PRELIMINARY CONSIDERATIONS. 63 



it, the main features of the great migrations ; and I 

 have before now expressed the opinion that the 

 British fauna forms the key to the solution of the 

 problem of the origin of European animals. W T e 

 know that our British species came to us by land 

 at least the bulk of them. But we want to 

 know what direction they came from, and at what 

 time they arrived. When Ireland became discon- 

 nected from Great Britain, and the latter from 

 Scandinavia and France, is another interesting 

 problem. Professor Boyd Dawkins has indicated 

 to us a method of the special line of research to 

 meet such inquiries. " The absence," he says (b y 

 p. xxix), " of the beaver and the dormouse from Ire- 

 land must be due to the existence of some barrier 

 to their westward migration from the adjacent main- 

 land, and the fact that the Alpine hare is indi- 

 genous, while the common hare is absent, implies 

 that, so far as relates to the former animal, the barrier 

 did not exist." 



Many members of the great Siberian invasion 

 reached England, but Ireland remained entirely 

 free from these migrants. The assumption there- 

 fore seems not unreasonable, that the latter country 

 at the time of their arrival was no longer joined 

 to England. The great bulk of the Irish fauna 

 is composed of Lusitanian, Alpine, and Oriental 

 immigrants, and there is besides a distinctly Arctic or 

 North American element. All these, of course, must 

 have established themselves in Ireland before the 



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 IWIVE T R*SITY 



