CHAPTER III. 



THE SOU,. 



72. To a common observer the soil is a heavy, cohesive, 

 torpid substance ; varying in color ; and, more or less, mixed 

 with stones. Examined scientifically, it is a compound sub 

 stance ; made up of many materials, each of them differing in 

 its qualities ; some of them lying in mere mechanical contact ; 

 others chemically combined. The soil is usually divided into 

 two parts, (a,) the surface soil ; (b,) the sub-soil. They usual 

 ly differ (c,) in constitution ; (d,) mechanical structure ; and 

 (e,) by the first (a,) containing more organic matter, and less 

 salts than the other. 



73. Strictly all accumulations of loose materials resting upon 

 rock constitutes the soil. These loose materials vary in depth 

 from a few inches to one or two hundred feet ; and occasionally 

 consist of different layers or beds placed one over the other. 



74. The earthy matter of all soils has been produced by the 

 gradual decay, degradation, or crumbling down of previously ex 

 isting rocks. 



75. Soils are formed (a,) immediately from the rock upon 

 which they rest ; or (b,) from deposites, drift, &c., brought by 

 water and other geological causes from a distance. In the latter 

 case, the soil may have no relation whatever, either in mineralo- 

 gical characters or in chemical constitution, to the immediately 

 subjacent rocks. To these constituents must be added the re 

 mains of plants and animals ; and carbon. 



