CHAP, vi.] RANGE OF LATE PLEISTOCENE MAMMALS. 153 



the remains of which happen to have been preserved, in 

 spite of the erosion of the surface by the glaciers and the 

 dash of the waves on the sea-shore, during the repeated 

 depressions and elevations of the land described in the 

 last chapter. 



The presence of the late Pleistocene mammalia in the 

 river deposits later than the boulder clays as far as the 

 North Eiding of Yorkshire, proves that they were in 

 Britain after the land had been elevated above the sea, 

 in which the icebergs had deposited their burdens of 

 upper boulder clay in the midland and northern counties. 

 They were, however, living in the south of England and 

 in France, while the boulder clays and marine sands 

 were being accumulated in the area north of London and 

 Bristol. As this rose above the sea, they gradually 

 passed farther north, and it is very probable that they 

 were prevented from invading Ireland and Scotland by 

 a barrier of sea, and that the higher parts of the country 

 were rendered inaccessible by the glaciers, as yet un- 

 melted. 



Thus we may picture to ourselves southern and 

 eastern Britain as inhabited by an abundant mammalian 

 fauna during the last phase of the Pleistocene age ; * 

 while ice and sea acted as barriers to the free migration 

 which afterwards took place over the whole country in 

 the Prehistoric age. We must further realise that all 

 the climatal and geographical changes, known as glacial, 

 happened while the late Pleistocene mammalia were 

 living in the regions not covered by glaciers or over- 

 whelmed by sea, and that they wandered to and fro as 

 the barriers to their migration were altered. The glacial 

 period did not define one fauna from another, and the 

 only mark it made on the mammalian life was to push 



