AEOLIAN SOILS, LOESS 61 



which is not clearly understood, but which appears to 

 owe its existence, at least in part, to wind deposition. 

 This is the so-called loess, a fine, silty soil of remarkable 

 uniformity in physical and mineralogical composition. 

 It covers thousands of square miles of country through- 

 out the Mississippi valley and its tributaries, from Cin- 

 cinnati to western Nebraska, and from west-central 

 Wisconsin to southern Mississippi. It lies uncomformably 

 over formations of many ages, as a mantle of soft earth 

 of varying thickness. It does not extend over the whole 

 of the region mentioned, but alternates with other 

 formations, especially drift. It imparts to the regions 

 on which it rests a soil character greatly different from 

 what would exist were it absent. 



Neither is it limited to the United States, for it occurs 

 extensively in central Europe, where it extends from 

 northern France across Belgium, and up the Rhine, 

 Oder and Vistula valleys in Germany; and into central 

 and southern Russia, where it is the basis of the famous 

 "black earth," or tschernosem. In northern China, von 

 Richtofen has described it as covering a large part of 

 the region drained by the Hoang-Ho, where it reaches 

 a thickness of 1,000 feet. 



In thickness it varies greatly. Over much of the 

 United States it is only a few feet in thickness, generally 

 thinning toward the outer margin. In the central 

 areas it may be 150 to 200 feet in thickness, and, simi- 

 larly, in other countries it is of variable thickness, 

 reaching the great depth mentioned above for China. 



A striking physical character of the loess is its 

 ability to stand for a long time in vertical cliffs, although 



