TEE LOESS. 419 



work of such animals as worms, crayfish, and ants. But these 

 creatures are limited in the depth to which they can pene- 

 trate the soil and convey it to the surface. Still, it is not im- 

 probable that in many places where the loess-like deposits are 

 shallow it may be the result of these agencies. 



The twenty years which have elapsed since this chapter 

 was written have been marked by continuous discussion of 

 this puzzling problem of the loess. But its solution seems still 

 about as far distant as ever. The Richthofen theory which 

 accounts for its accumulation and distribution by wind has 

 now more supporters than ever. But there is still a large 

 residuum of facts that resist explanation on that theory alone. 

 The loess of China has doubtless accumulated in the mountain- 

 ous region bordering on Mongolia through the agency of 

 wind, which has brought it in from the desert wastes which 

 stretch westward to the "roof of the World" in Central 

 Asia. But even so it is a question whether the material was not 

 ultimately of glacial origin. 



In the revised edition of Geikie's "Great Ice Age" it is rep- 

 resented that an ice field covered eastern Mongolia which would 

 presumably furnish the required glacial grist. But after the 

 demonstration that eastern Mongolia never supported ice 

 fields, the glacialists were compelled to resort to the theory 

 that the wind had brought the material across the desert of 

 Gobi, all the way from the base of the mountains, which on 

 three sides surround the Tarim Valley. Here during the 

 glacial period there was a great extension of glaciers in the 

 Pamir and in the Tian Shan and the Himalaya mountains. 

 It is to the floods pouring from the fronts of these glaciers that 

 some would look for the supply of loess which the winds 

 have brought into the mountain border of eastern Mongolia. 

 It is difficult to say that this cause is not adequate to the effect, 

 for the prevailing winds are westerly over this whole region 

 and loess when once started could easily be driven at succes- 

 sive stages for any required distance. I can add my personal 



