we ascend in the series, we find more and more of these identical with
species still existing upon earth, as if we had now reached the dawn of
the present state of the zoology of our planet. By the study of the
shells alone, Mr. Lyell has been enabled to divide the whole term into
four sub-periods, to which he has given names with reference to the
proportions which they respectively present of surviving species—first,
the eocene, (from ’ηως, the dawn; χαινος, recent;) second, the miocene,
(μειων, less;) third, older pliocene, (πλειων, more;) fourth, newer
pliocene.
EOCENE SUB-PERIOD.
The eocene period presents, in three continental groups, 1238 species of
shells, of which forty-two, or 3.5 per cent, yet flourish. Some of these
are remarkable enough; but they all sink into insignificance beside the
mammalian remains which the lower eocene deposits of the Paris basin
present to us, shewing that the land had now become the theatre of an
extensive creation of the highest class of animals. Cuvier ascertained
about fifty species of these, all of them long since extinct. A
considerable number are _pachydermata_, {127} of a character
approximating to the South American tapir: the names, palæotherium,
anthracotherium, anoplotherium, lophiodon, &c., have been applied to them
with a consideration of more or less conspicuous peculiarities; but a
description of the first may give some general idea of the whole. It was
about the size of a horse, but more squat and clumsy, and with a heavier
head, and a lower jaw shorter than the upper; the feet, also, instead of
hooves, presented three large toes, rounded, and unprovided with claws.
These animals were all herbivorous. Amongst an immense number of others
are found many new reptiles, some of them adapted for fresh water;
species of birds allied to the sea-lark, curlew, quail, buzzard, owl, and
pelican; species allied to the dormouse and squirrel; also the opossum
and racoon; and species allied to the genette, fox, and wolf.
MIOCENE SUB-PERIOD.
In the miocene sub-period, the shells give eighteen per cent. of existing
species, shewing a considerable advance from the preceding era, with
respect to the inhabitants of the sea. The advance in the land animals
is less marked, but yet considerable. The predominating forms are still
pachydermatous, and the tapir type continues to be conspicuous. One
animal of this kind, called the _dinotherium_, is supposed to have been
not less than eighteen feet long; it had a mole-like form of the
shoulder-blade, conferring the power of digging for food, and a couple of
tusks turning down from the lower jaw, by which it could have attached
itself, like the walrus, to a shore or bank, while its body floated in
the water. Dr. Buckland considers this and some similar miocene animals,
as adapted for a semi-aquatic life, in a region where lakes abounded.
Besides the tapirs, we have in this era animals allied to the glutton,
the bear, the dog, the horse, the hog, and lastly, several felinæ,
(creatures of which the lion is the type;) all of which are new forms, as
far as we know. There was also an abundance of marine mammalia, seals,
dolphins, lamantins, walruses, and whales, none of which had previously
appeared.
PLIOCENE SUB-PERIOD.
The shells of the older pliocene give from thirty-five to fifty; those of
the newer, from ninety to ninety-five per cent. of existing species. The
pachydermata of the preceding era now disappear, and are replaced by
others belonging to still existing families—elephant, hippopotamus,
rhinoceros—though now extinct as species. Some of these are startling,
from their enormous magnitude. The great mastodon, whose remains are
found in abundance in America, was a species of elephant, judged, from
peculiarities of its teeth, to have lived on aquatic plants, and reaching
the height of twelve feet. The mammoth was another elephant, but
supposed to have survived till comparatively recent times, as a specimen,
in all respects entire, was found in 1801, preserved in ice, in Siberia.
We are more surprised by finding such gigantic proportions in an animal
called the megatherium, which ranks in an order now assuming much humbler
forms—the edentata—to which the sloth, ant-eater, and armadillo belong.
The megatherium had a skeleton of enormous solidity, with an armour-clad
body, and five toes, terminating in huge claws, wherewith to grasp the
branches, from which, like its existing congener, the sloth, it derived
its food. The megalonyx was a similar animal, only somewhat less than
the preceding. Finally, the pliocene gives us for the first time, oxen,
deer, camels, and other specimens of the _ruminantia_.
Such is an outline of the fauna of the tertiary era, as ascertained by
the illustrious naturalists who first devoted their attention to it. It
will be observed that it brings us up to the felinæ, or carnivora, a
considerably elevated point in the animal scale, but still leaving a
blank for the quadrumana (monkeys) and for man, who collectively form, as
will be afterwards seen, the first group in that scale. It sometimes
happens, however, as we have seen, that a few rare traces of a particular
class of animals are in time found in formations originally thought to be
destitute of them, displaying as it were a dawn of that department of
creation. Such seems to be the case with at least the quadrumana. A
jaw-bone and tooth of an animal of this order, and belonging to the genus
macacus, were found in the London clay, (eocene,) at Kyson, near
Woodbridge, in 1839. Another jaw-bone, containing several teeth,
supposed to have belonged to a species of monkey about three feet high,
was discovered about the same time in a stratum of marl surmounted by
compact limestone, in the department of Gers, at the foot of the
Pyrenees. Associated with this last were remains of not less than thirty
mammiferous quadrupeds, including three species of rhinoceros, a large
anoplotherium, three species of deer, two antelopes, a true dog, a large
cat, an animal like a weasel, a small hare, and a huge species of the
edentata. Both of these places are considerably to the north of any
region now inhabited by the monkey tribes. Fossil remains of quadrumana
have been found in at least two other parts of the earth,—namely, the
sub-Himalayan hills, near the Sutlej, and in Brazil, (both in the
tertiary strata;) the first being a large species of semnopithecus, and
the second, a still larger animal belonging to the American group of
monkeys, but a new genus, and denominated by its discoverer, Dr. Lund,
protopithecus. The latter would be four feet in height.
One remarkable circumstance connected with the tertiary formation remains
to be noticed,—namely, the prevalence of volcanic action at that era. In
Auvergne, in Catalonia, near Venice, and in the vicinity of Rome and
Naples, lavas exactly resembling the produce of existing volcanoes, are
associated and intermixed with the lacustrine as well as marine
tertiaries. The superficies of tertiaries in England is disturbed by two
great swells, forming what are called anticlinal axes, one of which
divides the London from the Hampshire basin, while the other passes
through the Isle of Wight, both throwing the strata down at violent
inclination towards the north, as if the subterranean disturbing force
had _waved_ forward in that direction. The Pyrenees, too, and Alps, have
both undergone elevation since the deposition of the tertiaries; and in
Sicily there are mountains which have risen three thousand feet since the
deposition of some of the most recent of these rocks. The general effect
of these operations was of course to extend the land surface, and to
increase the variety of its features, thus improving the natural
drainage, and generally adapting the earth for the reception of higher
classes of animals.
ERA OF THE SUPERFICIAL FORMATIONS.
COMMENCEMENT OF PRESENT SPECIES.
WE have now completed our survey of the series of stratified rocks, and
traced in their fossils the progress of organic creation down to a time
which seems not long antecedent to the appearance of man. There are,
nevertheless, monuments of still another era or space of time which it is
all but certain did also precede that event.
Over the rock formations of all eras, in various parts of the globe, but
confined in general to situations not very elevated, there is a layer of
stiff clay, mostly of a blue colour, mingled with fragments of rock of
all sizes, travel-worn, and otherwise, and to which geologists give the
name of diluvium, as being apparently the produce of some vast flood, or
of the sea thrown into an unusual agitation. It seems to indicate that,
at the time when it was laid down, much of the present dry land was under
the ocean, a supposition which we shall see supported by other evidence.
The included masses of rock have been carefully inspected in many places,
and traced to particular parent beds at considerable distances.
Connected with these phenomena are certain rock surfaces on the slopes of
hills and elsewhere, which exhibit groovings and scratchings, such as we
might suppose would be produced by a quantity of loose blocks hurried
along over them by a flood. Another associated phenomenon is that called
_crag and tail_, which exists in many places,—namely, a rocky mountain,
or lesser elevation, presenting on one side the naked rock in a more or
less abrupt form, and on the other a gentle slope; the sites of Windsor,
Edinburgh, and Stirling, with their respective castles, are specimens of
crag and tail. Finally, we may advert to certain long ridges of clay and
gravel which arrest the attention of travellers on the surface of Sweden
and Finland, and which are also found in the United States, where,
indeed, the whole of these phenomena have been observed over a large
surface, as well as in Europe. It is very remarkable that the direction
from which the diluvial blocks have generally come, the lines of the
grooved rock surfaces, the direction of the crag and tail eminences, and
that of the clay and gravel ridges—phenomena, be it observed, extending
over the northern parts of both Europe and America—are _all from the
north and north-west towards the south-east_. We thus acquire the idea
of a powerful current moving in a direction from north-west to
south-east, carrying, besides mud, masses of rock which furrowed the
solid surfaces as they passed along, abrading the north-west faces of
many hills, but leaving the slopes in the opposite direction uninjured,
and in some instances forming long ridges of detritus along the surface.
These are curious considerations, and it has become a question of much
interest, by what means, and under what circumstances, was such a current
produced. One hypothetical answer has some plausibility about it. From
an investigation of the nature of glaciers, and some observations which
seem to indicate that these have at one time extended to lower levels,
and existed in regions (the Scottish Highlands an example) where there is
now no perennial snow, it has been surmised that there was a time,
subsequent to the tertiary era, when the circumpolar ice extended far
into the temperate zone, and formed a lofty, as well as extensive
accumulation. A change to a higher temperature, producing a sudden thaw
of this mass, might set free such a quantity of water as would form a
large flood, and the southward flow of this deluge, joined to the
direction which it would obtain from the rotatory motion of the globe,
would of course produce that compound or south-easterly direction which
the phenomena require. All of these speculations are as yet far too
deficient in facts to be of much value; and I must freely own that, for
one, I attach little importance to them. All that we can legitimately
infer from the diluvium is, that the northern parts of Europe and America
were then under the sea, and that a strong current set over them.
Connected with the diluvium is the history of _ossiferous caverns_, of
which specimens singly exist at Kirkdale in Yorkshire, Gailenreuth in
Franconia, and other places. They occur in the calcareous strata, as the
great caverns generally do, but have in all instances been naturally
closed up till the recent period of their discovery. The floors are
covered with what appears to be a bed of the diluvial clay, over which
rests a crust of stalagmite, the result of the droppings from the roof
since the time when the clay-bed was laid down. In the instances above
specified, and several others, there have been found, under the clay bed,
assemblages of the bones of animals, of many various kinds. At Kirkdale,
for example, the remains of twenty-four species were ascertained—namely,
pigeon, lark, raven, duck, and partridge; mouse, water-rat, rabbit, hare,
deer, (three species,) ox, horse, hippopotamus, rhinoceros, elephant,
weazel, fox, wolf, bear, tiger, hyena. From many of the bones of the
gentler of these animals being found in a broken state, it is supposed
that the cave was a haunt of hyenas and other predaceous animals, by
which the smaller ones were here consumed. This must have been at a time
antecedent to the submersion which produced the diluvium, since the bones
are covered by a bed of that formation. It is impossible not to see here
a very natural series of incidents. First, the cave is frequented by
wild beasts, who make it a kind of charnel-house. Then, submerged in the
current which has been spoken of, it receives a clay flooring from the
waters containing that matter in suspension. Finally, raised from the
water, but with no mouth to the open air, it remains unintruded on for a
long series of ages, during which the clay flooring receives a new
calcareous covering, from the droppings of the roof. Dr. Buckland, who
examined and described the Kirkdale cave, was at first of opinion that it
presented a physical evidence of the Noachian deluge; but he afterwards
saw reason to consider its phenomena as of a time far apart from that
event, which rests on evidence of an entirely different kind.
Our attention is next drawn to the erratic blocks or boulders, which in
many parts of the earth are thickly strewn over the surface, particularly
in the north of Europe. Some of these blocks are many tons in weight,
yet are clearly ascertained to have belonged originally to situations at
a great distance. Fragments, for example, of the granite of Shap Fell
are found in every direction around to the distance of fifty miles, one
piece being placed high upon Criffel Mountain, on the opposite side of
the Solway estuary; so also are fragments of the Alps found far up the
slopes of the Jura. There are even blocks on the east coast of England,
supposed to have travelled from Norway. The only rational conjecture
which can be formed as to the transport of such masses from so great a
distance, is one which presumes them to have been carried and dropped by
icebergs, while the space between their original and final sites was
under ocean. Icebergs do even now carry off such masses from the polar
coasts, which, falling when the retaining ice melts, must take up
situations at the bottom of the sea analogous to those in which we find
the erratic blocks of the present day.
As the diluvium and erratic blocks clearly suppose one last long
submersion of the surface, (_last_, geologically speaking,) there is
another set of appearances which as manifestly shew the steps by which
the land was made afterwards to reappear. These consist of _terraces_,
which have been detected near, and at some distance inland from, the
coast lines of Scandinavia, Britain, America, and other regions; being
evidently ancient beaches, or platforms, on which the margin of the sea
at one time rested. They have been observed at different heights above
the present sea-level, from twenty to above twelve hundred feet; and in
many places they are seen rising above each other in succession, to the
number of three, four, and even more. The smooth flatness of these
terraces, with generally a slight inclination towards the sea, the sandy
composition of many of them, and, in some instances, the preservation of
marine shells in the ground, identify them perfectly with existing
sea-beaches, notwithstanding the cuts and scoopings which have every here
and there been effected in them by water-courses. The irresistible
inference from the phenomena is, that the highest was first the coast
line; then an elevation took place, and the second highest became so, the
first being now raised into the air and thrown inland. Then, upon
another elevation, the sea began to form, at its new point of contact
with the land, the third highest beach, and so on down to the platform
nearest to the present sea-beach. Phenomena of this kind become
comparatively familiar to us, when we hear of evidence that the last
sixty feet of the elevation of Sweden, and the last eighty-five of that
of Chili, have taken place since man first dwelt in those countries; nay,
that the elevation of the former country goes on at this time at the rate
of about forty-five inches in a century, and that a thousand miles of the
Chilian coast rose four feet in one night, under the influence of a
powerful earthquake, so lately as 1822. Subterranean forces, of the kind
then exemplified in Chili, supply a ready explanation of the whole
phenomena, though some other operating causes have been suggested. In an
inquiry on this point, it becomes of consequence to learn some
particulars respecting the levels. Taking a particular beach, it is
generally observed that the level continues the same along a considerable
number of miles, and nothing like breaks or hitches has as yet been
detected in any case. A second and a third beach are also observed to be
exactly parallel to the first. These facts would seem to indicate quiet
elevating movements, uniform over a large tract. It must, however, be
remarked that the raised beaches at one part of a coast rarely coincide
with those at another part forty or fifty miles off. We might suppose
this to indicate a limit in that extent of the uniformity of the
elevating cause, but it would be rash to conclude positively that such is
the case. In the present sea, as is well known, there are different
levels at different places, owing to the operation of peculiar local
causes, as currents, evaporation, and the influx of large rivers into
narrow-mouthed estuaries. The differences of level in the ancient
beaches might be occasioned by some such causes. But, whatever doubt may
rest on this minor point, enough has been ascertained to settle the main
one, that we have in these platforms indubitable monuments of the last
rise of the land from the sea, and the concluding great event of the
geological history.
The idea of such a wide-spread and possibly universal submersion
unavoidably suggests some considerations as to the effect which it might
have upon terrestrial animal life. It seems likely that this would be,
on such an occasion, extensively, if not universally destroyed. Nor does
the idea of its universal destruction seem the less plausible, when we
remark, that none of the species of land animals heretofore discovered
can be detected at a subsequent period. The whole seem to have been now
changed. Some geologists appear much inclined to think that there was at
this time a new development of terrestrial animal life upon the globe,
and M. Agassiz, whose opinion on such a subject must always be worthy of
attention, speaks all but decidedly for such a conclusion. It must,
however, be owned, that proofs for it are still scanty, beyond the bare
fact of a submersion which appears to have had a very wide range. I must
therefore be content to leave this point, as far as geological evidence
is concerned, for future affirmation.
There are some other superficial deposits, of less consequence on the
present occasion than the diluvium—namely, lacustrine deposits, or
filled-up lakes; alluvium, or the deposits of rivers beside their
margins; deltas, the deposits made by great ones at their efflux into the
sea; peat mosses; and the vegetable soil. The animal remains found in
these generally testify to a zoology on the verge of that which still
exists, or melting into it, there being included many species which still
exist. In a lacustrine deposit at Market-Weighton, in the Vale of York,
there have been found bones of the elephant, rhinoceros, bison, wolf,
horse, felis, deer, birds, all or nearly all extinct species; associated
with thirteen species of land and fresh water shells, “exactly identical
with types now living in the vicinity.” In similar deposits in North
America, are remains of the mammoth, mastodon, buffalo, and other animals
of extinct and living types. In short, these superficial deposits shew
precisely such remains as might be expected from a time at which the
present system of things (to use a vague but not unexpressive phrase)
obtained, but yet so far remote in chronology as to allow of the dropping
of many species, through familiar causes, in the interval. Still,
however, there is no authentic or satisfactory instance of human remains
being found, except in deposits obviously of very modern date; a
tolerably strong proof that the creation of our own species is a
comparatively recent event, and one posterior (generally speaking) to all
the great natural transactions chronicled by geology.
GENERAL CONSIDERATIONS
RESPECTING
THE ORIGIN OF THE ANIMATED TRIBES.
THUS concludes the wondrous chapter of the earth’s history which is told
by geology. It takes up our globe at the period when its original
incandescent state had nearly ceased; conducts it through what we have
every reason to believe were vast, or at least very considerable, spaces
of time, in the course of which many superficial changes took place, and
vegetable and animal life was gradually developed; and drops it just at
the point when man was apparently about to enter on the scene. The
compilation of such a history, from materials of so extraordinary a
character, and the powerful nature of the evidence which these materials
afford, are calculated to excite our admiration, and the result must be
allowed to exalt the dignity of science, as a product of man’s industry
and his reason.
If there is any thing more than another impressed on our minds by the
course of the geological history, it is, that the same laws and
conditions of nature now apparent to us have existed throughout the whole
time, though the operation of some of these laws may now be less
conspicuous than in the early ages, from some of the conditions having
come to a settlement and a close. That seas have flowed and ebbed, and
winds disturbed their surfaces, in the time of the secondary rocks, we
have proof on the yet preserved surfaces of the sands which constituted
margins of the seas in those days. Even the fall of wind-slanted rain is
evidenced on the same tablets. The washing down of detached matter from
elevated grounds, which we see rivers constantly engaged in at the
present time, and which is daily shallowing the seas adjacent to their
mouths, only appears to have proceeded on a greater scale in earlier
epochs. The volcanic subterranean force, which we see belching forth
lavas on the sides of mountains, and throwing up new elevations by land
and sea, was only more powerfully operative in distant ages. To turn to
organic nature, vegetation seems to have proceeded then exactly as now.
The very alternations of the seasons has been read in unmistakable
characters in sections of the trees of those days, precisely as it might
be read in a section of a tree cut down yesterday. The system of prey
amongst animals flourished throughout the whole of the pre-human period;
and the adaptation of all plants and animals to their respective spheres
of existence was as perfect in those early ages as it is still.