LOKSS 



643 



the states along the Mississippi farther south. Within this area, 

 its distribution is peculiar in that it follows the main streams, and 

 is found especially on the bluffs overlooking the valleys. On this 

 armuiit it was formerly known as the Bluff formation. In this 

 bluff-position, it has more than its average thickness and coarseness 



Fig. 53.3- A section of loess in Iowa, showing its ability to stand with vertical 

 r cvrn overhanging faces. (Calvin.) 



of grain. It grows thinner and finer in grain back from the river 

 bluffs, until it is lost in a vanishing edge. As it thins, its material 

 loses its distinctive characteristics. 



South of the borders of the Illinois-Iowan and Wisconsin drift- 

 sheets, it mantles many of the divides between the main streams; but 

 farther south it is confined more to the valley borders. Within the 

 drift-covered part of the Mississippi basin, it occurs (i) as a surface 

 mantle overlying drift, and (2) between sheets of drift. South of 

 the drift there are in places (e.g. southern Illinois and northeastern 

 Arkansas) two distinct sheets of loess, separated by a well developed 

 soil zone. The surface of the lower sheet shows the effects of pro- 



