193 



The lino between tlie residual types and the loess covered tracts is 

 well defiiietl as to differences of plant growth aud crop production, but 

 the line between the pale silt and the black soils of the Wisconsin drift 

 is very conspicuous. 



The loess soils are easily cultivated, much of the surface of a well 

 tilled Held is frequently a loose floury dust, and wlien small clods occur 

 tliey are easily broken. The soil may be plowed when wet and yet 

 easily be worked to a loose pliable condition. There is a marked deficiency 

 of organic matter in the virgin soil and as this amount becomes less the 

 soils get in a poor physical condition and are sometimes difficult to man- 

 age. A systematic rotation of crops and good application of stable ma- 

 nure are necessary to keep the soils in good c-onditiou for cultivation. 

 Much of the land is used for pasture, but when left uncultivated for a 

 few years the gi'ound becomes covered with a browth of briars. 



The principal alluvial soils of the State are those of the White 

 Kiver, Wabash and Ohio Valleys. The valleys of these streams and 

 their tributaries are the results of stream erosion, and chiefly by the 

 streams which now occupy them. During the glacial period they were 

 largely choked with drift, only a small part of which has been removed ; 

 gorges and ravines exist in great numbers along the White Water, White 

 and Ohio rivers and their tributaries. The eastern tributaries of the Wa- 

 bash in Fountain and Parke counties flow thi'ough deep gorges cut in 

 jlie sandstone. The streams flowing from the glacial area had their 

 valleys flooded with glacial waters and choked with glacial debris. The 

 effect of tlais is shown by the extensive terraces of sand and gravel which 

 border their present channels. Between these terraces are the bottom 

 lands, large areas of which contain very productive soils. 



A larger percentage of the drift so/Is are suited for cultivation than 

 Ihose of the driftless area, but there are, however, large areas of the 

 former which are either t(JO rough for agricultural purposes, as in the 

 boulder morainic belts, or too wet, as in the lake and marsh districts of 

 tlie northern part of the State. 



ROCK OUTCROPS. 

 In the northern part of the State rock outcrops are few. At Mo- 

 mence, Illinois, occurs the first limestone outcrop along the Kankakee, 

 and from that point to its junction with the Iroquois there is a solid 



[13—29034] 



