88 ACTION OF THE ELEMENTS OF SOIL. 



this action is its carbonic acid, which gradually com- 

 bines with the alkaline base of the silicates, and the 

 potash, and soda, are converted into soluble salts, 

 whilst 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 nitration, 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 ac-- 

 tion though very marked on felspar, is comparative- 

 ly 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. If the class, salts, be now introduced, thc$a 

 only which act upon silicates by mutual decom- 

 position are earthy carbonates. The silicic acid acts 

 on the lime, forming silicate of lime, while the car- 

 bonic acid, now let loose, acts as such upon other 

 silicates, and eliminates or frees the alkaline bases. 

 Let it be supposed that there is silicate of alumina, 

 that is clay, or silicate of potash and alumina in the 

 soil. Let carbonate of lime, that is marble, and 

 slacked lime, shells, &c, be added to the soil. The 

 result is, that slowly but surely, chemical action takes 

 place, the silicic acid pulling one way and the car- 



