792 THE ILLINOIS GLACIAL LOBE. 



BOWLDER-CLAY SOILS. 



The soils formed on the bowlder clay are usually very productive, 



being- composed of a varied rock material, a large percentage of which is 



in a sufficiently fine state of division to be available for plant food. Several 



mechanical analyses of this class of soil were made under the direction of 



Prof. Milton Whitney, the results of which are given on a preceding page 



(p. 163). Professor Whitney has made the following statements regarding 



the bowlder-clay soils of Illinois: 1 



The texture of the bowlder-clay lauds, as shown by mechanical analysis, corre- 

 sponds very closely with the wheat and grass lands of Maryland, although none of the 

 samples are so rich in clay as the limestone soils of that State. There is this to be 

 considered, however, that there is a larger amouut of volatile matter in the Illinois 

 soils, showing that they contain probably twice as much organic matter as the Mary- 

 land soils. This would tend to make them more productive than soils otherwise 

 similar in texture. 



As to the actual tests of the bowlder-clay soils it may be said that, in 

 general, all classes of grains and fruits suitable to the latitude will nourish; 

 especially where the surface is rolling or well drained. On the flat tracts 

 corn and grass are exceptionally productive. 



GRAVELLY SOILS. 



Gravelly soils are varied in their method of deposition, occurring in 

 lake beaches and along streams, in drift knolls and ridges, and beneath 

 plains not now occupied by streams. In the last-named situation the plains 

 are usually so related to the drift ridges as to show that they were occupied 

 by glacial waters. The beaches have generally a poor soil, but the gravel 

 terraces along streams, especially those of glacial age, have as a rule a 

 capping of loam several feet thick, which renders them productive. The 

 same is often true of gravelly knolls and ridges. On the whole the soils 

 underlain by gravel possess more fertility than do sandy soils. This supe- 

 riority is, however, due to the capping of loam which constitutes the soil, 

 or, as in the drift knolls and ridges, to an admixture of clav or earthy 

 material with the surface portion of the gravel. The coarse fragments in 

 the gravel can furnish but little sustenance to crops, although, by weathering, 

 the stones may yield rich material to the soils and furnish a greater variety 

 of plant food than could be obtained from siliceous sand. 



1 Report of Illinois Board of World's Fair Commissioners, p. 100. 



