ScHARFF — On the Origin of the Eui'opean Fauna. 445 



A marine expansion from the "White Sea then spi'ead across Northern 

 Hussia into the North European plains, and the sea thus formed, which 

 I propose to call the North European Sea, joined the united basins of 

 the Aralo-Caspian and Black Seas. The Siberian fauna was, therefore, 

 unable to enter Europe, while the more southern Central Asiatic 

 fauna continued to migrate into Southern Europe, as in Miocene and 

 early Pliocene times, by a land-connexion which Joined Asia Minor 

 and Greece. 



A gradual retreat of the North European Sea to the north opened up 

 a passage in Eastern Europe by which the Siberian fauna poured into 

 Central Russia, Germany, Erance, and England. (See fig. 5, 461.) There 

 is distinct geological evidence that this vast migration of the Siberian 

 fauna and flora occurred after the deposition of the lower continental 

 boulder-clay. The advance guard composed of Mammals arrived in 

 England during the deposition of the Eorest-bed. This marks, there- 

 fore, not only the time of the first retreat of the North European 

 Glacial Sea, but also that of the disconnexion of Engk\nd and Ireland, 

 since none of the Siberian Mammals entered the latter. 



Meanwhile the Central and South Asiatic Mammals, which, as I 

 mentioned, had rambled into Southern Europe, spread into Northern 

 Africa and Western Europe along the shores of the Mediterranean. 

 Many subsequently invaded Central Europe, and also spread north 

 into Great Britain and Ireland. These and the Arctic Mammals 

 mostly retired before the Siberian invaders. Hence the purely Arctic 

 species had also reached "Western and Central Europe before the 

 advent of the latter. 



The Siberian Migration. 



As my conclusions contain much with which many geologists will 

 probably disagree, I shall commence by making some statements, 

 which are universally acknowledged to be founded on reliable evidence. 



There is a general concurrence of opinion among geologists that 

 the climate of Europe in early Tertiary times was almost- tropical, 

 and that during the succeeding epochs the temperature became more 

 and more temperate, and at last intensely cold, culminating in the 

 Glacial Period, and that since that time the climate has again amelio- 

 rated. To quote Sir Archibald Geikie's words (34, p. 837) : " At 

 the beginning the climate was of a tropical and sub-tropical character, 

 even in the centre of Europe and North America. It then gradually 

 became more temperate, birt flowering plants and shrubs continued to 

 live even far within the Arctic Circle, where, then, as now, there 



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