ALKALIES IN SOIL. 5? 



will be in proportion to the mica and felspar, for gi*anite 

 (35) is composed of these and quartz. 



72. The composition of granite, composed of two-fifths 

 quartz, two-fifths felspar, and one-fifth mica, is in every 100 

 parts, — 



Silex, 74.84 



Alumina, 12.80 



Potash, 7.48 



Magnesia. .99 



Lime, .37 



Oxide of Iron, ^ 1.93 



Oxide of Manganese, .12 



In every 100 lbs. of granite, 7J lbs. of potash, and f lb. 

 of lime. Difier, as opinions may, about the how, and the 

 why, of the operation of lime and alkali, it is evident, that 

 unexhausted and exhaustless stores of these substances are 

 already in barren pine plains. 



73. Let it be supposed that these are formed of the drift 

 of granite, composed as stated (72), and the amount per 

 acre of lime and alkali, taking the soil only six inches deep, 

 would be as follows : The cubic foot of such soil weighs 

 about 90 lbs. or at six inches deep, 45 lbs. The acre at this 

 depth contains 21,780 cubic feet, which will aflx)rd 3626 lbs. 

 of lime, and 73,311 lbs. of potash, or nearly a ton and a. 

 half of lime, and thirty -six tons of potash. 



74. The lime in such a soil would be enough to supply 

 that contained in a crop of rye, at 20 bushels per acre, for 

 7400 years; for at 20 bushels per acre, and at 50 lbs. per 

 bushel, each acre would aflford 1000 lbs. of grain, which 

 contain nearly -J- lb. of lime, or 0.49 (Schrceder), dividing 

 3626 by this, the quotient 7400 is the number of years the 

 lime would supply the grain. Wheat will not differ much 

 from rye, and if the time is diminished, by the amount of 



3* 



