and those which were living in the same area in the Pliocene age. The migration of the first two groups into Europe at the close of the Pliocene age throws a very great light on the ancient geography. Had not the animals which lived in Europe during the Pliocene age been insulated by some physical barrier from those which invaded Europe from Asia, the latter would occur in our Pliocene strata as well as the former, and we might have had the mammoth and the mastodon associated here as well as in North America. Such a barrier is offered by the northern extension of the Caspian along the low-lying valley of the river Obi; and that the Caspian has extended further north than now in comparatively modern times has been proved by Dr. Pallas. It is therefore very probable that this was the barrier which divided the Pliocene mammalia of Europe from those animals which were living at the time in Asia, and which subsequently passed into Europe. The animals of Northern and Central Asia could not pass westwards before this barrier was removed by the elevation of the sea-bottom between the Caspian sea and the southern portion of the Urals. When this took place the Musk-shrew, Lemming, Brown and Grizzly Bears, Mammoth, Woolly Rhinoceros, Musk-sheep, Reindeer, Stag, and Roe passed over into Europe[1], those of them which were fitted for a temperate or moderately warm climate, such as the Stag, Roe, Brown and Grizzly Bears, passing down to the extreme southwest, while the rest did not go further to the south than the Alps and Pyrenees. Then there must have been a continuous mass of land extending from Northern Asia to the margin of the Atlantic, which has been proved by Mr. Godwin -Austen and others to have passed from Scandinavia to the west of the present coast-line of Ireland, of the south of England, and of France. [See Map, p. 436.]
18. The Southern Extension of Europe.
The same argument may be based on the African mammalia. The African Elephant could not have found its way northwards to Spain and Sicily, or the Serval to Spain, or the Felis caffer to Britain without an extension of the African mainland, so as to allow of the migration; and the same may be said perhaps of the Spotted Hyæna, although this animal, so widely spread through Central and Southern Europe, may have arrived by way of Asia Minor, as well as by a direct line, passing through Sicily and Gibraltar. Nevertheless, as Dr. Falconer has remarked, the area of the Mediterranean must have been very much smaller than it is now during the time that Malta, Sicily, and Candia were inhabited by the Pleistocene mammalia. The presence of Hippopotamus Pentlandi in these three islands proves that they were connected during the life-time of the animal; and this mass of land would afford a passage northwards to the African mammalia. The objection which is offered by the depth of
- ↑ This is very nearly the same view as that held by Dr. Brandt, Imp. Acad. St. Petersb., 'Zoogeographische und Paläontographische Beitrage,' April 4, 1867. See also Lartet, 'Comptes Rendus,' tome lxvi. p. 409.
