296 A WORD ABOUT MANURES. 



ments of soil act on each other, so as to become soluble, 

 and, therefore, convertible into fertilizers. 



The great component parts of soils are the silicates, 

 (sands, quartz, etc.), salts, (as potash, soda, etc.), metallic 

 oxides and vegetable mould. Silica exists in limestone 

 rocks, in granite and in all sands. These silicates are 

 slowly soluble, but elements of decay though slow are 

 constant, and mountains have crumbled and been cast as 

 huge, misshapened masses over the plains. By this action 

 salts (soda, and potash) are freed and enter the soil, or are 

 washed away into the ocean. It is in this manner that the 

 ocean is made salty. But the sand is left, or rather the 

 silex, and the soil is made more friable thereby. But sup- 

 pose, instead of awaiting the action of nature, we intro- 

 duce some of the, earthy salts into the soil, lime, for in- 

 stance. The lime acts directly on the silica, forming a 

 silicate of lime that is soluble. Not only this, but the car- 

 bonic acid that is in the silica is freed, and this acts on other 

 silicates, freeing their salts, and thus alumina is set free, 

 the soil is impregnated with soda and potash, and instead 

 of sand altogether, clay is formed. In this manner sandy 

 soils are greatly improved by the addition of limes, either 

 quicklime slacked, or land plaster, which is the sulphate. 

 Some think this will impoverish the soil. So it will, if 

 crops are raised on it, and so will crops impoverish any 

 soil, but this store of mineral and earthy matters is useless 

 if allowed to remain so, and, in its improved condition, 

 nothing is taken out — it is only made available as plant 

 food. Besides the supply is well nigh inexhaustible when 

 we consider that less than two per cent, has supplied all the 

 fertility to vegetation in all the past ages. It is not to be 

 supposed a few pounds of these applications will make the 

 great mass of soil fertile. By no means, for it would re- 

 quire well nigh the same amount of solvents as the matter 

 to be dissolved. Still, it will enable the plants to get food 

 where none existed before, that could be assimilated. 



