xrv 



DISTRIBUTION 



603 



The reason of this remarkable contrast is not far to seek. 

 Geologically speaking, Great Britain is a recently detached portion 

 of Europe, having been united with it during the latter part of 

 the Glacial period (Pleistocene), and, at the present moment, an 

 elevation of the bed of the English Channel to the amount of 

 feet would bring about a re-union (Fig. 1251). Prior to this 



i\o 



65 



50 



1(0 



FlQ. 1251. Map showing the shallow bank connecting the British Isles with 

 the continent. The light shade indicates a depth of less than 100 fathoms ; 

 the figures show the depth in fathoms. (From Wallace.) 



union, moreover, it was largely submerged, so as to leave no trace 

 of its Pliocene fauna. Thus, the British animals are all migrants 

 from Europe, isolated by the post-glacial separation from Europe, 

 and the absence of certain European forms is due to the fact that 

 the separation took place too early to allow of complete migration. 

 New Zealand, on the other hand, instead of being separated from 



