ALLUVIAL DEPOSITS 315 



ments may almost entirely cease, since the water no longer rises 

 above the level of past accumulations. In such cases the final 

 stages consist simply in the accumulation of organic matter and 

 the deposits come to closely resemble, or are even superficially 

 identical with, the cumulose deposits already described. This 

 same statement holds good also for the closely related salt-water 

 marsh or paludal deposits, to be noted later. 



Loess and Adobe, — Under the head of transported deposits 

 must also be considered the so-called loess of the Mississippi val- 

 ley in our own country; of the Ehine valley, and other parts 

 of Europe; of northern China and the Eussian steppes, though, 

 as will be seen, the name includes deposits which, while having 

 many physical properties in common, may vary widely in com- 

 position as well as in method of deposition. It is more than 

 doubtful, indeed, if the name has not been so loosely applied as 

 to rob it of its proper geological significance. 



The loess of China, made famous through the researches of 

 Kichtofen, is now regarded by some authorities^ as of the same 

 nature as our adobe. Richtofen himself, it will be remembered, 

 regarded the Chinese loess as an ^eolian deposit, as due to the 

 action of wind in transporting for long distances the fine detritus 

 swept by rain and wind from mountain slopes into enclosed 

 basins, to ultimately become entangled and deposited among the 

 growing vegetation. This material, intermingled with the col- 

 lective residue of herbaceous plants, with the inorganic residuum 

 from the decay of prairie vegetation for countless generations, 

 makes up the mass of the loess over many hundreds of square 

 miles of territory, and in places to depths of thousands of feet. 

 The characteristics of the loess, as found in China, are those of a 

 fine calcareous silt or clay, of a yellowish or buff color, so slightly 

 coherent that it may be readily reduced to powder between the 

 thumb and fingers, and yet possessing such tenacity as to resist 

 the ordinary weathering action of the atmosphere, and, wherever 

 cut by stream erosion or other means, to stand with vertical walls, 

 even though they may be hundreds of feet in height. The loess 

 country is described as thus cut up by an almost impassable 

 system of gorges, so that to cross it in any fixed direction is 

 almost an impossibility. *'Wide chasms are surrounded by 

 castles, towers, peaks, and needles, all made up of yellow earth, 



^See I. C. Eussell, Subaerial Deposits of Korth America, G-eol. Mag., 

 August, 1889. 



