INORGANIC SUBSTANCES IN SOILS. 59 



arise from the different proportions of sanu and clay 

 which the various soils contain. 



The light soils are most easily and cheaply culti- 

 vated, and are found to be particularly well adapted 

 to the growing of some crops, such as barley, rye, 

 buckwheat, etc. They are porous, and for that reason 

 generally dry. 



The heavier soils require more skill and caution in 

 their cultivation, but are not so easily exhausted as 

 the others ; they are particularly adapted to growing 

 wheat, oats, indian corn, etc. Very heavy soils are 

 exceedingly liable to wetness, and can only be made 

 dry by draining. 



SECTION IV. NUMBER OF INORGANIC SUBSTANCES IN SOIL. 

 REASONS FOR FERTILITY OR BARRENNESS. 



It has been said that soils are chiefly made up of 

 three substances, lime, sand (silica), and clay (alu- 

 mina). But besides these, chemical analysis finds 

 smaller quantities of some seven or eight other bodies. 

 In the first column of the following table, representing 

 the composition of three different soils, is to be seen 

 the names of these. 



