ALKALIES IN SOIL. 43 



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, 7 1-2 lbs. of potash, 

 and 3-8 lb. of lime. Differ, as opinions may, about 

 the how, and the why, of the operation of lime, and 

 alkali, it is evident, that unexhausted and exhaust- 

 less 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 6 inches deep, 

 45 lbs. The acre at this depth, contains 21780 

 cubic feet, which will afford 3626 pounds of lime, 

 and 73311 pounds 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 



