GEOLOGICAL CLASSIFICATION OF SOILS 59 



bestow a characteristic topography to that region. The 

 loess soil is found also covering the great areas of China 

 and Siberia, and thus it is one of the important soils of 

 the world. Another soil, made up, at least partially, of 

 wind-blown material and found in Arizona and New 

 Mexico, is called adobe. Volcanic soils of the western 

 United States and elsewhere are to some extent of wind 

 origin. Sand dunes are of iEolian origin, but these sink 

 into insignificance as to agricultural value when com- 

 pared with the soils named above, especially loess. 



46. Loess soils. — Loess is usually a fine calcareous 

 silt or clay, of a yellowish or yellowish buff color. While 

 it may be readily pulverized when subjected to cultiva- 

 tion, it possesses remarkable tenacity in resisting ordinary 

 weathering. The vertical walls and escarpments formed 

 by this soil show one of its striking physical character- 

 istics. In China 1 caves that house thousands of persons 

 are dug in the defiles and canons existing in this deposit. 

 Another feature of loess is the presence of minute vertical 

 canals lined with a deposit of calcium carbonate. These 

 canals are supposed to give the soil its vertical cleavage 

 and its tenacity. The particles of loess are usually un- 

 weathered and angular. Quartz seems to predominate, 

 but large quantities of feldspar, mica, hornblende, augite, 

 calcite, and other substances are found. 



A few typical analyses 2 are given below : 



1 Richthofen, F. Chinese Loess. Geo!. Mag., May, 1882, 

 p. 293. 



2 Clark, F. W. The Data of Geochemistry. U. S. Geol. Sur- 

 vey, Bui. 491, p. 486. 1911. 



A. From near Dubuque, Iowa. 



B. From Vicksburg, Mississippi. 



C. From Kansas City, Missouri. 



D. From Cheyenne, Wyoming. 



