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Siwalik deposits lying along the foot of the Himalayas. These beds, especially the latter, contain the remains of an extensive and exceedingly interesting Mammalian fauna, which has hitherto been very inadequately explored, and will probably afford abundant opportunities of discovery to the palæontologist of the future.
The number of genera hitherto discovered in these formations amounts in all to about sixty, of which thirtynine are still in existence, while twenty-five are extinct. Among the recent genera are a considerable number which, though still occurring in Africa, have become extinct in the Oriental Region; such are Bubalis, Cobus, Oreas, and Strepsiceros—all genera of antelopes, Giraffa (the Giraffe), Hippopotamus, Locodon (the African Elephant), Cynocephalus (the African Baboon), and Anthropopithecus (the Chimpanzee), while others still survive in India.
The most remarkable feature, however, of the Siwalik fauna is the fact that, while certain of the genera are only found in Miocene beds in Europe, and not in more recent deposits, the greater number are only known, out of India, from the Pliocene and Pleistocene, so that it is very difficult to fix the age of the Siwaliks as compared with the formations of Europe.
Beds containing a somewhat similar fauna, in most cases not so rich, have been discovered in Greece, near Athens, in Samos, and in one or two other localities, at least, in South-Western Europe; while north of the Alps nothing of the sort has been found of a corresponding age. The most plausible explanation of the whole matter, therefore, so far as we can say at present, is that the increasing cold at the end of the Miocene and the beginning of the Pliocene times gradually drove the
northern inhabitants southwards. It thus came to pass that, at that period of the world's history, the Mammalian faunas of Southern Europe, South-Eastern Asia, and of India were so nearly uniform as to constitute these countries, as regards their mammals, one widely extended Region.
LIST OF THE PRINCIPAL AUTHORITIES REFERRED TO IN CHAPTER V.
(1) MILNE-EDWARDS, H. ET A.—“Recherches pour servir à l'histoire naturelle des Mammifères." Paris, 1868.
(2) BLANFORD, W. T._“The Fauna of British India : Mammalia,” London, 1888–91.
(3) OLDHAM, R. D.—“Manual of the Geology of India.” Calcutta, 1893.
THE NEARCTIC REGION
(PLATE VI, p. 176)
SECTION I.-BOUNDARIES OF THE NEARCTIC REGION
With the Nearctic Region we enter upon a subject on which there has been a great deal of controversy among the students of geographical distribution. As was pointed out in the introductory article of this volume, a certain number of writers maintain that this Region does not contain a sufficient quantity of distinctive and indigenous forms to entitle it to separation from the Palearctic Region. What should constitute a sufficient number of distinctive forms depends, of course, largely on the individual opinions of the writers, but if allowance be made for the undoubted similarities of the extreme northern parts of the Old and New Worlds, which together may be considered as forming a kind of intermediate district, the facts and figures given below will, we think, convince every one that the land-surfaces of the Palæarctic and Nearctic Regions have now, and have had in the past, quite sufficiently distinct faunas to warrant their division into two primary Regions.
The boundaries of the Nearctic Region are comparatively simple. They embrace the whole of North America as far as the southern limit of the tableland of Mexico, with which Greenland may be included. On either side of