NEWER PLIOCENE STRATA AND CAVERN DEPOSITS.
Chronological classification of Pleistocene formations, why
difficult--Freshwater deposits in valley of Thames--In Norfolk
cliffs--In Patagonia--Comparative longevity of species in the mammalia
and testacea--Fluvio-marine crag of Norwich--Newer Pliocene strata of
Sicily--Limestone of great thickness and elevation--Alternation of
marine and volcanic formations--Proofs of slow accumulation--Great
geographical changes in Sicily since the living fauna and flora began
to exist--Osseous breccias and cavern deposits--Sicily--Kirkdale--Origin
of stalactite--Australian cave-breccias--Geographical relationship of
the provinces of living vertebrata and those of the fossil species of
the Pliocene periods--Extinct struthious birds of New Zealand--Teeth
of fossil quadrupeds.
Having in the last chapter treated of the boulder formation and its
associated freshwater and marine strata as belonging chiefly to the close
of the Newer Pliocene period, we may now proceed to other deposits of the
same or nearly the same age. It should, however, be stated that it is
difficult to draw the line of separation between these modern formations,
especially when we are called upon to compare deposits of marine and
freshwater origin, or these again with the ossiferous contents of caverns.
If as often as the carcasses of quadrupeds were buried in alluvium during
floods, or mired in swamps, or imbedded in lacustrine strata, a stream of
lava had descended and preserved the alluvial or freshwater deposits, as
frequently happened in Auvergne (see above, p. 80,), keeping them free from
intermixture with strata subsequently formed, then indeed the task of
arranging chronologically the whole series of mammaliferous formations
might have been easy, even though many species were common to several
successive groups. But when there have been oscillations in the levels of
the land, accompanied by the widening and deepening of valleys at more than
one period,--when the same surface has sometimes been submerged beneath the
sea, after supporting forests and land quadrupeds, and then raised again,
and subject during each change of level to sedimentary deposition and
partial denudation,--and when the drifting of ice by marine currents or by
rivers, during an epoch of intense cold, has for a season interfered with
the ordinary mode of transport, or with the geographical range of species,
we cannot hope speedily to extricate ourselves from the confusion in which
the classification of these Pleistocene formations is involved.
At several points in the valley of the Thames, remnants of ancient
fluviatile deposits occur, which may differ considerably in age,
although the imbedded land and freshwater shells in each are of recent
species. At Brentford, for example, the bones of the Siberian Mammoth,
or _Elephas primigenius_, and the _Rhinoceros tichorhinus_, both of
them quadrupeds of which the flesh and hair have been found preserved in
the frozen soil of Siberia, occur abundantly, with the bones of an
hippopotamus, aurochs, short-horned ox, red deer, rein-deer, and great
cave-tiger or lion.[147-A] A similar group has been found fossil at
Maidstone, in Kent, and other places, agreeing in general specifically
with the fossil bones detected in the caverns of England. When we see
the existing rein-deer and an extinct hippopotamus in the same
fluviatile loam, we are tempted to indulge our imaginations in
speculating on the climatal conditions which could have enabled these
genera to co-exist in the same region. Wherever there is a continuity of
land from polar to temperate and equatorial regions, there will always
be points where the southern limit of an arctic species meets the
northern range of a southern species; and if one or both have migratory
habits, like the Bengal tiger, the American bison, the musk ox, and
others, they may each penetrate mutually far into the respective
provinces of the other. There may also have been several oscillations of
temperature during the periods which immediately preceded and followed
the more intense cold of the glacial epoch.
The strata bordering the left bank of the Thames at Grays Thurrock, in
Essex, are probably of older date than those of Brentford, although the
associated land and freshwater shells are nearly all, if not all,
identical with species now living. Three of the shells, however, are no
longer inhabitants of Great Britain; namely, _Paludina marginata_ (fig.
112. p. 127.), now living in France; _Unio littoralis_ (fig. 29. p.
28.), now inhabiting the Loire; and _Cyrena consobrina_ (fig. 26. p.
28.). The last-mentioned fossil (a recent Egyptian shell of the Nile) is
very abundant at Grays, and deserves notice, because the genus _Cyrena_
is now no longer European.
The rhinoceros occurring in the same beds (_R. leptorhinus_, see fig. 131.
p. 160.) is of a different species from that of Brentford above mentioned,
and the accompanying elephant belongs to the variety called _Elephas
meridionalis_, which, according to MM. Owen and H. von Meyer, two high
authorities, is the same species as the Siberian mammoth, although some
naturalists regard it as distinct. With the above mammalia is also found
the _Hippopotamus major_, and what is most remarkable in so modern and
northern a deposit, a monkey, called by Owen, _Macacus pliocenus_.
The submerged forest already alluded to (p. 130.) as underlying the drift
at the base of the cliffs of Norfolk is associated with a bed of lignite
and loam, in which a great number of fossil bones occur, apparently of the
same group as that of Grays, just mentioned. It has sometimes been called
"the Elephant bed." One portion of it, which stretches out under the sea at
Happisburgh, was overgrown in 1820 by a bank of recent oysters, and there
the fishermen dredged up, according to Woodward, in the course of thirteen
years, together with the oysters, above 2000 mammoths' grinders.[147-B]
Another portion of the same continuous stratum has yielded at Bacton,
Cromer, and other places on the coast, the bones of a gigantic beaver
(_Trogontherium Cuvierii_, Fischer), as well as the ox, horse, and deer,
and both species of rhinoceros, _R. tichorhinus_ and _R. leptorhinus_.
In studying these and various other similar assemblages of fossils, we have
a good exemplification of the more rapid rate at which the mammiferous
fauna, as compared to the testaceous, diverges when traced backwards in
time from the recent type. I have before hinted, that the longevity of
species in the class of warm-blooded quadrupeds is less great than in that
of the mollusca, the latter having probably more capacity for enduring
those changes of climate and other external circumstances which take place
in the course of ages on the earth's surface. This phenomenon is by no
means confined to Europe, for Mr. Darwin found at Bahia Blanca, in South
America, lat. 39 deg. S., near the northern confines of Patagonia, fossil
remains of the extinct mammiferous genera Megatherium, Megalonyx, Toxodon,
and others, associated with shells, almost all of species already
ascertained to be still living in the contiguous sea[148-A]; the marine
mollusca, as well as those of rivers, lakes, or the land, having died out
more slowly than the terrestrial mammalia.
I alluded before (p. 125.) to certain marine strata overlying till near
Glasgow, and at other points on the Clyde, in which the shells are for the
most part British, with an intermixture of some arctic species; while
others, about a tenth of the whole, are supposed to be extinct. This
formation may also be called Newer Pliocene.
_Fluvio-marine crag of Norwich._--At several places within five miles of
Norwich, on both banks of the Yare, beds of sand, loam, and gravel,
provincially termed "crag," occur, in which there is a mixture of marine,
land, and freshwater shells, with ichthyolites and bones of mammalia. It is
clear that these beds have been accumulated at the bottom of the sea near
the mouth of a river. They form patches of variable thickness, resting on
white chalk, and are covered by a dense mass of stratified flint gravel.
The surface of the chalk is often perforated to the depth of several inches
by the _Pholas crispata_, each fossil shell still remaining at the bottom
of its cylindrical cavity, now filled up with loose sand which has fallen
from the incumbent crag. This species of Pholas still exists and drills the
rocks between high and low water on the British coast. The most common
shells of these strata, such as _Fusus striatus_, _Turritella terebra_,
_Cardium edule_, and _Cyprina islandica_, are now abundant in the British
seas; but with them are some extinct species, such as _Nucula Cobboldiae_
(fig. 120.) and _Tellina obliqua_ (fig. 121.). _Natica helicoides_ (fig.
122.) is an example of a species formerly known only as fossil, but which
has now been found living in our seas.
Among the accompanying bones of mammalia is the _Mastodon_
_angustidens_[149-A] (see fig. 130.), a portion of the upper jawbone with a
tooth having been found by Mr. Wigham at Postwick, near Norwich. As this
species has also been found in the Red Crag, both at Sutton and at
Felixstow, and had hitherto been regarded as characteristic of formations
older than the Pleistocene, it may possibly have been washed out of the Red
into the Norwich Crag.
[Illustration: Fig. 120. _Nucula Cobboldiae._]
[Illustration: Fig. 121. _Tellina obliqua._]
[Illustration: Fig. 122. _Natica helicoides_, Johnston.]
Among the bones, however, respecting the authenticity of which there
seems no doubt, may be mentioned those of the elephant, horse, pig,
deer, and the jaws and teeth of field mice (fig. 141.). I have seen the
tusk of an elephant from Bramerton near Norwich, to which, many serpulae
were attached, showing that it had lain for some time at the bottom of
the sea of the Norwich Crag.
At Thorpe, near Aldborough, and at Southwold, in Suffolk, this
fluvio-marine formation is well exposed in the sea-cliffs, consisting of
sand, shingle, loam, and laminated clay. Some of the strata there bear
the marks of tranquil deposition, and in one section a thickness of 40
feet is sometimes exposed to view. Some of the lamellibranchiate shells
have both valves united, although mixed with land and freshwater
testacea, and with the bones and teeth of elephant, rhinoceros, horse,
and deer. Captain Alexander, with whom I examined these strata in 1835,
showed me a bed rich in marine shells, in which he had found a large
specimen of the _Fusus striatus_, filled with sand, and in the interior
of which was the tooth of a horse.
Among the freshwater shells I obtained the _Cyrena consobrina_ (fig. 26.
p. 28.), before mentioned, supposed to agree with a species now
living in the Nile.
I formerly classed the Norwich Crag as older Pliocene, conceiving that more
than a third of the fossil testacea were extinct; but there now seems good
reason for believing that several of the rarer shells obtained from these
strata do not really belong to a contemporary fauna, but have been washed
out of the older beds of the "Red Crag;" while other species, once supposed
to have died out, have lately been met with living in the British seas.
According to Mr. Searles Wood, the total number of marine species does not
exceed seventy-six, of which one tenth only are extinct. Of the fourteen
associated freshwater shells, all the species appear to be living. Strata
containing the same shells as those near Norwich have been found by Mr.
Bean, at Bridlington, in Yorkshire.
_Newer Pliocene strata of Sicily._--In no part of Europe are the Newer
Pliocene formations seen to enter so largely into the structure of the
earth's crust, or to rise to such heights above the level of the sea, as in
Sicily. They cover nearly half the island, and near its centre, at
Castrogiovanni, they reach an elevation of 3000 feet. They consist
principally of two divisions, the upper calcareous, the lower argillaceous,
both of which may be seen at Syracuse, Girgenti, and Castrogiovanni.
According to Philippi, to whom we are indebted for the best account of the
tertiary shells of this island, thirty-five species out of one hundred and
twenty-four obtained from the beds in central Sicily are extinct. Of the
remainder, which still live, five species are no longer inhabitants of the
Mediterranean. When I visited Sicily in 1828 I estimated the proportion of
living species as somewhat greater, partly because I confounded with the
tertiary formation of central Sicily the strata at the base of Etna, and
some other localities, where the fossils are now proved to agree entirely
with the present Mediterranean fauna.
Philippi came to the conclusion, that in Sicily there is a gradual
passage from beds containing 70 per cent. of recent shells, to those in
which the whole of the fossils are identical with recent species; but
his tables appear scarcely to bear out so important a generalization,
several of the places cited by him in confirmation having as yet
furnished no more than twenty or thirty species of testacea. The
Sicilian beds in question probably belong to about the same period as
the Norwich Crag, although a geologist, accustomed to see nearly all the
Pleistocene formations in the north of Europe occupying low grounds and
very incoherent in texture, is naturally surprised to behold formations
of the same age so solid and stony, of such thickness, and attaining so
great an elevation above the level of the sea.
The upper or calcareous member of this group in Sicily consists in some
places of a yellowish-white stone, like the calcaire grossier of Paris, in
others, of a rock nearly as compact as marble. Its aggregate thickness
amounts sometimes to 700 or 800 feet. It usually occurs in regular
horizontal beds, and is occasionally intersected by deep valleys, such as
those of Sortino and Pentalica, in which are numerous caverns. The fossils
are in every stage of preservation, from shells retaining portions of their
animal matter and colour, to others which are mere casts.
The limestone passes downwards into a sandstone and conglomerate, below
which is clay and blue marl, like that of the Subapennine hills, from
which perfect shells and corals may be disengaged. The clay sometimes
alternates with yellow sand.
South of the plain of Catania is a region in which the tertiary beds are
intermixed with volcanic matter, which has been for the most part the
product of submarine eruptions. It appears that, while the clay, sand,
and yellow limestone before mentioned were in course of deposition at
the bottom of the sea, volcanos burst out beneath the waters, like that
of Graham Island, in 1831, and these explosions recurred again and again
at distant intervals of time. Volcanic ashes and sand were showered down
and spread by the waves and currents so as to form strata of tuff,
which are found intercalated between beds of limestone and clay
containing marine shells, the thickness of the whole mass exceeding 2000
feet. The fissures through which the lava rose may be seen in many
places forming what are called _dikes_.
In part of the region above alluded to, as, for example, near Lentini, a
conglomerate occurs in which I observed many pebbles of volcanic rocks
covered by full grown _serpulae_. We may explain the origin of these by
supposing that there were some small volcanic islands which may have been
destroyed from time to time by the waves, as Graham Island has been swept
away since 1831. The rounded blocks and pebbles of solid volcanic matter,
after being rolled for a time on the beach of such temporary islands, were
carried at length into some tranquil part of the sea, where they lay for
years, while the marine _serpulae_ adhered to them, their shells growing and
covering their surface, as they are seen adhering to the shell figured in
p. 22. Finally, the bed of pebbles was itself covered with strata of shelly
limestone. At Vizzini, a town not many miles distant to the S.W., I
remarked another striking proof of the gradual manner in which these modern
rocks were formed, and the long intervals of time which elapsed between the
pouring out of distinct sheets of lava. A bed of oysters no less than 20
feet in thickness rests upon a current of basaltic lava. The oysters are
perfectly identifiable with our common eatable species. Upon the oyster
bed, again, is superimposed a second mass of lava, together with tuff or
peperino. In the midst of the same alternating igneous and aqueous
formations is seen near Galieri, not far from Vizzini, a horizontal bed,
about a foot and a half in thickness, composed entirely of a common
Mediterranean coral (_Caryophyllia caespitosa_, Lam.). These corals stand
erect as they grew; and, after being traced for hundreds of yards, are
again found at a corresponding height on the opposite side of the valley.
[Illustration: Fig. 123. _Caryophyllia caespitosa_, Lam.
(_Cladocora caespitosa_, Ehr.)
_a._ Stem with young stem growing from its side.
_a*._ Young stem of same twice magnified.
_b._ Portion of branch, twice magnified, with the base of a lateral
branch; the exterior ridges of the main branch appearing through
the lamellae of the lateral one.
_c._ Transverse section of same, proving, by the integrity of the main
branch, that the lateral one did not originate in a subdivision
of the animal.
_d._ A branch, having at its base another laterally united to it, and
two young corals at its upper part.
_e._ A main branch, with a full grown lateral one.
_f._ A perfect terminal star.]
The corals are usually branched, but not by the division of the animals as
some have supposed, but by the attachment of young individuals to the sides
of the older ones; and we must understand this mode of increase, in order
to appreciate the time which was required for the building up of the whole
bed of coral during the growth of many successive generations.[152-A]
Among the other fossil shells met with in these Sicilian strata, which
still continue to abound in the Mediterranean, no shell is more
conspicuous, from its size and frequent occurrence, than the great
scallop, _Pecten jacobaeus_ (see fig. 124.), now so common in the
neighbouring seas. We see this shell in the calcareous beds at Palermo
in great numbers, in the limestone at Girgenti, and in that which
alternates with volcanic rocks in the country between Syracuse and
Vizzini, often at great heights above the sea.
[Illustration: Fig. 124. _Pecten jacobaeus_; half natural size.]
The more we reflect on the preponderating number of these recent shells,
the more we are surprised at the great thickness, solidity, and height
above the sea of the rocky masses in which they are entombed, and the vast
amount of geographical change which has taken place since their origin. It
must be remembered that, before they began to emerge, the uppermost strata
of the whole must have been deposited under water. In order, therefore, to
form a just conception of their antiquity, we must first examine singly the
innumerable minute parts of which the whole is made up, the successive beds
of shells, corals, volcanic ashes, conglomerates, and sheets of lava; and
we must afterwards contemplate the time required for the gradual upheaval
of the rocks, and the excavation of the valleys. The historical period
seems scarcely to form an appreciable unit in this computation, for we
find ancient Greek temples, like those of Girgenti (Agrigentum), built of
the modern limestone of which we are speaking, and resting on a hill
composed of the same; the site having remained to all appearance unaltered
since the Greeks first colonised the island.
The modern geological date of the rocks in this region leads to another
singular and unexpected conclusion, namely, that the fauna and flora of a
large part of Sicily are of higher antiquity than the country itself,
having not only flourished before the lands were raised from the deep, but
even before their materials were brought together beneath the waters. The
chain of reasoning which conducts us to this opinion may be stated in a few
words. The larger part of the island has been converted from sea into land
since the Mediterranean was peopled with nearly all the living species of
testacea and zoophytes. We may therefore presume that, before this region
emerged, the same land and river shells, and almost all the same animals
and plants, were in existence which now people Sicily; for the terrestrial
fauna and flora of this island are precisely the same as that of other
lands surrounding the Mediterranean. There appear to be no peculiar or
indigenous species, and those which are now established there must be
supposed to have migrated from pre-existing lands, just as the plants and
animals of the Neapolitan territory have colonised Monte Nuovo, since that
volcanic cone was thrown up in the sixteenth century.
Such conclusions throw a new light on the adaptation of the attributes
and migratory habits of animals and plants to the changes which are
unceasingly in progress in the physical geography of the globe. It is
clear that the duration of species is so great, that they are destined
to outlive many important revolutions in the configuration of the
earth's surface; and hence those innumerable contrivances for enabling
the subjects of the animal and vegetable creation to extend their range;
the inhabitants of the land being often carried across the ocean, and
the aquatic tribes over great continental spaces. It is obviously
expedient that the terrestrial and fluviatile species should not only be
fitted for the rivers, valleys, plains, and mountains which exist at the
era of their creation, but for others that are destined to be formed
before the species shall become extinct; and, in like manner, the marine
species are not only made for the deep and shallow regions of the ocean
existing at the time when they are called into being, but for tracts
that may be submerged or variously altered in depth during the time that
is allotted for their continuance on the globe.
OSSEOUS BRECCIAS AND DEPOSITS IN CAVES OF THE PLIOCENE PERIOD.
_Sicily._--Caverns filled with marine breccias, at the base of ancient
sea-cliffs, have been already mentioned in the sixth chapter; and it was
noticed, respecting the cave of San Ciro, near Palermo (p. 75.), that upon
a bed of sand filled with sea-shells, almost all of recent species, rests
a breccia (_b_, fig. 93.), composed of fragments of calcareous rock, and
the bones of animals. In the sand at the bottom of that cave, Dr. Philippi
found about forty-five marine shells, all clearly identical with recent
species, except two or three. The bones in the incumbent breccia are
chiefly those of the mammoth (_E. primigenius_), with some belonging to an
hippopotamus, distinct from the recent species, and smaller than that
usually found fossil. (See fig. 132.) Several species of deer also, and,
according to some accounts, the remains of a bear, were discovered. These
mammalia are probably referable to the Post-Pliocene period.
The Newer Pliocene tertiary limestone of the south of Sicily, already
described, is sometimes full of caverns; and the student will at once
perceive that all the quadrupeds of which the remains are found in the
stalactite of these caverns, being of later origin than the rocks, must be
referable to the close of the tertiary epoch, if not of still later date.
The situation of one of these caves, in the valley of Sortino, is
represented in the annexed section.
[Illustration: Fig. 125. Cross section.
_a_. Alluvium, } containing the remains of quadrupeds
_b_, _b_. Deposits in caves, } for the most part extinct.
C. Limestone, containing the remains of shells, of which between 70 and
80 per cent. are recent.]
_England._--In a cave at Kirkdale, about twenty-five miles N.N.E. of York,
the remains of about 300 hyaenas, belonging to individuals of every age,
have been detected. The species (_Hyaena spelaea_) is extinct, and was larger
than the fierce _Hyaena crocuta_ of South Africa, which it most resembled.
Dr. Buckland, after carefully examining the spot, proved that the Hyaenas
must have lived there; a fact attested by the quantity of their dung,
which, as in the case of the living hyaena, is of nearly the same
composition as bone, and almost as durable. In the cave were found the
remains of the ox, young elephant, hippopotamus, rhinoceros, horse, bear,
wolf, hare, water-rat, and several birds. All the bones have the appearance
of having been broken and gnawed by the teeth of the hyaenas; and they occur
confusedly mixed in loam or mud, or dispersed through a crust of stalagmite
which covers it. In these and many other cases it is supposed that portions
of herbivorous quadrupeds have been dragged into caverns by beasts of prey,
and have served as their food, an opinion quite consistent with the known
habits of the living hyaena.
No less than thirty-seven species of mammalia are enumerated by Professor
Owen as having been discovered in the caves of the British islands, of
which eighteen appear to be extinct, while the others still survive in
Europe. They were not washed to the spots where the fossils now occur by a
great flood; but lived and died, one generation after another, in the
places where they lie buried. Among other arguments in favour of this
conclusion may be mentioned the great numbers of the shed antlers of deer
discovered in caves and in freshwater strata throughout England.[155-A]
Examples also occur of fissures into which animals have fallen from time to
time, or have been washed in from above, together with alluvial matter and
fragments of rock detached by frost, forming a mass which may be united
into a bony breccia by stalagmitic infiltrations. Frequently we discover a
long suite of caverns connected by narrow and irregular galleries, which
hold a tortuous course through the interior of mountains, and seem to have
served as the subterranean channels of springs and engulphed rivers. Many
streams in the Morea are now carrying bones, pebbles, and mud into
underground passages of this kind.[155-B] If, at some future period, the
form of that country should be wholly altered by subterranean movements and
new valleys shaped out by denudation, many portions of the former channels
of these engulphed streams may communicate with the surface, and become the
dens of wild beasts, or the recesses to which quadrupeds retreat to die.
Certain caves of France, Germany, and Belgium, may have passed successively
through these different conditions, and in their last state may have
remained open to the day for several tertiary periods. It is nevertheless
remarkable, that on the continent of Europe, as in England, the fossil
remains of mammalia belong almost exclusively to those of the Newer
Pliocene and Post-Pliocene periods, and not to the Miocene or Eocene
epochs, and when they are accompanied by land or river shells, these agree
in great part, or entirely, with recent species.
As the preservation of the fossil bones is due to a slow and constant
supply of stalactite, brought into the caverns by water dropping from the
roof, the source and origin of this deposit has been a subject of curious
inquiry. The following explanation of the phenomenon has been recently
suggested by the eminent chemist Liebig. On the surface of Franconia, where
the limestone abounds in caverns, is a fertile soil, in which vegetable
matter is continually decaying. This mould or humus, being acted on by
moisture and air, evolves carbonic acid which is dissolved by rain. The
rain water, thus impregnated, permeates the porous limestone, dissolves a
portion of it, and afterwards, when the excess of carbonic acid evaporates
in the caverns, parts with the calcareous matter, and forms stalactite.
_Australian cave-breccias._--Ossiferous breccias are not confined to
Europe, but occur in all parts of the globe; and those lately discovered
in fissures and caverns in Australia correspond closely in character
with what has been called the bony breccia of the Mediterranean, in
which the fragments of bone and rock are firmly bound together by a
red ochreous cement.
Some of these caves have been examined by Sir T. Mitchell in the Wellington
Valley, about 210 miles west of Sidney, on the river Bell, one of the
principal sources of the Macquarie, and on the Macquarie itself. The
caverns often branch off in different directions through the rock, widening
and contracting their dimensions, and the roofs and floors are covered with
stalactite. The bones are often broken, but do not seem to be water-worn.
In some places they lie imbedded in loose earth, but they are usually
included in a breccia.
The remains found most abundantly are those of the kangaroo, of which there
are four species, besides which the genera _Hypsiprymnus_, _Phalangista_,
_Phascolomys_, and _Dasyurus_, occur. There are also bones, formerly
conjectured by some osteologists to belong to the hippopotamus, and by
others to the dugong, but which are now referred by Mr. Owen to a marsupial
genus, allied to the _Wombat_.
[Illustration: Fig. 126. _Macropus atlas_, Owen.
_a._ permanent false molar, in the alveolus.]
[Illustration: Fig. 127. Lowest jaw of largest living species of kangaroo.
(_Macropus major._)]
In the fossils above enumerated, several species are larger than the
largest living ones of the same genera now known in Australia. The annexed
figure of the right side of a lower jaw of a kangaroo (_Macropus atlas_,
Owen) will at once be seen to exceed in magnitude the corresponding part of
the largest living kangaroo, which is represented in fig. 127. In both
these specimens part of the substance of the jaw has been broken open, so
as to show the permanent false molar (_a._ fig. 126.) concealed in the
socket. From the fact of this molar not having been cut, we learn that the
individual was young, and had not shed its first teeth. In fig. 128. a
front tooth of the same species of kangaroo is represented.
[Illustration: Fig. 128. Incisor of _Macropus_.]
Whether the breccias, above alluded to, of the Wellington Valley, appertain
strictly to the Pliocene period cannot be affirmed with certainty, until we
are more thoroughly acquainted with the recent quadrupeds of the same
district, and until we learn what species of fossil land shells, if any,
are buried in the deposits of the same caves.
The reader will observe that all these extinct quadrupeds of Australia
belong to the marsupial family, or, in other words, that they are referable
to the same peculiar type of organization which now distinguishes the
Australian mammalia from those of other parts of the globe. This fact is
one of many pointing to a general law deducible from the fossil vertebrate
and invertebrate animals of the eras immediately antecedent to the human,
namely, that the present geographical distribution of organic _forms_ dates
back to a period anterior to the creation of existing _species_; in other
words, the limitation of particular genera or families of quadrupeds,
mollusca, &c., to certain existing provinces of land and sea, began before
the species now contemporary with man had been introduced into the earth.
Mr. Owen, in his excellent "History of British Fossil Mammals," has called
attention to this law, remarking that the fossil quadrupeds of Europe and
Asia differ from those of Australia or South America. We do not find, for
example, in the Europaeo-Asiatic province fossil kangaroos or armadillos,
but the elephant, rhinoceros, horse, bear, hyaena, beaver, hare, mole, and
others, which still characterize the same continent.
In like manner in the Pampas of South America the skeletons of Megatherium,
Megalonyx, Glyptodon, Mylodon, Toxodon, Macrauchenia, and other extinct
forms, are analogous to the living sloth, armadillo, cavy, capybara, and
llama. The fossil quadrumana, also associated with some of these forms in
the Brazilian caves, belong to the Platyrrhine family of monkeys, now
peculiar to South America. That the extinct fauna of Buenos Ayres and
Brazil was very modern has been shown by its relation to deposits of marine
shells, agreeing with those now inhabiting the Atlantic; and when in
Georgia in 1845, I ascertained that the Megatherium, Mylodon, _Harlanus
americanus_ (Owen), _Equus curvidens_, and other quadrupeds allied to the
Pampean type were posterior in date to beds containing marine shells
belonging to forty-five recent species of the neighbouring sea.
There are indeed some cosmopolite genera, such as the Mastodon (a genus of
the elephant family), and the horse, which were simultaneously represented
by different fossil species in Europe, North America, and South America;
but these few exceptions can by no means invalidate the rule which has been
thus expressed by Professor Owen, "that in the highest organized class of
animals the same forms were restricted to the same great provinces at the
Pliocene periods as they are at the present day."
However modern, in a geological point of view, we may consider the
Pleistocene epoch, it is evident that causes more general and powerful
than the intervention of man have occasioned the disappearance of the
ancient fauna from so many extensive regions. Not a few of the species
had a wide range; the same Megatherium, for instance, extended from
Patagonia and the river Plata in South America, between latitudes 31 deg.
and 39 deg. south, to corresponding latitudes in North America, the same
animal being also an inhabitant of the intermediate country of Brazil,
where its fossil remains have been met with in caves. The extinct
elephant, likewise, of Georgia (_Elephas primigenius_) has been traced
in a fossil state northward from the river Alatamaha, in lat. 33 deg. 50' N.
to the polar regions, and then again in the eastern hemisphere from
Siberia to the south of Europe. If it be objected that, notwithstanding
the adaptation of such quadrupeds to a variety of climates and
geographical conditions, their great size exposed them to extermination
by the first hunter tribes, we may observe that the investigations of
Lund and Clausen in the ossiferous limestone caves of Brazil have
demonstrated that these large mammalia were associated with a great many
smaller quadrupeds, some of them as diminutive as field mice, which have
all died out together, while the land shells formerly their
contemporaries still continue to exist in the same countries. As we may
feel assured that these minute quadrupeds could never have been
extirpated by man, so we may conclude that all the species, small and
great, have been annihilated one after the other, in the course of
indefinite ages, by those changes of circumstances in the organic and
inorganic world which are always in progress, and are capable in the
course of time of greatly modifying the physical geography, climate, and
all other conditions on which the continuance upon the earth of any
living being must depend.[158-A]
The law of geographical relationship above alluded to, between the
living vertebrata of every great zoological province and the fossils of
the period immediately antecedent, even where the fossil species are
extinct, is by no means confined to the mammalia. New Zealand, when
first examined by Europeans, was found to contain no indigenous land
quadrupeds, no kangaroos, or opossums, like Australia; but a wingless
bird abounded there, the smallest living representative of the ostrich
family, called the Xivi, by the natives (_Apteryx_). In the fossils of
the Post-Pliocene and Pleistocene period in this same island, there is
the like absence of kangaroos, opossums, wombats, and the rest; but in
their place a prodigious number of well preserved specimens of gigantic
birds of the struthious order, called by Owen Dinornis and Palapteryx,
which are entombed in superficial deposits. These genera comprehended
many species, some of which were 4, some 7, others 9, and others 11 feet
in height! It seems doubtful whether any contemporary mammalia shared
the land with this population of gigantic feathered bipeds.
To those who have never studied comparative anatomy it may seem scarcely
credible, that a single bone taken from any part of the skeleton may enable
a skilful osteologist to distinguish, in many cases, the genus, and
sometimes the species, of quadruped to which it belonged. Although few
geologists can aspire to such knowledge, which must be the result of long
practice and study, they will nevertheless derive great advantage from
learning what is comparatively an easy task, to distinguish the principal
divisions of the mammalia by the forms and characters of their teeth. The
annexed figures, all taken from original specimens, may be useful in
assisting the student to recognize the teeth of many genera most frequently
found fossil in Europe:--
[Illustration: Fig. 129. _Elephas primigenius_ (or Mammoth); molar of upper
jaw, right side; one third of nat. size.
_a._ grinding surface.
_b._ side view.]
[Illustration: Fig. 130. _Mastodon angustidens_ (Norwich Crag, Postwick,
also found in Red Crag, see p. 149.); second true molar, left side, upper
jaw; grinding surface, nat. size. (See p. 149.)]
[Illustration: Fig. 131. Rhinoceros.
_Rhinoceros leptorhinus_; fossil from freshwater beds of Grays, Essex
(see p. 147.); penultimate molar, lower jaw, left side; two-thirds
of nat. size.]
[Illustration: Fig. 132. Hippopotamus.
Hippopotamus; from cave near Palermo (see p. 154.); molar tooth; two-thirds
of nat. size.]
[Illustration: Fig. 133. Pig.
_Sus scrofa_, Lin. (common pig); from shell-marl, Forfarshire; posterior
molar, lower jaw, nat. size.]
[Illustration: Fig. 134. Horse.
_Equus caballus_, Lin. (common horse); from the shell marl, Forfarshire;
second molar, lower jaw.
_a._ grinding surface, two-thirds nat. size.
_b._ side view of same, half nat. size.]
[Illustration: Fig. 135. Tapir.
_Tapirus Americanus_; recent; third molar, upper jaw; nat. size.]
[Illustration: Fig. 136. _a._ _b._ Deer.
Elk (_Cervus alces_, Lin.); recent; molar of upper jaw.
_a._ grinding surface.
_b._ side view; two-thirds of nat. size.]
[Illustration: Fig. 137. _c._ _d._ Ox.
Ox, common, from shell marl, Forfarshire; true molar upper jaw;
two-thirds nat. size.
_c._ grinding surface.
_d._ side view.]
[Illustration: Fig. 138. Bear.
_a._ canine tooth or tusk of bear (_Ursus spelaeus_); from cave
near Liege.
_b._ molar of left side, upper jaw; one third of nat. size.]
[Illustration: Fig. 139. Tiger.
_c._ canine tooth of tiger (_Felis tigris_); recent.
_d._ outside view of posterior molar, lower jaw; one-third of nat. size.]
[Illustration: Fig. 140. _Hyaena spelaea_; second molar, left side, lower
jaw; nat. size. Cave of Kirkdale. (See p. 154.)]
[Illustration: Fig. 141. Teeth of a new species of _Arvicola_
(field-mouse); from the Norwich Crag. (See p. 149.)
_a._ grinding surface.
_b._ side view of same.
_c._ nat. size of a and b.]
FOOTNOTES:
[147-A] Morris, Geol. Soc. Proceed., 1849.
[147-B] Woodward's Geology of Norfolk.
[148-A] Zool. of Beagle, part 1. pp. 9. 111.
[149-A] Owen, Brit. Foss. Mamm. 271. _Mastodon longirostris_,
Kaup, see _ibid._
[152-A] I am indebted to Mr. Lonsdale for the details above given
respecting the structure of this coral.
[155-A] Owen, Brit. Foss. Mam. xxvi., and Buckland, Rel. Dil. 19. 24.
[155-B] See Principles of Geology.
[158-A] See Principles of Geology, chaps. xli. to xliv.