THE SIBERIAN MIGRATION. 



225 



sheet in Northern Europe during the Glacial period, 

 such a connection must either have been pre-glacial 

 or have existed after that period. But the connec- 

 tion must have occurred at a time when the Caspian 



FIG. 17. Map of European Russia (after Karpinski). The faintly 

 dotted parts indicate the areas covered by boulder-clay, the 

 strongly dotted ones those exhibiting Aralo-Caspian and other 

 post-pliocene deposits. 



extended far to the north when indeed the so-called 

 post-tertiary Caspian deposits were laid down (Fig. 

 17). Since the boulder-ciay which covers the plain 

 of Northern Russia is assumed to be the ground- 



15 



