OF THE SPREAD OF THE EUROPEAN FAUNA. 



113 



to Arctic migration, but of fishes Dr. Scharff regards the salmon 

 family, the sticklebacks, the perches, many of the cod family, 

 the herrings, and several flat-fish as of Arctic origin. 



The ISTorth-Easterx Immigrants. 



The last great faunal invasion of the European area followed 

 the retreat of the early Glacial sea and the establishment of 

 land conditions extending from the east of Asia to the west of 

 Europe northwards of the Caspian Sea. This has been called 

 the Siberian migration, but as a large portion of Western 

 Siberia had been under water, and the animals w ere, from the 

 more eastern area of central and northern Asia, I prefer to 

 •designate them the Xorth-Eastern immigrants. 



Impelled probably by search for food, the newly established 

 land communication determined the route of the migrants along a 

 zone due west to Central and Western Europe from the north of 

 the Caspian Sea, to the south of which lay the route of the 

 previous great migration of Asiatic animals which I have called 

 the South-Eastern Immigration. The route of the second Asiatic 

 immigration is very clearly indicated not only by the identity 

 of living species in Eastern, Central and Western Europe with 

 Xorthern, Central and Eastern Asiatic species, and their absence 

 from the more northern and the more southern parts of our 

 continent, but also by the fossil remains in the Post-Glacial 

 deposits of a long and broad zone stretching westwards from 

 Siberia across Europe midway between north and south. 



Some of the immigrants prolonged their journey until they 

 readied as far westwards as what is now England, demonstrating 

 the land connection of this country with the continent then 

 existing, and the more recent cutting through of the Straits of 

 Dover. But these species are not, with one or two exceptions 

 found in Ireland, demonstrating also that although England was 

 joined to continental land, Ireland was then, as now, separated 

 by a sea which prevented the further migration of these eastern 

 animals. 



Thus it is found that the very interesting difference between 

 the fauna of Great Britain and that of Ireland produced by 

 earlier migrations was increased and intensified by this later 

 immigration of iSTorthern Asiatic species. By these considera- 

 tions we have an explanation of the absence from Ireland of 

 many British animals, amongst which may be named the 

 beaver, the dormouse, the common hare, the mole {Talpa 

 curopcca), the shrew (Sorex vulgaris), all lizards, all snakes, all 



