GEOLOGICAL CLASSIFICATION OF SOILS 61 



47. Distribution of loess. — Not only is loess found 

 over thousands of square miles in the central part of the 

 United States, but it occurs elsewhere in large areas. 

 It is greatly developed in northern France and Belgium, 

 and along the Rhine in Germany, where it is. an important 

 soil in all the valleys that are tributary to that river. 

 Silesia, Poland, southern Russia, Bohemia, Hungary, 

 and Roumania, all have deposits of this highly fertile 

 material. In Europe it extends from sea level to eleva- 

 tions of 5000 feet, showing its independence of water 

 as a formative agent. In China it is found over a very 

 large part of the valley of the Hoangho, a region prob- 

 ably larger in area than France and Germany combined. 

 The thickness of the deposit is variable, ranging from a 

 few feet to several thousand feet in certain places. The 

 depth is practically always sufficient for any form of 

 agricultural operations. 



Wherever moisture relations are favorable loess is an 

 exceedingly fertile soil, due to its rich stores of potash, 

 phosphorus, and lime. Its organic content is usually 

 medium to high, depending on conditions. In general 

 it may be classified as the richest soil in the world, 

 considering its wide extension and the great variety 

 of climate and of crops to which it is subjected. In 

 the United States it occurs in the Corn Belt region, 

 and might be called the great corn soil of the Mississippi 

 Valley. 



48. Adobe soils. — The term adobe is a name applied 

 to a fine calcareous clay or silt formed in a manner some- 

 what like that in which loess is formed. It is supposed 

 that, while part of the deposit came from the waste of 

 talus slopes as mountains were weathered under conditions 

 of aridity, the remainder had an origin similar to that of 



