2 86 CARNEGIE INSTITUTION OF WASHINGTON. 



The Loess. — Among the problems of geology in China, none has 

 been more widely discussed than that of the origin and occurrence 

 of the extensive and thick mantle of yellow earth, characterized by 

 fine texture and vertical structure, to which Baron von Richthofen 

 gave the name of loess. It is typically developed in Shansi and 

 northern Shensi, along the route of our expedition, and presents 

 those anomalie sof distribution which in part led Von Richthofen to 

 the theory that the material is wind- carried dust from the deserts of 

 central Asia. It occurs frequently on mountain slopes, where 

 waters could not possibly have deposited it under existing topo- 

 graphic conditions, and he consequently rejected the idea that it 

 might have been deposited by rivers. The hypothesis of purely eolian 

 origin excites doubt in view of the enormous mass of the loess, as well 

 as because of facts of occurrence, and in America leading students 

 of the loess of the Missouri Valley incline to attribute its special 

 character to interaction of rivers and winds. The problem in China 

 is much more complex than in the United States, but light is thrown 

 on it by a proper understanding of the history of the mountains. 



In the development of the topography there was a stage when 

 there were broad valleys which became overspread with alluvial 

 deposits. Later the surface was strongly warped, stream courses 

 became readjusted, and the alluvium was in part redistributed, but 

 in part remains in remnants on hills produced b}' the warping of the 

 flood-plains. The alluvium was and is loess. It owes its fine, uni- 

 form texture to sifting by wind, and its peculiar structure may be 

 a physical effect of the capillary movement of water in the impal- 

 pable dust beds, but it probably accumulated as the alluvium of the 

 Huang-ho and other streams. The interaction of winds and rivers 

 was specially favored by the climatic conditions of the Pleistocene, 

 which in America and Europe gave rise to the great ice-sheets. In 

 China there was no glaciation, but, according to the history of the 

 mountains, the time of loess accumulation fell in early Pleistocene, 

 and the deposit may be considered the representative in eastern 

 Asia of our glacial beds. The observations made during our jour- 

 ney bring the facts of the loess into accord with the physiographic 

 history of the region in which it occurs, and into agreement with the 

 similar formation in America. We supplement the views of Baron 

 von Richthofen : We regard the agency of wind, upon which he laid 

 stress, as of prime importance in producing the peculiar texture of 

 the loess and in distributing the dust locally ; we show that, at 

 present, winds and streams are both engaged in transporting it, 



