xv The Continental Area 297 



the few rivers which flow into it from the surrounding 

 mountains end in the sand or in small salt lakes, and the 

 process of desiccation seems still going on. Rising on the 

 western slope of the Khingan with tributaries from the 

 eastern slope of the Yablonoi, the great Amur River cuts 

 through the Khingan Chain and several parallel ranges, 

 and finds its way into the Pacific. 



382. Northern Low Plain. The Tian Shan and 

 other northern mountains descend in terraces to a narrow 

 belt of undulating land about 1000 feet in elevation, which 

 sinks into the wide low plain less than 600 feet above the 

 sea. Lake Balkash, without outlet and intensely salt, 

 occupies a depression north of the Tian Shan, from which 

 it receives several rivers, but its area is steadily diminishing 

 by evaporation. Lake Baikal ( 333), to the north-east 

 at a higher level, receives much water from the Altai and 

 surrounding heights, but its outflow is comparatively 

 trifling. The northern plain bears evidence in its gravel 

 beds of having emerged from the sea in the Quaternary 

 period, and the gradual desiccation of Asia probably dates 

 from the time when its upheaval cut off from the interior 

 the tempering influence of the sea. Three vast rivers, only 

 matched for length of course and area of basin by the 

 giant streams of Africa and America, flow from the moun- 

 tains across the plain to the Arctic Sea during the few 

 months when they remain unfrozen. The Lena, farthest east, 

 rising near Lake Baikal, terminates in a wide delta. The 

 Yenisei flows due north from the Sajan Mountains, and re- 

 ceives no considerable tributaries on its left bank, but the 

 Angara, from Lake Baikal, and the two Tunguskas flowing 

 from the east, join on its right bank. The Ob and Irtish 

 flowing north from the Altai unite, and after receiving tribut- 

 aries from the eastern slope of the Urals, enter the head of a 

 long narrow gulf of the Arctic Sea. From the Pamir the Amu 

 Daria and Syr Daria (Oxus and Jaxartes) flow across the 

 desert low plain, rapidly dwindling by evaporation, to Lake 

 Aral, the area of which is shrinking. In the time of the 

 early Greek geographers the Oxus swerved to the west and 

 entered the Caspian, and its old bed, from which it seems 



