EOLIAL OR WIND-LAID DEPOSITS 61 



It is never carried any distance by the wind but is rolled along the 

 surface of the ground. Sand dunes rarely travel more than ten or 

 fifteen miles. Finer material, however, may be picked up by the 

 wind and transported for hundreds or even thousands of miles. 

 This brings about a very wide distribution of the finer soil material. 

 In many cases this is carried in sufficient amounts to form deposits 

 several hundred feet in thickness. This fine deposit has been called 

 " loess" by the Germans and the term is applied to the same deposit 

 in this country. Loess is distributed over a large area in North 

 America, comprising over 600,000 square miles, but is really limited 

 to the states bordering the Mississippi River and its tributaries. Its 

 depth varies from, two to six feet over the principal part of this 

 loess-covered area, but near the larger streams reaches a depth of 

 25 to 150 feet. In Europe the loess is not so generally distributed as 

 in North America, but occurs in somewhat isolated areas and seldom 

 over 12 feet in depth. It extends, however, from northern France 

 across Belgium, Germany, Austria, and southern Russia, where it 

 forms the soil known as the " black earth," or chernozem. It con- 

 tinues eastward across Asia into China, where some of the deepest 

 and most interesting deposits occur that are to be found anywhere. 

 This deposit covers an area of 400,000 square miles in China, mostly 

 in the basin of the Hoang Ho, in places to a depth of 1,500 to 2.000 

 feet. It will be noticed that this belt follows the temperate zone. 

 Loess deposits are found in Argentina and South Africa, but little is 

 known of their extent. 



The origin of loess has been much discussed and several theories 

 have been advanced, but it is very likely that no one theory will 

 account for the deposit in all cases. Since a careful study of the 

 work of the wind has been made it is generally conceded that this 

 agency is responsible for much the larger part of the deposit. There 

 is little doubt. but that some loess may have been deposited as a 

 sediment from water and in some instances both wind and water 

 have played a part. 



As evidence of its eolial origin, it is found at all altitudes up 

 to 5,000 feet tibove sea level in Europe and probably as much as 

 3.500 feet in the Tinted States. To have this deposited by water 

 would have required these regions to have been submerged to that, 

 extent, and there is no evidence of such submergence. The depth 

 of the deposit is quite uniform over hills and valleys as if it came 

 like a gentle snow. In the I'nitcd States, where the subject has 

 received much attention, it is believed that the material has been 



