54 
AMERICAN GEOLOGY. 
or hornblende. The proportion of quartz is very great at some 
localities in Maryland and North Carolina, and so large that 
the mass is regarded as a sandstone. Quartz, however, has its 
associates among the metals and oxides and sulphurets of the 
metals. The auriferous formations are so constantly asso¬ 
ciated with quartz, that it is scarcely ever absent. Even 
the fine talcose slates, wdiich appear at first much like talc 
alone, when examined with a glass are found to be made up 
mostly of fine grains of quartz. 
The oxides of iron, when in mass or in veins, are usually 
accompanied with quartz. Carbonate of lime, which is so com¬ 
mon, and as the veinstone of Galena, is rarely, if ever, the vein¬ 
stone of the oxides of iron. The sulphurets of iron and copper 
are usually accompanied with quartz, especially if auriferous. 
It is not well determined how the fissures now occupied with 
quartz have been filled. Some seem to be disposed to regard 
them as products of fusion. Black tourmalin is common in 
quartz, penetrating it in a very remarkable manner. 
The talco-micaceous slates furnish the staurotides, garnet, 
and kyanite. The two former are frequently so abundant that 
they protect the rock from weathering in consequence of their 
hardness. Garnet and staurotide are composed of 
Garnet. 
Staurotide. 
Silex, 
43-00 
33-00 
Alumina, 
16-00 
44-00 
Lime, 
20-00 
3-84 
Oxide of iron, 
16-00 
13-00 
Manganese, 
0-25 
1-00 
Garnet gives different results by analysis; in some the lime is 
wanting, and in others the iron is increased sufficiently to 
warrant its use as an iron ore. The manganese too is variable 
in quantity, and in consequence of the difference of composition 
it furnishes several varieties, as the precious garnet, the melanite, 
colophonite, manganesian garnet, &c. 
§ 44. Serpentine group. Serpentine must he regarded as an 
igneous product, and like other rocks of this class, it has been 
