254 ATLANTIC CLOSED ON THE NORTH. 



tuents of our present Atlantic fauna are not met 

 with in the older fauna of the Faluns, nor in the 

 equivalent assemblages further south. Northern 

 forms had not, at that time, extended into that part 

 of the Atlantic which lies west and south of the 

 British Islands. Their great migration southwards 

 took place subsequently to those great physical 

 changes, which converted into dry land those por- 

 tions of western France above referred to, and 

 which changes were trifling in amount when com- 

 pared with those of the same date in other parts of 

 the Atlantic, and within the Mediterranean area. 



The physical change which liberated the northern 

 fauna has been indicated on independent considera- 

 tions. It has been shown (p. 56) that there is 

 good evidence of the former continuity of a coast- 

 line from the north of Greenland to the north of 

 Lapland, and that, consequently, the Atlantic did 

 not then communicate with the Arctic basin ; it 

 was only when this barrier was removed that a free 

 passage south was opened out to Arctic forms. 



The breadth of this connecting link between the 

 Old "World and the New extended, probably, from 

 70° to 75° north latitude, and completed in its 

 northern coast-line the symmetrical form of the 

 Arctic basin. Sir John Richardson was the first to 

 suggest both the existence and the date of this con- 

 nection, in order to account for the remarkable agree- 

 ment which the Boreal regions of the two continents 

 present in their vertebrate fauna. In the small 



