SOILS. 191 



prove of some essential service to the increasingly large number of 

 our agriculturists who desire to study the interests of their professioii 

 in a comprehensive and philosophic manner. The following descrip- 

 tions will, however, be found quite closely applicable in detailed study. 



CLASS I. Prairie Loam. This class is too well known to need 

 much description. It sometimes arises from the decomposition of 

 the underlying limestone, sometimes from the disintegration of lime- 

 stone gravel, and sometimes it arises from the deposit of an ancient 

 lake. There are several varieties, but all have at least a moderate 

 degree of fineness of texture while some manifest this quality in a 

 very high degree. This is more particularly true of those that are 

 derived directly from the decomposition of the limestone, the type of 

 which is a black " light " soil, that works like an ash bed when dry, 

 and rolls into little pill-like pellets when wet, and refuses to scour ex- 

 cept with the very best of plows. It is a warm soil, but not so rich 

 as its blackness might lead one to suppose, yet very responsive to 

 proper fertilizers. This particular variety occupies but limited areas. 

 The other kinds are slightly more arenaceous and work with the 

 greatest ease. 



In chemical composition, silica is the chief ingredient, with which 

 is associated a variety of mineral substances that constitute plant food, 

 as shown by the analysis at the close of these descriptions. 



The small quantity of the carbonates of lime and magnesia may 

 seem at first strange, since the soil is chiefly derived from magnesian 

 limestone, but it becomes clear enough when we consider that the 

 disintegration by which it was formed consisted of the dissolving out 

 of the lime and magnesia, leaving the residue. But as these sub- 

 stances exist in abundance in the stratum immediately beneath, and 

 impregnate the water, they are brought to the surface in dry weather 

 by capillary action so that these soils rarely suffer for the want of 

 mineral substances. In judging of the strength of our soils from 

 analysis it should be borne in mind that there exists in the immediate 

 substratum an inexhaustible supply of the soluble mineral substances 

 needed for plant food. Our soils are new geologically as well as new 

 in the history of cultivation. 



Vegetable matter in the form of humus penetrates this soil to 

 greater depths than in most of the following classes, and imparts to 

 it a darker color. 



The areas occupied by it will be found on the map above referred 

 to. It will be observed that they are mainly confined to the south- 

 western third of the district under consideration, or, as it happens, 

 perhaps casually, to the Mississippi basin. 



