GEOLOGICAL CLASSIFICATION OF SOILS 55 



by a terminal moraine wherever the ice margin was station- 

 ary long enongh to permit such an accumulation. Many 

 other moraines are found to the northward, marking points 

 where the iee became stationary for a time as it retreated 

 by melting/ "While the moraines are generally outstand- 

 ing topographic features, they are commonly unimportant 

 agriculturally due to their small area and unfavorable physi- 

 ography. The ground moraine is the material which fur- 

 nishes the bulk of the soils which have directly resulted from 

 glaciation. This ground moraine is of wide extent and pos- 

 sesses a favorable agricultural topography. The weathering 

 in situ of this great area of soil material has evolved one of 

 the most productive soil provinces of the world. 



31. Glacial soils. — The soils which have been developed 

 from the glacial till are usually rather heavy, loams, silt 

 loams, and clay loams predominating. The subsoil is gen- 

 erally finer than the surface and may induce poor drainage. 

 The individual particles of such soils are less weathered than 

 those of residual soils. The feldspars have retained their 

 normal luster and the iron staining so common in the Pied- 

 mont Plateau is almost absent. The color is usually sub- 

 dued, grays and browns prevailing. Eed glacial soil may 

 occur, however, where red sandstones have been ground up 

 or where considerable residual soil has been incorporated 

 in the till. The subsoils usually present colors ranging from 

 light gray and yellows to brown. Mottling is common, es- 

 pecially in the subsoil, due to lack of aeration. 



The chemical composition of glacial soils approaches that 

 of the parent rock more nearly than does any other, since 



^The position of the ice front of a glacier is determined by the 

 relationship between the forward movement of the iee and the rate 

 of melting. When the former is dominant, the ice front advances. 

 When melting in dominant, the iee front recedes. When these two 

 forces are balanced, conditions are favorable for a stand of the 

 ice and the building of a moraine. 



