CLASSIFICATION OF SOILS. 



223 



ferences in the heat acquired in various soils depend, 1st, on the 

 state of their surface ; 2d, on their composition ; 3d, on the quantity 

 of water which they contain ; and, 4th, on the angle of incidence of 

 the sun's rays. M. Schiibler, by a method which is far from being" 

 unobjectionable, but which may 'be excused, considering the diffi- 

 culties of the subject, measured the temperature acquired by different 

 soils exposed to the sun for the same length of time, and in circum- 

 stances as nearly alike as possible ; the numbers obtained are given 

 in the followins table : 



In comparing the circumstances which concur in assisting the 

 action of the sun's rays in raising the temperature of the soil, it 

 appears that the color and moistness of the soil and the angle of 

 incidence of the sun's rays are the most influential ; they may occa- 

 sion differences in the temperature acquired of from 14° to 15° C, 

 (25° to 27° F.) The nature of the surface and the composition of 

 the soil are far from producing such marked differences ; although, 

 according to M. Schiibler, the effect of inclination is very decided, 

 dnd may occasion a difference to the amount of 25° C, (45° F.) 



CLASSIFICATION OF SOILS. 



Agriculturists class soils according to their fertility, and the 

 cropping which they will stand to advantage. In practice two grand 

 divisions have been adopted : strong soils, and light soils ; every 

 soil belongs wholly or in part to one or other of these divisions. 



In strong soils clay is tue predominating element ; in light soils it 

 is sand which prevails. The first are stiff, little permeable, and 

 slow in drying; the second are loose, dry speedily and readily, are 

 permeable, and less difficult to labor. Humus always adds to the 

 qualities of these two kinds of soil, though possessed of properties 

 so opposite ; but its utility is especially remarkable in argillaceous 

 or clayey soils, the extreme stiffness of which it diminishes. 



