THE SIBERIAN MIGRATION. 



to Mr. Clement Reid (p. 186), are at present living 

 in Norfolk, six are extinct, two are continental 

 forms living in the same latitudes as Norfolk, and the 

 other three are all southern forms. Not a single 

 species has a particularly northern range. Of the 

 land and freshwater mollusca of the South of Eng- 

 land in the succeeding pleistocene deposits, six 

 species are now no longer living in the British 

 Islands, but only one (Helix ruderata) can be looked 

 upon as an Arctic or Alpine form. After this short 

 digression on the mollusca, I will briefly recapitulate 

 what is known about the early history of the Siberian 

 mammals, which will assist us in tracing the cause of 

 their migration to Europe. 



We have in Siberia problems quite as difficult of 

 solution as the European ones. Volumes have been 

 written to explain the former presence of Arctic 

 mammals like the Reindeer in Southern Europe, and 

 the most extraordinary demands on the credulity of 

 the public have been made by some geologists in 

 their attempts to account for this comparatively simple 

 problem. In Northern Asia a somewhat similar 

 phenomenon, but much more difficult of explanation, 

 has taken place. Mammals have been found fossil in 

 recent geological deposits in localities where they do 

 not now occur, and apparently the Siberian and the 

 European deposits are of about the same age. Now, 

 however, comes the extraordinary difference. In 

 Europe the Arctic mammals went southward, but 

 in Siberia the Southern ones went northward. Not 



