FELSPAR. 113 



causes. Mechanically, the rock is continually 

 worn by strong winds loaded with minute par- 

 ticles of sand; and by the freezing of water 

 within its minute pores, small particles are split 

 off by the expansion attending such congelation. 

 Chemically, the action of rain water containing 

 carbonic acid, would remove the potash from the 

 felspar and mica, in the form of carbonate of 

 potash, which removal, breaking the bond of 

 connection between the different particles or 

 grains, the quartz and silicate of alumina, on 

 combining with a certain amount of water, 

 would form clay. Every hundred pounds of 

 granite yield about one pound of potash, which 

 is the most valuable part of the rock for the 

 purposes of vegetation. 



A cubic foot of pure felspar is sufficient to 

 supply half an acre of growing oak trees with 

 the necessary potash required, for five years, if 

 it was present in a soluble form. Each 100 Ibs. 

 of this pure felspar contains 16*17 Ibs. of pot- 

 ash, equal to 24*52 Ibs. of carbonate of potash, 

 or, 26*44 Ibs. of the muriate. 



Still this potash in felspar requires a long 

 time to become soluble when only acted on by 

 atmospheric agencies. 



The most important mineral ingredient of fer- 

 tile soils is lime, in its different compounds of 



