The Student's Elements of Geology Part 17

In 1860, Professor Malaise, of Liege, explored with me this same cave of Engihoul, and beneath a hard floor of stalagmite we found mud full of bones of extinct and recent animals, such as Schmerling had described, and my companion, persevering in his researches after I had returned to England, extracted from the same deposit two human lower jaw-bones retaining their teeth. The skulls from these Belgian caverns display no marked deviation from the normal European type of the present day.

The careful investigations carried on by Dr. Falconer, Mr. Pengelly, and others, in the Brixham cave near Torquay, in 1858, demonstrated that flint knives were there imbedded in such a manner in loam underlying a floor of stalagmite as to prove that man had been an inhabitant of that region when the cave-bear and other members of the ancient post-pliocene fauna were also in existence.

The absence of gnawed bones had led Dr. Schmerling to infer that none of the Belgian caves which he explored had served as the dens of wild beasts; but there are many caves in Germany and England which have certainly been so inhabited, especially by the extinct hyaena and bear.

A fine example of a hyaena's den was afforded by the cave of Kirkdale, so well described by the late Dr. Buckland in his Reliquiae Diluvianae. In that cave, above twenty-five miles north-north-east of York, the remains of about 300 hyaenas, belonging to individuals of every age, were detected. The species (Hyaena spelaea) has been considered by palaeontologists as extinct; it was larger than the fierce Hyaena crocuta of South Africa, which it closely resembled, and of which it is regarded by Mr. Boyd Dawkins as a variety. Dr.

Buckland, after carefully examining the spot, proved that the hyaenas must have lived there; a fact attested by the quant.i.ty 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.

AUSTRALIAN CAVE-BRECCIAS.

Ossiferous breccias are not confined to Europe, but occur in all parts of the globe; and those 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 were examined by the late Sir T. Mitch.e.l.l in the Wellington Valley, about 210 miles west of Sidney, on the river Bell, one of the princ.i.p.al 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 stalact.i.te. 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 belong to marsupial animals. Among the most abundant are those of the kangaroo, of which there are four species, while others belong to the genera Phascolomys, the wombat; Dasyurus, the ursine opossum; Phalangista, the vulpine opossum; and Hypsiprymnus, the kangaroo-rat.

(FIGURE 91. Part of lower jaw of Macropus atlas. Owen. A young individual of an extinct species.

a. Permanent false molar, in the alveolus.)

(FIGURE 92. Lower 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. Figure 91 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 Figure 92. In both these specimens part of the substance of the jaw has been broken open, so as to show the permanent false molar (a, Figure 91), 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.

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 organisation 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 times immediately antecedent to our own, namely, that the present geographical distribution of organic FORMS dates back to a period anterior to the origin of existing SPECIES; in other words, the limitation of particular genera or families of quadrupeds, mollusca, etc., to certain existing provinces of land and sea, began before the larger part of the species now contemporary with man had been introduced into the earth.

Professor 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 characterise 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 a.n.a.logous to the living sloth, armadillo, cavy, capybara, and llama. The fossil quadrumana, also a.s.sociated 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 sh.e.l.ls, agreeing with those now inhabiting the Atlantic.

The law of geographical relations.h.i.+p 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 Kiwi by the natives (Apteryx).

In the fossils of the Post-pliocene 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 four, some seven, others nine, and others eleven feet in height! It seems doubtful whether any contemporary mammalia shared the land with this population of gigantic feathered bipeds.

Mr. Darwin, when describing the recent and fossil mammalia of South America, has dwelt much on the wonderful relations.h.i.+p of the extinct to the living types in that part of the world, inferring from such geographical phenomena that the existing species are all related to the extinct ones which preceded them by a bond of common descent.

CLIMATE OF THE POST-PLIOCENE PERIOD.

The evidence as to the climate of Europe during this epoch is somewhat conflicting. The fluviatile and land-sh.e.l.ls are all of existing species, but their geographical range has not always been the same as at present. Some, for example, which then lived in Britain are now only found in Norway and Finland, probably implying that the Post-pliocene climate of Britain was colder, especially in the winter. So also the reindeer and the musk-ox (Ovibos moschatus), now inhabitants of the Arctic regions, occur fossil in the valleys of the Thames and Avon, and also in France and Germany, accompanied in most places by the mammoth and the woolly rhinoceros. At Grays in Ess.e.x, on the other hand, another species both of elephant and rhinoceros occurs, together with a hippopotamus and the Cyrena fluminalis, a sh.e.l.l now extinct in Europe but still an inhabitant of the Nile and some Asiatic rivers. With it occurs the Unio littoralis, now living in the Seine and Loire. In the valley of the Somme flint tools have been found a.s.sociated with Hippopotamus major and Cyrena fluminalis in the lower-level Post-pliocene gravels; while in the higher-level (and more ancient) gravels similar tools are more abundant, and are a.s.sociated with the bones of the mammoth and other Post-pliocene quadrupeds indicative of a colder climate.

It is possible that we may here have evidence of summer and winter migrations rather than of a general change of temperature. Instead of imagining that the hippopotamus lived all the year round with the musk-ox and lemming, we may rather suppose that the apparently conflicting evidence may be due to the place of our observations being near the boundary line of a northern and southern fauna, either of which may have advanced or receded during comparatively slight and temporary fluctuations of climate. There may then have been a continuous land communication between England and the North of Siberia, as well as in an opposite direction with Africa, then united to Southern Europe.

In drift at Fisherton, near Salisbury, thirty feet above the river Wiley, the Greenland lemming and a new species of the Arctic genus Spermophilus have been found, along with the mammoth, reindeer, cave-hyaena, and other mammalia suited to a cold climate. A flint implement was taken out from beneath the bones of the mammoth. In a higher and older deposit in the vicinity, flint tools like those of Amiens have been discovered. Nearly all the known Post-pliocene quadrupeds have now been found accompanying flint knives or hatchets in such a way as to imply their coexistence with man; and we have thus the concurrent testimony of several cla.s.ses of geological facts to the vast antiquity of the human race. In the first place, the disappearance of a great variety of species of wild animals from every part of a wide continent must have required a vast period for its accomplishment; yet this took place while man existed upon the earth, and was completed before that early period when the Danish sh.e.l.l-mounds were formed or the oldest of the Swiss lake-dwellings constructed. Secondly, the deepening and widening of valleys, indicated by the position of the river gravels at various heights, implies an amount of change of which that which has occurred during the historical period forms a scarcely perceptible part. Thirdly, the change in the course of rivers which once flowed through caves now removed from any line of drainage, and the formation of solid floors of stalagmite, must have required a great lapse of time. Lastly, ages must have been required to change the climate of wide regions to such an extent as completely to alter the geographical distribution of many mammalia as well as land and fresh-water sh.e.l.ls. The 3000 or 4000 years of the historical period does not furnish us with any appreciable measure for calculating the number of centuries which would suffice for such a series of changes, which are by no means of a local character, but have operated over a considerable part of Europe.

RELATIVE LONGEVITY OF SPECIES IN THE MAMMALIA AND TESTACEA.

I called attention in 1830 to the fact, which had not at that time attracted notice, that the a.s.sociation in the Post-pliocene deposits of sh.e.l.ls, exclusively of living species, with many extinct quadrupeds betokened a longevity of species in the testacea far exceeding that in the mammalia.

(Principles of Geology 1st edition volume 3 page 140.) Subsequent researches seem to show that this greater duration of the same specific forms in the cla.s.s mollusca is dependent on a still more general law, namely, that the lower the grade of animals, or the greater the simplicity of their structure, the more persistent are they in general in their specific characters throughout vast periods of time. Not only have the invertebrata, as shown by geological data, altered at a less rapid rate than the vertebrata, but if we take one of the cla.s.ses of the former, as for example the mollusca, we find those of more simple structure to have varied at a slower rate than those of a higher and more complex organisation; the Brachiopoda, for example, more slowly than the lamellibranchiate bivalves, while the latter have been more persistent than the univalves, whether gasteropoda or cephalopoda. In like manner the specific ident.i.ty of the characters of the foraminifera, which are among the lowest types of the invertebrata, has outlasted that of the mollusca in an equally decided manner.

TEETH OF POST-PLIOCENE MAMMALIA.

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 quadrupeds 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 princ.i.p.al divisions of the mammalia by the forms and characters of their teeth.

Figures 93 through 105 represent the teeth of some of the more common species and genera found in alluvial and cavern deposits.

(FIGURE 93. Elephas primigenius (or Mammoth ); molar of upper jaw, right side; one-third of natural size. Post-pliocene.

a. Grinding surface.

b. Side view.)

(FIGURE 94. Elephas antiquus, Falconer. Penultimate molar, one-third of natural size. Post-pliocene and Pliocene.)

(FIGURE 95. Elephas meridionalis, Nesti. Penultimate molar, one-third of natural size. Post-pliocene and Pliocene.)

(FIGURE 96. Rhinoceros leptorhinus, Cuvier-- Rhin. megarhinus, Christol; fossil from fresh-water beds of Grays, Ess.e.x; penultimate molar, lower jaw, left side; two-thirds of natural size. Post-pliocene and Newer Pliocene.)

(FIGURE 97. Rhinoceros tichorhinus; penultimate molar, lower jaw, left side; two-thirds of natural size. Post-pliocene.)

(FIGURE 98. Hippopotamus; from cave near Palermo; molar tooth; two-thirds of natural size. Post-pliocene.)

(FIGURE 99. Horse. Equus caballus, L. (common horse); from the sh.e.l.l-marl, Forfars.h.i.+re; second molar, lower jaw. Recent.

a. Grinding surface, two-thirds natural size.

b. Side view of same, half natural size.)

(FIGURE 100. Deer.

Moose (Cervus alces, L.); recent; molar of upper jaw.

a. Grinding surface.

b. Side view, two-thirds of natural size.)

(FIGURE 101. Ox.

Ox, common, from sh.e.l.l-marl, Forfars.h.i.+re; true molar, upper jaw; two-thirds natural size. Recent.

c. Grinding surface.

d. Side view, fangs uppermost.)

(FIGURE 102. Bear.

a. Canine tooth or tusk of bear (Ursus spelaeus); from cave near Liege.

b. Molar of left side, upper jaw; one-third of natural size. Post-pliocene.)

(FIGURE 103. Tiger.

c. Canine tooth of tiger (Felis tigris); recent.

d. Outside view of posterior molar, lower jaw: one-third of natural size.

Recent.)

(FIGURE 104. Hyaena spelaea, Goldf. (variety of H. crocuta); lower jaw.

Kent's Hole, Torquay, Devons.h.i.+re; one-third natural size. Post-pliocene.)

(FIGURE 105. Teeth of a new species of Arvicola, field-mouse; from the Norwich Crag. Newer Pliocene.

a. Grinding surface.

b. Side view of the same.

c. Natural size of a and b.)