ACTION OP ELEMENTS OF SOIL. 45 



supposed to be formed of any other rock, the 

 amount of lime and alkali, would still be seen to be 

 almost inexhaustible. And whether rocks be sup- 

 posed or not, to form the soil over them, it may be 

 established, as the 4th leading principle of agricultu- 

 ral chemistry, that all soil contains enough op 



LIME, ALKALI, AND OTHER INORGANIC ELEMENTS, 

 FOR ANY CROP GROWN ON THEM. 



76. These elements do not exist in soil, free ; they 

 exist as silicates, urets, or salts, compounds regulat- 

 ed by the unbending laws of affinity, and fixed, as 

 are the laws of gravitation. The decompounding 

 of these combinations, or the gradual decay of rocks 

 and soil, takes place also by similar laws. Gradu- 

 ally acted upon by the carbonic acid of the air, the 

 agency of growing plants, the action of various salts, 

 formed by urets, in atmospheric exposure, the sili- 

 cates yield to new affinities. The alkalies, freed 

 from the embrace of silica, dissolve, and are borne 

 seaward, the silica itself is dissolved by the water 

 used for drink ; the insoluble alumina remains, form- 

 ing the great mass of clays, or mixed with granitic 

 sand, forms loam. 



77. Felspar, mica, hornblende, are constantly 

 acted upon by air and moisture. This action is 

 chemical. It is twofold. 1st. The action of the 



