GEOLOGY OF ARCTIC EURASIA 85 



Frozen Soil and Ground Ice 



The ground of Arctic Eurasia is usually frozen many tens and even 

 some hundreds of feet deep. During the summer it thaws only i to 

 3 feet down. Frozen ground gives Arctic Eurasia its typical ap- 

 pearance and in summer turns the tundras into swamps covered with 

 many small lakes. This effect is brought about in spite of the fact 

 that the climate is often very dry. The amount of precipitation in 

 northeastern Asia corresponds, for example, very closely to that of 

 the Transcaspian region with its dry steppes and desolate deserts. 

 The frozen ground in many places contains small lenticles and even 

 large layers of ground ice, called also rock ice. Many theories have 

 been devised to explain this phenomenon. Each one serves to explain 

 some particular case, but none has a universal application. Undoubt- 

 edly the origin of rock ice is dependent upon climatic conditions, as 

 the origin of frozen ground itself, and this form of ice can develop 

 only on the land. Present climatic conditions have existed in the 

 country for a long time, therefore rock ice may be very old in some 

 outcrops, comparatively very young in others. For example, some 

 outcrops of ice on the New Siberian Islands are covered with sediments 

 of the Boreal transgression. Frozen ground has attained its greatest 

 development in northeastern Asia, where at Yakutsk it has been dis- 

 covered, in a pit, extending down 382 feet from the surface. Perhaps 

 it may be brought into connection with the absence of Boreal trans- 

 gression in eastern Asia as well as with the absence of a glacial cover, 

 as mentioned above. Thus for a long time it had uninterrupted 

 conditions of extremely severe climate as at present. 



Mammoth and Other Remains 



The frozen ground of northern Siberia is famous on account of the 

 well-preserved corpses of mammoth, rhinoceros, and other extinct 

 animals found within it in quite unusual conditions. Remnants of 

 mammoth are so common in Siberia that there is a regular ivory in- 

 dustry which gives a quite decent income to local hunters and makes an 

 important item of trade and export. The remnants are found in 

 many places in Arctic Eurasia, but real ivory "mines" are worked 

 chiefly on the New Siberian Islands and on the neighboring shores 

 of the mainland. The remnants of other post-Tertiary mammals 

 have also been found there abundantly. Although there has been 

 much speculation as to the conditions in which these animals dwelt 

 on the islands, it appears to be probable that, to a great extent, they 

 were brought there by the same rivers which delivered silt for the 

 building up of the islands themselves. The island localities would be 

 therefore mostly (but certainly not exclusively) secondary, and more of 



