage of to-day, wear them as ornaments. The
Greek physician and philosopher, Aristotle, is said to have been the
first to study the formation of shells, and to raise the knowledge
thus acquired into the position of a science; by him shells were
divided into three orders--an arrangement preserved, with some small
changes, by Linnæus. It is possible that the world-wide renown of the
Swedish naturalist during the last century, and the ardour with which
he pursued his investigations, may have given an impetus to the study
of natural objects, for we find that at that period large sums were
often given by collectors for choice specimens of shells. Nor is this
to be wondered at, for few things look nicer, or better repay trouble
expended on them, than does a well-arranged and carefully mounted and
named collection of shells. Certainly nothing looks worse than a
number of shells of all descriptions, of every kind, shape, and
colour, thrown promiscuously into a box, like the unfortunate animals
in a toy Noah's ark, to the great detriment of their value and beauty;
for, as the inevitable result of shaking against each other, the
natural polish is taken off some, the delicate points and ornaments
are broken off others, the whole collection becoming in time unsightly
and disappointing, and all for want of a little care at the outset.
In this, as in every other undertaking, "how to set about it" is the
chief difficulty with beginners; and here, perhaps, a few hints
gathered from experience may not be without value. One thing a young
collector should always bear in mind, however, is, that no
instructions can be of any avail to him unless, for his part, he is
prepared to bring patience, neatness, and attention to detail, to bear
upon his work.
Since it is important to know the best way of storing specimens
already acquired, we will, in the first place, devote a few words to
this point, and then proceed to describe the best means of collecting
specimens, and of naming, mounting, and arranging the same.
HOW TO MAKE A CABINET.
It is a common mistake, both with old and young, to imagine that a
handsome cabinet is, in the first instance, a necessity; but no
greater blunder can be made: the cabinet should be considered merely
an accessory, the collection itself being just as valuable, and
generally more useful, when kept in a series of plain wooden or
cardboard boxes. We intend, therefore, to describe the simplest
possible means of keeping a collection of shells, leaving elaborate
and costly methods to those who value the case more than its contents.
The first thing required is some method of keeping the different
species of shells apart, so that they may not get mixed, or be
difficult to find when wanted. The simplest plan of doing this is to
collect all the empty chip match-boxes you can find, throw away the
cases in which they slide, and keep the trays, trying to get as many
of a size as possible. (The ordinary Bryant & May's, or Bell &
Black's, are the most useful, and with them the trays of the small
Swedish match-boxes, two of which, placed side by side, occupy nearly
exactly the same space as one and a half of the larger size, and so
fit in with them nicely.) In these trays your shells should be placed,
one kind in each tray; but although very convenient for most
specimens, they will of course be too small for very many, and so the
larger trays must be made. This may easily be done as follows: cut a
rectangular piece of cardboard two inches longer one way than the
length of the match-tray, and two inches more the other way than twice
the width of the match-tray; then with a pencil rule lines one inch
from the edges and parallel with them (Fig. 1); next cut out the
little squares (_a_ _a_, _a_ _a_) these lines form in the corners of
the piece of cardboard, and then with a penknife cut _half_ through the
card, exactly on the remaining pencil-lines, and bend up the pieces,
which will then form sides for your tray; and by binding it round with
a piece of blue paper, you will have one that will look neat, uniform
with the others, and yet be just twice their size. If required, you
can make in the same way any size, only take care that they are all
multiples of one standard size, as loss of space will thereby be
avoided when you come to the next process in your cabinet. This is, to
get a large box or tray in which to hold your smaller ones.
[Illustration: Fig. 1. How to cut a cardboard tray.]
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The simplest plan is to get some half-dozen cardboard boxes (such as
may be obtained for the asking or for a very trifling cost at any
draper's), having a depth of from one to two inches (according to the
size of your shells); in these your trays may be arranged in columns,
and the boxes can be kept one above the other in a cupboard or in a
larger box. More boxes and trays can, from time to time, be added as
occasion requires, and thus the whole collection may be kept in good
working order at a trifling cost. A more durable form of cheap cabinet
may be made by collecting the wooden boxes so common in grocers'
shops, cleaning them with sand-paper, staining and varnishing them
outside, and lining them inside with paper; or, if handy at
carpentering, you may make all your boxes, or even a real cabinet, for
yourself.
HOW TO COLLECT SHELLS.
Provision being thus made for the comfortable accommodation of your
treasures, the next consideration is, how to set about collecting
them. Mollusca are to be found all over the globe, from the frozen
north to the sun-baked tropics, on the land or in lakes, rivers, or
seas--wherever, in fact, they can find the food and other conditions
suitable for their growth and development; but the collector who is
not also a great traveller, must of course rely for his foreign
specimens upon the generosity of friends, or else procure them from
dealers. In most districts of our own country, there are, however, to
be found large numbers of shells whose variety and beauty will
astonish and reward the efforts of any patient seeker. Begin with your
own garden,--search in the out-of-the-way, and especially damp,
corners; turn over the flower-pots and stones which have lain longest
in one place, search amongst the roots of the grass growing under
walls, and in the moss round the roots of the trees, and you will be
surprised at the number of different shells you may find in a very
short space of time. When the resources of the garden have been
exhausted, go into the nearest lanes and again search the grass and at
the roots of plants, especially the nettles which grow beside ditches
and in damp places; hunt amongst the dead leaves in plantations, and
literally leave no stone unturned. All the apparatus it is necessary
to take on these excursions consists of a few small match or
pill-boxes in which to carry home the specimens; a pair of forceps to
pick up the smaller ones, or to get them out of cracks; a hooked stick
to beat down and pull away the nettles; and, above all, sharp eyes
trained to powers of observation. The best time to go out, is just
after a warm shower, when all the grass and leaves are still wet, for
the land-snails are very fond of moisture, and the shower entices them
out of their lurking-places. Where the ground is made of chalk or
limestone, they will be found most abundant; for as the snail's shell
is composed of layers of animal tissue, strengthened by depositions of
calcareous earthy-matter which the creature gets from the plants on
which it feeds, and these in their turn obtain from the soil--it
naturally follows that the snail prefers to dwell where that article
is most abundant, as an hour's hunt on any chalk-down will soon show.
When garden and lanes are both exhausted, you may then turn to the
ponds and streams in the neighbourhood, where you will find several
new kinds. Some will be crawling up the rushes near the margin of the
water, others will be found in the water near the bank, while others
may be obtained by pulling on shore pieces of wood and branches that
may be floating in the water; but the best are sure to be beyond the
reach of arm or stick, and it will be necessary to employ a net, which
may be easily made by bending a piece of wire into a circle of about
four inches in diameter, and sewing to it a small gauze bag; it may be
mounted either on a long bamboo, or, better still, on one of those
ingenious Japanese walking-stick fishing-rods. For heavier work,
however, such as getting fresh-water mussels and other mollusca from
the bottom, you will require a net something like the accompanying
figure (Fig. 2), about one foot in diameter. This, when attached to a
long rope, may be thrown out some distance and dragged through the
water-weeds to the shore, or if made with a square instead of a
circular mouth, it may be so weighted that it will sink to the bottom,
and be used as a dredge for catching the mussels which live
half-buried in the mud. To carry the water-snails home, you will find
it necessary to have tin boxes (empty mustard-tins are the best), as
match-boxes come to pieces when wetted.
[Illustration: Fig. 2. Net for taking water-snails.]
The finest collections of shells, however, are to be made at the
sea-side, for the marine mollusca are both more varied in kind and
more abundant than the land and fresh-water ones, and quite an
extensive collection may be made in the course of an afternoon's
ramble along the shore; it is necessary, however, to carefully reject
such specimens as are worn by having been rolled by the waves upon the
beach, as they are not of any great value in a collection; it is
better, in fact, if possible, to go down to the rocks at low water and
collect the living specimens. Search well about and under the
sea-weeds, and in the rock-pools, and, when boating, throw your
dredge-net out and tow it behind, hauling it in occasionally to see
what you have caught, and to empty the stones and rubbish out.
At low tide also, look out for rocks with a number of round holes in
them, all close together, for in these holes the Pholas (Fig. 22)
dwells, having bored a burrow in the solid rock, though _how_ he does
it we do not yet quite know.
The Razor-shells and Cockles live in the sand, their presence being
indicated by a small round hole; but they bury themselves so fast that
you will find it difficult to get at them. Some good specimens, too,
of the deeper water forms are sure to be found near the spots where
fishermen drag their boats ashore, as they are often thrown away in
clearing out the nets; moreover, if you can make friends with any of
the said fishermen, they will be able to find and bring you many nice
specimens from time to time.
The reason that so much has been said about collecting living
specimens, is not only because in them the shell is more likely to be
perfect, but also because in its living state the shell is coated with
a layer of animal matter, sometimes thin and transparent, at others
thick and opaque, called the _periostracum_ (or _epidermis_), which
serves to protect the shell from the weather, but which perishes with
the animal, so that dead shells which have lain for some time
tenantless on the ground, or at the bottom of the water, exposed to
the destructive agencies that are constantly at work in nature, have
almost invariably lost both their natural polish and their varied
hues, and are besides only too often broken as well. Since, however,
even a damaged specimen is better than none at all, such should always
be kept until a more perfect example can be obtained.
HOW TO PREPARE THE SHELLS FOR THE CABINET.
The question with which we have next to deal is, after collecting a
number of living mollusks, how, in the quickest and most painless
manner possible, to kill the animals in order to obtain possession of
their shells. There is but one way we know of in which this may be
accomplished, and that is by placing the creatures in an earthen jar
and pouring _boiling_ water on them. With land, or fresh-water snails,
the addition of a large spoonful of table-salt is advisable, as it
acts upon them chemically, and not only puts them sooner out of pain,
but also renders their subsequent extraction far easier. Death by this
process is instantaneous, and consequently painless; but to leave
snails in cold salt water is to inflict on them the tortures of a
lingering death; while for the brutality of gardeners and other
thoughtless persons who seek to destroy the poor snail they find
eating their plants by crushing it under foot on the gravel path, no
words of condemnation are too strong, since it must always be borne in
mind that snails have not, like us, _one_ nervous centre, but three,
and are far more tenacious of life; hence, unless all the nerves are
destroyed at once, a great deal of suffering is entailed on the poor
creature; and if merely crushed under foot, the mangled portions _will
live for hours_. Hot water has also the advantage of tending to remove
the dirt which is almost sure to have gathered on the shells, and so
helping to prepare them better for the cabinet. As soon as the water
is cool enough, fish out the shells one by one and proceed to extract
the dead animals. This, if the mollusk is _univalve_ (_i.e._, whose
shell is composed of a single piece), such as an ordinary garden
snail, can easily be done by picking them out with a pin; you will
find, probably, that some of the smaller ones have shrunk back so far
into their shells as to be beyond the reach of a straight pin, so it
will be necessary to bend the pin with a pair of pliers, or, if none
are at hand, a key will answer the purpose if the pin be put into one
of the notches and bent over the edge until sufficiently curved to
reach up the shell. You will find it convenient to keep a set of pins
bent to different curves, to which you may fit handles by cutting off
the heads and sticking them into match stems. It is a good plan to
soak some of the smaller snails in clean cold water before killing
them, as they swell out with the water, and do not, when dead, retreat
so far into their shells. If you have a microscope, and wish to keep
the animals till you have time to get the tongues out, drop the bodies
into small bottles of methylated spirit and water, when they will keep
till required, otherwise they should of course be thrown away at once.
The now empty shells should be washed in clean warm water, and, if
very dirty, gently scrubbed with a soft nail or tooth brush, and then
carefully dried.
In such shells as the Periwinkle, Whelk, etc., whose inhabitants close
the entrance of their dwelling with a trap-door, or _operculum_ as it
is called, you should be careful to preserve each with its proper
shell.
If you are cleaning _bivalves_, or shells composed of two pieces, like
the common mussel, you will have to remove the animal with a penknife,
and while leaving the inside quite clean, be very careful not to break
the ligament which serves as a hinge; then wash as before, and tie
them together to prevent their gaping open when dry.
Sometimes the fresh-water or marine shells are so coated over with a
vegetable growth that no scrubbing with water alone will remove it,
and in these cases a weak solution of caustic soda may be used, but
very carefully, since, if too strong a solution be employed, the
surface of the shell will be removed with the dirt, and the specimen
spoilt. In some shells the periostracum is very thick and coarse, and
must be removed before the shell itself can be seen; but it is always
well to keep at least one specimen in its rough state as an example.
In other shells the periostracum is covered over with very fine,
delicate hairs (_Helix sericea_ and _Helix hispida_, Fig. 3), and
great care must then be taken not to brush these off.
[Illustration: Fig. 3. (_a_) _Helix sericea_ and
(_b_) _Helix hispida_.]
HOW TO MOUNT THE SHELLS FOR THE CABINET.
When the specimens are thoroughly cleaned, the next process is to sort
out the different kinds, placing each description in a different tray,
and then to get them ready for mounting, for no collection will look
well unless each kind is so arranged that it may be seen to the best
advantage, and is also carefully named. Where you have a good number,
pick out first the largest specimens of their kind, then the smallest,
then a series, as you have room for them, of the most perfect; and
finally those which show any peculiarity of structure or marking. Try,
too, to get young forms as well as adult, for the young are often very
different in appearance from the full-grown shell. Mark on them,
especially on such as you have found yourself, the locality they came
from, as it is very important to the shell collector to know this,
since specimens common enough in one district are often rare in
another. Either write the name of the place in ink on a corner of the
shell itself, or gum a small label just inside it, or simply number
it, and write the name of the place with a corresponding number
against it in a book kept for the purpose. Next select a tray large
enough to hold all you have of this kind; place a piece of cotton wool
at the bottom, and lay your shells upon it. For small shells, however,
this method is not suitable, as the cotton wool acts on them like a
spring mattress, and they are liable on the least shock to be jerked
out of their trays and lost. This difficulty may be met by cutting a
piece of cardboard so that it just fits into your tray, and then
gumming the shells on to it in rows; but remember that, in this plan
of mounting, it is impossible to take the shells up and examine them
on all sides as you do the loose ones, and so you must mount a good
many, and place them in many different positions, so that they may be
seen from as many points of view as possible. The gum used should
always have nearly one-sixth of its bulk of pure glycerine added to
it; this prevents it from becoming brittle when dry, otherwise your
specimens would be liable after a time to break away from the card and
get lost. If the shells will not stay in the position you require,
wedge them up with little pieces of cork until the gum is dry.
When the shells are mounted, you must try, if you have not already
done so, to get the proper names for them; it is as important to be
able to call shells by their right names as it is to know people by
theirs. The commoner sorts you will be able to name from the figures
of them given in text-books, such as those quoted in the list at the
end of this little work; but some you will find it very difficult to
name, and it will then be necessary to ask friends who have
collections to help you, or to take them to some museum and compare
them with the named specimens there exhibited. When the right name is
discovered, your label must then be written in a very small, neat
hand, and gummed to the edge of the tray or on the card if your
specimens are mounted. At the top you put the Latin name, ruling a
line underneath it, and then, if you like, add the English name; next,
put the name of the place and the date at which it was found, thus:--
=====================================
Helix aspersa (Common snail),
-----------------------------
Lane near Hampstead Heath,
July 10th, 1882.
=====================================
A double red ink line ruled at the top and bottom will add a finished
appearance to it.
HOW TO CLASSIFY THE SHELLS FOR THE CABINET.
All the foregoing processes, except the naming of your specimens, are
more or less mechanical, and are only the means to the end--a properly
arranged collection. For, however well a collection may be mounted, it
is practically useless if the different shells composing it be not
properly classified. By classification is meant the bringing together
those kinds that most resemble each other, first of all into large
groups having special characteristics in common, and then by
subdividing these into other smaller groups, and so on. Thus the
animal kingdom is divided, first of all, into _Sub-kingdoms_, then
each _Sub-kingdom_ into so many _Classes_ containing those which have
further characteristics in common, the _Classes_ into _Orders_, the
_Orders_ into _Families_, the _Families_ into _Genera_, and these
again into species or kinds.
The Mollusca, or soft-bodied animals, of whose protecting shells your
collection consists, form a sub-kingdom, and are subdivided into four
classes:--
1. Cephalopoda.
2. Gasteropoda.
3. Pteropoda.
4. Lamellibranchiata (or Conchifera).
And these again into Families, Genera, and Species.
The space at our disposal being limited, it is impossible to do more
than furnish some general outlines of the different forms. For further
details it will be necessary to refer to one of the larger works, a
list of which will be found on the last page.
[Illustration: Fig. 4. _Argonauta Argo._]
[Illustration: Fig. 5. "Bone" of _Sepia officinalis_.]
CLASS I.--The CEPHALOPODA (Head-footed) contains those mollusca that,
like the common Octopus, have a number of feet (or arms) set round
the mouth, and is divided into those having two gills. (Order I.
Dibranchiata); and those with four (Order II. Tetrabranchiata). Order
I. is again divided into: (_a._) Those with _eight_ feet like the
Argonaut (or Paper-nautilus, Fig. 4), which fable has so long endowed
with the power of sailing on the surface of the ocean, (it is even
represented in one book as propelling itself through the air!) and the
common Octopus. (_b._) Those with _ten_ feet, such as the Loligo (or
Squid, Fig. 6), whose delicate internal shell so much resembles a pen
in shape; the Cuttle-fish (Sepia, Figs. 5 & 7), whose so-called
"bone" (once largely used as an ink eraser) is frequently found on our
southern coasts; and the pretty little _Spirula_ (Fig. 8).
[Illustration: Fig. 6. _Loligo vulgaris_, and "Pen."]
[Illustration: Fig. 7. _Sepia officinalis._]
The only representative of the four-gilled order now living is the
well-known Pearly Nautilus; but in former times the Tetrabranchiata
were extremely numerous, especially the _Ammonites_.
[Illustration: Fig. 8. _Spirula_.]
CLASS II.--GASTEROPODA (Belly-footed) comprises those mollusca which,
like the common snail, creep on the under-surface of the body, and
with one exception (_Chiton_, Fig. 20) their shells are univalve
(_i.e._, composed of one piece). But before we go further, it may be
well to point out the names given to different parts of a univalve
shell. The aperture whence the animal issues is called the _mouth_,
and its outer edge the _lip_; each turn of the shell is a _whorl_; the
last and biggest, the _body-whorl_, the whorls, from the point at the
top, or _apex_, down to the mouth form the _spire_; and the line where
the whorls join each other is called the _suture_. The axis of the
shell around which the whorls are coiled is sometimes open or hollow,
and the shell is then said to be _umbilicated_ (as in Fig. 3_b_); when
closely coiled, a pillar of shell, or _columella_, is left (as in Fig.
9). Sometimes the corner of the mouth farthest from the spire and
next the columella, is produced into a channel, the _anterior canal_
(as in Fig. 9); whilst where the mouth meets the base of the spire
there may be a kind of notch which is termed the _posterior canal_.
Most Gasteropods are _dextral_, that is to say, the mouth is to the
right of the axis as you look at it; a few, however, are _sinistral_,
or wound to the left (like _Physa_); whilst reversed varieties of both
kinds are met with.
Gasteropods of the first order have comb-like gills placed in advance
of the heart, and are hence termed PROSOBRANCHIATA. They are divided
into two groups: (_a_) _Siphonostomata_ (Tube-mouthed), in which the
animal has a long proboscis, and a tube, or siphon, from the
breathing-chamber that passes along the anterior canal of the shell,
which in this group is well developed. They have a horny operculum, or
lid, with which to close the aperture. (_b_) _Holostomata_ (or
Whole-mouthed). In these the siphon is not so produced, and does not
want to be protected; accordingly the mouth of the shell is _entire_,
_i.e._ has no canal. The operculum is horny or shelly. The former
(group _a_) includes several families:
1. _Strombidæ_, comprising shells, like the huge _Strombus_, or
"Fountain-shell," which is so often used to adorn the mantelpiece or
rockery, and from which cameos are cut.
2. The _Muricidæ_, of which the _Murex_ (an extraordinary form of this
is the "Venus' comb," _Murex tenuispina_, Fig. 9), the Mitre-shells,
and the Red-Whelks (_Fusus_) are examples.
[Illustration: Fig. 9. _Murex tenuispina._]
3. The _Buccinidæ_, taking its name from its type, the Common Whelk
(_Buccinum undatum_), and including such other forms as the Dog-Whelk
(_Nassa_), the _Purpura_, the strange _Magilus_, and the lovely
Harp-Shells and Olives (Fig. 10).
[Illustration: Fig. 10. _Oliva tessellata._]
4. The _Cassididæ_, or "Helmet-Shells." _Cassis rufa_, from West
Africa, is noted as the best species of shell for cameo engraving;
with it are classed the "Tun" (_Dolium_) and the great "Triton"
(_Triton tritonis_), such as the sea-gods of mythology are represented
blowing into by way of trumpet, and which are used by the Polynesian
Islanders to this day instead of horns.
5. The _Conidæ_, whose type, the "Cone-shell" (Fig. 11), is at once
distinctive and handsome, but which in the living state is covered by
a dull yellowish-brown periostracum that has to be carefully removed
before the full beauties of the shell are displayed.
[Illustration: Fig. 11. Conus vermiculatus.]
6. The _Volutidæ_, embracing the Volutes and "Boat-shells" (_Cymba_).
7. The _Cypræidæ_, or Cowries (Fig. 12), which owe their high polish
to the size of the shell-secreting organ (mantle), whose edges meet
over the back of the shell, concealing it within its folds. With these
is classed the "China-shell" (_Ovulum_).
[Illustration: Fig. 12. Cypræa oniscus.]
The second group, or _Holostomata_, is divided into nineteen families,
beginning with--
1. The _Naticidæ_, whose type, the genus _Natica_, is well known to
all shell-collectors through the common _Natica monilifera_ of our
coasts.
2. The _Cancellariadæ_, in which the shells are cancellated or
cross-barred by a double series of lines running, one set with the
whorls, and the other across them.
3. The _Pyramidellidæ_, which are high-spired, elongated, and slender
shells, with the exception of the genus _Stylina_, which lives
attached to the spines of sea-urchins or buried in living star-fishes
and corals. 4. The _Solaridæ_ or "Staircase-shells," whose umbilicus
is so wide that, as you look down it, the projecting edges of the
whorls appear like a winding staircase. It is a very short-spired
shell.
5. The _Scalaridæ_, "Wentle-traps" or "Ladder-shells," which may be
readily recognised from their white and lustrous appearance and the
strong rib-like markings of the periodic mouths that encircle the
whorls.
6. The _Cerithiadæ_, or "Horn-shells," which are very high-spired, and
whose columella and anterior canal are produced in the form of an
impudent little tail, the effect of which, however, in the genus
_Aporrhais_, or "Spout-shells," is taken away by the expanded and
thickened lip.
7. In the next family, the _Turritellidæ_, or "Tower-shells," the type
Turritella is spiral; but in the allied form _Vermetus_, though the
spire begins in the natural manner, it goes off into a twisted tube
resembling somewhat an ill-made corkscrew. The mouth in this family is
often nearly round.
8. The _Melaniadæ_, and 9. The _Paludinidæ_, are fresh-water shells.
The former are turreted, and the latter conical or globular. Both are
furnished with opercula, but the mouth in the first is more or less
oval and frequently notched in front, while in the latter it is
rounded and entire.
10. The _Litorinidæ_, or Periwinkles, need no word from us.
11. The _Calyptræidæ_ comprise the "Bonnet-limpet," or _Pileopsis_,
and "Cup-and-saucer-limpets" (_Calyptræa_). They may be described
briefly as limpets with traces of a spire left. The genus _Phorus_,
however, is spiral, and resembles a _Trochus_. They have been called
"Carriers" from their strange habit of building any stray fragments of
shell or stone into their house, thus rendering themselves almost
indistinguishable from the ground on which they crawl.
12. The _Turbinidæ_, or "Top-shells," are next in order, and of these
the great _Turbo marmoreus_ is a well-known example, being prepared as
an ornament for the whatnot or mantelpiece by removing the external
layer of the shell in order to display the brilliant pearly nacre
below. These mollusca close their mouths with a horny operculum,
coated on its exterior by a thick layer of porcelain-like shelly
matter. With them are classed the familiar _Trochus_ and other closely
allied genera.
13. The _Haliotidæ_ offer in the representative genus _Haliotis_, or
the "Ear-shell," another familiar mantelpiece ornament.
14. The _Ianthinidæ_, or "Violet-snails," that float about in
mid-Atlantic upon the gulf-weed, and at certain seasons secrete a
curious float or raft, to which their eggs are attached, are next in
order, and are followed by--
15. The _Fissurellidæ_, or "Key-hole" and "Notched limpets," whose
name sufficiently describes them. To these succeed--
16. The _Neritidæ_, an unmistakable group of globular shells, having
next to no spire and a very glossy exterior, generally ornamented with
a great variety of spots and bands.
17. The _Patellidæ_, or true Limpets, are well known to every sea-side
visitor: large species, as much as two inches across, are to be found
on the coast of Devon, but these are pigmies compared with a South
American variety which attains a foot in diameter.
18. The _Dentaliadæ_, represented by the genus _Dentalium_, or
"Tooth-shell," are simply slightly curved tubes, open at both ends and
tapering from the mouth downwards, and cannot be mistaken.
19. Lastly, we have the _Chitonidæ_, whose single genus _Chiton_
possesses shells differing from all other mollusca in being composed
of eight plates overlapping each other, and in appearance reminding
one of the wood-louse. This animal is not only like the limpet in form
but also in habits, being found adhering to the rocks and stones at
low-water.
Order II.--PULMONIFERA. Contains the air-breathing _Gasteropods_, and
to it consequently belong all the terrestrial mollusca, though some
few aquatic genera are also included. The members of this order have
an air-chamber instead of gills, and are divided into two groups,
(_a_) those without an operculum, and (_b_) those having an operculum.
Foremost in the first group stands the great family--
1. _Helicidæ_, named after its chief representative, the genus
_Helix_. It also includes the "Glass-shell" (_Vitrina_), the
"Amber-shell" (_Succinea_), and such genera as _Bulimus_, _Achatina_,
_Pupa_, _Clausilia_ (Fig. 13), etc., which differ from the typical
_Helix_ in appearance, possessing as they do comparatively high
spires.
[Illustration: Fig. 13. _Clausilia biplicata._]
2. The _Limacidæ_, or "slugs," follow next; of these only one, the
genus _Testacella_, has an external shell stuck on the end of its
tail; the rest have either a more or less imperfect shell concealed
underneath the mantle, or else none at all.
3. The _Oncidiadæ_ are slug-like, and devoid of shell.
4. The _Limnæidæ_ embrace the "Pond-snails," chief of whom is the
well-known, high-spired _Limnæa stagnalis_. Other shells of this
family associated with _Limnæa_ are, however, very different in shape;
for instance, _Physa_ has its whorls turning to the left instead of to
the right; _Ancylus_ (Fig. 24), or the freshwater limpet, is of course
limpet-like; while _Planorbis_, or the "Coil-shell," is wound like a
watch-spring.
5. The _Auriculidæ_ includes both spiral shells, such as _Auricula_
and _Charychium_, and a limpet-like one _Siphonaria_.
At the head of group _b_ stands 1, _Cyclostomidæ_. _Cyclostoma
elegans_ is a common shell on our chalk-downs, and well illustrates
its family, in which the mouth is nearly circular. Foreign examples of
this genus are much esteemed by collectors. The other two families
are, (2) _Helicinidæ_ and (3) _Aciculidæ_.
Order III.--OPISTHOBRANCHIATA. These animals carry their gills exposed
on the back and sides, towards the rear of the body. Only a few have
any shell. 1. The _Tornatellidæ_, which have a stout little spiral
shell. 2. The _Bullidæ_, in which the spire is concealed (Fig. 26). 3.
The _Aplysiadæ_, where the shell is flat and oblong or triangular in
shape. The remaining families are slug-like and shell-less.
[Illustration: Fig. 14. _Bulla ampulla._]
Order IV.--NUCLEOBRANCHIATA. Derives its name from the fact that the
animals constituting it have their respiratory and digestive organs in
a sort of nucleus on the posterior part of the back, and covered by a
minute shell. As they are pelagic, the shells are not readily to be
obtained. They are divided into two families, _Firolidæ_ and
_Atlantidæ_.
CLASS III.--PTEROPODA. Like the last, these pretty little mollusca are
ocean-swimmers. The members of one division of them, to which the
_Cleodora_ belongs, is furnished with iridescent external shells.
[Illustration: Fig. 15. _Petunculus guerangeri._]
[Illustration: Fig. 16. _Venus plicata._]
CLASS IV.--The LAMELLIBRANCHIATA (Plate-gilled), or CONCHIFERA
(Shell-bearing), includes the mollusca commonly known as "bivalves,"
the animal being snugly hidden between two more or less closely
fitting shelly valves. The oysters, cockles, etc., are examples of
this class. The two valves are fastened together near their points, or
beaks (technically called _umbones_), by a tough elastic ligament,
sometimes supplemented by an internal cartilage. If this be severed
and the valves parted, it will be found that in most cases they are
further articulated by projecting ridges or points called the _teeth_,
which, when the valves are together, interlock and form a hinge; the
margin of the shell on which the teeth and ligament are situated is
termed the _hinge-line_. A bivalve is said to be _equivalve_ when the
two shells composing it are of the same size, _inequivalve_ when they
are not. If the umbones are in the middle, the shell is _equilateral_
(Fig. 15); but _inequilateral_ when they are nearer one side than the
other (Fig. 16). If the shell be an oyster or a scallop, you will find
on the inside a single circular scar-like mark near the centre; this
is the point to which the muscles that close the valves and hold them
so tightly together are attached. In the majority of bivalves,
however, there are two such muscular impressions, or scars, one on
either side of each valve of the shell. The former group on this
account are often called _Monomyaria_ (having one shell-muscle), and
the latter _Dimyaria_ (having two shell-muscles). In the last named
the two muscular impressions are united by a fine groove (or
_pallial-line_), which in some runs parallel to the margin of the
shell (Fig. 15), whilst in others it makes a bend in (_pallial-sinus_)
on one side of the valve towards the centre (Fig. 16). In Monomyaria
it will be found running parallel to the margin of the shell. It marks
the line of attachment of the mantle or shell-secreting organ of the
animal to the shell which grows by the addition of fresh matter along
its edges, so that the concentric curved markings so often seen on the
exterior correspond in their origin with the periodic mouths of the
Gasteropods. The bivalves are all aquatic, and many bury themselves in
the sand or mud by means of a fleshy, muscular foot. These are
furnished with two siphons, or fleshy tubes, sometimes united,
sometimes separate, through which they respire, drawing the water in
through one and expelling it by the other. Those kinds whose habit it
is to bury themselves below the surface of the mud or sand are
furnished with long retractile siphons, and to admit of their
withdrawal into the shell, the mantle is at this point attached
farther back, giving rise to the _pallial-sinus_ above described; this
sinus is deeper as the siphons are proportionately longer, and in
many cases, too, the valves do not meet at this point when the shell
is closed.
Attention to these particulars is necessary when arranging your
bivalves, as on them their classification depends, the class being
divided into--
_a._ ASIPHONIDA (Siphonless).
_b._ SIPHONIDA _Integro-pallialia_ (with Siphons).--Pallial-line entire.
_c._ SIPHONIDA _Sinu-pallialia_ (with Siphons).--Sinus in pallial-line.
DIVISION _a_.--ASIPHONIDA--is next subdivided into--
1. The _Ostreidæ_, or oysters, which are deservedly a distinct family
in themselves.
2. The _Anomiadæ_, comprising the multiform and curiously constructed
_Anomia_, with the "Window-shells" (_Placuna_).
3. The _Pectinidæ_, taking its name from the genus _Pecten_, or
"Scallop-shells," of which one kind (_P. maximus_) is frequently to be
seen at the fishmongers' shops. The "Thorney oysters" (_Spondylus_)
take rank here, and are highly esteemed by collectors, one specimen
indeed having been valued at £25!
4. The _Aviculidæ_, or "Wing-shells," among which are numbered the
"Pearl-oyster" of commerce (_Meleagrina margaritifera_). The strange
T-shaped "Hammer oyster" belongs to this family, as does also the
_Pinna_. The Pinnas, like the mussels and some other bivalves, moor
themselves to rocks by means of a number of threads spun by the foot
of the mollusc, and termed the _byssus_, which in this genus is finer,
more silky, than in any other, and has been woven into articles of
dress.
5. The _Mytilidæ_, or mussels, including the _Lithodomus_, or
"Date-shell," which bores into corals and even hard limestone rocks.
[Illustration: Fig. 17. Hinge-teeth of _Arca barbata_.]
6. The _Arcadæ_, or "Noah's-ark-shells," characterized by their long
straight hinge-line set with numerous very fine teeth (Fig. 17). The
"Nut-shell" (_Nucula_) belongs to this family.
7. The _Trigoniadæ_, whose single living genus, the handsome _Trigonia_
(Fig. 18), is confined to the Australian coast-line, whereas in times
now long past they had a world-wide distribution.
[Illustration: Fig. 18. _Trigonia margaritacea._]
8. The _Unionidæ_, comprising the fresh-water mussels.
DIVISION _b_.--SIPHONIDA _Integropallialia_.
1. The _Chamidæ_, represented by the reef-dwelling _Chama_.
2. The _Tridacnidæ_, whose sole genus _Tridacna_ contains the largest
specimen of the whole class of bivalves, the shells sometimes
measuring two feet and more across.
3. The _Cardiadæ_, or cockles.
4. The _Lucinidæ_, in which the valves are nearly circular, and as a
rule not very attractive in appearance, though the "Basket-shell"
(_Corbis_) has an elegantly sculptured exterior.
5. The _Cycladidæ_, whose typical genus _Cyclas_, with its round form
and thin horny shell, is to be found in most of our ponds and streams.
6. The _Astartidæ_, a family of shells having very strongly developed
teeth, and the surface of whose valves is often concentrically ribbed.
[Illustration: Fig. 19. Hinge of _Cardita sinuata_.]
7. The _Cyprinidæ_, which have very solid oval or elongated shells and
conspicuous teeth (Fig. 19). The "Heart-cockle" (_Isocardia_) belongs to
this family.
DIVISION _c_.--SIPHONIDA _Sinu-pallialia_.
1. The _Veneridæ_. The hard, solid shells of this family are for
elegance of form and beauty of colour amongst the most attractive a
collector can posses. Their shells are more or less oval and have
three teeth in each valve (Fig. 20).
[Illustration: Fig. 20. Hinge of _Cytherea crycina_.]
[Illustration: Fig. 21. Hinge of _Lutraria elliptica_]
2. The _Mactridæ_ are somewhat triangular in shape, and may be at once
recognised by the pit for the hinge-ligament, which also assumes that
form, as seen in the accompanying figure of _Lutraria elliptica_
(Fig. 21).
3. The _Tellinidæ_ comprise some of the most delicately tinted, both
externally and internally, of all shells. In some, coloured bands
radiate from the umbones, and well bear out the fanciful name of
"Sunset shells" bestowed upon them. Their valves are generally much
compressed.
4. The _Solenidæ_, or "Razor-shells," rank next, and are readily
recognised by the extreme length of the valves in proportion to their
width, and also by their gaping at both ends.
5. The _Myacidæ_ or "Gapers," have the siphonal ends wide apart (in
the genus _Mya_ both ends gape), and are further characterized by the
triangular process for the cartilage, which projects into the interior
of the shell. One valve (the left) is generally smaller than the
other.
6. The _Anatinidæ_ have thin, often inequivalve pearly shells. The
genus _Pandora_ is the form most frequently met with in collections.
7. The _Gastrochænidæ_ embraces two genera (_Gastrochæna_ and
_Saxicava_) of boring mollusca, which perforate shells and rocks, and
also, the remarkable tube-like "Watering-pot-shell" (_Aspergillum_)
which is hardly recognisable as a bivalve at all.
[Illustration: Fig. 22. _Pholas dactylus._]
8. The _Pholadidæ_ concludes the list of bivalves, and comprises the
common rock-boring Pholas (Fig. 22) of our coasts and the wood-boring
shipworm "Teredo" (Fig. 23).
* * * * *
Although the _Brachiopoda_, or "Lamp-shells," are not true mollusca,
they are not very far removed from them, and are so often to be found
in cabinets that it will not do to pass them over, especially since in
past times they were very abundant, an enormous number occurring in
the fossil state. Only eight genera are now living. Shells belonging
to this class are readily recognised by the fact of one valve being
larger than the other, and possessing a distinct peak, the apex of
which is perforated. The _Terebratulidæ_ are the most extensive family
of this class.
[Illustration: Fig. 23. _Teredo navalis._]
HOW TO ARRANGE THE SHELLS IN THE CABINET.
When you have arranged your specimens in the order above indicated,
proceed to place them in your boxes, arranging and labelling them after
the manner shown in the accompanying diagram.
+----------+----------+----------+----------+----------+
| Class. | | | | |
+----------+ Species. | Species. | Species. | Species. |
| Order. | | | | |
+----------+----------+----------+----------+----------+
| Family | | | | |
| Name. | | | | |
+----------+ Species. | Species. | Species. | Species. |
| Generic | | | | |
| Name. | | +----------+ |
+----------+----------+----------+ Family +----------+
| | | | Name. | |
| Species. | Species. | Species. +----------+ Species. |
| | | | Generic | |
+----------+----------+----------+ Name. +----------+
| | | +----------+ |
| | Generic | | | |
| Species. | Name. | Species. | Species. | Species. |
| | | | | |
+----------+----------+----------+----------+----------+
| | | | | Generic |
| Species. | Species. | Species. | Species. | Name. |
| | | | | |
+----------+----------+----------+----------+----------+
| | | Generic | | |
| Species. | Species. | Name. | Species. | Species. |
| | | | | |
+----------+----------+----------+----------+----------+
| | | | | |
| Species. | Species. | Species. | Species. | Species. |
| | | | | |
+----------+----------+----------+----------+----------+
On the lid, or on a slip of paper or card placed at the head of your
columns of trays, write the class and order, with its proper number
(I., II., etc., as the case may be); then at the top of your left-hand
column place the family and its number, and under it the name of the
first genus. The species (one in each tray) come next, then the name
of the next genus following it, succeeded by its species, and so on.
The object of the young collector should be to obtain examples of as
many _genera_ as possible, since a collection in which a great number
of genera are represented is far more useful and instructive than one
composed of a great many species referable to but few genera. He will
also find it very convenient to separate the British Shells from his
general collection, sub-dividing them for convenience into "Land and
Fresh-water," and "Marine." Of these he should endeavour to get every
species, and even variety, making the thing as complete as possible.
Or a separate collection may be made of all those kinds which he can
find within a certain distance of his own home. A collection of this
sort possesses, in addition to its scientific worth, an interest of
its own, owing to the local associations that invariably connect
themselves with it.
TABLE OF SOME OF THE MORE IMPORTANT GENERA, SHOWING THE APPROXIMATE
NUMBER OF SPECIES BELONGING TO EACH GENUS AND THEIR DISTRIBUTION.
CLASS I.--CEPHALOPODA.
ORDER I.--Dibranchiata.
Section A.--_Octopoda._
Family. Genus. No. of Species. Distribution.
1. Argonauta 4 Tropical seas.
2. Octopus 46 Rocky coasts in temperate and
tropical regions.
Section B.--_Decapoda_.
3. Loligo 19 Cosmopolitan.
4. Sepia 30 On all coasts.
5. Spirula 3 All the warmer seas.
ORDER II.--_Tetrabranchiata_.
6. Nautilus 3 or 4 Chinese Seas, Indian Ocean,
Persian Gulf.
CLASS II.--GASTEROPODA.
ORDER I.--Prosobranchiata.
Division _a_.--_Siphonostomata._
No. of
Family. Genus. Species. Distribution.
1. Strombus 60 W. Indies, Mediterranean, Red Sea,
Indian Ocean, Pacific--low water
to 10 fathoms.
Pteroceras 12 India, China.
2. Murex 180 On all coasts.
Columbella 200 Sub-tropical regions, in shallow
water on stones.
Mitra 350 Tropical regions, from low water
to 80 fathoms.
Fusus 100 On all coasts.
3. Buccinum 20 Northern seas, from low water to
140 fathoms.
Eburna 9 Red Sea, India, Australia, China,
Cape of Good Hope.
Nassa 210 World-wide--low water to 50 fathoms.
Purpura 140 World-wide--low water to 25 fathoms.
Harpa 9 Tropical--deep water, sand, muddy
bottoms.
Oliva 117 Sub-tropical--low water to 25 fathoms.
4. Cassis 34 Tropical regions, in shallow water.
Dolium 15 Mediterranean, India, China, W.
Indies, Brazil, New Guinea, Pacific.
Triton 100 Temperate and sub-tropical regions,
from low water to 50 fathoms.
Ranella 50 Tropical regions, on rocks and
coral-reefs.
Pyrula 40 Sub-tropical regions, in 17 to 35
fathoms.
5. Conus 300 Equatorial seas--shallow water to 50
fathoms.
Pleurotoma 500 Almost world-wide--low water to 100
fathoms.
6. Voluta 100 On tropical coasts, from the shore to
100 fathoms.
Cymba 10 West Coast of Africa, Lisbon, Straits
of Gibraltar.
Marginella 90 Mostly tropical.
7. Cypræa 150 Warmer seas of the globe, on rocks
and coral-reefs.
Ovulum 36 Britain, Mediterranean, W. Indies,
China, W. America.
Division _b_.--_Holostomata._
8. Natica 90 Arctic to tropical regions, on sandy
and gravelly bottoms, from low water
to 90 feet.
Sigaretus 26 E. and W. Indies, China, Peru.
9. Cancellaria 70 W. Indies, China, S. America, E.
Archipelago--low water to 40 fathoms.
10. Pyramidella 11 W. Indies, Mauritius, Australia, in
sandy bays and on shallow mud-banks.
Odostomia 35 Britain, Mediterranean, and
Madeira--low water to 50 fathoms.
Chemnitzia 70 World-wide--low water to 100 fathoms.
Eulima 26 Cuba, Norway, Britain, India,
Mediterranean, Australia--5
to 90 fathoms.
11. Solarium 25 Sub-tropical and tropical--widely
distributed.
12. Scalaria 100 World-wide--low water to 100 fathoms.
13. Cerithium 100 World-wide.
Potamides 41 Africa and India, in mud of large
rivers.
Aporrhais 3 Labrador, Norway, Britain,
Mediterranean--20 to 100 fathoms.
14. Turritella 50 World-wide--low water to 100 fathoms.
Vermetus 31 Portugal, Mediterranean, Africa,
India.
15. Melania 160 S. Europe, India, Philippines and
Pacific Islands--in rivers.
Melanopsis 20 Spain, Australia, Asia Minor, New
Zealand--in rivers.
16. Paludina 60 Northern Hemispheres, Africa, India,
China, etc.--in lakes and rivers.
Ampullaria 50 S. America, W. Indies, Africa,
India--in lakes and rivers.
17. Litorina 40 On all shores.
Rissoa 70 World-wide--in shallow water on
sea-weed to 100 fathoms.
18. Calyptrea 50 World-wide--adherent to rocks, etc.
Crepidula 40 West Indies, Mediterranean, Cape of
Good Hope, Australia.
Pileopsis 7 Britain, Norway, Mediterranean, E.
and W. Indies, Australia.
Hipponyx 70 W. Indies, Galapagos, Philippines,
Australia.
Phorus 9 W. Indies, India, Javan and Chinese
Seas--in deep water.
19. Turbo 60 On the shores of Tropical seas.
Phasinella 30 Australia, Pacific, W. Indies,
Mediterranean.
Imperator 20 S. Africa, India, etc.
Trochus 150 World-wide--from low water to 100
fathoms.
Rotella 18 India, Philippines, China, New
Zealand.
Stomatella 20 Cape, India, Australia, etc.
20. Haliotis 75 Britain, Canaries, India, Australia,
California--on rocks at low water.
Stomatia 12 Java, Philippines, Pacific, etc.--
under stones at low water.
21. Ianthina 6 Gregarious in the open seas of the
Atlantic and Pacific.
22. Fissurella 120 World-wide--on rocks from low water
to 5 fathoms.
Emarginula 26 Britain, Norway, Philippines,
Australia--from low water to
90 fathoms.
23. Nerita 116 On the shores of all warm seas.
Neritina 110 In fresh waters of all warm countries,
and in Britain.
Navicella 24 India, Mauritius, Moluccas, Australia,
Pacific--in fresh water, attached
to stones.
24. Patella 100 On all coasts--adhering to stones and
rocks.
25. Dentalium 30 World-wide--buried in mud.
26. Chiton 200 World-wide--low water to 100 fathoms.
ORDER II.--Pulmonifera.
Division _a_.--_Inoperculata._
No. of
Family. Genus. Species. Distribution.
27. Helix 1,600 }
Succinea 68 } World-wide--on land in moist places.
Bulimus 650 }
Achatina 120 World-wide--burrowing at roots and
bulbs.
Pupa 236 World-wide--amongst wet moss.
Clausilia 400 Europe and Asia--in moist spots.
28. Limax 22 Europe and Canaries--on land in damp
localities.
Testacella 3 S. Europe, Canaries, and Britain--
burrowing in gardens.
29. Oncidium 16 Britain, Red Sea, Mediterranean--on
rocks on the seashore.
30. Limnæa 50 Europe, Madeira, India, China, N.
America--in ponds, rivers, lakes, etc.
Physa 20 America, Europe, S. Africa, India,
Philippines--in ponds, rivers,
lakes, etc.
Ancylus 14 Europe, N. and S. America--in ponds,
rivers, lakes, etc.
Planorbis 145 Europe, N. America, India, China--in
ponds, rivers, lakes, etc.
31. Auricula 50 Tropical--in salt marshes.
Siphonaria 30 World-wide--between high and low water.
Division _b_.--_Operculata._
32. Cyclostoma 80 S. Europe, Africa }
Cyclophorus 100 India, Philippines }--on land.
Pupina 80 Philippines, New Guinea }
33. Helicina 150 W. Indies, Philippines, Central
America, Islands in Pacific--on land.
34. Acicula 5 Britain, Europe, Vanicoro--on leaves
and at roots of grass.
Geomelania 21 Jamaica--on land.
ORDER III.--Opisthobranchiata.
Division _a_.--_Tectibranchiata._
No. of
Family. Genus. Species. Distribution.
35. Tornatella 16 Red Sea, Philippines, Japan--in deep
water.
36. Bulla 50 Widely distributed--low water to 30
fathoms.
37. Aplysia 40 Britain, Norway, W. Indies--low water
to 15 fathoms on sea-weed.
38. Pleurobranchus 20 Britain, Norway, Mediterranean.
Division _b_.--_Nudibranchiata._
39-44. All shell-less.
ORDER IV.--Nucleobranchiata.
No. of
Family. Genus. Species. Distribution.
45. Firola 8 Atlantic, Mediterranean.
Carinaria 5 Atlantic and Indian Oceans.
46. Atlanta 15 Warmer parts of the Atlantic.
CLASS III.--PTEROPODA.
Division _a_.--_Thecosomata._
No. of
Family. Genus. Species. Distribution.
1. Hyalea 19 }
Cleodora 12 } Atlantic, Mediterranean, Indian Ocean.
2. Limacina 2 Arctic and Antarctic Seas.
Division _b_.--_Gymnosomata._
3. Clio, etc. Shell-less.
CLASS IV.--LAMELLIBRANCHIATA.
No. of
Family. Genus. Species. Distribution.
Division _a_.--_Asiphonida._
1. Ostrea 100 World-wide--in estuaries, attached.
2. Anomia 20 India, Australia, China, Ceylon--
attached to shells from low water
to 100 fathoms.
Placuna 4 Scinde, North Australia, China--in
brackish water.
3. Pecten 176 World-wide--from 3 to 40 fathoms.
Lima 20 Norway, Britain, India, Australia--
from 1 to 150 fathoms.
Spondylus 70 Tropical seas--attached to coral-reefs.
4. Avicula 25 Britain, Mediterranean, India--
25 fathoms.
Perna 18 In tropical seas--attached.
Pinna 30 United States, Britain, Mediterranean,
Australia, Pacific--low water to
60 fathoms.
5. Mytilus 70 World-wide--between high and low water
mark.
Modiola 70 British and tropical seas--low water
to 100 fathoms.
6. Arca 400 In warm seas--from low water to 200
fathoms.
Pectunculus 58 West Indies, Britain, New Zealand--
from 8 to 60 fathoms.
Nucula 70 Norway, Japan--from 5 to 100 fathoms.
7. Trigonia 3 Off the coast of Australia.
8. Unio 420 World-wide--in fresh waters.
Anodon 100 North America, Europe, Siberia--in
fresh waters.
Division _b_.--_Siphonida._
9. Chama 50 In tropical seas on coral reefs.
10. Tridacna 7 Indian and Pacific Oceans, Chinese Seas.
11. Cardium 200 World-wide--from the shore line to
140 fathoms.
12. Lucina 70 Tropical and temperate seas--sandy and
muddy bottoms--from low water to
200 fathoms.
Kellia 20 Norway, New Zealand, California--low
water to 200 fathoms.
13. Cyclas 60 Temperate regions--in all fresh waters.
Cyrena 130 From the Nile and other rivers to
China--and in mangrove swamps.
14. Astarte 20 Mostly Arctic--from 30 to 112 fathoms.
Crassatella 34 Australia, Philippines, Africa, etc.
15. Cyprina 1 From Britain to the most northerly
point yet reached--from 5 to
80 fathoms.
Circe 40 Britain, Australia, India, Red Sea--
8 to 50 fathoms.
Isocardia 5 Mediterranean, China, Japan--burrowing
in sand.
Cardita 54 Tropical seas--from shallow water to
150 fathoms.
16. Venus 176 } World-wide--buried in sand, from low
Cytherea 113 } water to 100 fathoms.
Artemis 100 Northern to tropical seas--from low
water to 100 fathoms.
Tapes 80 Widely distributed--burrowing in sand,
from low water to 100 fathoms.
Venerupis 20 Britain, Canaries, India, Peru--in
crevices of rocks.
17. Mactra 125 World-wide--burrowing in sand.
Lutraria 18 Widely distributed--burrowing in sand.
18. Tellina 300 In all seas--from the shore line to
15 fathoms.
Psammobia 50 Britain, Pacific and Indian Oceans--
from the littoral zone to 100 fathoms.
Sanguinolaria 20 W. Indies, Australia, Peru.
Semele 60 Brazil, India, China, etc.
Donax 68 Norway, Baltic, Britain--in sand near
low water mark.
19. Solen 33 World-wide--burrowing in sand.
Solecurtus 25 Britain, Africa, Madeira,
Mediterranean--burrowing in sand.
20. Mya 10 North Seas, W. Africa, Philippines,
etc.--river mouths from low water to
25 fathoms.
Corbula 60 United States, Britain, Norway,
Mediterranean, W. Africa, China--
from 15 to 80 fathoms.
21. Anatina 50 India, W. Africa, Philippines,
New Zealand.
Thracia 17 Greenland to Canaries and China--from
4 to 120 fathoms.
Pandora 18 Spitzbergen, Panama, India--from 4 to
110 fathoms, burrowing in sand and mud.
22. Gastrochæna 10 W. Indies, Britain, Red Sea, Pacific
Islands--from shore line to 30 fathoms.
Saxicava Arctic Seas, Britain, Mediterranean,
Canaries and the Cape--in crevices
and boring into limestone and rocks.
Aspergillum 21 Red Sea, Java, New Zealand--in sand.
23. Pholas 32 Almost universal--from low water to
25 fathoms.
Xylophaga 2 Norway, Britain, S. America--boring
into floating wood.
Teredo 14 In tropical seas--from low water to
100 fathoms.
SOME WORKS OF REFERENCE.
MOLLUSCA IN GENERAL.
"A Manual of Mollusca." By Dr. S. P. Woodward.
"Tabular View of the Orders and Families of the Mollusca." Published by
the Society for Promoting Christian Knowledge.
"Cassell's Natural History," latest edition, article on the Mollusca. By
Dr. Henry Woodward.
BRITISH MOLLUSCA.
"A History of British Mollusca and their Shells." By Professor E. Forbes
and S. Hanley.
"British Conchology." By J. G. Jeffreys.
"Common Shells of the Sea-shore." By Rev. J. G. Wood.
BRITISH LAND AND FRESH-WATER MOLLUSCA.
"Land and Fresh-water Mollusca indigenous to the British Isles." By
Lovell Reeve.
"A Plain and Easy Account of the Land and Fresh-water Mollusca of Great
Britain." By Ralph Tate.
[Illustration]
FOSSILS.
BY
B. B. WOODWARD.
FOSSILS.
INTRODUCTORY.
Geology is of all "hobbies" the one best calculated not only to develop
the physical powers, but also, if pursued with any degree of
earnestness, to train and extend the mental faculties. To study geology
properly, the rocks themselves must be visited and carefully observed,
their appearance noted, and the fossils, if any, which they contain,
collected. This necessitates many a pleasant walk into the open country
to quarries and cuttings, or rambles along the sea-shore to cliffs which
may be worth investigating, whilst botany, entomology, or any other
congenial pursuit, may be followed on the way; for natural science in
its different branches has so many points of connection that it is
impossible to study one of them without increasing one's interest in,
and knowledge of, all the others. Again, in arranging, classifying, and
studying at home the specimens collected on these expeditions, many an
hour may be usefully spent; habits of exactitude and neatness are
acquired; whilst in endeavouring to draw correct conclusions as to the
way in which particular rocks were formed, and by what agencies brought
to their present position, the reasoning faculties are exercised and
developed.
The existence of fossil shells and bones in various strata of the
earth's crust attracted attention at a very early date of the world's
history; the Egyptian priests were aware of the existence of marine
shells in the hills bounding the Nile valley, and from this fact
Herodotus drew the conclusion that the sea formerly covered the spot.
The bones of the larger mammalia (rhinoceros, elephant, etc.), were,
however, thought by the ancients to be human, and hence arose the idea
of a race of giants having existed at some previous period of the
earth's history. It was not, however, until near the end of the last
century that geology began to be recognised as a science, and the true
bearing of fossils in relation to the rocks in which they were found was
conclusively proved. William Smith in England, and Werner in Germany,
while working independently of each other, both came to the same
conclusion, viz. that the numerous strata invariably rested on each
other in a certain order, and that this order was never inverted,[1]
whilst William Smith in addition proved that each group of rocks, and
even each stratum, had its own peculiar set of fossils, by which it
might be recognised wherever it occurred. From that time forth the study
of the various fossils began to be considered as a separate science
apart from that of the beds containing them; this is now known as
Palæontology, the study of the composition of the rocks themselves being
termed Petrology.
[1] Except in such cases where the rocks themselves have been
displaced by movements of the earth's crust.
At this moment, however, we are less concerned with the study of rocks
and fossils than with the best and simplest way of collecting,
preparing, and arranging specimens as a means to this study.
THE CABINET.
With regard to the cabinet for such specimens as you are able to
collect, the same advice holds good as that given in a previous Manual
(The Young Collector's Shell Book), namely, the simpler the cabinet the
better, though of course card-board boxes would not as a rule be strong
enough to stand the weight of the specimens, and hence it is advisable
to have wooden ones. The boxes in which Oakey's Wellington Knife-powder
is sent out (they measure about 15 in. × 10 in. × 3 in.) are on the
whole the most convenient size, and are easily obtainable at any oil and
colourman's. These, when painted over with Berlin Black, after first
removing the external labels, look very neat. The inside may be papered
according to taste, when the trays may be arranged in order ready for
the reception of your specimens.[2]
[2] For description of trays, see "The Young Collector's Shell-Book."
IMPLEMENTS REQUIRED WHEN COLLECTING.
A certain amount of apparatus is needful in collecting geological
specimens. It is necessary to break open the hard rocks in order to get
at the fossils within, and for this purpose a strong hammer is required.
One end of the hammer-head should be square, tapering, slightly, to a
flat striking face; for when thus shaped the edges and corners are less
likely to break off; the other side should be produced into a rather
long, flat, and slightly curved pick, terminating in a chisel-edge at
right-angles to the handle; the total length of the head should not
exceed 9½ in., the striking face being 3 in. from the centre of the eye
in which the handle (18 in. long) is inserted; the latter should be made
of the toughest ash, American hickory, or "green-heart," and fixed in
with an iron wedge ("roughed" to prevent its coming out again), taking
care that ¼ in. of the handle protrudes on the other side. It is the
usual practice, but a mistaken one, to cut it off level with the hammer
head, which is likely, under these circumstances, to come off after it
has been in use for a time, whereas, by leaving a small portion of the
wedged-out end projecting, this mischance is avoided, and your weapon
will not fail even when used to drag its owner up a stiff ascent. It is
better to shape and fix the handle yourself, as by this means you can
not only cut it to fit your hand, but may rely upon its being properly
fastened in. By filing grooves around it an inch apart, it will serve to
take rough measurements with, while a firm grasp may be insured by
bees-waxing instead of polishing it. Another and much smaller hammer
will also be necessary, chiefly for home use, to trim the specimens
before putting them away in the cabinet; the head of this hammer must
not be more than 2½ inches long, the handle springing from the centre;
one end has a flat striking face, square in section, the other, instead
of being formed like a pick, is wedge-shaped, the sharp edge being at
right-angles to the handle. Next to a hammer, a cold chisel is
indispensable to the collector, since without its aid many a choice
specimen embedded in the middle of a mass of rock too large to break
with the hammer would have to be left behind. There is one thing,
however, to beware of in using this tool--it has sometimes to be hit
with great force, and should you chance to miss it and strike your hand
instead, the result may be more serious than even a severe bruise. To
prevent this, procure from the shoemaker or saddler a piece of thick
leather, about 4 inches in diameter, having a hole cut in the centre
through which to pass the shank of the chisel, and, thus protected, you
may wield the hammer with impunity.
For digging fossils out of clay, an old, stout knife, such as the
worn-down stump of a carver, is handy, and in sandy beds an ordinary
garden trowel is very useful, whilst in a chalk-pit a small saw is
sometimes of great aid in extricating a desirable specimen. The same may
be said of an ordinary carpenter's wood-chisel. For picking up small and
delicate specimens, a pair of forceps should be carried, whilst without
a pocket lens no true naturalist ever stirs abroad. An ordinary stout
canvas satchel, such as is commonly used by schoolboys, is the best
thing for carrying home your specimens; this may be made much stronger
by the addition of two short strips of leather stitched on the back and
running, one from each ring, to which the strap passing over the
shoulder is fastened, down to the bottom of the bag; by leaving a small
portion unstitched near the bottom of each of these, wide enough for the
shoulder-strap to pass through, the satchel may at a moment's notice be
slung knapsackwise on the shoulders--a method of carrying it which is,
as all who have tried it know, by far the most convenient when it is
heavily laden or not in immediate requisition. A stout leather belt may
be worn in which to carry all your hammers, supporting it on the side
where the heavy hammer hangs by a band passing over the opposite
shoulder. Before starting on an excursion, make a practice of seeing
that you have everything with you, or when the critical moment comes,
and some choice and fragile specimen is ready to be borne off, you may
find that you are without the means necessary for taking it home. For
ordinary hard specimens, newspaper well crumpled around them is without
its equal, but some of the more delicate must be first wrapped in tissue
paper or even cotton-wool, whilst the most fragile fossils should be
packed in tins with bran or sawdust, the particles of which fill in all
the corners and press equally everywhere, a useful faculty which cotton
wool does not possess. When neither of these are to be obtained, dry
sand will answer quite as well, though it is heavier to carry.
Although not absolutely necessary in the field, it is often useful to
have a small bottle of acid in your pocket (nitric acid diluted to
1-12th with distilled water is the best) with which to test for
limestones; a drop of acid placed on a rock will, if there be any
carbonate of lime in it, immediately begin to fizz. Finally, every young
collector should carry a note-book, and carefully record in it what he
sees in each pit he visits, while, if it can be procured or borrowed, a
geological map of the district you are exploring is a great help, for
with its aid and that of a good compass you become practically
independent of much extraneous assistance.
HOW TO USE YOUR IMPLEMENTS.
We will suppose by way of illustration that near us flows a river, on
the rising ground above which is a pit that we propose to visit for the
purpose of putting our apparatus into practical operation. When we have
reached the floor of the pit, and stand looking up at the section before
us, we are at first rather puzzled as to what the beds, which we see
before us, are; for as the pit has not been worked for some time, its
sides are partially overgrown with grass, and in places bits and pieces
of the upper beds have fallen down and form a heap beneath which the
lower ones lie buried. We must therefore make our way to those spots
where the beds are left clear, and find out, if possible, what they are.
By climbing up one of the heaps of fallen earth (_talus_) we reach the
top, where, first of all, under the roots of the grass and shrubs, we
find the mould in which these grow, and which is formed of the broken up
(_disintegrated_) rocks forming the still higher ground above, and which
the rains, frosts and snows, aided afterwards by the earthworms, have
converted into mould. This, geologically speaking, is called _surface
soil_, and is here about two feet deep. Just below it we find a layer of
coarse gravel; the pebbles of which this is composed are of all sorts,
sizes, and shapes, and are stained a deep brown by oxide of iron. Most
of them are flints, and by diligent search you may find casts and
impressions in these of sponges, shells, spines of sea urchins, etc.
Flints, whether from gravel or their parent rock the chalk, are easiest
broken by a light smart tap of the hammer, though when it is desired to
shape them for the cabinet a soft iron hammer should be used, and the
piece to be shaped placed on a soft pad on the knee, for when struck
with a steel hammer flints splinter in all directions, and often through
the very portion you most desire to preserve. In one spot we find a mass
of sand included in the gravel; this mass is thickest in the middle, and
tapers away towards each end, its total length being about fifty feet.
Could we see the whole mass, we should probably find it to be a patch
lying on the gravel and thinning out all around its edges; in other
words it would be shaped like a lens--"_lenticular_" as geologists term
it. When we examine this mass more closely, we find that the layers of
sand do not run parallel with the bed, but are inclined in different
directions, sometimes lying one way, sometimes another. This _false
bedding_ is due to the sand having been thrown down in waters agitated
by strong currents that swept over the spot, now in one direction and
now in another, scattering at one moment half the sand they had just
piled up one way only to redeposit it the next minute in another. In the
gravel also may be observed a similar though less marked arrangement,
owing to the larger size of its constituents, which of course required a
still stronger current action to wash them down.
Amongst the sand we now see some shells, and set to work to dig them out
very carefully, for they are exceedingly brittle. The best specimens are
to be obtained by throwing down masses of the sandy material and
searching in it; but only the stronger and finer examples will bear such
usage. We next notice that these shells are precisely similar to those
still found with living occupants in the river below, only they are no
longer of a brownish colour, but owing to the loss of the animal matter
of the shell have an earthy, dirty-white appearance. To carry these home
they should be packed in bran in one of your tins with a note as follows
made on a piece of paper and placed just inside--"Sand in gravel:
topmost bed ---- pit, August 2nd, 188-." Then if you are not able to
work them out at once on reaching home, you will not forget whence they
came. From the appearance of these sands and gravels, and the presence
in them of shells exactly like those in the river below, it may
reasonably be inferred that they once formed a portion of the bed of
that river long ago, before it had scooped out its valley to the present
depth. There is, however, something else in this sand-bed--a piece of
bone protruding; clear away the sand above it, and dig back until the
whole is visible. It is broken through in one or two places, but
otherwise is in fair condition; remove the pieces carefully one by one,
and wrap them in separate pieces of paper, and then proceed to search
for others. These bones, which are plentiful in some of our river valley
gravel-beds, are the remains of animals that once roamed in the forests
which at that time covered the country; they were probably either
drowned in crossing the water, or got stuck in the mud on the banks on
coming down to drink. A fine collection was made at Ilford by the late
Sir Antonio Brady, and is now in the British Museum (Natural History) at
South Kensington. Besides the bones of animals, you may expect to find
examples of all, or nearly all, the different rocks in which the river
has cut its valley, and samples of these may be picked out and taken
home. Each specimen should be wrapped in a separate piece of paper to
prevent its rubbing against others, care being taken to note the
locality either by writing it on the paper or by affixing to the
specimen a number corresponding to one in your note book against the
description you have written of the bed. The gravel, with its
accompanying bed of sand, may be traced down, by scraping away the
surface, for about ten feet, when you will discover that it rests
unevenly upon the beds below, which, instead of being horizontal, slope
(_dip_) in a N.N.E. direction, making an angle of about 45° with the
floor of the pit; the gravel therefore rests successively upon the
upturned ends of the lower beds, and, geologically speaking, is
"unconformable" to them. Now as these underlying rocks were of course
originally deposited in an horizontal position, they must have been
pushed up and the upper parts worn away (_denuded_) before the gravel
was deposited on them, for the accomplishment of which process an amount
of time must have elapsed that it would be impossible to reckon by
years.
When we come to examine these lower beds, we find first a stratum of
stiff dark-brown clay containing fossils disposed in layers: those near
the outer surface have been rendered so brittle by the weather, that it
is necessary to make use of the pick end of the hammer and dig a little
way into the face of the section before we come upon some which will
bear removal by cutting them out with a knife. Pack them in a tin with
bran, or, where much clay still adheres to them, wrap them in paper.
The true top of this bed is not visible, being concealed beneath a heap
of earth in the corner of the pit, but we can see and measure about six
feet of it.
The next bed in order is a light brownish band of sandy clay that
splits along its layers into thin pieces or "_laminæ_," whence we may
describe it as a sandy, _laminated_ clay. On the freshly split surface
of one piece we see scattered a number of small darker brown
fragments; an examination with a pocket lens clearly shows that these
are little bits of leaves and stems, with here and there a more
perfect specimen. These beds must have been deposited in the still
waters just off the main stream of a large river which brought the
plants floating down to this spot, where they became water-logged and
sunk; so, too, if you examine the shells in the bed immediately above,
you will see that they are very like though not the same as those
which at the present day love to dwell in the mud off the estuaries of
big rivers in warmer parts of the globe; hence we discover that at
some far distant period a big river, but one which had no connection
with that running close by, once flowed over this very spot. On
tracing the leaf-bed down, we come all at once, at about three feet
from its upper surface, upon a narrow band one or two inches thick of
a substance composed of numerous bits of sticks and stalks closely
matted together and partially mineralized. Vegetable matter in this
form is known as lignite, and is one of the first stages towards the
formation of coal out of plant remains. Below this lignite band we
find our leaf-bed getting sandier and sandier, and losing all trace of
the plants by degrees till it becomes almost pure sand. Here and
there, however, it contains some curiously shaped masses, which, when
broken through with the hammer, seem composed of nothing but the same
grains of sand cemented together into a hard mass. In one there is,
however, a curiously shaped hollow, which, upon examining it closely,
you will see is a perfect cast of a small shell that has itself
disappeared. A drop of acid on it fizzes away and sinks in between the
grains of sand which in this spot become loose. A mass of sand or
particles of clay thus cemented together, be it by iron, lime, or any
other substance, is termed a "_nodule_" or "_concretion_," and in this
particular instance has been formed as follows:--The rain-water
falling on the sand where it comes to the surface sinks in and filters
through the bed. Now there is always a certain amount of carbonic acid
in rain-water, and this acid acted on the carbonate of lime of which
the shell was composed, dissolving and dispersing it amongst the
neighbouring grains of sand where it was re-deposited, cementing them
together as we have seen. The bottom of this bed of sand we find to be
just fifteen feet from the lignite band when measured at right-angles
to the bed, and it is succeeded by a hard greyish rock, which requires
a smart blow of the hammer to break it, but the surface of which,
where it has been exposed to the weather, is much crumbled
("_weathered_"), and breaks readily into small pieces. It is easily
scratched with the point of a knife, and therefore is not flint;
moreover, it fizzes strongly when touched with acid--hence there is a
great deal of carbonate of lime in it, and we know that it is
limestone.
Limestones are very largely, sometimes almost entirely, made up of the
calcareous portions of marine creatures, such as the hard parts of
corals, the tests of sea-urchins, the shells of mollusca, etc.,
welded, so to speak, into one mass by the heat, pressure, and chemical
changes which the bed has undergone since its deposition at the bottom
of the sea. There would be every reason, therefore, one might suppose,
to expect a number of fossils in this bed; but, alas! disappointment
awaits the young explorer, for with the exception of chalk and a few
other limestones, these rocks are generally of such uniform texture
that on being struck with the hammer they split through fossils and
all, the fractured surface only too frequently showing nought save a
few obscure markings. But what we fail to accomplish in our
impatience, nature effects by slow degrees, and if you will turn over
the weathered pieces and blocks lying about, you will soon find plenty
of fossils sticking out all over them; by a judicious use of hammer
and chisel any of these may be detached and added to your stock, each
being separately packed in paper and the locality written on the
outside. Some seventy or eighty feet is all that is visible of this
limestone; the rest is unexcavated.
Before leaving the pit, it will be as well to select such rock
specimens as you wish to place in your cabinet, trimming them to the
required size on the spot, for should you, as is not unlikely, spoil
two or three, you can readily pick a fresh one. Having secured our
specimens, we will take a look at our note-book, to see if we have
noted all the details we require. If so, our entries should run
something as follows:--First, we have made a rough sketch of the
position of the beds, carefully numbering each one; then follow our
notes on the individual beds, preceded by numbers corresponding with
those in the sketch, thus:--
1. Surface Soil 2 ft.
2. River Gravel, including a lenticular mass of }
3. Sand, with land and fresh-water shells and bones of } 10 ft.
animals }
4. Stiff dark-brown clay, with estuarine shells 6 ft. seen.
5. Light-brown sandy clay, with leaves and stems of plants 3 ft.
6. Band of Lignite 2 in.
7. Same as 5, passing into-- }
8. Pure Sand, with layers of concretions containing casts }
of shells } 15 ft.
9. Dark-Grey Limestone, with numerous fossils 80 ft. seen.
Beds 4 to 9 dip at an angle of 45° to the N.N.E.
Our imaginary pit is of course only a sort of geological Juan Fernandez,
but it will serve in some degree to illustrate the method of dealing
with various rocks and fossils when met with in the field, and how they
may best be collected and carried home. A few additional suggestions
where to look for fossils may, however, be given here. To begin with, I
never neglect to search the fallen masses, especially their weathered
surfaces, or to look carefully over the heaps of quarried materials,
whatever they may happen to be, piled on the floor of the pit. In
working at the beds themselves, remember that fossils frequently occur
in layers which of course represent the old sea-bottom of the period; to
find these, it is necessary to follow the beds in a direction at right
angles to their stratification, till you arrive at the sought-for
layers, or _zones_.
Do not be surprised, when collecting from a formation you have never
before studied, if the fossils are not at first apparent, though many
are known to be present. The eye requires a few days in which to become
accustomed to its fresh surroundings, and when the same spot has been
carefully hunted over every day for a week, it is astonishing what a
quantity of fossils are discernible where not one in the first instance
was recognised.
HOW TO PREPARE THE SPECIMENS FOR THE CABINET.
The first thing to be done on unpacking our specimens is to pick out
those which require the least attention, and get them out of the way.
These will be your rock specimens, which, if they have been trimmed
properly in the pit, will not need much further manipulation; a word or
two, however, as to the best method of proceeding when it is desirable
to reduce a specimen, will not be out of place. If you wish to divide it
in two, or detach any considerable portion, the specimen may, while held
in the hand, be struck a smart blow with the hammer; as, however, it not
frequently happens that even with the greatest care the specimen under
this treatment breaks in an opposite direction to that required, it is
advisable to adopt a somewhat surer method, namely, to procure a block
of tough wood, and in the centre bore a hole just large enough to
receive the shank of the cold chisel, and thus hold it in an upright
position with the cutting edge uppermost; placing the specimen on this,
and then hitting it immediately above with the hammer, it may be
fractured through in any required direction. To trim off a small
projection, hold the specimen in your hand with the corner towards you
and directed slightly downwards, then with the edge of the striking face
of the hammer hit it a smart blow at the line along which you wish it to
break off; the object of inclining the specimen is to make sure that the
blow shall fall in a direction inclined away from the portion you wish
to preserve, a _modus operandi_ which it is necessary to bear well in
mind if you would not spoil many a choice specimen. Anything beyond very
general directions, however, it is impossible to give in such matters as
this: experience, and a few hints from those who have themselves had
practice in collecting and arranging specimens, are worth more than any
written description, however lengthy and elaborate.
Having reduced your specimen to the required size and shape, the next
thing to be done is to write a neat little label for it--the smaller the
better--stating, first the nature of the specimen, secondly the
geological formation to which it belongs, thirdly the locality from
which it was procured, and fourthly the date when acquired, thus--
Limestone.
Lower Carboniferous.
Quarry, 1 mile N.W. of ----
21. 8. 8-.
ruling a neat line at the top and bottom (red ink lines give a more
finished appearance than black). When the label is dry, damp it to
render it more pliant, and gum it on to the flattest available surface
of the specimen, pressing it well into any small inequalities that it
may hold the firmer. A small quantity of pure glycerine (about an eighth
part) should be added to the gum before use, in order to prevent its
drying hard and brittle. The specimen is now ready to place in its tray
and be put away in the cabinet.
In the next place, pick out the fossils which you obtained from the
limestone. With the cold chisel set in its block of wood, and the
trimming hammer, remove as much of the surrounding rock (_matrix_) as
you can without damaging the fossil, and with a smaller chisel any
pieces that may be sticking to and obscuring it. Fossils in soft
limestone, such as chalk, are best cleaned with an old penknife, and
needles fixed into wooden handles, and finished off by the application
of water with a nail-brush. Should you have the misfortune to break any
specimen in the process of trimming, it should at once be mended. The
most effectual cement for this purpose is made by simply dissolving
isinglass in acetic acid, or, where the specimen contains much iron
pyrites, and there would be a danger in starting decomposition, shellac
dissolved in spirits of wine. When, however, neither of these are handy,
chalk scraped with a penknife into a powder, and mixed with gum to the
consistency of a thick paste, answers admirably. Failing this, however,
gum alone will frequently suffice.
The next thing is to place the like kinds together in their several
trays, writing a label, as before, for each tray, but leaving a blank
space at the top for the insertion of the name when ascertained. The
commoner sorts may be named from the figures of them given in the
text-books (see list at the back of the title page); but failing this,
it will be the best plan to seek the help of any friends who have
collections, or to take the fossils to some museum, and compare them
with the named specimens there exhibited. The label may be laid at the
bottom of the tray with the fossils loose on the top of it, each fossil
being marked with a number corresponding to one on the label. Another
plan is to fasten the label by one of its edges to the side of the tray;
or, if the fossils are small and mounted on a piece of card fitting into
the tray, it may be gummed with them to the card.
Now let us take the shells we obtained from the dark-blue clay, with
those and the bones from the old river bed up above. Gently turn them
out of the tins, in which they were packed in the quarry, on to a paper
or the lid of a card-board box, and with a pair of forceps pick them
carefully out of the bran, and place them in large shallow trays, taking
care not to mix those from the different beds. As we found when
collecting them, these shells are extremely brittle from loss of animal
matter, and our first object is therefore to harden them by some
process, so that they will bear handling. To accomplish this you must
get a saucepan, one of those wire contrivances for holding eggs when
boiling, or a big wire spoon, such as formerly was used for cooking
purposes, a packet of gelatine, and some flat pieces of tin, which last
are easily procured by hammering out an old mustard or other tin, having
previously melted in a gas flame the solder wherewith it is joined. Half
fill the saucepan with clean water, and put in as much gelatine as when
cold will make a stiff jelly; melt this over the fire, placing the
fossils meanwhile in a warm (not hot) corner of the fire-place; then
when the gelatine is quite dissolved, pile as many of them, whole or in
pieces, into the egg-boiler, or spoon, as it will contain, hold them for
a second in the steam, and then lower them gradually into the hot
gelatine until it completely covers them. Little bubbles of air will
rise and float on the surface. As soon as these cease to appear, raise
the fossils above the surface and allow them to drip; then pick them up
one by one with the forceps, and spread them out on pieces of tin before
the fire, but not too close to it. As soon as their exterior surfaces
become dry, and before the gelatine gets hard, they should be taken up
(they may be handled fearlessly now), and the superfluous gelatine
sticking to the surface gently removed with a camel's-hair brush dipped
in clean warm water; otherwise, when dry, they present an unnatural
varnished appearance, and have a tendency, on small provocation, to
become unpleasantly sticky.
Small bones may be treated in like manner, but for large ones, weak glue
is to be preferred to gelatine, which is only suitable for the finer and
more delicate objects. Where it is desired to harden only a few things,
it is better to mix the gelatine in a gallipot, which can be heated when
required by standing it in a saucepan of water on the fire. In any case
the gelatine need never be wasted, as it will keep almost any length of
time, and can therefore be put by for future use. In default of the
egg-boiler or wire-net spoon, an equally useful plan is to make a
strainer from a piece of perforated zinc by turning up the edges all
around, and attaching copper wire to it by which to lower the fossils
into the gelatine, and raise them again.
When the fossils are quite dry they can be sorted, and those which have
come to pieces may be mended with diamond cement (_i.e._ isinglass
dissolved in acetic acid), and then properly labelled and placed in
trays, or mounted as previously described.
To the plant remains and Lignite there is little that can be done beyond
trimming them to suit the trays. Should there be much iron pyrites in
the Lignite, it is sure, sooner or later, to decompose, when all that
can be done is to throw it away. In the case, however, of valuable
fruits and seeds, such as those from the London Clay of Sheppey, it is
worth while to preserve them, if possible, in almost the only way known,
viz. by keeping them in glycerine in wide-mouthed stoppered bottles, or
by saturating them with paraffin.
Having prepared the specimens for the cabinet, the next thing is to
arrange them in proper order. There are several ways of doing this, but
for those who have not had much experience the following plan will be
found the best:--Group the specimens according to the formations to
which they belong, and arrange these groups in proper sequence (_vide_
Table, p. 16); then take each group, and arrange the specimens it
comprises in columns. Beginning at the top of the left-hand corner,
place first the specimens of the rock itself, and under it any examples
of minerals, concretions, etc., found in that rock; next the fossil
plants, if any; and finally, such animal remains as you have arranged
according to their zoological sequence, beginning with the lower forms
(_vide_ Table, p. 32). Unless cramped for room, each formation should
begin a new box, its name being written on a slip of paper and placed at
the head of the columns of trays. A label setting forth its contents
should be fixed outside each of the boxes, which can then be put away on
your cupboard shelves.
TABLE OF THE PRINCIPAL FOSSILIFEROUS STRATA ARRANGED IN CHRONOLOGICAL
ORDER.
_Land Plants._-----------+
_Invertebrata._--------+ |
_Fishes._------------+ | |
_Amphibia._--------+ | | |
_Reptiles._------+ | | | |
_Birds._-------+ | | | | |
_Mammalia._--+ | | | | | |
_Man._-----+ | | | | | | |
| | | | | | | |
| | | | | | | |
{Alluvial Deposits, | | | | | | | |
_Quaternary, { River Valley | | | | | | | |
or { Gravels and | | | | | | | |
Pleistocene._ { Cave Deposits. | | | | | | | |
{Drift and Glacial | | | | | | | |
{ Deposits. V | | | | | | |
| | | | | | |
_Cainozoic, {Pliocene. | | | | | | |
or {Miocene. | | | | | | |
Tertiary._ {Eocene. | | | | | | |
| | | | | | |
{ {Chalk. | | | | | | |
M { _Cretaceous._ {Upper Greensand. | | | | | | |
E { {Gault. | | | | | | |
S { | | | | | | |
O { _Neocomian._ {Lower Greensand. | V | | | | |
Z { {Wealden. | : | | | | |
O { | : | | | | |
I { { {Purbeck. | : | | | | |
C, { {_Upper._{Portland. | : | | | | |
{ { {Kimmeridge Clay. | : | | | | |
or { { | : | | | | |
{ { _Mid._ {Coral Rag. | : | | | | |
S { { _Oo- { {Oxford Clay. | : | | | | |
E { {lites._{ | : | | | | |
C { { { {Cornbrash and | : | | | | |
O { { { { Forest Marble. | : | | | | |
N { _Jurassic._{ {_Lower._{Great Oolite. | : | | | | |
D { { { {Fullers' Earth. | : | | | | |
A { { { {Inferior Oolite. | : | | | | |
R { { | : | | | | |
Y { { Lias. | : | | | | |
| : | | | | |
{ {Trias, or New | : | | | | |
P { _Poikilitic._ { Red Sandstone. V ? V | | | |
A { {Permian. | | | |
L { | | | |
Æ { {Coal Measures. V | | |
O { {Millstone Grit | | |
Z { _Carboniferous._ { and Yoredale | | |
O { { Rocks. | | |
I { {Carboniferous | | |
C, { { Limestone, etc. | | |
{ | | |
or { Devonian and Old | | |
{ Red Sandstone. | | |
P { | | |
R { {Ludlow Beds. | | |
I { {Wenlock Beds. | | V
M { _Silurian._ {Woolhope Beds. | |
A { {Tarannon Shale. | |
R { {Llandovery or May | |
Y. { { Hill Group. V |
{ |
{ {Bala and |
{ { Caradoc Beds. |
{ {Llandeilo Flags. |
{ {Arenig Group. |
{ _Cambrian._ {Tremadoc Slates. |
{ {Lingula Flags. |
{ {Menevian Beds. |
{ {Longmynd and |
{ { Harlech Group. V
{ :
{ Pre-Cambrian and :
{ Laurentian. ?
NOTES ON THE DIFFERENT FORMATIONS MENTIONED IN THE TABLE.
RECENT.--The alluvial deposits of most river valleys and some estuaries
still in course of formation, containing fossil shells and mammals, all
of living species.
QUATERNARY, POST-PLIOCENE, or PLEISTOCENE.--1. Including the raised
beaches around the coast, the older gravels of river valleys and the
cave deposits, in all of which the shells are identical with those
living in the rivers and seas of to-day, whilst the animals are many of
them extinct, only a few being now found living on the spot.
2. The glacial drifts that cover all England north of the Thames, and
which consist of sands, gravels, and clays, full of big angular stones
frequently flattened on one side, scratched and sometimes polished from
having been fixed in moving ice and forced over other rocks. A very
interesting collection of these "boulders," as they are called, can be
easily made, for they belong to almost every formation in England, and
have some of them been brought from great distances, whilst the number
and variety obtainable from a single pit is astonishing.
CAINOZOIC, or TERTIARY.--Beds of this age, in England at all events, are
for the most part made up of comparatively soft rocks, gravels, sands,
and clays, and are found in the eastern and south-eastern counties. They
are divided into--
1. Pliocene, mainly consisting of a series of iron-stained sands, with
abundant shell remains, and locally known as "crags." The shells are
very partial in their distribution, the beds in places being almost
entirely made up of them, whilst in others scarcely one is to be found.
The great majority are of the same species as many still living. The
Pliocene is subdivided into three groups:--
_a._ The _Norwich Crag Series_, sometimes called the "Mammaliferous
Crag," as at its base the bones of mastodon, elephant, hippopotamus,
rhinoceros, and some deer have been found. The shells in it are such as
still abound on the beaches of the eastern coast to-day--whelks, scallop
shells, cockles, periwinkles, etc.
_b._ The _Red_ or _Suffolk Crag_, its two names indicating its
characteristic colour (a dark red-brown) and chief locality. From
the base are obtained the celebrated phosphatic nodules miscalled
"Coprolites," whence is manufactured an artificial manure, and with them
are found the rolled and phosphatized bones and teeth of whales, sharks,
etc. Amongst the shells the Reversed Whelks (_Fusus contrarius_),
_Fecten opercularis_, _Pectunculus glycimeris_, several kinds of
_Mactra_ and _Cardium_, etc., are the commonest. Walton-on-the-Naze,
Felixstowe, and Woodbridge are the best known localities.
_c._ The _White_ or _Coralline Crag_ is generally of a pale buff colour,
and is in places almost entirely composed of the remains of Polyzoa.
These (formerly called Corallines, whence the name Coralline Crag) are
beautiful objects for a low-power microscope, or pocket lens, and are
easily mounted in deep cells on slides. The bits of shell and sand that
stick to them should be carefully removed with the point of a needle. A
very large number of shells occur in this crag: of bivalves, the
_Pecten_ is very abundant, and its valves are frequently thickly grown
over with Polyzoa; _Cyprina Islandica_, _Cardita Senilis_ are also
plentiful; and of univalves, the genus _Natica_ is common. The Coralline
Crag is best seen in the neighbourhood of Aldborough, Orford,
Woodbridge, and other places in Suffolk.
2. Miocene, possibly represented in the British Isles by a small patch
of clays and lignites at Bovey Tracey.
3. Eocene, divided into--
_a._ _Upper Eocene_, consisting of a series of very fossiliferous sands,
clays, and limestones, exposed in the cliffs at the eastern and western
ends of the Isle of Wight and on the neighbouring coast of Hampshire.
They are partly of freshwater origin, when they contain the remains of
freshwater shells such as _Limnoea Paludina_, _Planorbis_, etc.;
partly of marine origin, when shells belonging to such genera as
_Ostrea_, _Venus_, etc., take their place; partly of estuarine, when the
brackish water mollusca are found with bones and scutes of crocodiles
and tortoises.
_b._ _Middle Eocene_, or the _Bagshot Beds_, composed of sands and
clays. The beautiful coloured sands of Alum Bay, the sands of the Surrey
and Hampstead Heaths, are familiar examples of the beds of this age.
Very few fossils indeed have been found in them. The clay-beds on the
contrary as seen at Barton and Hordwell on the Hampshire coast and again
in the Isle of Wight, abound with shells belonging to genera such as
_Conus_, _Voluta_ and _Venus_, that inhabit warm seas. With them are the
Nummulites, looking externally very like buttons, but on the inside
divided into innumerable chambers in which the complex animal that
formed the nummulite dwelt.
_c._ _Lower Eocene_, the well-known London clay, may almost be said to
compose this division, for the underlying sands, gravels, and clays are
in mass comparatively insignificant. The London clay contains plenty of
fossils, only as they are disposed in layers (_zones_) at a considerable
distance apart, they are not often hit upon. Layers of Septaria or
cement-stones are of frequent occurrence. Sheppy is the great locality
for London clay fossils, as the sea annually washes down large masses of
the cliffs and breaks them up on the beach. A great many fossil fruits
and seeds, remains of crabs, shells of Nautili, Volutes, and other
mollusca, besides turtles, a species of snake, a bird with teeth, and a
tapir-like animal, have at different times and in various places been
found in this deposit, which sometimes attains a thickness of over 400
ft. The "Bognor Rock" is a local variety of the basement bed of this
formation.
[Illustration: _Aturia Zic-zac_ (from the London clay).]
The MESOZOIC or SECONDARY rocks embrace a series of limestone, clays,
sands, and sandstones that on the whole are well consolidated. The main
mass of them lies to the west of a line drawn across the map of England
from the mouth of the Tyne, in Northumberland, southwards to Nottingham,
and thence to the mouth of the Teign in Devonshire. In the south-eastern
counties they underlie the tertiary rocks of the London and Hampshire
basins, as they are called, at no great depth from the surface. Outlying
patches of secondary rocks occur in Scotland, where they are found near
Brora on the east coast, and in the islands of Skye and Mull on the
west. In Ireland they are scantily represented round about the
neighbourhood of Antrim. The secondary rocks are divided into--
1. Cretaceous.
_a._ The _Chalk_ is too well known to need description, though
technically it may be described as a soft white limestone chiefly built
up of the microscopic shells of _Foraminifera_, and characterized in its
upper part by nodules and bands of flint. These flints frequently
inclose casts of fossils (sponges, sea-urchins, etc.), and sometimes
shells themselves. Fossils, too, are fairly abundant, scattered
throughout the mass. Amongst the commoner may be noticed the
sea-urchins, such as the "sugar loaf" (_Ananchytes_) and the
heart-shaped _Micraster_, the Brachiopods or Lamp-shells (_Terebratula_,
_Rhynchonella_), a "Thorny Oyster" (_Spondylus spinosus_), besides
Ammonites, Belemnites (part of the internal shell of a kind of
cuttle-fish), and the teeth of several species of sharks. Altogether the
chalk is about 1,000 feet thick.
[Illustration: _Ammonites various_ (from the chalk).]
_b._ _Upper Greensand_ is a series of greenish-grey sands and
sandstones. The green colour, on close inspection, is seen to be due to
the presence of innumerable small green grains of a mineral called
glauconite. These are frequently casts of the chambers of the very same
foraminifera that the chalk is so largely composed of.
[Illustration: _Rhynchonella depressa_ (a Brachiopod, from the Upper
Greensand).]
Nodules and layers of "chert" (an impure kind of flint) occur in it,
whilst in places it forms a hard rock called "firestone." The commonest
fossils are Brachiopods, very similar to those in the chalk, a
scallop-shell with four strongly marked ribs on it (_Pecten
quodricostatus_), an oyster with a curved beak (_Exogyra columba_), and
a pear-shaped sponge (_Siphonia pyriformis_). The Upper Greensand is
better seen at places in the southern part of the Isle of Wight, in
cliffs on the Dorsetshire coast, in Wiltshire, at Sidmouth, and in some
parts of Surrey.
[Illustration: _Ammonites auritus_ (from the Gault).]
_c._ _Gault_, a stiff blue clay abounding in fossils: Ammonites often
retaining their pearly shell; Belemnites, a bivalve with very deep
furrows on it (_Inoccramus sulcatus_), and its first cousin (_I.
concentricus_, p. 21), in which the ridge-like markings correspond with
the lines of growth, besides many others, may be obtained in abundance
from it. Layers of phosphatic nodules occur at irregular intervals. The
gault is best studied at East Wear Bay, near Folkstone; it may also be
seen in Dorsetshire, Wiltshire, and Cambridgeshire; lately it has been
found as far west as Exeter.
2. Neocomian.
_a._ The so-called _Lower Green Sand_, named in contradistinction to the
_Upper Green Sand_, includes a series of iron stained sands, sandstones
and clays of great thickness. The clayey beds are seen at Atherfield in
the Isle of Wight, and at Nutfield in Surrey, while the sandy beds are
met with at Speeton, at Folkestone, and near Reigate. Besides
brachiopods and oysters, these beds have furnished a species of _Perna_
(_P. Mulleti_), an elongated mussel (_Gervillia anceps_), a pretty
_Trigonia_ (_T. cordata_), some _Ammonites_ and Nautili, with the teeth
and bones of big reptiles. The celebrated "Kentish Rag" and the sponge
gravels of Farringdon are of this age.
_b._ _Wealden._ The main mass of these rocks occupies the area inclosed
between the North and South Downs, and forms the Valley of the Weald,
whence they take their name. They consist of a series of sands,
sandstones, clays, and shelly limestones that were deposited in the
delta and off the mouth of a big river. The shells in them belong to
freshwater genera, _Cyrena_, _Unio_, _Paludina_, etc. Bones of a huge
lizard that hopped along on his hind legs (_Iguanodon_), and those of
crocodiles, etc., are from time to time brought to light. The Wealden
rocks occur also on both eastern and western sides of the Isle of Wight,
and in Dorsetshire.
[Illustration: _Inoceramus concentricus_ (from the Gault).]
3. Oolites (or Roe-stones) are so named because the characteristic
limestones of this formation resemble very much the roe of a fish. The
small round grains, of which the typical examples are built up, when cut
or broken through will be seen to be formed of numerous layers of
carbonate of lime, disposed like the coats of an onion, around some
central nucleus, generally a grain of sand, a fragment of coral, or the
shell of one of the Foraminifera. They are divided into Upper, Middle,
and Lower Oolites, and these again are subdivided as follows--
Upper Oolite.
_a._ _Purbeck Beds_, a series of fresh-water, with a few estuarine, or
marine beds, which in point of fact connect the deposits we are next
coming to with the Wealden just passed. They contain numerous
fresh-water shells--_Paludina_, _Physa_, _Limnæa_, etc., with the
microscopic valves of the little fresh-water crustacean _Cypris_, whose
descendants are abundant in the rivers and lakes of to-day. An oyster
occurs in the "Cinder Bed" and Plant remains in the "Dirt Beds." But the
Purbecks are best known for the numerous remains of small mammals
(_Plagiaulax_) allied to the kangaroo rat, at present living in
Australia.
_b._ The _Portland Stone and Sand_, which come next in order, are
largely quarried in the island whence they take their name. The
quarrymen point out fossils in the stone, which they call
"Horses'-heads" and "Portland screws." The former is the cast of a
_Trigonia_ shell; the latter, that of a tall spired univalve
(_Cerithium_).
In Wiltshire, a coral (_Isastrea oblonga_) is found in the sandy beds,
the original calcareous matter of which has been replaced by silex.
_c._ _Kimmeridge Clay._ This, by the pressure of the rocks subsequently
deposited on it, has in greater part been hardened, and possesses a
tendency to split in thin layers, and hence is termed by geologists a
shale. It is seen at various points between Kimmeridge on the
Dorsetshire coast and the Vale of Pickering in Yorkshire, and forms
broad valleys. The principal fossils in it are Ammonites, a
triangular-shaped oyster (_Ostrea deltoidea_), and one resembling a
comma (_Exogyra virgula_).
Middle Oolites.
_a._ The _Coral Rag_, or _Coralline Oolite_, comprises a most variable
set of beds, but principally a series of limestone, with fossil corals
still in the position in which they grew, and resembling in form the
reef-building corals of the Pacific. They rest on
_b._ _Oxford Clay_, a dark blue or slate-coloured clay without any
corals, but containing a great many _Ammonites_ and _Belemnites_. The
_Kelloway Rock_, a sandy limestone at the base of the Oxford Clay, is
well developed in Yorkshire, and furnishes amongst other fossils a large
belemnite and an oyster (_Gryphæa dilatata_).
Lower Oolites.
_a._ _Cornbrash_, a very shelly deposit of pale-coloured earthy, and
rubbly or sometimes compact limestone with plenty of fossils. The
commonest are Brachiopods, Limas, oysters (_Ostrea Marshii_),
Pholadomyas and Ammonites. It is best seen in Dorsetshire,
Somersetshire, and near Scarborough in Yorkshire.
_b._ _Forest Marble_ and _Bradford Clay_. The former is an exceedingly
shelly limestone, often splitting into thin slabs. On the surfaces of
some of the beds may be seen the ripple marks the sea made countless
years ago, and the tracks of worms and crabs that dwelt in the mud or
crawled on its surface at a time when it was soft mud. The Bradford clay
is a very local deposit, taking its name from Bradford in Wiltshire,
where it is most developed, and its characteristic fossil is the
pear-shaped Encrinite or "stone-lily" (_Apiocrinus Parkinsoni_).
_c._ The _Great_ or _Bath Oolite_, comprising a series of shelly
limestones and fine Oolites, or freestones. The latter are largely
quarried in the neighbourhood of Bath, and used for mantelpieces and the
stone facings of windows. The great Oolite is rich in univalve mollusca,
amongst which may be noted a limpet (_Patella rugosa_) and the handsome,
tall-spired _Nerinæa Voltzii_, numerous bivalves belonging to the genera
_Pholadomya Trigonia_, _Ostrea_ (_O. gregaria_), and _Pecten_, besides
Brachiopods (_Terebratula digona_, which looks very like a sack of
flour, and _T. perovalis_, etc.).
At the base of the Great Oolite are the "Stonesfield slates,"
so-called--a series of thin shelly Oolites, etc., that split readily
into very thin slabs. They are principally of interest to geologists on
account of the discovery in them of the remains of small insect-feeding
and possibly pouched mammals. With these are associated the bones of
that big reptile the _Megalosaurus_; the flying lizards called
Pterodactyles; fish teeth and spines; lamp shells; oysters, a _Trigonia_
(_T. impressa_); and the impressions of insects, including a butterfly,
and of plants.
_d._ _Fullers' Earth_, a clayey deposit occurring in the southwestern
parts of England, but not in the north. It abounds with a small oyster
(_O. acuminata_) and Brachiopods (e.g. _Terebratula ornithocephala_),
etc.
_e._ _Inferior Oolite_ (including the Midford Sands). As these beds are
followed across the country from the south-west of England to Yorkshire,
they are found to change greatly in character. Limestone and marine beds
in the south are replaced by sandy and estuarine beds in the north.
Amongst other fossils from beds of this age may be found several
Echinoderms, a crinkly lamp shell (_Terebratula frimbriata_), and a
spiny one (_Rhynchonella spinosa_), bivalves belonging to the Genera
_Ostrea_, _Trigonia_, _Pholadomya_, etc., and some very handsome
Ammonites (e.g. _A. Humphresianus_).
[Illustration: _Ichthyosaurus_, or Fish-lizard (from the Lias).]
[Illustration: _Plesiosaurus_ (from the Lias).]
4. Lias.
This for the most part consists of very regular alternations of
argillaceous (clayey) limestone and clay, or shale. It is of great
thickness, and hence for convenience has been divided into (a) _Upper
Lias_, (b) _Middle Lias_ or _Marl-stone_, and (c) _Lower Lias_. A large
number of fossils are to be found in it. Lyme Regis and Whitby are
perhaps the best known localities; the former, on account of the great
number of specimens obtained of the huge fish-lizard (_Ichthyosaurus_,
p. 24), and long-necked _Plesiosaurus_ (p. 25), besides numberless fish;
whilst the latter is renowned for its jet (or fossilized wood) and its
"snake-stones" (_Ammonites_), concerning which curious old stories are
told. _Ammonites_ are plentiful in the Lias, which has been subdivided
into zones, or layers, named after the ammonite occurring in greatest
numbers in that particular zone. There is one thin limestone band in the
Marlstone composed entirely of the shells of _Ammonites planicostatus_.
A curious kind of oyster (_Gryphæa incurva_), locally known as the
devil's toenail, a huge _Lima_ (_L. gigantea_), a magnificent Encrinite
(_Extracrinus Briareus_), and numerous other fossils, are also to be
obtained by patient search.
[Illustration: _Belemnitas elongatus_(from the Lias).]
5. Rhætic, Penarth Beds, or White Lias.
These beds are not of any considerable thickness, but are very
persistent, and of great interest, inasmuch as they yield the remains of
the oldest known mammal (_Microlestes_), a small insect-feeder. They are
composed of limestones, shales and marls (_i.e._ limey clays), and are
best studied in Somersetshire and Dorsetshire. The "landscape marble"
belongs to this formation, which also contains a bone bed, or thin layer
made up of the bones and teeth, etc., of fish. Shells are not numerous,
though the casts of one species (_Avicula contorta_) is plentiful.
6. Trias, or New Red Sandstone, a thick series of sandstones and marls,
the great mass of which forms the subsoil of the western midland
counties, Birmingham being nearly in the centre, thence they extend in
three directions, one branch passing towards the north-west, through
Cheshire, to the sea at Liverpool, reappearing on the coast line of
Lancashire, Westmoreland, and Cumberland, where it also forms the Valley
of the Eden. Another branch extends through Derby and York to South
Shields, whilst the third may be traced southwards in isolated patches
down into Devonshire.
There are scarcely any fossils in it, but in Worcestershire and
Warwickshire the bivalve shell of a small crustacean (_Estheria minuta_)
occurs in the upper beds; whilst now and again the teeth and bones of
some strange amphibians (_Labyrinthodon_), or the impressions of their
feet (_Cheirotherium_) where they crawled on the then soft mud of the
foreshore, are found. The Trias is divided into Upper Trias or Keuper,
and Lower Trias or Bunter. The middle beds (Muschelkalk), which are
found in Germany, where they contain plenty of fossils, are wanting in
this country. In the lower beds of the Keuper, layers of rock salt,
sometimes of great thickness, occur, whilst casts (called pseudomorphs)
of detached salt-crystals are found abundantly in the sandy marls.
Northwich, Nantwich, Droitwich, and several other towns in Cheshire and
Worcestershire, are famed for their salt works, the salt being either
mined or pumped up as brine from these beds.
[Illustration: _Ceratites nodosus_ (from the Muschelkalk).]
PALÆOZOIC or PRIMARY.--Beds of this age generally possess a more
crystalline and slaty structure than any of those already mentioned, are
usually more highly inclined and disturbed, and form for the most part
more elevated ground. They are the principal store-houses of our mineral
wealth, containing as they do coal, iron, and other metals. The
Palæozoic rocks are found in England to the north and west of the
secondary series, beneath which they disappear when traced to the
south-east. Wales, and the greater part of Scotland and Ireland, consist
of beds of this age.
1. Permian. Under this term are included beds of red sandstones and
marls, closely resembling those of Trias, and like them containing but
few fossils, as well as a very fossiliferous limestone, known as the
Magnesian Limestone, from the abundance of magnesia it contains. A
pretty polyzoan (_Fenestella retiformis_), a spiny brachiopod
(_Productus horridus_), various genera of fish, chiefly found in a marl
state underlying the limestone, some Labyrinthodonts and plant remains,
are the principal forms met with in this formation.
2. Carboniferous. This, from a commercial point of view, is the most
important of all the formations, comprising as it does the coal-bearing
strata. It is subdivided into--
_a._ _Coalmeasures_, a series of sandstones and shales with which are
interstratified the seams of coal, varying in thickness from six inches
to as much in one instance as thirty feet.
Coal is the carbonized remains of innumerable plants, chiefly ferns and
gigantic clubmosses, that grew in swamps bordering on the sea-coast of
the period. Each coal seam is underlain by a bed of clay called
"under-clay," containing the roots of the plants that grew on it. Some
of the best impressions of ferns, etc., are to be obtained in the shaley
beds forming the roof of the coal seam; many good specimens, however,
are to be got by searching the refuse heap at the pit's mouth. Besides
plants, the remains of fish are abundant in some of the beds of shale.
And in Nova Scotia the bones of air-breathing reptiles and land snails
have been discovered. Cockroaches and other insects were also denizens
of the carboniferous forests.
The following are the principal coalfields:--
1. Northumberland and Durham coalfield.
2. South Lancashire coalfield.
3. Derbyshire coalfield.
4. Leicestershire and Staffordshire coalfields.
5. South Wales coalfield.
6. Bristol and Somerset coalfields.
_b._ _Millstone grit_ or _Farewell-rock_. The former term explains
itself, the latter designation has been applied to it in the southern
districts, because when it is reached, then good-bye to all workable
coal-seams.
It consists of coarse sandstones, shales, and conglomerates with a few
small seams of coal. Fossils are not very common in it.
_c._ Yoredale Rocks, a series of flagstones, gritstones, limestones and
shales, with seams of coal, occurring in the northern counties. It is
underlain by--
_d._ _Carboniferous_ or _Mountain Limestone_, which in places is upwards
of 1,000 feet thick, and full of fossils. The stems of encrinites, or
"stone-lilies," corals, brachiopods (_e.g._ _Productus_, _Orthis_,
etc.), and Mollusca, including some Cephalopods, like _Goniatites_ and
the straight Nautilus (_Orthoceras_), with fish teeth, etc., go to
compose this tough, bluish-grey limestone which is largely quarried for
marble mantlepieces, etc.
_e._ The _Tuedian group_ in the north, and _Lower Limestone Shale_ in
the south, follow next, and consist of shales, sandstones, limestones,
and conglomerates, varying greatly in different districts, and
containing few fossils.
3. Devonian or Old Red Sandstone. To this age are assigned a perplexing
series of strata, the principal members of which consist of (_a_) a
thick limestone, well seen in the cliffs and marble quarries of south
Devon, and full of fossil-corals (_e.g._ _Favosites polymorpha_ [or
_cervicornis_]) Brachiopods, and Mollusca, etc.
_b._ A series of sandstones, slates, and limestones in North Devon
containing Trilobites (_Phacops_, _Bronteus_, etc.), Brachiopods, and
other fossils.
_c._ The _Old Red Sandstone_ of Wales, the North of England, and
Scotland, consisting of red and grey sandstone and marly beds, with
remains of fish.
These fish, unlike most now living, were more or less covered with hard
external plates, and possessed merely a cartilaginous skeleton. In one
set of individuals, indeed (_Pterichthys_), the armour plates formed
quite a little box. These creatures propelled themselves by means of two
arm-like flippers, rather than fins. They were but a few inches long,
and appear pigmies in contrast to the strange half-lobster-like
crustacean, _Pterygotus_, that lived with them, and attained sometimes
as much as five feet in length.
4. Silurian. Named by Sir Roderick Murchison after a tribe of Ancient
Britons that dwelt in that part of Wales, where these rocks were first
observed. Some of Murchison's Lower Silurian beds were included by
Professor Sedgwick in his Cambrian, of which we shall have to speak
next; and as these two geologists never could agree on a divisional line
between their respective formations, and since succeeding observers have
followed sometimes one and sometimes the other method of classification,
considerable confusion has resulted. Here, however, for several reasons,
we propose to follow Sedgwick's arrangement; and hence, under the term
Silurian, retain only Murchison's Upper beds. They consist of a series
of sandstones, gritstones, conglomerates, shales, limestones, etc.
Amongst the more important fossils, which are very abundant in the
limestones, are various corals (_e.g._ the Chain-coral _Halysites_),
Star-fish, Crinoids, Trilobites (_Phacops_, etc.), Polyzoa, Brachiopods
and Mollusca, especially Cephalopoda (_Orthoceras_, _Nautilus_, etc.).
These rocks occur principally in the border land between England and
Wales, and the adjacent counties; but are also represented in
Westmoreland, Scotland, and Ireland. Their principal subdivisions are
given in the Table on p. 16.
[Illustration: Trilobite (_Asaphus candatus_), (from the Silurian).]
[Illustration: _Orthoceras subannulatum_ (from the Silurian).]
5. Cambrian. Under this term, derived from the old name for Wales, are
included many sandstones, grits, slates and flags, with here and there a
limestone band. They form the greater part of the western counties of
Wales, where they rise to a considerable height above the sea level. The
highest hills of Westmoreland and more than half of Scotland are
composed of beds of this age.
The fossils, save in the limestone bands, are not easy to find, but in
places they are fairly abundant. Brachiopods are far more numerous than
the Mollusca properly so-called. Of these, the genus _Orthis_ was most
abundant at about the close of this period. Certain beds of this age
have received the name of Lingula Flags, owing this prevalence in them
of the curious Brachiopod _Lingula_ so like the species now living in
some of the warm seas of the tropics. The Trilobites included several
forms, and one species (_Paradoxides Davidis_) attained the length of
nearly two feet. A few star-fish, some Hydrozoans (_Graptolites_), and
the tubes and casts of Annelides and tracks of Trilobites, complete the
list of more remarkable fossils. The subdivisions of the Cambrian rocks
will be found in the table on p. 16.
6. Pre-Cambrian.--Near St. David's Head and some other places in Wales,
in Anglesea, Shropshire, etc., some yet older rocks have been found.
They are probably for the most part of volcanic origin, but they have
been so much changed since they were first deposited, and as hitherto no
fossils have been found in them, little is known concerning them.
Parts of the western coast of Northern Scotland and the Hebrides are
composed of a crystalline rock called Gneiss, and supposed to be the
oldest member of the British strata. No fossils have been found in it.
[Illustration: Skull of _Deinotherium giganteum_, a huge extinct
animal, related to the elephants (from the Miocene of Germany).]
VOLCANIC ROCKS. Although there are fortunately no volcanoes to disturb
the peace of our country at the present day, there is abundant evidence
of their existence in the past. Not only are some of the beds,
especially those of Paleozoic age, composed of the dust and ashes thrown
out of volcanoes, with here and there a lava flow now hardened into
solid rock, but the stumps of the volcanoes themselves are left to tell
the tale. The cones indeed are gone, carried off piecemeal by the rain
and frosts, and other destructive agencies, in the course of countless
ages: not so the once fluid rock within; _that_ cooled down into
Granite, and though originally below the surface, it now, owing to the
removal of the overlying softer strata, forms raised ground overlooking
the surrounding country. The granite masses of Cornwall, of Dartmoor, in
the south-west of Mt. Sorrel; the variety called Syenite at Malvern and
Charnwood Forest; the Basalts of the Cheviot Hills and of Antrim; the
volcanic rocks of Arthur's Seat, Edinburgh, and of the islands of Skye
and Mull, etc., are examples of this class of rock. They are of
different ages, and belong to different periods of the earth's history,
from early Palæozoic down to Miocene times.
TABLE OF THE PRINCIPAL DIVISIONS OF THE ANIMAL KINGDOM, TO SHOW THE
ORDER IN WHICH THE FOSSILS SHOULD BE ARRANGED.
INVERTEBRATA.
_Foraminifera_, minute chambered shells like the Nummulite.
_Spongida_, Sponges.
_Hydrozoa_, Graptolites, etc.
_Actinozoa_, Corals.
_Echinodermata_, Sea-urchins, Stone-lilies, Starfish, etc.
_Annelida_, Worm tracks.
_Crustacea_, Trilobites, Crabs, etc.
_Arachnida_, Scorpions and Spiders.
_Myriapoda_, Centipedes.
_Insecta_, Beetles, Butterflies, etc.
_Polyzoa_ (_Bryozoa_) or Moss Animals.
_Brachiopods_, Lampshells.
{ _Lamellibranchiata_, Bivalves.
_Mollusca_ { _Gasteropoda_, Univalves.
{ _Cephalopoda_, Cuttlefish, Ammonites.
VERTEBRATA.
_Pisces_, Fish.
_Amphibia_, Labyrinthodonts, Frogs, and Newts.
_Reptilia_, Reptiles.
_Aves_, Birds.
_Mammalia_, Mammals.
WORKS OF REFERENCE.
FOR NAMING COMMON FOSSILS.
=Tabular View of Characteristic British Fossils Stratigraphically
Arranged.=
By J. W. LOWRY. _Soc. Prom. Christ. Knowledge._ 1853.
=Figures of the Characteristic British Tertiary Fossils (Chiefly
Mollusca)
Stratigraphically Arranged.= By J. W. LOWRY and others. _London_
(_Stanford_). 1866.
PALÆONTOLOGY.
=The Ancient Life History of the Earth.=
By H. A. NICHOLSON. 8vo. _Edinburgh and London._ 1877.
=A Manual of Palæontology.=
By H. A. NICHOLSON. 2nd edition. 2 vols. 8vo. _Edinburgh and
London._ 1879.
PETROLOGY.
=The Study of Rocks.=
By F. RUTLEY. (Text Books of Science.) 8vo. _London._ 1879.
FIELD GEOLOGY.
=A Text-Book of Field Geology.=
By W. H. PENNING. With a Section on Palæontology, by A. J.
JUKES-BROWN. 2nd edition. 8vo. _London._ 1879.
GEOLOGY IN GENERAL.
=The Student's Elements of Geology.=
By SIR CHARLES LYELL, Bart. 4th edition. 8vo. _London._ 1884.
=The Principles of Geology.=
By SIR CHARLES LYELL, Bart. 12th edition. 2 vols. 8vo. _London._
1875.
=Phillip's Manual of Geology.=
2nd edition. By SEELEY AND ETHERIDGE. 2 vols., 8vo. _London._ 1885.
=Tabular View of Geological Systems, with their Lithological
Composition and Palæontological Remains.=
By D. E. CLEMENT. _London (Sonnenschein)._ 1882.
BRITISH GEOLOGY.
=The Physical Geology and Geography of Great Britain.=
By SIR ANDREW C. RAMSEY. 5th edition. 8vo. _London._ 1878.
=The Geology of England and Wales.=
By HORACE B. WOODWARD. 8vo. _London._ 1876.
=Geology of the Counties of England and Wales.=
By W. J. HARRISON. 8vo. _London._ 1882.
* * * * *
POPULAR ILLUSTRATED SCIENTIFIC BOOKS, PUBLISHED BY SWAN SONNENSCHEIN & CO.
UNIFORM WITH THIS VOLUME. ALL FULLY ILLUSTRATED.
=BRITISH BUTTERFLIES, MOTHS, AND BEETLES.=
By W. F. KIRBY (Brit. Mus.). Crown 8vo, cloth, 1_s._
=MOSSES, LICHENS, AND FUNGI.=
By PETER GRAY and E. M. HOLMES. Crown 8vo, cloth, 1_s._
=ENGLISH COINS AND TOKENS.=
By LLEWELLYNN JEWITT, F.S.A.; with a chapter on =Greek and Roman
Coins=, by BARCLAY V. HEAD, M.R.A.S. Crown 8vo, cloth, 1_s._
=FLOWERS AND FLOWER LORE.=
By Rev. HILDERIC FRIEND, F.L.S. Illustrated. Third Edition,
demy 8vo, cloth gilt, 7_s._ 6_d._
=THE DYNAMO: How Made and How Used.=
By S. R. BOTTONE. Numerous Cuts. Crown 8vo, cloth, 2_s._ 6_d._
=A SEASON AMONG THE WILD FLOWERS.=
By Rev. H. WOOD. Illustrated. Crown 8vo, cloth gilt, 2_s._ 6_d._
=HISTORY OF BRITISH FERNS.=
By E. NEWMAN, F.L.S. Fifth Edition, Illustrated. 12mo, cloth, 2_s._
=THE INSECT HUNTER'S COMPANION.=
By Rev. J. GREENE. Third Edition. Cuts. 12mo, boards, 1_s._
=TABULAR VIEW OF GEOLOGICAL SYSTEMS.=
By Dr. E. CLEMENT. Crown 8vo, limp cloth, 1_s._
SWAN SONNENSCHEIN & CO., PATERNOSTER SQUARE.
* * * * *
TRANSCRIBER'S NOTES:
As there appear to be section and subsections in the second and third
units (Shells and Fossils) of this book, Tables of Contents were
created for the electronic edition. A number of the images were moved
where they split paragraphs. There is a reference to a Figure 24 for
Ancylus; but no Fig. 24 was included. The reference to Fig. 26 for
Bullidæ was assumed to be a reference to Fig. 14. Bulla ampulla.
With the exception of the following items, all page number references
in the original text were retained. There are references to two tables
on Page 77. The first was listed a "vide Table, p. 16" and the second
as "vide Table, p. 32" which appear to refer to the tables on page 78
and 94 respectively. The page references were corrected.
Species name are assumed to be correct for the time of publication
(ca. 1886). For example, Charychium is today listed as Carychium.
Text Emphasis
_Text_ - Italics
=Text+ - Bold
Typographic Corrections
Page Correction
---- ------------------------
14 fond => foot
27 it => if
27 pencil => brush
55 beak => peak
56 tis => its
60 Keilia => Kellia
73 inever => "I never"
91 crustucean => crustacean
End of the Project Gutenberg EBook of Sea-Weeds, Shells and Fossils, by
Peter Gray and B. B. Woodward
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