94 MA^T'UKS. 



It is a singular fact concerning leaching, that 

 water is able to carry no part of the organic con- 

 stituents of vegetables to any considerable depth 

 below the surface in a fertile soil. They would 

 probably be carried to an unlimited distance in pure 

 sand, as it contains nothing which is capable of ar- 

 resting them ; but, in most soils, the clay and car- 

 bon which they contain retain all of the ammonia ; 

 also nearly all of the matters which go to form the 

 ashes of plants very near the surface of the soil. If 

 such were not the case, the fertility of the earth 

 must soon be destroyed, as all of those elements 

 which the soil must supply to growing plants would 

 be carried down out of the reach of roots, and leave 

 the world a barren waste, its surface having lost its 

 elements of fertility, while the downward filtration 

 of these would render the water of wells and springs 

 unfit for our use. Now, however, they are all re- 

 tained near the surface of the soil, and the water 

 issues from springs comparatively pure. 

 EVAPORATION removes from manure 



Carbon, in the form of carbonic acid. 

 Hydrogen and oxygen, in the form of 



water. 



Nitrogen, in the form of ammonia. 

 LEACHING removes from manure 



The soluble and most valuable parts of 

 the ash in solution in water, besides 

 carrying away some of the above- 

 named forms of organic matter. 



