THE ARCTIC FAUNA. l8l 



intercalation of perfectly stratified sands and gravels 

 and of boulder-clay, as well as the not infrequent 

 signs of bedding in the latter. Two divisions are 

 generally recognisable in the continental boulder-clay 

 a lower and an upper. An inter-glacial phase 

 characterised by a less severe climate is assumed 

 to have intervened between the deposition of the 

 two. In Russia no such division can as a rule be 

 made out, and sea-shells are either entirely absent or 

 extremely scarce. It has been pointed out by Pro- 

 fessor J. Geikie that the erratics a name applied to 

 boulders in boulder-clay in the upper division have 

 travelled in a different direction from those contained 

 in the lower. Taking for granted that the boulder- 

 clay is a marine deposit, this phenomenon seems 

 to indicate that the current which prevahed during 

 the early part of the Glacial period in this North 

 European ocean was different from the prevailing 

 current during the latter part. I have attempted 

 to explain this circumstance by the supposition 

 that during the early part of the Glacial period 

 the Northern Sea had a connection with the Ponto- 

 Caspian Sea a sea formed by the junction of the 

 Black Sea and the Caspian (Fig. 12, p. 156). There 

 is geological evidence, as will be explained in the 

 following chapter, that the area of these two seas was 

 considerably larger in glacial times than it is now, 

 and that they were joined across the valley of the 

 Manytch. After the inter-glacial phase of the Glacial 

 period, the North European Ocean became connected 



