208 HISTORY OF THE EUROPEAN FAUNA. 



alone to the Siberian migration. In the case of the 

 Arctic one, precisely the same thing has happened, 

 and we shall see that the Southern (migration from 

 the south) agrees in this respect with the others. 



As for the immediate cause of these migrations, it is 

 to be looked for either in the scarcity of food dependent 

 upon a temporary or permanent change of climate, or 

 in an excessive increase in numbers of a particular 

 species. I do not propose to trace back migrations 

 beyond the Pliocene Epoch, or indeed much beyond 

 the beginning of the Glacial period, which is regarded 

 as a phase of the most recent geological epoch, viz., 

 the Pleistocene. During the period in question, we 

 have indirect evidence of one vast migration from 

 Siberia into Europe across the lowlands lying to the 

 north of the Caspian and to the south of the Ural 

 Mountains. There is a general consensus of opinion 

 that this migration took place in Pleistocene times. 

 Professor Nehring thinks that there can be no doubt 

 (p. 222) that the Siberian migrants arrived in 

 Northern Germany after the first stage or division 

 of the Glacial period, and lived there probably 

 during the inter-glacial phase which occurred be- 

 tween the first and second stages if indeed we look 

 upon this period as being divisible into two distinct 

 stages. 



Judging from the evidence of distribution of 

 mammals in pleistocene Europe, Professor Boyd 

 Dawkins came to the conclusion (p. 113) that the 

 climate of our continent "was severe in the north 



