THE SIBERIAN MIGRATION. 221 



northern regions during the earlier portion of the 

 succeeding epoch. It was only after the marine 

 connection above referred to ceased to exist, or 

 became disconnected, that an entry into Europe 

 was possible. 



A fauna, to some extent composed of species now 

 inhabiting the steppes of Eastern Europe and Siberia, 

 poured into the neighbouring continent. On p. 95 I 

 have given a list of those which reached as far west 

 as the British Islands, but, as I mentioned, many 

 other species came from the east about this time. 

 With regard to the early history of the Siberian 

 mammals, I favour a view somewhat between that 

 of Tcherski and that of Brandt. The outpouring of 

 the fauna into Europe seems to me to indicate that 

 there was a sudden change of climate in Siberia. 

 This was produced, perhaps, by the rupture of the 

 marine connection between the Arctic Ocean and 

 the Aralo-Caspian. Such an event would not only 

 have caused the sudden shrinkage of the area avail- 

 able for food-supply by lowering the temperature in 

 Siberia, it would have acted also as a means in 

 assisting the fauna to enter a new continent where 

 an inconsiderable number of mammals, already estab- 

 lished, were mostly dispossessed of their homes by the 

 advancing eastern host. 



Brandt's theory, however, of a marine connection 

 between the Arctic Ocean and the Aralo-Caspian is 

 by no means generally accepted. That the Caspian 

 Sea was at that time greatly larger than it is at 



