134 G. F. WRIGHT — LOESS IN NORTHERN CHINA AND CENTRAL ASIA 



It is possible that this remarkable gravel deposit, which certainly 

 covers several square miles, is the delta of some old drainage line from 

 the interior which has been covered by the basaltic flow now extending 

 all along the edge of the border ; but it is more readily explained as a 

 shoreline deposit of recent age when the water stood at that level.' What 

 lends some color to this hypothesis is that the accumulation projects 

 from what would have been the apex of a broad promontory extending 

 into the sea where cross-currents coming down from the valleys on the 

 northeast and the northwest would be likely to meet. 



Absence of glacial Evidence in Region northwest of Kalgan 



But, whatever theory is entertained as to the distribution of the loess 

 and gravel at these elevations, its glacial origin can not be maintained, 

 since there is a marked absence of all signs of glaciation over the area 

 from which the material must have come. This we ascertained not only 

 by an extensive detour into the mountainous region to the northwest of 

 Kalgan, extending over the watershed of the Mongolian border, but sub- 

 sequently by one of 2,000 or 3,000 miles through the center of Manchuria 

 across the Little Kinghan mountains and the Vitim plateau to the south 

 end of lake Baikal. Here, if anywhere in eastern Asia, we had been led 

 to look for clear evidences of extensive glacial action, but it does not 

 exist, and no extensive glaciers ever covered that portion of the Asiatic 

 continent which could by any stretch of the imagination be supposed to 

 furnish the material for the loess in northwestern China. We must 

 therefore look to some other source for its origin. 



Wind and Water combined as distributing Agencies 



The source of the loess is probably to be found, as Richtofen pointed 

 out, in the desiccated area of central Mongolia now occupied by the desert 

 of Gobi. Here during long ages the superficial rocks have been slowly 

 disintegrating under the conditions of an exceedingly dry climate, accom- 

 panied with great alternations of heat and cold, while the wind has been 

 constantly transporting it in clouds of dust toward the eastern and north- 

 eastern borders, where it has been detained in excessive quantity in the 

 moister climate of the mountain valleys lying east of the Mongolian 

 escarpment. 



But it seems necessary, from the facts presented, to believe that its 

 present distribution over northwestern China was mainly secured by the 

 agency of gradually receding water, the presence of which would be 

 obtained by a temporary general depression of the land about 3,000 feet. 



