FERTILITY OF GRANITE SOILS. 125 



the component parts of which contribute every necessary 

 element for abundant and vigorous vegetable growth ; w T hile 

 the large proportion of silica existing in them, with the 

 alumina and magnesia, give them a loose open texture which 

 makes them easy of cultivation and permeable to water. 

 These soils produce wheat and all the grains, grasses, fodder 

 crops, and fruit, to perfection. They may be readily dis- 

 tinguished by the glistening of the small bright particles of 

 mica which glitter in the sunlight, and by their loose open 

 mellow texture. They bear a forest growth of oak, hick- 

 ory, elm, basswood and white pines of the largest dimen- 

 sions and finest quality; and having a deep surface soil with 

 an open subsoil rarely require artificial drainage. 



The principal constituents of the feldspar of which these 

 soils largely consist are silica, alumina, potash, and soda ; 

 the soda feldspar is called albite; the potash feldspar is 

 called orthoclase. These minerals have the following com- 

 position. 



Orthoclase. Albite. 



Silica G5.21 69.09 



Alumina 18.13 19.22 



Potash 16.66 



Soda 11.69 



100.00 100.00 



The mica contained in the granite has a varied composi- 

 tion, one kind containing magnesia in considerable propor- 

 tion. The following are analyses of these two kinds; 



Potash Mica. Magnesia Mica. 



Silica 46.10 40.00 



Alumina 31.60 12.67 



Oxide of iron 8.65 19..03 



Potash 8.39 5.61 



Magnesia 1.40 16.33 



Fluoric acid 1.12 2.10 



Water 1.00 



Titanic acid 1.63 



98.26 97.37 



When the granite contains hornblende in place of mica 

 it is called Syenite. Hornblende is a black glassy mineral, 

 very tough and hard; and contains the following substances.. 



