Scenery of the carboniferous forests--Contrast in the
appearance of coal districts at the present day--Abundance
of animal life in the Carboniferous era--Advantages
of palæontology over fossil-botany--Carboniferous
fauna--Actiniæ--Cup-corals--Architecture of the present
day might be improved by study of the architecture of the
Carboniferous period--Mode of propagation of corals--A
forenoon on the beach--Various stages in the decomposition of
shells--Sea-mat--Bryozoa--Fenestella--Retepora--Stone-lilies--
Popular superstitions--Structure of the stone-lilies--Aspect
of the sea-bottom on which the stone-lilies
flourished--Sea-urchins--Crustacea, their high
antiquity--Cyprides--Architecture of the Crustacea and
mollusca contrasted--King-crabs.
The forms of vegetation that flourished during the Carboniferous era
seem to have been in large measure marshy plants, luxuriating on low
muddy delta-lands, like the cypress-swamps of the Mississippi, or the
Sunderbunds of the Ganges. We can picture but faintly the general
scenery of these old forests from the broken and carbonized remains
that have come down to us. But though perhaps somewhat monotonous
on the whole, it must have been eminently beautiful in detail. The
sigillariæ raised their sculptured stems and lofty waving wreaths of
fronds high over the more swampy grounds, while a thick underwood of
ferns and star-leaved asterophyllites clustered amid the shade below.
The lepidodendra shot forth their spiky branches from the margin of
green islets, and dropped their catkins into the sluggish water that
stole on among the dimpled shadows underneath. Tree-ferns spread out
their broad pendant fronds, and wrapt the ground below in an almost
twilight gloom, darker and deeper far than that
"Hospitable roof
Of branching elms star-proof,"
which rose so often in the visions of Milton; or that "graceful arch"
so exquisitely sung by Cowper, beneath which
"The chequered earth seems restless as a flood
Brushed by the wind. So sportive is the light
Shot; through the boughs, it dances as they dance,
Shadow and sunshine intermingling quick,
And darkening and enlightening, as the leaves
Play wanton, every moment, every spot."
Thickets of tall reeds rose out of the water, with stems massive as
those of our forest-trees, encircled at regular distances by wreaths of
pointed leaflets, and bearing on their summits club-like catkins. Far
away, the distant hills lay shaggy with pine-woods, and nursed in their
solitudes the springs and rivulets that worked a devious course through
forest, and glen, and valley, until, united into one broad river, they
crept through the rich foliage of the delta and finally passed away out
to sea, bearing with them a varied burden of drift-wood, pine-trees
from the hills, and stray leaves and cones from the lower grounds.
How different such a scene from that now presented by the very same
areas of country! These old delta lands are now our coal-fields, and
have exchanged the deep stillness of primeval nature for the din and
turmoil of modern mining districts. In these ancient times, not only
was man uncreated, but the earth as yet lacked all the higher types of
vertebrated being. None of the animals that we see around us existed
then; there were no sheep, nor oxen, horses, deer, nor dogs. Neither
were the quadrupeds of other lands represented; the forests nourished
no lions or tigers, no wolves or bears, no opossums or kangaroos. In
truth, the land must have been a very silent one, for we know as yet of
no animated existence that could break the stillness, save perchance
some chirping grasshopper, or droning beetle, or quivering dragon-fly.
No bee hummed along on errands of industry; it is doubtful, indeed,
whether honey-yielding flowers formed part of the carboniferous flora;
no lark carolled blithely in the sky, nor rook croaked among the
woods. All was still; and one might, perhaps, have stood on some of
those tree-crested islets, and heard no sound but the rippling of the
water along the reedy and sedgy banks, and the rustling of the gloomy
branches overhead.
To one who muses on these bygone ages it is no unimpressive situation
to stand in the midst of a large coal district and mark its smoking
chimneys, clanking engines, and screaming locomotives, its squalid
villages and still more squalid inhabitants, and its mingled air of
commercial activity, physical wretchedness, and moral degradation.
It is from such a point of view that we receive the most forcible
illustration of those great changes whereof every country has been the
scene, and which are so tersely expressed by one who has gazed on the
revelations of geology with the eye of a true poet--
"There rolls the deep where grew the tree.
O earth, what changes hast thou seen!
There where the long street roars, bath been
The stillness of the central sea."
But the lifelessness of the carboniferous forests was amply compensated
by the activity that reigned in river, lagoon, and sea. Coral groves
gleamed white beneath the waves, fishes of many a shape disported in
stream and lake, and the bulkier forms, armed in massive plates of
bone, ascended the rivers or haunted the deeper recesses of the open
sea. In some beds of rock the remains of these various animals lie
crowded together like drifted tangle on the sea-shore, and the whole
reminds us of a vast cemetery or charnel-house. The bones lie at all
angles, many of them broken and disjointed as though the owner had died
at a distance, and his remains, sadly mutilated on the way, had been
borne to their last resting-place by the shifting currents; others
lie all in place, covered with their armature of scales, as though
the creature, conscious of approaching dissolution, had sought out a
sheltered nook and there lain down and died. It is not uninteresting
or uninstructive to tract; out in an old quarry stratum above stratum,
each with its groups of once living things. I know of few employments
more pleasant than to sit there, amid the calm stillness of a summer
evening, when the shadows are beginning to steal along the valleys and
creep up the hill-sides, and in that dim fading light to try in fancy
to clothe these dry bones with life, to picture the time when they
lived and moved in the glassy depths of lakes and seas, or amid the
solitudes of jungles and forests, and so to spend a pleasant hour in
reverie, till roused at last by the vesper song of the lark, or the low
meanings of the night wind as it sighs mournfully through the woods.
The study of fossil animals embraces a much greater range of subject
than that of fossil plants. The _fauna_ of any particular geological
formation, that is to say, its embedded animal remains, for the most
part vastly exceeds in number its _flora_, or vegetable remains, and is
likewise usually better preserved. About the nature and affinities of
several tribes of fossil plants there hangs an amount of uncertainty
which renders them a dubious guide to the climatal and other conditions
of the period and locality in which they lived. Generic distinctions
among living plants often rest on the character of those parts which
are the most perishable, such as flowers and seed-vessels. These
delicate structures we, of course, can hardly look to find preserved
in the rocks, and we have in place of them only detached leaflets,
twigs, branches, and stems, often sorely mutilated in outward form, and
presenting no trace of internal organization. But the tribes of the
animal kingdom have, for the most part, harder frameworks. The minute
infusoria, which by their accumulated remains help to choke up the
delta of the Nile, and swarm by millions in every ocean of the globe,
have their silicious or calcareous shells so minute that Ehrenberg
has estimated a cubic inch of tripoli to contain forty-one thousand
millions of them. The polypi have their internal calcareous skeletons,
which abound in all the older limestones, and form the coral reefs of
the present day. The mollusca, too, though, as their name imports, they
have perishable bodies, are yet, in most cases, furnished with hard
calcareous shells, that indicate by their various modifications of form
and structure, the character of the animal that lived within them. They
are found in all the formations from the earliest upwards, and as they
vastly exceed in numbers all the other classes with which the geologist
has to deal, they form the larger part of that basis of evidence from
which he interprets the past history of organized existence. Hugh
Miller loved to talk of them as the "shell alphabet," out of which the
language of palæontological history should be compiled. The vertebrata,
too, all have their hard skeletons, easily capable of preservation,
whether it be in the form of the massive exo-skeleton of bone that
characterized the older ganoidal fishes, or the compact endo-skeleton
of the reptiles and mammals. A greater amount of attention is,
therefore, due to the study of fossil animals, since they thus not
only far exceed fossil plants in number, but possess a higher value as
evidence of ancient physical conditions.
The _fauna_ of the Carboniferous system is a very numerous one,
exhibiting specimens of almost every class of animal life, from the
tiny _foraminifer_ up to the massive bone-covered sauroidal fish,
and even to occasional traces of true reptilian remains. By far the
larger number are peculiar to the sea, such as the molluscan tribes
and corals; others are undoubtedly terrestrial organisms, such as the
wings and wing-sheaths of several kinds of insects; while some appear
to be peculiar to fresh or brackish water, such as shells allied to
our _unio_ or river-mussel, and minute crustaceous animals known as
_cyprides_, of which we have still representatives in our ponds and
ditches. It is plain, then, that if we rightly ascertain the class or
family to which one of these fossils belonged, we shall obtain a clue
to the history of the physical geography, during Carboniferous times,
of the district in which the fossil occurs. A bed of unios will tell
us of old rivers and lakes that spread out their blue waters where
now, perchance, there lie waving fields of corn. A bed of corals and
stone-lilies will lay before us the bottom of an ancient ocean that
rolled its restless waves where to-day, perhaps, the quarryman plies
his task amid the gloom of dark pine-woods. In short, these organic
remains are to the history of the earth what ancient monuments are to
the history of man. They enable us to trace out the varied changes
of our planet and its inhabitants down to the human era, just as the
wooden canoe, the flint arrow-head, the stone coffin, the bronze sword,
the iron cuirass, the ruined abbey, and the feudal castle, teach us the
successive stages of progress in the history of our own country.
Whoever has spent a few days on some rocky coast, must have noticed
adhering to half-tide stones numerous solitary _actiniæ_. Arrayed in
all the colours of the rainbow--purple, green, and gold--these little
creatures hang out their tentacles like so many flowers, and have hence
received the popular name of sea-anemones. Their internal structure is
no less beautiful. They resemble so many large plump gooseberries, and
consist of a little sack suspended within a larger one. The outer sack
is fringed along its upper edges with one or more rows of slim hollow
tentacles, which diverge outwards like the petals of the daisy, and can
be contracted at pleasure so as somewhat to resemble the daisy when
folded up at sunset. The inner sack, which forms the stomach of the
animal, has a short opening or gullet, at the upper part of which is
the mouth lying in the centre of the cavity surrounded by the fringes
of tentacles. The inner sack is connected with the outer by means of
thin membranes, like so many partition-walls, which radiate inwards
like spokes towards the axle of a wheel. The space between each of
these membranes, or lamellæ, forms an independent chamber, but it has
a communication with those on either side by a window in each wall,
and further opens upwards into the hollow tentacles, which, with minute
orifices at their outer points, may be compared to chimneys. These
chambers form the breathing apparatus of the little creature. Sea-water
passes down through the tentacle into the hollow chamber below,
whence, by the constant action of minute hairlike cilia that line the
walls like tapestry, it is driven through the window into the next
chamber, thence into the next, and so on, passing gradually through the
tentacles back to the sea.
The actiniæ are of a soft perishable substance, but many of the other
_Anthozoa_, or flower-like animals, have hard calcareous skeletons. Of
such a kind are the polypi that in the Pacific Ocean have raised those
stupendous reefs and islands of coral. It does not appear that, during
the Carboniferous period, there existed any reef-building zoophytes,
but some of the most abundant forms of life belonged to a kindred
tribe, and are known by the name of _Cyathophyllidæ_, or cup-corals.
As the name imports, the typical genus has a general cup-shaped form,
but this is liable to many aberrations in the cognate genera. The
younger specimens of one species (_Cyathopsis fungites_) have a curved
outline somewhat like the bowl of a tobacco-pipe, whence the quarrymen
know them as pipe-heads. The older individuals are generally more or
less wrinkled and twisted, sometimes reaching a length of eight or nine
inches, and have been named by the workmen _rams'-horns_.
[Illustration: Fig. 16.--Cyathopsis (clisiophyllum ?) fungites.]
The annexed figure (Fig. 16) shows their general appearance and
structure. The lower end was fixed to the rock like the flat
sucker-like disc of the actinia. Around the outer margin there diverged
one or more rows of slim tentacles, hollow, soft, and retractile, like
those of the actinia. From the margin to the centre there radiated
more than a hundred lamellæ, but these differed from the corresponding
membranes of the modern animal, inasmuch as they were strengthened
internally by a skeleton of hard carbonate of lime; and to this
difference we owe their preservation. They stand out in high relief
upon weathered specimens, showing the long, narrow chambers that ran
between them. Their walls were once doubtless hung with countless
vibratile cilia, and perhaps pierced each with its window, through
which the currents of water passed in their ceaseless progress to and
from the sea. At the centre lay the mouth, communicating by a short
gullet with the stomach, which occupied the central portion of the
animal, and from the outer walls of which the lamellæ diverged like so
many buttresses. In its youngest stages, the animal occupied the whole
length of the cup, but, us it increased in size, it gradually retreated
from the narrow end, which was then divided off by a thin calcareous
membrane. At each successive stage of its growth, a new membrane was
added, each further and further from the lower end, so that eventually
the creature left below it a series of empty chambers all firmly
built up. Thus, in a specimen six or eight inches long, there would
in reality only be a small part tenanted--in fact merely the upper
floor--all the lower storeys remaining silent and uninhabited. The
house of this old-world architect differed widely in one respect from
human dwellings. Man begins his basement story of the same dimensions
as those that are to succeed it, or, if any difference is made at all,
the upper floors are built each less than the one below it, so that
the whole structure tapers upward to a point, as in the Pyramids. But
the cyathopsis reversed this latter process; it inverted the cone,
commencing the smallest chamber at the bottom, and placing the widest
at the top. Indeed, one is sometimes puzzled to conjecture how so bulky
a building could be securely poised on so narrow a basis, and it is
certainly difficult to see how the creature could move about with such
a ponderous load to drag along. The snail carries his house on his
back, yet it is a slim structure at the best; but the cup-coral must
not merely have carried his house, but some dozen or two of old ones
strung one after another to his tail. Perhaps, though free to move
about and try change of residence in its youthful days, the creature
gradually settled down in life, and took up its permanent abode in some
favourite retreat, the more especially as in process of time it became
what we should call a very respectable householder.
Allied to the cyathopsis is another and still more beautiful coral,
described so long ago as the latter part of the seventeenth century
by the Welsh antiquary and naturalist, Lhwyd, under the name of
_Lithostrotion_. Although many perfect specimens of it have been
found, and it is usually as well preserved as any of its congeners,
men of science have been sadly at a loss what to call it. Four or
five synonyms may be found applied to it in different works on
palæontology. There seems now, however, a tendency to return to the
name that old Lhwyd gave it two centuries ago; the family to which
it belongs, and of which it is the type, has accordingly been termed
the _Lithostrotionidæ_, and the species in question _Lithostrotion
striatum_ (Fig. 17). It differed from the cyathopsis in several
respects, but chiefly in this, that it lived in little congregated
groups or colonies, whereas the cyathopsis, like our own actinia, dwelt
alone.
[Illustration: Fig. 17.--Lithostrotion striatum.]
Each of these colonies was formed of a cluster of hexagonal, or rather
polygonal pillars, fitting closely into each other, like the basaltic
columns of Fingal's Cave, and springing from a common base at the sea
bottom.[30] Each pillar constituted the abode of a single animal,
and resembled generally the stalk of the cyathopsis. It had the same
minute diverging partitions running from the outer walls towards the
centre, and the same thin diaphragms, which, stretching horizontally
across the interior of the column at short intervals, marked the
successive stages of the animal's growth. Within these partitions,
which vary from forty to eighty in number, there runs an inner circular
tube with thin lamellæ and diaphragms. The exterior of the columns is
ribbed longitudinally by a set of long fine striæ, which give somewhat
the appearance of the fluting on a Corinthian pillar. The columns,
moreover, are not straight, but have an irregular, wrinkled outline,
so that, by a slant light, they look like some old pillar formed of
many layers of stone, the joints of which have wasted away, producing
an undulating profile in place of the original even one. But in these
ancient coral columns there is no blunted outline, no worn hollow;
the sculpturing stands out as sharp and fresh, and the wavy curves as
clearly defined, as though the creature had died but yesterday. They
resemble no order of human architecture, save faintly, perhaps, some of
the wavy outlines of the Arabesque.
[Footnote 30: Sir Roderick Murchison figures in his _Siluria_, p. 282,
a gigantic specimen, which measured two feet four inches in width.]
Despite all the improvements and inventions of modern times, classic
architecture has made no progress since the days of Pericles. All that
we do now is but to reproduce what the Greeks created 2000 years ago,
and he is reckoned the best architect who furnishes the best imitation.
Our architects might find some useful hints, however, by studying the
lowlier orders of nature. They would see there patterns of beauty far
more delicate than the Grecian capital, and more light and airy than
the Gothic shaft. And whether or not they could found a new order of
architecture, they could not fail to discover many modifications and
improvements upon some of the old. They could not readily light upon
a more graceful form than that of the lithostrotion, would they but
picture it as it grew at the bottom of the old carboniferous sea. A
group of hexagonal pillars, firmly compacted together like those of
the Giant's Causeway, or Fingal's Cave, rose from a white calcareous
pediment, as columns from the marble steps of an Athenian temple. Each
side of the pillar had a wavy undulating surface, delicately fluted by
long slender striæ, the whole being so arranged that the convexities
of one surface fitted into the sinuosities of the adhering one. Each
pillar was crowned above by a capital, consisting of the soft vibratile
tentacles of the animal, that hung over like so many acanthus leaves.
Of the form of these tentacles, their design and grouping, we know
nothing save what may be gathered from the analogy of living corals.
There can be little doubt, however, that, like the flower-shaped buds
of the existing reef-building polyps, they must have been eminently
beautiful, and in strict keeping with the graceful column which they
crowned.
Another kindred form was that known as the _lithodendron_. It, too,
grew in colonies, and seems to have closely resembled the last, save
that the pillars, in place of being six-sided, were round. I have seen
a bed of these corals several yards in extent, and seven or eight
inches deep, where the individuals were closely crowded together, so
as to resemble a series of tobacco-pipe stems, or slim pencils set on
end. The tubes, however, were not all quite straight; many being more
or less curved, and sometimes crossing their neighbours obliquely.
The internal arrangement was on the same plan as in the two previous
corals. The same numerous partitions ran from the exterior wall
towards the central tube, the same thick-set diaphragms crossed the
entire breadth of the column, imparting the same minute honey-combed
appearance to a cross section. The exterior of the column (in _L.
fasciculatum_) was likewise traversed by the same longitudinal striæ.
Both these corals seem to have been _fissiparous_, that is to say, they
propagated by splitting into two parts, each of which formed the base
of a new column with a new animal. The evidence for this statement
rests on the fact, that many of the tubes are seen to bifurcate in
their course, so that two new tubes are produced equal in size and
completeness to the old one from which they proceed. Another mode of
generation which, in at least its earlier stages, would produce a
somewhat similar appearance is called _gemmation_, and consists in
the protrusion of a bud or gemmule from the side of the animal, which
shortly develops into a new and perfect individual. It is probable,
however, that the ordinary mode of propagation among these old corals
was the usual one by impregnated ova. These ova, like those of our
sea-anemones, were probably generated within the partitions, between
the central stomach and the outer wall, whence they passed down into
the stomach, and were ejected by the mouth of the parent as little
gemmules, furnished with the power of locomotion by means of vibratile
cilia. Some of the _Medusa_ family possess this three-fold mode of
propagation; but, in all, the last-mentioned is the most usual.
Has the reader ever stretched himself along the shore, while, perhaps,
a July sun blazed overhead, and a fitful breeze came over the sea, just
strong enough to chase ashore an endless series of rippling wavelets,
and breathe over his temples a delicious and refreshing coolness?
Thus placed, and gazing dreamily now, perchance, at the distant sails
like white specks along the boundary line of sea and sky; now at the
gulls wheeling in broad circles through the air, and shooting swift
as arrows down into the blue water, he must often have turned to look
for a little at the sand which, heaped up in little mounds around him,
formed a couch well-nigh as soft as the finest down. Many a varied
fragment entered into the composition of that sand. Mingled among the
minuter quartzy particles lay scores of shells, some with the colour
not yet faded, and the valves still together--the delicate tellina,
with its polished surface, and its flush of pink; the cardium with its
strong white plaited sides, and the turritella with its circling spire;
some were worn down and sorely effaced, others broken into fragments
by the ceaseless grinding of the waves. It was pleasant labour in such
a sultry noon to pick out the shells of one species in all stages of
decay. The _Trochus lineatus_, or Silver Willie, as young ramblers by
the sea-shore love to call it, showed well the process of destruction.
The perfect shell, cast ashore, perhaps, by the last storm, and still
uninjured by the tides, displayed its russet epidermis, or outer skin,
covered with fine brown zig-zag lines, running across the whorls from
the creature's wide pearl-lined mouth to the apex. A second shell
exhibited a surface that had begun to suffer; the point had been
divested of its thin outer skin, and laid bare the silvery coating of
pearl below. A third had undergone a still longer period of abrasion,
for the whole of the epidermis was gone, and the surface gleamed with
a pearly iridescence. In yet a fourth, this bright exterior had been
in large measure worn away, and the blunted, rounded shell displayed
the dull white calcareous substance of which it was mainly built up.
But there were other objects of interest in the sand: bits of tangle,
crusted over with a fine net-work of gauze, and fragments of thin
leaf-like membrane, consisting of a similar slender network known
popularly as the _sea-mat_, occasionally turned up among the pebbles
and shells. No one who met with these organisms for the first time
could fail to be struck with the extreme delicacy of finish, if one
may so speak, that characterizes them. And yet he might be puzzled to
know what to make of them. The leaf-like membrane, at a first glance,
looks not unlike some of the flat-leaved algæ, and such the observer
might readily take them to be. Such, too, they were long regarded by
naturalists; but a more careful examination of them showed that the
so-called plants really belonged to the animal kingdom, and that the
supposed leaves were, in truth, the organic dwelling-places of minute
zoophytes, of which many hundreds lay grouped together on every square
inch. For many years these little creatures were called "celliferous
corallines," and classed among the polypi, that great tribe which has
its representatives in every ocean, from the coral reefs of the Pacific
to the little bell-shaped _hydra_ amid the tangle of our own seas.
But the microscope--that lamp which lights us into the inner recesses
of nature--revealed at last their true character. Fixed to one spot,
living in communities, and exceedingly minute, in short, with many of
the outward features of the true corallines, they were yet found to
possess a structure so complex and highly organized, as to entitle them
to rank among the higher tribes of the invertebrate animals, and they
are now accordingly pretty generally subjoined to the mollusca, under
the name of _Bryozoa_.
Each bryozoon consists externally of a single horny or calcareous cell,
sometimes furnished with a valve-like lid that folds down when the
animal withdraws itself. When danger is past, and the creature begins
again to emerge, the upper parts, which were drawn in like the inverted
finger of a glove, are pushed out until a series of tentacles, covered
with minute hair-like bodies, called cilia, are expanded. The vibratile
motion of these cilia causes a constant current in the direction of
the mouth, which lies in the centre of the hollow whence the tentacles
spring; animalcules are in this way brought in rapid succession within
reach of the mouth, and form a never-failing source of nourishment.
The interior is greatly more complex than that of the _polypi_. The
stomach is connected above with a cavity like the gizzard of a bird,
furnished with pointed sides, which serve to triturate the food before
it passes into the stomach. There is also a distinct intestine. The
muscular action for the expansion and retraction of the animal is
highly developed, and the generative system is a greatly more complex
one than that of the polyps already referred to. In short, however
closely they might be thought to resemble the corals in outward form,
their internal structure undoubtedly links them with a much higher type
of organization, and justifies the naturalist in subjoining them as a
sub-order to the mollusca.
The cells are grouped at short intervals along a horny or calcareous
substance, that sometimes encrusts sea-weed, or spreads out as a flat
leaf-like membrane, or rises into cup-shaped or dendritic forms. A
series of cells constituting a separate and independent colony, is
termed a polypidom. The cells are further connected together by an
external jelly-like integument, in which they are sunk, and which
serves to secrete the calcareous particles from the sea.
It is interesting to know that creatures so minute and yet so complexly
organized, existed abundantly in the seas of the Carboniferous period.
No less than fifty-four species are enumerated as having been obtained
from the carboniferous strata of the British Islands, and scarcely a
year passes without one or two new species being added to the list.
The most frequent belong to the genus _Fenestella_, or little window,
a name indicative of the reticulated grouping of the branches like the
wooden framework of a window. Each of these branches, or interstices,
as they are called, was more or less straight, being connected with
that on either side by a row of transverse bars, just as the central
mullion of an abbey window is connected with the flanking ones by means
of cross-bars of stone. Not unfrequently some of the branches subdivide
into two, as we saw to be the case among the cup-corals.
[Illustration: Fig. 18.--_a_, Fenestella oculata (M'Coy), nat. size;
_b_, magnified portion of the same.]
Fig. 18 illustrates the relative disposition of these branches. In _a_,
the natural size of the fossil is given; _b_ is a portion of the same
magnified, to show the form and arrangement of the ribs and cross-bars.
Each rib is seen to have two sides separated by a rounded ridge. Along
each side there runs a row of circular hollows or cells, every one
of which once formed the abode of a distinct bryozoon. The back or
inner surface of the branch, was ribbed and granulated irregularly,
without any cells. The connecting bars or dissepiments have no cells,
and served merely to bind the interstices together into one firm
organically-united polypidom. Such fragments as that here figured
are the most usual traces to be found of these animals among the
carboniferous rocks. But perfect specimens are sometimes met with which
show how delicate and graceful a structure the polypidom of some of the
fenestellæ must have been. All these bars sprung from a common point
as their basis, and rose up in the form of a cup. It was, in short, a
cup of network, hung with waving tentacles and quivering cilia. I have
seen some dissections of flowers in which all the softer tissue had
been removed, so as to present only the harder veinings of the leaves
with their thousand ramifications bleached to a delicate whiteness.
Out of these skeleton-leaves there were formed groups of lilies,
crocuses, geraniums, and roses, like patterns of the finest gauze. Some
of the larger-stemmed leaves that had been artistically moulded into a
tulip form, seemed not inaptly to represent the general contour of the
skeleton of the old carboniferous fenestella.
An allied form is called the _Retepora_. It differed from the previous
organism in having the ribs not straight, but irregularly anastomosing,
that is, running into and coalescing with each other, so as to form
a close network with oval interspaces, like a piece of very minute
wire-fence. Each of these wavy libs was completely covered over on one
side with oval pores or cells, which, as in the fenestella, formed the
abode of the living animals. The differences in organization between
the animal of fenestella and that of retepora can, of course, only be
matter of speculation. The general structure in both must, however,
have been pretty much alike. The former genus is now no longer extant,
but the latter, which was ushered into the world during the era of the
Old Red Sandstone, still lives in the deeper recesses of the ocean, and
manifests in its structure and habits the leading characteristics of
bryozoan life.
What rambler among old lime-quarries is not familiar with the
stone-lily, so abundant an organism in most of the Palæozoic and
many of the Secondary limestones? In some beds of the carboniferous
limestone its abundance is almost incredible. I have seen a weathered
cliff in which its remains stood out in bold relief, crowded together,
to use an expression of Dr. Buckland's, "as thickly as straws in a
corn-rick." The joints of this animal, known now as _entrochi_ or
wheel-stones, forced themselves on the notice of men during even the
middle ages, and an explanation was soon found for their existence.
From their occurring largely about the coast at Holy Island, they were
set down as the workmanship of Saint Cuthbert.
"On a rock by Lindisfarne,
St. Cuthbert sits and toils to frame
The sea-born beads which bear his name."
The aged saint was represented as employing his nights in this highly
intellectual task, sitting on a lone rock out in the sea, and using an
adjacent one as his anvil.
"Such tales had Whitby's fishers told,
And said they might his shape behold,
And hear his anvil sound,
A deaden'd clang,--a huge dim form
Seen but, and heard, when gathering storm
And night were closing round."
But these wheel-stones were not the only geological curiosities
to which this simple mode of explanation was applied. In the same
storied neighbourhood there occur in considerable numbers the round
whorled shells of the genus _Ammonites_. These were gravely set down
as petrified snakes wanting the head, and their petrifaction and
decapitation were alike reverently ascribed to the power of the sainted
abbess of Whitby.
"They told
How of a thousand snakes each one
Was changed into a coil of stone
When holy Hilda prayed."
The stone-lily belonged to that large class of animals ranked together
as _Echinodermata_, a name taken from one of the leading subdivisions
of the group--the _Echini_ or sea-urchins. It seems to have been one
of the earliest forms of life upon our planet, its disjointed stalks
occurring largely in some of the oldest Silurian limestones. In the
Secondary ages it began gradually to wane, until at the present day its
numerous genera appear to be represented by but the _comatula_ and the
_pentacrinite_, two tiny forms that float their jointed arms in the
profounder depths of the sea.
[Illustration: Fig. 19.--_a_, Cyathocrinites planus. _b_, Encrinal
stem, with uniform joints. _c_, Single joint, or wheelstone.]
As its name imports, the stone-lily or encrinite had a plant-like
form. It consisted of a long stalk fixed by the lower end to the
sea-bottom, and supporting above a lily-shaped cup, in which were
placed the mouth and stomach (Fig. 19 _a_). The stalk consisted of
circular plates (some of them not so thick as a sixpence), having
their flat sides covered with a set of minute ribs radiating from the
centre, and so arranged that the prominent lines of one joint fitted
into corresponding depressed lines of the adhering ones. The centre
of each joint was pierced by a small aperture, like the axle of a
wheel, which, when the stem was entire, formed part of the long tube
or canal that traversed the centre of the stem, and served to convey
aliment to the remotest part of the animal. Detached joints have thus
a wheel-like appearance (Fig 19 _c_), and hence their common name of
wheel-stones. In many species they were not all of the same diameter,
but alternately larger and smaller, as if the stem had been made up of
a tall pile of sixpences and threepenny pieces in alternate succession.
This variation gives a remarkably elegant contour to the stalk. The
flower-shaped cup consisted of a cavity formed of geometric calcareous
plates, and fringed along its upper margin with thick calcareous
arms, five or ten in number, that subdivided into still more slender
branches, which were fringed along their inner side with minute _cirri_
or feelers. All these subdivisions, however fine, were made up of
calcareous joints like the stalk, so that every stone-lily consisted
of many thousand pieces, each perfect in its organization and delicate
in its sculpturing. One species peculiar to the Liassic formation
(_Extracrinus Briareus_) has been calculated to contain one hundred and
fifty thousand joints!
The effect of this minute subdivision was to impart the most perfect
flexibility to even the smallest pinnule. The flower could instantly
collapse, and thus the animals on which the encrinite preyed were
seized and hurried to the central mouth. The lower part of the cup, or
_pelvis_, as it is called, contained the stomach and other viscera, and
communicated with the most distant part of the body by the central
alimentary canal.
But while this continued the general type on which the encrinites
were constructed, it received many minor modifications. These were
effected chiefly on the form and arrangement of the cup-shaped body
and its appendages, and form now the basis of our classification
into genera and species. Thus, in the genus known as _Platycrinus_,
the lower part of the cup consists of two rows of large hexagonal or
polygonal plates fitting closely into each other, while the upper part
rises into a dome-like elevation formed of smaller polygonal plates,
which have often a mammillated exterior. The arms sprang from the
widest part of the body where the large pieces of the lower cup were
succeeded by the small pieces of the upper. In an Irish species (_P.
triacontadactylus_), the arms subdivided into thirty branches, each
fringed with minuter pinnules and folding round the central elevated
spire, as the petals of a crocus close round its central pistil. In
another encrinite (_Poteriocrinites conicus_), the cup was shaped like
an inverted cone, the point being affixed to the summit of the stalk,
and the broad part throwing out from its edges the lateral arms. The
_Woodocrinus macrodactylus_ had such gigantic arms as well-nigh to
conceal the position of the cup, which relatively was very small in
size. They sprang from near the base of the cup, five in number, but
soon subdivided each into two, the ten arms thus produced being closely
fringed with the usual jointed calcareous pinnules.
The size and arrangement of the joints of the stalk also differed in
different genera. The Woodocrinus and many others had them alternately
broad and narrow, like a string of buttons of unequal sizes; others had
all the joints of the same relative diameter (Fig. 19 _b_), so that the
stalk tapered by a uniform line from base to point. I may add, that
on some specimens of both these kinds of stems, we can notice small,
solitary _areolæ_, or scars, which may mark the points of attachment
of cirri, or little tentacles, like those on the stem of the existing
Pentacrinite. But though each of these varieties of stem is peculiar to
a certain number of genera, there is often so little distinction among
the detached fragments, that it becomes difficult, indeed impossible,
to assign each to its appropriate individual. We may say, that certain
encrinal stalks could not have belonged to a poteriocrinus, and others
could never have fitted on to the cup of an actinocrinus; but we cannot
often say positively to what species they actually would have fitted.
There can, however, be no doubt about their being encrinites, and so
we have in them a safe and evident test for the origin of the rock in
which their remains occur. But to this I shall afterwards revert.
In the meantime, I would have the reader to fix the stone-lily in
his memory as peculiarly and emphatically a marine animal, dwelling
probably in the deeper and stiller recesses of the ocean, like the
Pentacrinite of existing times. Let him try to remember it, not in the
broken and sorely mutilated state in which we find it among the blocks
of our lime-quarries, but as it must have lived at the bottom of the
carboniferous seas. The oozy floor of these old waters lay thickly
covered with many a graceful production of the deep, submarine gardens
of
"Violet, asphodel, ivy, and vine-leaves, roses and lilies,
Coral and sea-fan, and tangle, the blooms and the palms of the ocean."
Amid this rich assemblage of animated forms, the stone-lilies must have
occupied a conspicuous place. Grouped in thick-set though diminutive
forests, these little creatures raised their waving stems, and spread
out their tremulous arms, like beds of tulips swaying in the evening
air. Their flower like cups, so delicately fringed, must have presented
a scene of ceaseless activity as they opened and closed, coiling up
while the animal seized its prey, or on the approach of danger, and
relaxing again when the food had been secured, or when the symptoms
of a coming enemy had passed away. Only from this animated action
would one have been apt to conjecture these organisms to be other
than vegetable. They lived, too, not in detached patches, like the
tulip-beds of the florist, but, to judge from the abundance of their
remains, must have covered acre after acre, and square mile 'after
square mile, with a dense growth of living, quivering flowers. As one
individual died out, another took its place, the decaying steins and
flowers meanwhile falling to pieces among the limy sediment that lay
thickly athwart the sea-bottom, and contributing, by their decay and
entombment, to build up those enormous masses of rock, known as the
mountain-limestone, which stretch through Yorkshire and the central
counties into Wales.
In addition to the stone-lilies, the carboniferous rocks contain the
remains of several other kinds of _Echinodermata_. Some of them find
their nearest modern analogues among the sea-urchins so common on
our shores; but I pass on to notice another very interesting class
of fossils known by the name of _Crustacea_, and still abundantly
represented, the crab and lobster being familiar examples.
The Crustacea, so called from the hard crust or shell which envelops
them, form, with all their orders and genera, a very numerous family.
They are of interest to us as containing among their number some of
the oldest forms of life. Away down in the lower Silurian rocks, among
the most ancient fossiliferous strata, we find the crustacean with
its armour of plates and its prominent sessile eyes set round with
lenses, still visible on the stone. Thus, on the first page of the
stony records of our planet's history are these primeval organisms
engraved. In some localities, where oxide of iron is largely present,
they are coated with a bright yellow efflorescence, and stand out
from the dull grey stone like figures embossed in gold.[31] On all
the subsequent leaves of this ancient chronicle, we can detect the
remains of crustacean life, and many tribes still swarm in our seas
and lakes. It is interesting, however, as marking the onward progress
of creation, to notice that, though this great family has continued
to live during all the successive geological ages, its members have
ever been changing, the older types waning and dying out, while newer
genera rose to supply for a time their place, and then passed away
before the advance of other and yet later forms. The trilobites that
meet us on the very verge of creation, swarmed by millions in the seas
of the Silurian ages, diminished gradually during the era of the Old
Red Sandstone, and seem to have died out altogether in the times of
the Coal. In no ocean of the present day is a trace of any of their
many genera to be seen. The _decapods_, of which our common crab is a
typical form, began to be after the trilobites had died out. In all the
subsequent eras they gradually increased in numbers, and at the present
day they form the most abundant order of crustacean life. The history
of these two divisions, to adopt Agassiz's mode of representation, may
be illustrated by two long tapering bands like two attenuated pyramids.
The one has its broad base resting upon the existing now, and thinning
away into the past, till at last it comes to a point. At a little
interval the apex of the other begins, and gradually swells outward as
it recedes, till the wide base terminates at the first beginnings of
life.
[Footnote 31: Such is the aspect of the organisms in some of the
Silurian sandstones near Girvan. I have seen the same bright tint
on a set of fossils from the Llandeilo flags of Wales, and from the
slates of Desertcreat, Ireland, and have disinterred similarly gilded
shells from the vertical greywackè slates of the Pentland Hills and
Peeblesshire. Nothing can be more beautiful than the aspect of these
fossils when first laid open, but the bright gleam eventually passes
away on exposure.]
But there are also some orders that would be best illustrated by a
long line of nearly uniform breadth, extending from the first geologic
periods to the present day. In other words, they seem to have retained
during all time pretty much the same amount of development. I shall
confine my notice of the carboniferous Crustacea to the description of
a single genus belonging to a family that seems to have begun during
the period of the Lower Silurian, and still flourishes abundantly in
existing waters.
[Illustration: Fig. 20.
1. Carboniferous cypris, nat. size, and magnified.
2. Recent cypris, highly magnified.
3. Carboniferous king-crab (_Limulus trilobitoides_).
]
The genus to which I refer is a well-known fossil in some parts of
the Coal-measure series, and has been named _Cypris_. The shells of
_cyprides_ are very minute, considerably less than the heads of small
pins (Fig. 20-1). They can be seen quite well, however, without the
use of a magnifying power. In shape they resemble beans, and when seen
scattered over a slab of shale, look much liker seeds than the relics
of animal life. Yet, under this simple exterior, they concealed a
somewhat complex organization. The little bean-shaped shells, which
are all that now remains to us of their structure, formed the crust
or outer shell in which their viscera were contained, and answered to
the massive carapace and segments of the crab. They consisted of two
valve-like cases fitting to each other, so as to resemble the united
valves of a bivalve shell. From the upper end there were protruded
through the opening between the valves a pair of slim jointed antennæ,
each furnished at its point with a bundle of minute hair-like cilia
(Fig. 20-2). These, when set in rapid motion, served to impel the
creature through the water. The legs, four in number, were encrusted
with the same hard membrane, and had the same jointed structure as
those of our common shrimps and crabs. The foremost pair were pointed
like the antennæ with fine hairs, the incessant action of which
assisted the animal in swimming. Of the little, confluent, sessile
eyes, the delicate branchia or gills, and all the complex internal
structure of the nervous, circulating, and other systems, no trace
has survived on the stone; but enough of the general external form is
left to show us the true affinities of these organisms in the animated
world of the present time. By studying the forms and habits of the
cyprides that swarm in some of our ponds and marshes, a just conception
is obtained of the structure and habitat of the animals that once
occupied the minute bean-shaped shells, which lie by millions among the
shales of the Carboniferous system. From such a comparison we infer,
that just as the cyprides of to-day are fresh-water animals abounding
among the green slime of stagnant pools, so, in past ages, they must
have preserved with the same organization the same habits. And thus
we arrive at the important conclusion that the strata in which the
remains of cyprides abound must have been deposited in lakes or rivers.
This gives us a key by which to interpret some of the changes of a
geological system, and the ancient physical revolutions of large tracts
of country.
The shales of the coal-measures sometimes contain the cypris cases in
such abundance as to derive therefrom a sort of fissile structure.
It should be borne in mind, however, that each animal may during its
lifetime have possessed in succession several of these cases. Among the
shell-bearing molluscous animals, the little shell which contains the
creature in its youngest stages remains ever after as an integral part
of the outer calcareous case. As the inhabitant grows, it continues
to add band after band to the outer edge of the shell, each of which,
whilst preserving the general symmetry and proportions of the whole
structure, increases its dimensions in every way. Among the univalves,
such, for example, as the turritella, so common on our shores, the
layers of growth succeed each other like the steps of one of those
long spiral stairs that our feudal forefathers loved to build from
the court-yard to the watch-tower of their castles. Each new layer
exceeding in bulk its predecessors, adds a new step to the ascending
pile, and thus the ever-widening mouth winds spirally upwards around
the central pillar. The bivalves exemplify the same principle. The
successive additions are made in a crescent form to the outer edges,
and form those prominent concentric ridges so conspicuous on many of
our commoner shells, such, for instance, as some of those in the genera
_Astarte_ and _Venus_.
But the architecture of the Crustacea (and, of course, that of the
cyprides) is conducted on a very different principle. Their houses
admit of no additions or enlargements, and so, when the animals find
themselves getting somewhat straitened, they retire to a sheltered
spot, and there, separating the walls that hem them in, crawl out like
soft lumps of dough. The outer membrane of the moulted animal quickly
acquires strength and hardness, and in a day or two the renovated
creature is as healthy and vigorous as ever. In this process it is
not merely an external shell, like that of a mollusc, which is thrown
off, but a veritable skin, so that when the old shell is abandoned
it frequently could not be detected on a first glance to be empty,
the outer crust of every leg and joint, and sometimes even of thin
bristles, remaining just as in the living animal.
It is not unlikely that this process of moulting takes place annually
in most of the Crustacea, so that if we suppose a fossil member of the
group to have lived six years, it would have left six crusts to be
entombed in any deposits that might be forming at the time. Of course
there would be many chances against all the six being preserved, but
the possibility of at least several of them becoming fossilized should
be borne in mind when we speculate on the abundance of such organisms
in any geological formation.
I might refer to another very interesting group of crustacean animals
known as the _Limuli_, or king-crabs, of which there were at least
three representatives during the times of the English Carboniferous
system (Fig. 20-3). They are remarkable chiefly for their large
crescent-shaped shield, their long sword-like tail, and their double
pair of eyes, of which the outer ones are large, sessile, and compound,
like those of the trilobites, while the middle pair are small, simple,
and set close together on the forehead, like those of the single-eyed
Cyclops in the old mythology. Altogether, with their shields, swords,
watchful waking eyes, strong massive armour, and great size (for some
of them measure two feet in length), they form a most warlike genus.