The clay-beds, “which vary in thickness from a few inches to more
than ten feet, are penetrated in all directions by a confused and
tangled collection of the roots and leaves, as they may be, of the
_Stigmaria ficoides_, these being frequently traceable to the main
stem (_Sigillaria_), which varies in diameter from about two inches
to half a foot. The main stems are noticed as occurring nearer
the top than the bottom of the bed, as usually of considerable
length, the leaves or roots radiating from them in a tortuous
irregular course to considerable distances, and as so mingled with
the under-clay that it is not possible to cut out a cubic foot of it
which does not contain portions of the plant.”
It is a natural inference to suppose that the present indurated
under-clay is only another condition of that soft, silty soil, or
of that finely levigated muddy sediment--most likely of still and
shallow water--in which the vegetation grew, the remains of which
were afterward carbonized and converted into coal.
In order thoroughly to comprehend the phenomena of the transformation
into coal of the forests and of the herbaceous plants which
filled the marshes and swamps of the ancient world, there is
another consideration to be presented. During the coal-period, the
terrestrial crust was subjected to alternate movements of elevation
and depression of the internal liquid mass, under the impulse of the
solar and lunar attractions to which they would be subject, as our
seas are now, giving rise to a sort of subterranean tide, operating
at intervals, more or less widely apart, upon the weaker parts of
the crust, and producing considerable subsidences of the ground.
It might, perhaps, happen that, in consequence of a subsidence
produced in such a manner, the vegetation of the coal-period would
be submerged, and the shrubs and plants which covered the surface
of the earth would finally become buried under water. After this
submergence new forests sprung up in the same place. Owing to another
submergence, the second forests were depressed in their turn, and
again covered by water. It is probably by a series of repetitions
of this double phenomenon--this submergence of whole regions of
forest, and the development upon the same site of new growths of
vegetation--that the enormous accumulations of semi-decomposed
plants, which constitute the Coal-measures, have been formed in a
long series of ages.
But, has coal been produced from the larger plants only--for example,
from the great forest-trees of the period, such as the Lepidodendra,
Sigillariæ, Calamites, and Sphenophylla? That is scarcely probable,
for many coal-deposits contain no vestiges of the great trees of the
period, but only of Ferns and other herbaceous plants of small size.
It is, therefore, presumable that the larger vegetation has been
almost unconnected with the formation of coal, or, at least, that it
has played a minor part in its production. In all probability there
existed in the coal-period, as at the present time, two distinct
kinds of vegetation: one formed of lofty forest-trees, growing on the
higher grounds; the other, herbaceous and aquatic plants, growing on
marshy plains. It is the latter kind of vegetation, probably, which
has mostly furnished the material for the coal; in the same way
that marsh-plants have, during historic times and up to the present
day, supplied our existing peat, which may be regarded as a sort of
contemporaneous incipient coal.
To what modification has the vegetation of the ancient world been
subjected to attain that carbonized state which constitutes coal?
The submerged plants would, at first, be a light, spongy mass, in
all respects resembling the peat-moss of our moors and marshes.
While under water, and afterward, when covered with sediment,
these vegetable masses underwent a partial decomposition--a moist,
putrefactive fermentation, accompanied by the production of much
carbureted hydrogen and carbonic acid gas. In this way, the hydrogen
escaping in the form of carbureted hydrogen, and the oxygen in the
form of carbonic acid gas, the carbon became more concentrated, and
coal was ultimately formed. This emission of carbureted hydrogen gas
would, probably, continue after the peat-beds were buried beneath
the strata which were deposited and accumulated upon them. The mere
weight and pressure of the superincumbent mass, continued at an
increasing ratio during a long series of ages, have given to the coal
its density and compact state.
The heat emanating from the interior of the globe would also
exercise a great influence upon the final result. It is to these two
causes--that is to say, to pressure and to the central heat--that we
may attribute the differences which exist in the mineral characters
of various kinds of coal. The inferior beds are _drier_ and more
compact than the upper ones; or less bituminous, because their
mineralization has been completed under the influence of a higher
temperature, and at the same time under a greater pressure.
THE PALÆONTOLOGICAL HISTORY OF ANIMALS
--HUGH MILLER
However much the faunas of the various geologic periods may have
differed from each other, or from the fauna which now exists, in
their general aspect and character, they were all, if I may so speak,
equally underlaid by the great leading ideas which still constitute
the master types of animal life. And these leading ideas are four in
number. _First_, there is the _star-like_ type of life--life embodied
in a form that, as in the corals, the sea-anemones, the sea-urchins,
and the star-fishes, radiates outward from a centre; _second_,
there is the _articulated_ type of life--life embodied in a form
composed, as in the worms, crustaceans, and insects, of a series of
rings united by their edges, but more or less movable on each other;
_third_, there is the bilateral or _molluscan_ type of life--life
embodied in a form in which there is a duality of corresponding
parts, ranged, as in the cuttle-fishes, the clams, and the snails,
on the sides of a central axis or plane; and _fourth_, there is
the _vertebrate_ type of life--life embodied in a form in which
an internal skeleton is built up into two cavities placed the one
over the other; the upper for the reception of the nervous centres,
cerebral and spinal--the lower for the lodgment of the respiratory,
circulatory, and digestive organs. Such have been the four central
ideas of the faunas of every succeeding creation, except, perhaps,
the earliest of all, that of the Lower Silurian System, in which, so
far as is yet known, only three of the number existed--the radiated,
articulated, and molluscan ideas or types.
The fauna of the Silurian System bears in all its three great types
the stamp of a fashion peculiarly antique, and which, save in a few
of the mollusca, has long since become obsolete. Its radiate animals
are chiefly corals, simple or compound, whose inhabitants may have
somewhat resembled the sea-anemones; with zoophytes, akin mayhap to
the sea-pens, though the relationship must have been a remote one;
and numerous crinoids, or stone lilies, some of which consisted of
but a sculptured calyx without petals, while others threw off a
series of long flexible arms, that divided and subdivided like the
branches of a tree, and were thickly fringed by hair-like fibres.
The articulata of the Silurian period bore a still more peculiar
character. They consisted mainly of the Trilobites--a family in
whose nicely jointed shells the armorer of the Middle Ages might
have found almost all the contrivances of his craft anticipated,
with not a few besides which he had failed to discover; and which,
after receiving so immense a development during the middle and later
times of the Silurian period that whole rocks were formed almost
exclusively of their remains, gradually died out in the times of
the Old Red Sandstone, and disappeared forever from creation after
the Carboniferous Limestone had been deposited. The mollusca of
the Silurians ranged from the high cephalopoda, represented in our
existing seas by the nautili and the cuttle-fishes, to the low
brachiopods, some of whose cogeners may still be detected in the
terebratulæ of the Highland lochs and bays, and some in the lingulæ
of the Southern Hemisphere. The cephalopods of the system are all of
an obsolete type, that disappeared myriads of ages ago. At length, in
an upper bed of the system, immediately under the base of the Old Red
Sandstone, the remains of the earliest known fishes appear, blended
with what also appears for the first time--the fragmentary remains
of a terrestrial vegetation. The rocks beneath this ancient bone-bed
have yielded no trace of any plant higher than the Thallogens,
or at least not higher than the Zosteraceæ--plants whose proper
habitat is the sea; but, through an apparently simultaneous advance
of the two kingdoms, animal and vegetable--though, of course, the
simultaneousness may be but merely apparent--the first land-plants
and the first vertebrates appear together in the same deposit. The
earliest fishes--first-born of their family--seem to have been all
placoids. The Silurian System has not yet afforded trace of any other
vertebral animal. With the Old Red Sandstone the ganoids were ushered
upon the scene in amazing abundance; and for untold ages, comprising
mayhap millions of years, the entire ichthyic class consisted, so far
as is yet known, of but these two orders. During the times of the Old
Red Sandstone, of the Carboniferous, of the Permian, of the Triassic,
and of the Oolitic Systems, all fishes, though apparently as numerous
individually as they are now, were comprised in the ganoidal and
placoidal orders. The period of these orders seems to have been
nearly correspondent with the reign, in the vegetable kingdom, of the
Acrogens and Gymnogens, with the intermediate classes, their allies.
At length, during the ages of the Chalk, the Cycloids and Ctenoids
were ushered in, and were gradually developed in creation until the
human period, in which they seem to have reached their culminating
point, and now many times exceed in number and importance all other
fishes. The delicate Salmonidæ and the Pleuronectidæ--families to
which the salmon and turbot belong--were ushered into being as early
as the times of the Chalk; but the Gadidæ or cod family--that family
to which the cod proper, the haddock, the dorse, the whiting, the
coal-fish, the pollock, the hake, the torsk, and the ling belong,
with many other useful and wholesome species--did not precede man by
at least any period of time appreciable to the geologist. No trace of
the family has yet been detected in even the Tertiary rocks.
Of the ganoids of the second age of vertebrate existence--that of
the Old Red Sandstone--some were remarkable for the strangeness
of their forms, and some for constituting links of connection,
which no longer exist in nature, between the ganoid and placoid
orders. The Acanth family, which ceased with the Coal-measures, was
characterized, especially in its Old Red species, by a combination
of traits common to both orders; and among the extremer forms, in
which palæontologists for a time failed to detect that of the fish
at all, we reckon those of the genera Coccosteus, Pterichthys, and
Cephalaspis. The more aberrant genera, however, even while they
consisted each of several species, were comparatively short-lived.
The Coccosteus and Cephalaspis were restricted to but one formation
apiece; while the Pterichthys, which appears for the first time in
the lower deposits of the Old Red Sandstone, becomes extinct at its
close. On the other hand, some of the genera that exemplified the
general type of their class were extremely long-lived. The Celacanths
were reproduced in many various species, from the times of the Lower
Old Red Sandstone to those of the Chalk; and the Cestracions, which
appear in the Upper Ludlow Rocks as the oldest of fishes, continue in
at least one species to exist still.
The ancient fishes seem to have received their fullest development
during the Carboniferous period. Their number was very great: some
of them attained to an enormous size, and, though the true reptile
had already appeared, they continued to retain till the close of
the System the high reptilian character and organization. Nothing,
however, so impresses the observer as the formidable character of the
offensive weapons with which they were furnished, and the amazing
strength of their defensive armature. I need scarce say that the
palæontologist finds no trace in nature of that golden age of the
world, of which the poets delighted to sing, when all creatures lived
together in unbroken peace, and war and bloodshed were unknown. Ever
since animal life began upon our planet there existed, in all the
departments of being, carnivorous classes, who could not live but by
the death of their neighbors, and who were armed, in consequence,
for their destruction, like the butcher with his axe and knife, and
the angler with his hook and spear. But there were certain periods
in the history of the past during which these weapons assumed a more
formidable aspect than at others; and never were they more formidable
than in the times of the Coal-measures. The teeth of the Rhizodus--a
ganoidal fish of our coal-fields--were more sharp and trenchant than
those of the crocodile of the Nile, and in the larger specimens fully
four times the bulk and size of the teeth of the hugest reptile of
this species that now lives. The dorsal spine of its contemporary,
the Gyracanthus, a great placoid, much exceeded in size that of any
existing fish; it was a mighty spearhead, ornately carved like that
of a New Zealand chief, but in a style that, when he first saw a
specimen in my collection, greatly excited the admiration of Mr.
Ruskin. But one of the most remarkable weapons of the period was
the sting of the Pleuracanthus, another great placoid of the age of
gigantic fishes. It was sharp and polished as a stiletto, but, from
its rounded form and dense structure, of great strength; and along
two of its sides, from the taper point to within a few inches of the
base, there ran a thickly set row of barbs, hooked downward, like
the thorns that bristle on the young shoots of the wild rose, and
which must have rendered it a weapon not merely of destruction, but
also of torture. The defensive armor of the period, especially that
of its ganoids, seems to have been as remarkable for its powers of
resistance as the offensive must have been for their potency in the
assault; and it seems probable that in the great strength of the bony
and enameled armature of this order of fishes we have the secret of
the extremely formidable character of the teeth, spines, and stings
that coexisted along with it.
The oldest known reptiles appear just a little before the close of
the Old Red Sandstone, just as the oldest known fishes appeared
just a little before the close of the Silurian System. What seems
to be the Upper Old Red of Great Britain, though there still hangs
a shade of doubt on the subject, has furnished the remains of a
small reptile, equally akin, it would appear, to the lizards and the
batrachians; and what seems to be the Upper Old Red of the United
States has exhibited the foot-tracks of a larger animal of the same
class, which not a little resemble those which would be impressed on
recent sand or clay by the alligator of the Mississippi, did not the
alligator of the Mississippi efface its own footprints (a consequence
of the shortness of its legs) by the trail of its abdomen. In the
Coal-measures the reptiles hitherto found are all allied, though
not without a cross of the higher crocodilian or lacertian nature,
to the batrachian order--that lowest order of the reptiles to which
the frogs, newts, and salamanders belong. It was not, however, until
the Permian and Triassic Systems had come to a close, and even the
earlier ages of the Oolitic System had passed away, that the class
received its fullest development in creation. And certainly very
wonderful was the development which it then did receive. Reptiles
became everywhere the lords and masters of this lower world. When
any class of the air-breathing vertebrates is very largely developed,
we find it taking possession of all the three old terrestrial
elements--earth, air, and water. The human period, for instance,
like that which immediately preceded it, is peculiarly a period of
mammals; and we find the class _free_, if I may so express myself, of
the three elements, disputing possession of the sea with the fishes,
in its Cetaceans, its seals and its sea-lions, and of the air with
the birds, in its numerous genera of the bat family. Further, not
until the great mammaliferous period is fairly ushered in do either
the bats or the whales make their appearance in creation. Remains of
Oolitic reptiles have been mistaken in more than one instance for
those of Cetacea; but it is now generally held that the earliest
known specimens of the family belong to the Tertiary ages, while
those of the oldest bats occur in the Eocene of the Paris basin,
associated with the bones of dolphins, lamantines, and morses. Now,
in the times of the Oolite it was the reptilian class that possessed
itself of all the elements. Its gigantic enaliosaurs, huge reptilian
whales mounted on paddles, were the tyrants of the ocean, and must
have reigned supreme over the already reduced class of fishes; its
pterodactyles--dragons as strange as were ever feigned by romancer
of the Middle Ages, and that to the jaws and teeth of the crocodile
added the wings of a bat and the body and tail of an ordinary
mammal--had the “power of the air,” and, pursuing the fleetest
insects in their flight, captured and bore them down; its lakes and
rivers abounded in crocodiles and fresh-water tortoises of ancient
type and fashion; and its woods and plains were the haunts of a
strange reptilian fauna of what has been well termed “fearfully great
lizards”--some of which, such as the iguanodon, rivaled the largest
elephant in height, and greatly more than rivaled him in length and
bulk. Judging from what remains, it seems not improbable that the
reptiles of this Oolitic period were quite as numerous individually,
and consisted of wellnigh as many genera and species as all the
mammals of the present time. In the cretaceous ages, the class,
though still the dominant one, is visibly reduced in its standing:
it had reached its culminating point in the Oolite and then began to
decline; and with the first dawn of the Tertiary division we find it
occupying, as now, a very subordinate place in creation. Curiously
enough, it is not until its times of humiliation and decay that
one of the most remarkable of its orders appears--an order itself
illustrative of extreme degradation, and which figures largely in
every scheme of mythology that borrowed through traditional channels
from Divine revelation, as a meet representative of man’s great
enemy, the Evil One. I, of course, refer to the ophidian or serpent
family. The earliest ophidian remains known to the palæontologist
occur in that ancient deposit of the Tertiary division known as the
London Clay, and must have belonged to serpents, some of them allied
to the Pythons, some to the sea-snakes, which, judging from the
corresponding parts of recent species, must have been from fourteen
to twenty feet in length.
Birds make their first appearance in a Red Sandstone deposit of the
United States in the valley of the Connecticut, which was at one time
supposed to belong to the Triassic System, but which is now held to
be at least not older than the times of the Lias. No fragments of
the skeletons of birds have yet been discovered in formations older
than the Chalk; the Connecticut remains are those of footprints
exclusively; and yet they tell their extraordinary story, so far as
it extends, with remarkable precision and distinctness. They were
apparently all of the Grallæ or stilt order of birds--an order to
which the cranes, herons, and bustards belong, with the ostriches and
cassowaries, and which is characterized by possessing but three toes
on each foot (one species of ostrich has but two), or, if a fourth
toe be present, so imperfectly is it developed in most of the cases
that it fails to reach the ground. And in almost all the footprints
of the primeval birds of the Connecticut there are only three toes
exhibited. The immense size of some of these footprints served to
militate for a time against belief in their ornithic origin. The
impressions that are but secondary in point of size greatly exceed
those of the hugest birds which now exist; while those of the
largest class equal the prints of the bulkier quadrupeds. There are
tridactyle footprints in the Red Sandstones of Connecticut that
measure eighteen inches in length from the heel to the middle claw,
nearly thirteen inches in breadth from the outer to the inner toe,
and which indicate, from their distance apart in the straight line,
a stride of about six feet in the creature that impressed them in
these ancient sands--measurements that might well startle zoologists
who had derived their experience of the ornithic class from existing
birds exclusively. In a deposit of New Zealand that dates little
if at all in advance of the human period, there have been detected
the remains of birds scarce inferior in size to those of America in
the Liassic ages. The bones of the _Dinornus giganteus_, exhibited
by Dr. Mantell in Edinburgh in 1850, greatly exceeded in bulk those
of the largest horse. The larger thigh-bone referred to must have
belonged, it was held, to a bird that stood from eleven to twelve
feet high--the extreme height of the great African elephant. Such
were the monster birds of a comparatively recent period; and their
remains serve to render credible the evidence furnished by the great
footprints of their remote predecessors of the Lias. The huge feet of
the greatest Dinornus would have left impressions scarcely an inch
shorter than those of the still huger birds of the Connecticut.
With the Stonesfield slates--a deposit which lies above what is known
as the Inferior Oolite--the remains of mammaliferous animals first
appear.
The Eocene ages were peculiarly the ages of the Palæotheres--strange
animals of, that pachydermatous or thick-skinned order to which the
elephants, the tapirs, the hogs, and the horses belong. It had been
remarked by naturalists that there are fewer families of this order
in living nature than of almost any other, and that of the existing
genera not a few are widely separated in their analogies from the
others. But in the Palæotheres of the Eocene, which ranged in size
from a large horse to a hare, not a few of the missing links have
been found--links connecting the tapirs to the hogs, and the hogs to
the Palæotheres proper; and there is at least one species suggestive
of a union of some of the more peculiar traits of the tapirs and the
horses. It was among these extinct Pachydermata of the Paris basin
that Cuvier effected his wonderful restorations, and produced those
figures in outline which are now as familiar to the geologist as
any of the forms of the existing animals. The London Clay and the
Eocene of the Isle of Wight have also yielded numerous specimens of
these pachyderms, whose identity with the Continental ones has been
established by Owen; but they are more fragmentary, and their state
of keeping less perfect than those furnished by the gypsum quarries
of Velay and Montmartre.