THE LOESS-DEPOSITS OF NORTHERN CHINA. 247 



connection with the waters compressed below, when, owing to the law 

 of diffusion, the ingredients, being released, mix with the moisture of 

 the little canals, and are there taken from the lowest to the topmost 

 levels, permeating the ground and furnishing nourishment to the 

 plant-roots at the surface. It is on account of this curious action of 

 loess that a copious rainfall is more necessary in Northern China than 

 elsewhere, for with a dearth of rain the capillary communication from 

 above, below, and vice versa, is interrupted, and vegetation loses both 

 its moisture and manure. Drought and famine are consequently 

 synonymous terms here. 



As to the origin of loess, Baron von Richthofen's theory is sub- 

 stantially as follows : The uniform composition of this material over 

 extended areas, coupled with the absence of stratification and of ma- 

 rine or fresh-water organic remains, renders impossible the hypothesis 

 that it is a water-deposit. On the other hand, it contains vast quan- 

 tities of land-shells and the vestiges of animals (mammalia) at every 

 level both in remarkably perfect condition. Concluding, also, that 

 from the conformation of the neighboring mountain-chains and their 

 peculiar weathering, the glacial theory is inadmissible, he advances the 

 supposition that loess is a subaerial deposit, and that its fields are the 

 drained analogues of the steppe-basins of Central Asia. They date 

 from a geological era of great dryness, before the existence of the 

 Yellow and other rivers of the northern provinces. As the rocks and 

 hills of the highlands disintegrated, the sand was removed, not by 

 water-courses seaward, but by the high winds ranging over a treeless 

 desert landward, until the dust settled in the grass-covered districts of 

 what is at present China Proper. New vegetation was at once nour- 

 ished, while its roots were raised by the constantly arriving deposit ; 

 the decay of old roots produced the lime-lined canals which impart to 

 this material its peculiar characteristics. Any one who has observed 

 the terrible dust-storms of Northern China, when the air is filled with an 

 impalpable yellow powder, which leaves its coating upon everything, 

 and often extends in a fog-like cloud hundreds of miles to sea, will 

 understand the power of this action during many thousand centuries. 

 This deposition received the shells and bones of innumerable animals, 

 while the dissolved solutions contained in its bulk staid therein, or sat- 

 urated the water of small lakes. By the sinking of mountain-chains 

 in the south, rain-clouds emptied themselves over this region with 

 much greater frequency, and gradually the system became drained, 

 the erosion working backward from the coast, slowly cutting into one 

 basin after another. "With the sinking of its salts to lower levels, un- 

 exampled richness was added to the wonderful topography of this sin- 

 gular formation. 



Mr. Pumpelly, while accepting this ingenious theory in place of 

 his own (that of a fresh-water lake deposit), adds that the supply of 

 loess might have been materially increased by the vast mers-de-glace 



