704 



THE ILLINOIS GLACIAL LOBE. 



connection with the discussion of the loess (p. 161). Concerning these 

 samples Professor Whitney remarks: 1 



They are lighter in texture than the best wheat lands of Maryland, although 

 they have rather more organic matter to balance the low percentage of clay. They 

 are more like onr fruit and tobacco lands, although the higher percentage of volatile 

 matters indicate that they are rather more retentive of moisture. 



The loess differs markedly from the agricultural lands of Maryland in 

 the relative amounts of clay in the soil and subsoil. It is the rule of the 

 Maryland agricultural lands to present a larger amount of clay in the sub- 

 soil than in the soil, but in the loess the reverse appears to be the case, as 

 the following table indicates: 



Percentage of clay in soil and subsoil of Illinois loess. 



Locality. 



Virginia City, No. 1. 

 Virginia City, No. 2. 



Carrollton 



Rock Island 



oladstoue 



Subsoil (per 

 cent of clay). 



6.75 

 7.10 

 12.52 



The bluff loess yields fair crops of all kinds, but is especially valuable 

 for fruit, both orchard and small fruits. Its superiority in fertility over the 

 white clay and finer silts seems due to the physical condition of porosity. 

 Nothing has been found to indicate that it contains a better supply of plant 

 food. Moreover, the fertility of the latter is made certain by the rich 

 growth of such crops as will flourish in a compact soil. 



SILTS SLOWLY PERVIOUS TO WATER. 



The silts slowly pervious to water embrace the rich black soil district 

 of the western portion of Illinois. The southern boundary lies near a 

 line connecting Alton, Litchfield, and Pana. The eastern boundary of 

 the main district may be placed at the border of the newer or Wisconsin 

 drift. The northern boundary is near the south border of the Green River 

 Basin, while the western boundary is found in the loess that borders the 

 Mississippi. Through this district there passes the belt of porous loess 



1 Report of Illinois Board of World's Fair Commissioners, p. 101. 



