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but also differ in the mode of their origin. These are the 

 Drift, Bluff, and Allnvial soils, and belong respectively to the 

 deposits bearing the same names. The drift soil occupies a 

 mnch greater part of the surface of the State than both the 

 others ; the blnff soil has the next greatest area of surface 

 and the alluvial least. 



1. DRIFT SOIL. 



All soil is disintegrated rock, and its excellence or sterility 

 depends both upon the composition of the rocks from which 

 it is derived and the degree of comminution to which they 

 have been subjected. A soil composed of material that has 

 been suspended in and thus transported by the waters of a 

 stream and then deposited, as the bluff soil has, always 

 possesses a sufficient degree of fineness, while both the drift 

 and alluvial soils may, and sometimes do, contain too great 

 a proportion of coarse materials for good soil. This, 

 however, is very seldom the case with the drift soil of Iowa, 

 for upon the greater part of it not a pebble or boulder is to 

 be seen. This character of the drift soil of Iowa arises 

 primarily from the character of the rocks from which its drift 

 material was originally derived. 



If the rocks from which a drift deposit has been derived 

 were hard and unyielding, the accumulation of drift from 

 them would have been comparatively slight, although they 

 may have been subjected to violent glacial action during the 

 whole Glacial epoch. The soil of such a slight accumulation 

 of drift would also be light and poor, because the materials 

 of it would lack, for the same reason, that degree of fineness 

 necessary to the formation of good soil, although both they 

 and the rocks from which they were derived may contain all 

 the elements necessary for it. These facts are believed to 

 afford sufficient explanation of the cause of the sterility of 

 much of the soil of New England, and of the remarkable 

 fertility of the drift soil of Iowa. 



As stated in the preceding pages, the drift deposit of Iowa 

 was derived to a considerable extent from the rocks of 



