SOILS. 779 



RESIDUARY SOILS. 



The residuary soils show variations which correspond in a rude way 

 with variations in the structure of the rocks from which they are derived. 

 In regions underlain by limestone there is usually a reddish-brown clay. 

 In shale areas the residuary material is an adhesive clay varying in color 

 to correspond with the underlying shale In sandstone and freestone areas 

 the residuary material is siliceous rather than clayey or argillaceous. It 

 often presents a color and texture similar to the deposits of lowan silt that 

 overlie it so that the line of junction is difficult to determine. With proper 

 rotation of crops the residuary soils are usually productive and profitable 

 for agriculture, though they can scarcely compete with the soils formed 

 on glacial drift. The fertility of the unglaciated tracts is also difficult to 

 maintain because of the steepness of the slopes and the resulting great 

 erosion. 



STONY-CLAY SOILS. 



The soils formed on the bowlder clay or till are usually very produc- 

 tive, being composed of a varied rock material, a large part of which is in 

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

 physical constitution also it is well calculated for agriculture, being suffi- 

 ciently porous, as a rule, to allow air and water to penetrate it readily. 

 Portions of it, however, have so compact a texture that underdraining by 

 tile has been found necessary. In general all grains and fruits suitable to 

 the latitude will flourish, especially where the surface is rolling or well 

 di-ained. It has been found necessary to use fertilizers to insure a wheat 

 crop on land that has been in cultivation for periods of forty to fifty years, 

 and advantageous on ground which has been under cultivation but a few 

 years, a fact which testifies to the v^lue of certain chemical ingredients to 

 the growth of that cereal. The importance of the stony-clay soil may be 

 appreciated from the fact that it constitutes the soil of the major part of 

 the great agricultural States of Ohio and Indiana, as well as the most 

 productive portions of western New York and northwestern Pennsylvania. 



GRAVELLY OR STONY SOILS. 



On the older drift of northwestern Pennsylvania and the gi-avelly 

 portions of the moraines of Wisconsin age throughout the region under 

 discussion as well as on the kames, the soil is usually stony. There are, 

 however, but a few places where there is not a sufficient matrix of fine 



