58 
AMERICAN GEOLOGY. 
with all these rocks, as in New York, Massachusetts, and New 
Jersey, where it frequently accompanies them. 
The pyrocrystalline limestones abound in pyroxene, horn¬ 
blende, chondrodite, brown tourmalin, spinelle, sulphurets of 
iron and copper, and phosphate of lime. In veins of Galena 
calcspar is often the gangue. The foregoing minerals never 
form rocks in combination with limestone, excepting serpen¬ 
tine. The minerals imbedded in limestone have a peculiar 
composition, though it may not be due to the rock in which 
they occur. Thus chondrodite and spinelle are composed of 
Chondrodite. 
Spinelle, 
Silex, 
32-66 
2*00 
Magnesia, 
51*00 
12-00 
Peroxide of iron, 
2*33 
16-00 
Fluoric acid, 
4 08 
Potash, 
2*10 
Water, 
1*00 
Alumina, 
68.00 
In the compositions of tourmalins boracic acid is found. It 
is a rare substance. It is volatile at a high temperature, but 
possesses active solvent powers. The dissolved matters crys¬ 
tallize from its solutions. Black tourmalin is composed of 
Silex, 
Black Tourmalin. 
36*03 
Alumina, 
35*82 
Magnesia, 
4-44 
Lime, 
0-28 
Potash, 
0*73 
Soda, 
1*56 
Oxide of iron, 
12-71 
Manganese, 
0*75 
Boracic acid, 
4*02 
Tourmalins accompany the coarse granites. They are quite 
rare in the greenstones. A vein of green, red, and blue tour¬ 
malin occurs in the coarse granite at Chesterfield. They are 
more commonly disseminated in the rock, especially the indico- 
lite, and sometimes so abundantly as to have given its name 
(schorl rock) to the compound. Graphite in tables, and 
