84 POLAR PROBLEMS 



bution the sediments of Boreal transgression are confined chiefly to 

 river •valleys. In the most eastern isolated localities they are known 

 only in the Anadyr region, where they are of a distinctive Pacific 

 type. 



In Europe a Boreal transgression covered old moraines of the Scan- 

 dinavian ice sheet, and in the Scandinavian region deposits marking 

 the same transgressions are covered by moraines of the last glaciation. 

 Old moraines cover the whole of northern Europe and the northwestern 

 corner of Asia. The northern Ural region was probably an independent 

 glacial center. Old moraines built up Kolguev Island and probably 

 Little Taimyr Island (Tsesarevich Alexei Island). The largest part 

 of Arctic Asia did not have glaciers of a general Ice Age, although 

 in different parts of it there are indisputable records of former local 

 glaciation. The Ice Age phenomena did not acquire the sanie im- 

 portance as in Europe chiefly on account of the low relief of northern 

 Asia. The glacial deposits have therefore no importance here, and 

 continental drift is brought out chiefly by rivers, deposited in lakes 

 or more usually in the sea, and accumulated by waves near the shore. 

 Oscillations of the seashore have exposed large tracts of shallow sea 

 bottom with the result that huge areas of Arctic Eurasia are composed 

 of reworked drift. 



The time preceding the Boreal transgression, and more or less 

 corresponding to the greatest glaciation in Europe, in Arctic Asia was 

 the time of the highest emergence of the land or the deepest sinking 

 of the sea. During that time the great Siberian rivers had built up 

 huge deltas and accumulated abundant drift along the shore. At that 

 time the Yamal Peninsula probably originated; the New Siberian 

 Islands (then a portion of the mainland) were constructed, completely 

 or partially, of drift; and Bering Strait did not exist at all, north-, 

 eastern Asia and northwestern North America being joined together. 

 After that emergence a subsidence followed and was accompanied by 

 Boreal transgression. A new emergence has brought marine sediments 

 of Boreal type above the level of the sea. 



At the present time most of the shores of Arctic Eurasia are sub- 

 siding, but in some sections they are rising and in others standing still. 

 The recent alterations of the shore line are therefore dependent upon 

 the movement of the land itself; they are not an effect of the oscilla- 

 tion of the sea. The subsidence of the shore is proved here by the 

 overflowing of the lower parts of river valleys and the consequent 

 transformation of them into estuaries; by the presence of river chan- 

 nels on the bottom of the sea; by the discovery of rock ice below the 

 sea level; by the separation of islands, composed of drift, from the 

 mainland, a part of which they were but recently. 



