GEOLOGICAL CLASSIFICATION OF SOILS 61 



tion. It is a well-known fact tliat lakes are only enlarged 

 stream beds, and are doomed ultimately to be filled by river 

 sediments. Such soils have been reclaimed to a certain ex- 

 tent, but their acreage is not large enough to give them the 

 importance of the glacial lake soils. The lake soil is usually 

 of a fine character, rich in organic matter and of good tilth. 

 If properly drained, it is almost invariably highly produc- 

 tive, and is adapted to a variety of crops depending on cli- 

 matic conditions. 



35. ^olian soils. — Loess. — During glaciation much fine 

 material was carried miles below the front of the ice sheets 

 by streams that found their source within the glaciers. This 

 fine sediment was deposited over wide areas by the over- 

 loaded rivers. The accumulations occurred below the ice 

 front at all points, but seem to have reached their greatest 

 development in what is now the Missouri Valley and the 

 Great Plains. Much of the sediment in the latter area prob- 

 ably came from local glaciers, which debouched from the 

 Eockies. 



It is generally agreed by glacialists, that a period of aridity, 

 at least as far as this particular region is concerned, im- 

 mediately followed the retreat of the ice. The low rain- 

 fall of this period was accompanied by strong westerly winds. 

 These winds, active perhaps through centuries, were instru- 

 mental in the picking-up and distributing of this fine ma- 

 terial over wide areas of the Mississippi, Ohio, and Missouri 

 valleys. One strong argument for this seolian origin is that 

 the soil is in its deepest and most characteristic development 

 along the eastern banks of the large streams. Especially 

 noticeable is the extension down the eastern side of the Missis- 

 sippi River almost to the Gulf of Mexico. This wind-blown 

 material, called loess, is found over wide areas in the United 

 States, in most cases covering the original till mantle. It 

 covers eastern Nebraska and Kansas, southern and central 

 Iowa and Illinois, northern Missouri and parts of Ohio and 



