420 THE ICE AGE IN NORTH AMERICA. 



testimony to the extent and effects of the dust storms in east- 

 ern Mongolia, where for a day at a time the dust raised by 

 the wind was so dense. that objects could not be distinguished 

 half way across the road. And I have described immense drifts 

 of loess near the summits of the mountains in that region five 

 thousand feet above the sea, where it was impossible to invoke 

 the agency of water to account for the accumulation. 



But the investigations of Huntington and others seem to 

 show that loess is not exclusively of glacial origin, but may 

 be the finer product of subaerial disintegration, such as is 

 going on all the while in desert regions such as exist in Central 

 Asia and in the Rocky Mountain plateau. Still, whatever 

 be the ultimate origin of the material, and however much 

 influence we may attribute to the wind in transporting it 

 from its original place of formation, water must be allowed 

 a large share in its final distribution, and its accumulation 

 belongs to a definite period corresponding to that of the glacial 

 period. It is perfectly evident to one who traverses the moun- 

 tainous region of eastern Mongolia that loess is not now 

 accumulating there through the agency of wind as fast as it 

 is being removed by water, and carried down to the lower 

 levels of the Yangtsi and Hoang rivers, and by them distrib- 

 uted along the shores of the Chinese Sea. At the same time 

 there are numerous level-topped areas of loess of great size 

 all over northwestern China which indicate deposition by 

 water. 



The same is true of the loess in the Mississippi and Mis- 

 souri valleys. While it is doubtless true that in many places 

 the accumulations are due to wind, it is equally evident that 

 there are many level-topped areas of loess along the borders 

 of the Missouri which betoken the height reached by the 

 overflowing floods of the stream when, as already shown, it 

 was gorged by silt-laden water from the melting ice in the 

 closing stages of the glacial period. Both wind and water 

 had their share in the distribution. The absence of true 



