XXX VI INTUOWUCTION. 



Britain, the discrepancy between the pliocene extinct and 

 the existing groups of Mammalia appears to be extreme. 

 But if we regard Great Britain in connection with the 

 rest of Europe, and if we extend our view of the 

 geographical distribution of extinct Mammals beyond 

 the limits of technical geography, and it needs but a 

 glance at the map to detect the artificial character of 

 the line which divides Europe from Asia, we shall then 

 find a close and interesting correspondence between the 

 extinct Europseo- Asiatic Mammalian Fauna of the plio- 

 cene period, and that of the present day. The very fact 

 of the pliocene Fossil Mammalia of England being almost 

 as rich in generic and specific forms as those of Europe, 

 leads, as already stated, to the inference that the inter- 

 secting branch of the ocean which now divides this island 

 from the continent did not then exist as a barrier to the 

 migration of the Mastodons, Mammoths, Ehinoceroses, 

 Hippopotamuses, Bisons, Oxen, Horses, Tigers, Hyaenas, 

 Bears, &c., which have left such abundant traces of their 

 former existence in the superficial deposits and caves 

 of Great Britain.*' Now, it is a most interesting fact, 

 that, in the Europseo-Asiatic expanse of dry land, 

 species continue to exist of nearly all those genera which 

 are represented by pliocene and post-pliocene Mammalian 

 fossils of the same natural continent and of the imme- 

 diately adjacent island of Great Britain. The Bear has 

 its haunts in both Europe and Asia ; the Beaver of the 

 B/hone and Danube represents the great Trogontherium ; 

 the Lagomys and the Tiger exist on both sides of the 

 Himalayan mountain chain ; a Hysena ranges through 



* Mr. Lyell infers the former existence of an isthmus between Dover and 

 Calais on other grounds. See his Memoir on the relative ages of the " Crag " 

 of Norfolk and Suffolk. Mag. Nat. Hist. 1839, p. 326. 



