24 CHEMISTRY OF SOIL. 



geological formations, and which form the crust of 

 the globe. 



39. The chemical constitution of rocks, the na- 

 ture, properties and relations of their elements, 

 proves to be of the highest value, when it is known, 

 that the elements of these seven minerals are also 

 the earthy parts of all plants. The farmer should 

 therefore be so far a chemist, as to understand the 

 results to which the analysis of minerals conducts. 



The number of elements which chemistry has de- 

 tected, is fifty-five. Of these, some are metallic, 

 others are earthy, others inflammable, or volatile. Of 

 the fifty-five elements, fourteen are found in rocks. 

 This includes the elements of water, or oxygen and 

 hydrogen. Excluding the last, and retaining oxy- 

 gen in its various compounds, there remain twelve 

 substances only in rocks. Of the earthy and me- 

 tallic, eight ; and of the volatile and combustable, 

 four only are found in soil. These all are called by 

 names so familiar, that their enumeration conveys at 

 once an idea of their distinguishing properties. 

 These twelve substances are divided, for the conve- 

 nience of the farmer, into three classes. First, sili- 

 cates — second, urets — third, salts. The term urets, 

 is here only used provisionally, and it is by no 

 means intended to burthen science with a new name, 



