AECTIC EUSSIA. 



345 



nmuiug north-west and south-east parallel with those scored on the rocks of 

 Finland and Olonetz. 



The uplands sepiratiug- the Volga and arctic basins still bear the traces of the 

 frozen masses by which they were fornierl}^ covered. As thé}^ gradually melted, 

 these glaciers formed the fresh-water lakes now filling all the hollows of the 

 land, and which formerly rose 60 or 70 feet above their present level. This 



Fig. 182. — Northern Urals. 

 Scale 1 : 3,600,OCO. 



E ofP 



59°|40' 



63 40' 



E of G 



20 Miles. 



region seems never to have been invaded by the sea, so that during recent epochs 

 no communication can have existed between the Baltic and the Arctic Ocean, as 

 was at one time supposed. The seas were, however, indirectly connected by a laby- 

 rinth of lakes and rivers sufficiently to account for the exchange of fishes and 

 Crustacea which h;is taken place between the two marine basins. In this way the 

 inland waters may have also been colonised by the Phoca ritulina, a species of seal 

 109 



