34 



CHEMISTRY OF SOIL. 



bers. They are easily apprehended, and for all 

 practical agricultural purposes, correct. 



59. Viewed in this light, rocks are masses of sili- 

 cates. The simple minerals composing rocks are 

 truly only silicates in fixed proportions. The simple 

 minerals are quartz, felspar, mica, hornblende, talc, 

 serpentine. Their composition is presented in the 

 following 

 TABLE OF CONSTITUTION OF SIMPLE MINERALS 



In each, the silex acts as an acid. This is not 

 only the most constant, but the most abundant in- 

 gredient of rocks. Next is alumina. The average 

 quantity of these elements in the most important 

 rocks, is silica 62*79, alumina 25*15. 



60. In each simple mineral, the alkaline bases 

 (45) being combined with silica, a compound, or sil- 

 icate is formed. In this case, the few simple miner- 

 als forming rocks, may be arranged in three classes, 

 and it will be perceived, that notwithstanding their 



