permanent when once deposited, subject to no change, save the successive
superposition of other strata upon them. But this is very far from being
true. Enormous displacements, upheavings, contortions, and fractures,
are observed in the strata, which tell of mighty forces having been at
work upon them after their formation. The explanation of these phenomena
is due to the internal heat, which ever and anon seems to concentrate
its action on some special point, seeking and finding vent for itself by
some alteration in the already consolidated crust.
Sometimes, the mode of action has been the transmission of undulations
through the crust, producing earthquakes, cracking and forcing apart
strata already petrified, and bending and variously contorting those
that have but partially become solid. Sometimes, the fiery impulse is
sufficiently concentrated to break through the superincumbent materials,
forcing a passage for the molten and incandescent rock, which then flows
forth from the surface, penetrates into the cracks and fissures of the
fractured strata, and frequently spreads into the hollows and over the
summits of the latest formations.
It is owing to such causes as these, that we find the rocky layers so
often inclined at various angles to the horizon, instead of being
parallel to it, as they would be of course deposited; occasionally
standing quite perpendicularly, and even to a small extent reversed. The
outcropping of formations, the long lines of cliff running across a
country in parallel series, ("crag and tail,") the dipping of strata
from some central point or ridge, and the non-correspondence between the
bottom of one stratum and the top of the underlying one,--are all
phenomena of this sort of powerful action, which has been more or less
energetic at all periods.
After the deposit of the Old Red Sandstone, the internal fire appears to
have enjoyed a lull of its energy, if not a complete cessation, until
the Coal Measures were complete. Then the long tranquility was again
broken, and concussions so extensive and violent ensued, that hardly a
single square mile of country can anywhere be found which is not full of
fractured and contorted strata, the record of subterranean movements,
which mostly occurred between the Carboniferous and the Premian
deposits.
The effects of these convulsions were manifest in the changed relations
of land and sea, existing continents and islands being dislocated,
severed, and swallowed up, while others were elevated from the depths of
the previous ocean.
It was from the wave-worn materials thus obtained from pre-existing
strata, that the New Red Sandstone was consolidated. It consists chiefly
of sand and mud, with few organic remains; and the hiatus thus found, in
animals and vegetables, seems to be almost a complete one between the
organisms of the preceding and the succeeding periods.
The most interesting traces of the earth's tenants during the New Red
formation, consist of foot-tracks impressed by the progress of animals
along the yielding mud between the ranges of high and low tide. They
afford a remarkable example (not, I think, sufficiently dwelt on) of the
extreme rapidity with which deposits were consolidated; since the tracks
must have been made, and the material consolidated, during the few
hours, _at most_, that intervened between the recess and the reflux of
the tide; since, if the mud had not so soon become solid, the flow of
the sea would have instantly obliterated such marks, as it does now on
our shores.
[Illustration: LABYRINTHODON PACHYGNATHUS.]
The principal animal, whose foot-prints have been identified, was an
enormous Frog (_Labyrinthodon_), as big as a hippopotamus, but
apparently allied, in its serried teeth, and in the bony plates with
which it was covered, to the Crocodiles, which were its associates.
It is curious that marks in the same material have chronicled the
serpentine trail of a Sea-worm, the scratchings of a Crab, the ripple of
the wavelets, and even the drops of a passing shower; the last
revealing, by their margins, the direction of the wind by which the
slanting rain was driven.
If the Triassic formations display but little evidence of organic
existence, the lack is supplied by the abundance of such records, which
is contained in the Oolitic system, and specially in its lowest
component,--the Lias. Animals now existed in profusion, but of species
which were for the most part peculiar. The coral-making Polypes existed
not (or very rarely) in the seas of that age, but lime was secreted by
an unusual number of Crinoid Echinoderms, which seem to have fringed the
rocks and floating pieces of timber, much as Barnacles do now.
Among the Mollusca now began to appear the inhabitants of those very
elegant shells, the _Ammonites_, allied to the Nautilus of our Southern
seas, which may be considered as the lingering representative of those
swarms of shelled Cephalopoda. They were accompanied by their near
relations, the _Belemnites_, more resembling a Cuttle, with a long
internal, pointed shell.
Fishes, chiefly belonging to a curiously armed tribe of Sharks, together
with some enclosed in bony-mail like pavement, were present in the
shallows, where the Lias was probably deposited.
[Illustration: SNAKE-NECKED MARINE LIZARDS.
_Plesiosaurus dolichodeirus_ and _P. macrocephalus_.]
But the most characteristic animals were great marine Reptiles, of
strange and uncouth forms, to which the present world presents us no
known analogy. One of these was the _Ichthyosaurus_, which closely
resembled a porpoise in form, but thirty or forty feet in length, with
a vertical fish-like tail, and two pairs of paddles; a mouth set with
stout crocodilian teeth, and enormous eyes. Another form was that of the
_Plesiosaurus_, scarcely less in size than its fellow, which in the
outline of its body it resembled: it was distinguished, however, by an
extraordinary length of neck, slender and swan-like, consisting of
thirty or forty vertebrae.
It adds to the interest of these great marine Reptiles, that around
their fossil skeletons are preserved pellets of excrement (known as
Coprolites) containing fragments of bone, teeth, and scales of fishes,
which clearly reveal the nature of their food. In some instances, the
stomach and intestines of these great carnivorous creatures, filled with
half-digested food, have left indubitable traces of their presence _in
situ_.
Again, the geography of the Globe changed. New lands arose from the sea,
and old lands partially or wholly sank. The German Ocean, and part of
Western Europe, of our maps, were a great group of islands. The Oolitic
formation was deposited. The general character of the organization of
this period differed little from that of the Lias. New forms of plants,
such as _Cycadeae_, were abundant, with, considerable numbers of Corals,
Encrinites, Sea-urchins and Mollusks. Macrurous Crustacea, much like
those of our times (but essentially different in species), inhabited the
sea, and some Beetles and Flies represented the Insects of the land. The
Fishes and Marine Reptiles were pretty much the same with those of the
Lias, though they received some important additions.
[Illustration: MEGALOSAURUS BUCKLANDI.]
It is, however, among the terrestrial Vertebrata that we must look for
the characteristic organisms of this age. And these are, still,
Reptiles. The huge _Megalosaurus_, with a body as big as an elephant's,
stood high on his legs, and stretched open a pair of gaping jaws, set
with jagged teeth. The _Pterodactyles_ flew about,--carnivorous
lizards, with the body and wings of bats,[33] except that the membrane
was stretched upon the enormously developed little finger;--creatures,
perhaps, the most unlike to anything familiar to us, of all fossil
forms. And, in the marshy margins of the great river valley which formed
the Wealden of our South-eastern districts, the giant _Iguanodon_, and
his fellow, the _Hylaeosaurus_, waged their peaceful warfare on the
succulent plants that became their unresisting prey.
[Illustration: BAT-LIZARDS.
_Pterodactylus crassirostris_, and _P. brevirostris_.]
[Illustration: HYLAEOSAURUS ARMATUS.]
The circle of animal life was completed in this epoch, thus far, that
every class was represented by some one or more of its constituent
species. No fossil skeletons of Birds have, indeed, been found so low as
the Oolite, but numerous foot-prints of some of the Grallatores are
found in a sandstone of this period; and in the Stonesfield slate,
which is contemporary with it, a genus of Mammalia has been
discovered,--a small Marsupial, allied to the Opossums of America.
The duration of the Oolitic period must have been considerable. "The
lias sea-bottom was succeeded first by a sandy, and then by a calcareous
deposit, and the animals were modified accordingly." The deposit of
carbonate of lime, which took place under circumstances that caused it
to attract around its nodules the organic particles, whence the name
_oolite_ (egg-stone) is derived, was not continuous, but repeated at
intervals. The shells of Mollusks were developed in great abundance, and
accumulations of these formed thick bands, which consolidated into
layers of shell-limestone. Three hundred feet of strata, largely
composed of organic remains, were formed before the clay was deposited
which made the Stonesfield and contemporaneous slates.
Once more the dry land sank, probably by slow successive subsidences,
and the sea flowed many fathoms deep above the great European
archipelago. And upon its quiet bottom settled down, first a few sandy
and clayey beds, and then the great layer of the Chalk.
Creatures of very minute size and low grades of organization were now
playing a very important part. A large portion of the lime that was
deposited, in the form of a pure carbonate, was doubtless supplied by
the Coral structures, which, were exceedingly numerous; the polypidoms
being gnawed down by strong-jawed fishes that fed upon the Zoophytes.
_Foraminifera_ also were abundant, and contributed to the supply.
Nodules of flint exist in the Chalk, sometimes scattered, sometimes
arranged in bands. Two sources are indicated for this substance. One is
Sponge, the most common kinds of which are composed of skeletons of
siliceous spicula; and these can be discerned with the microscope in the
interior of the chalk-flints. But millions upon millions of Infusoria
swam through the waters, and many of these were encased in siliceous
loricae, while the rocks and sea-weeds were fringed with as incalculably
numerous examples of siliceous _Diatomaceae_, whose elegant forms are
recognisable without difficulty throughout the Chalk. The inconceivable
abundance of these forms may be illustrated by the often-cited fact,
that whole strata of solid rock appear to be so exclusively composed of
their solid remains, that a cube of one-tenth of an inch is computed by
Ehrenberg to contain five hundred millions of individuals.
The increase of these organisms is very rapid, and their duration
proportionately short; but allowing for this, what period would elapse
before the successive generations of entities, of which forty-one
thousand millions are required to make a cubic inch, would have
accumulated into solid strata fourteen feet in thickness?
Without pausing to examine the whole Cretaceous fauna, we may observe
that the Mollusca with chambered shells--the Ammonites and their
allies--were developed in singular variety and profusion during this
period, after which they suddenly disappeared from the ocean. The Fishes
present little that is remarkable; of Birds, few, and of Mammals, no
remains exist; and the Reptiles, while not absolutely extinct, are few
and rare. One great marine form, however, the _Mosasaurus_, was added to
their number.
At length the sea ceased to deposit chalk, and its bed appears to have
been slowly elevated, until all the animals that had inhabited the
waters of that formation were destroyed; so that their race and
generation perished.[34] The grand epoch of Secondary Formations was
closed.
It was followed by an extensive disruption of the then existing strata,
and by changes and modifications so great as to alter the whole face of
nature. "It would appear that a long period of time elapsed before newer
beds were thrown down, since the chalky mud not only had time to harden
into chalk, but the surface of the chalk itself was much rubbed and
worn." During this protracted period, eruptions of molten rock occurred
of enormous extent, producing the Basaltic formation which covers the
Chalk in the north of Ireland, and in some of the Hebrides. In the south
of Europe the Pyrenees were elevated, and the Apennines and Carpathians
were pushed to a greater altitude than before, if they were not then
formed. The Alps and the Caucasus also experienced a series of upward
movements, continuing through a considerable range of the Tertiary
epoch.
The rich collections of vegetable remains--chiefly fruits and
seeds--that have been made from the London Clay, show that the earliest
land of this period was clothed with a great abundance and variety of
plants; and these are of such alliances as would now require a tropical
climate. Many species of Palms, Screw-pines, Gourds, _Piperaceae_,
_Mimoseae_, and other _Leguminosae_, _Malvaceae_, and _Coniferae_, dropped
their woody pods and fruits where now these pages are written; and the
animals manifest no less interesting an approximation to existing forms
than the plants. The Zoophytes, the Echinoderms, the Foraminifera, the
Worms, the Crustacea, the Mollusca, the Fishes and the Reptiles of the
Eocene beds, exhibit a great preponderance of agreement with those that
now exist, _so far as genus is concerned_, though the _species_ are
still almost wholly distinct. The approximation is particularly marked
in the Molluscous sub-kingdom, by the almost entire disappearance of the
hitherto swarming Brachiopod and Cephalopod forms, and the progressive
substitution for them of the _Conchifera_ and _Gastropoda_, which had,
however, throughout the Secondary epoch, been gradually coming forward
to their present predominance in nature.
Among the Fishes, the Placoid type was diminished in number; and those
that were produced were mostly Sharks and Rays, of modern genera; but
the chief difference was the paucity of those mailed forms (Ganoids),
which were so abundant during the Oolitic period. On the other hand, the
Ctenoid and Cycloid forms, which had begun to make their appearance in
small numbers in the Chalk, are well represented. In both this
deficiency and this plenitude, there is a very decided approach to
existing conditions; for the Ganoids are almost unknown with us, while
the last-named two orders are abundant. Representatives of our Perches,
Maigres, Mackerels, Blennies, Herrings, and Cods, were numerous;
_distinct, however, from the present species_. But not a single member
of the great Salmon family was yet introduced.
The great Saurian Reptiles had entirely disappeared, and were quite
unrepresented in the tertiary beds, except by a Crocodile or two, and a
small Lizard. Turtles were, however, numerous, both of the marine and
lacustrine kinds; and there is an interesting stranger, in the form of a
large Serpent, allied to our Pythons, some twenty feet in length.
Birds and Mammals began now to assume their place on the land. The
London Clay presents us with a little Vulture; and the Paris basin
contains remnants of species representing the Raptores, the Rasores, the
Grallatores, and the Natatores.
The Quadrupeds came in in some force; not developed from the lowest to
the highest scale of organization; for the Monkey and the Bat occur in
sands, certainly not later, if not earlier, than the London Clay,
contemporaneously with the Racoon, and before the existence of any
Rodent or Cetacean. Some Carnivora, as the Wolf and the Fox, roamed the
woods, but the character of the epoch was given by the Pachyderms.
These, however, were not the massive colossi that browse in the African
or Indian jungles of our days; no Elephant, no Rhinoceros, no
Hippopotamus was as yet formed. But several kinds of Tapir wallowed in
the morasses; and a goodly number of largish beasts, whose affinities
were with the Pachydermata, while their analogies were with the
Ruminantia, served as substitutes for the latter order, which was wholly
wanting. These interesting quadrupeds, forming the genus
_Anoplotherium_, were remarkable for two peculiarities,--their feet were
two-toed, and their teeth were ranged in a continuous series, without
any interval between the incisors and the molars. They varied in size
from that of an ass to that of a hare.
The physical conditions of our earth, when it was tenanted by these
creatures, is thus described:--"All the great plains of Europe, and the
districts through which the principal rivers now run, were then
submerged; in all probability, the land chiefly extended in a westerly
direction, far out into the Atlantic, possibly trending to the south,
and connecting the western shores of England with the volcanic islands
off the west coast of Africa. The great mountain chains of Europe, the
Pyrenees, the Alps, the Apennines, the mountains of Greece, the
mountains of Bohemia, and the Carpathians, existed then only as chains
of islands in an open sea. Elevatory movements, having an east and west
direction, had, however, already commenced, and were producing important
results, laying bare the Wealden district in the south-east of England.
The southern and central European district, and parts of western Asia,
were the recipients of calcareous deposits (chiefly the skeletons of
_Foraminifera_), forming the Apennine limestone; while numerous islands
were gradually lifted above the sea, and fragments of disturbed and
fractured rock were washed upon the neighbouring shallows or
coast-lines, forming beds of gravel covering the Chalk. The beds of
Nummulites and Miliolites, contemporaneous with those containing the
Sheppey plants and the Paris quadrupeds, seem to indicate a deep sea at
no great distance from shore, and render it probable that there were
frequent alternations of elevation and depression, perhaps the result of
disturbances acting in the direction already alluded to.
"The shores of the islands and main land were, however, occasionally low
and swampy, rivers bringing down mud in what is now the south-east of
England, and the neighbourhood of Brussels, but depositing extensive
calcareous beds near Paris. Deep inlets of the sea, estuaries, and the
shifting mouths of a river, were also affected by numerous alterations
of level not sufficient to destroy, but powerful enough to modify, the
animal and vegetable species then existing; and these movements were
continued for a long time."[35]
After the elevation of the mountain summits of Europe above the sea, and
while the same causes were still in operation, deposits were being made
in the narrow intervening seas of the Archipelago, such as the present
south of France, the valleys of the Rhine and Danube, the eastern
districts of England and Portugal. These deposits were partly marine and
partly lacustrine; the former consisting largely of loose sands, mingled
with shells and gravel. In Switzerland is a thick mass of conglomerate;
and in the district around Mayence, there is a series of fresh-water
limestones, and sandstones charged with organic remains.
The changes which took place during this comparatively recent epoch
were not sudden, but gradual; the results of operations which were
probably going on without intermission, and perhaps have not yet ceased.
The land was more and more upheaved, till at length, what had been an
archipelago of islands became a continent, and Europe assumed the form
which it bears on our maps.
The most interesting addition to the natural history of the Miocene, or
Middle Tertiary period, was the _Dinotherium_--a huge Pachyderm, twice
as large as an elephant, with a tapir-like proboscis, and two great
tusks curving downward from the lower jaw. It was, doubtless, aquatic in
its habits, and possibly (for its hinder parts are not known), it may
have been allied to the Dugong and Manatee, those whale-like Pachyderms,
with a broad horizontal tail, instead of posterior limbs.
Other great herbivorous beasts roamed over the new-made land. The
Mastodons, closely allied to the Elephant, had their head-quarters in
North America, but extended also to Europe. And the Elephants
themselves, of several species, were spread over the northern
hemisphere, even to the polar regions. The Hippopotamus, the
Rhinoceros, and other creatures, now exclusively tropical, were also
inhabitants of the same northern latitudes.
[Illustration: MAMMOTH.]
From some specimens of Elephants and Rhinoceroses of this period, which
seem to have been buried in avalanches, and thus to have been preserved
from decomposition, even of the more transitory parts, as muscle and
skin, we learn something of the climate that prevailed. The very fact of
their preservation, by the antiseptic power of frost, shows that it was
not a tropical climate in which they lived; and the clothing of thick
wool, fur, and hair, which protected the skin of the Mammoth, or
Siberian Elephant, tends to the same conclusion. At the same time, those
regions were not so intensely cold as they are now. For the district in
which the remains of Elephants and their associates are found, in almost
incredible abundance, is that inhospitable coast of northern Asia which
bounds the Polar Sea.
The trees of a temperate climate--the oak, the beech, the maple, the
poplar, and the birch--which now attain their highest limit somewhere
about 70 deg. of north latitude, and there are dwarfed to minute shrubs,
appear then to have grown at the very verge of the polar basin; and that
in the condition of vast and luxuriant forests, perhaps occupying
sheltered valleys between mountains whose steep sides were covered with
snow, already become perennial, and ever and anon rolling down in
overwhelming avalanches, such as those which now occasionally descend
into the valleys of the Swiss Alps.
The coast of Suffolk displays a formation known as the Crag--a local
name for gravel--which rests partly on the chalk; but, as it lies in
other parts over the London Clay, it is assigned to the later Tertiary,
or what is called the Pleiocene period. It is divided into the
_coralline_ and the _red_ crag, the latter being uppermost where they
exist together, and therefore being the more recent. The Coralline Crag
is nearly composed of corals and shells, the former almost wholly
extinct now; but the latter containing upwards of seventy species still
existing in the adjacent seas. The Red Crag contains few zoophytes, but
is remarkable for the remains of at least five species of Whales. Other
Mammalia occur in this formation, among which are the red deer and the
wild boar of modern Europe.
The gradual but rapid approximation of the Tertiary fauna to that of the
present surface is well indicated by Mr. Lyell's table (1841) of recent
and fossil species in the English formations:--
Per-centage No. of
Periods. Localities. of fossils
recent. compared.
Eocene {London and Hampshire } 1 or 2 400
Miocene {Red and Coralline } 20 to 30 450
{ Crag, Suffolk }
Older Pleiocene {Mamaliferous or Norwich } 60 to 70 111
{ Crag }
Newer Pleiocene {Marine strata near } 85 to 90 160
{ Glasgow }
Post Pleiocene {Fresh-water of the valley} 99 to 100 40
{ of the Thames }
It is to this period that are assigned the animals whose bones are found
in astonishing numbers in limestone caverns, as, for example, that
notable one at Kirkdale, in Yorkshire, which was examined by Professor
Buckland.