•102 ACTlOir. OF -ELEMENTS OF SOIL. 



which limit and control the operations which are performed 

 to effect that end. Theory may teach a rational and success- 

 ful practice; this last may lead to a rational theory. But 

 without a knowledge of the elements of soil, and of their 

 mutual action, which is to be learned from chemistry only, 

 the practical application of science to agriculture is but the 

 dream of enthusiasts. 



130. How do the elements of soil act? The answer 

 involves two important considerations. 1st. The mutual 

 chemical action of the elements of soil, their organic and 

 inorganic parts on each other ; and 2d. This action, as influ- 

 enced and modified by the presence of living, growing 

 plants. 



131. The elements of soil are silicates, salts and geine. 

 The silicates, as such, have no tendency to react on each 

 other. These are gradually decomposed by the action of 

 the air. The great agent in this action is its carbonic acid, 

 which gradually combines with the alkaline base of the sili- 

 cates, and the potash and soda are converted into soluble 

 salts, while the silex and alumina remain. 



132. The result of this action is, that the land becomes 

 gradually more clayey and tenacious; while the alkaline 

 bases, carried away by drainage or filtration, enter brooks 

 and rivers, and are finally found in sea water. The potash 

 of the ocean arises from the decomposition of rocks and soil. 

 This action, though very marked on felspar, is comparatively 

 nothing except on the naked and exposed surface of rocks. 

 Soil suffers but little from this cause. The silicates of soil 

 may be considered as stationary. 



133. Let the class, salts, be now introduced into the soil ; 

 of these the earthy carbonates only act upon silicates by 

 mutual decomposition. The silicic acid acts on the lime, 

 forming silicate of lime, while the carbonic acid, now let 



