CORUNDUM TN IGNEOUS ROCKS. 35 
from the usual one observed in North Carolina and (Jeoroia is found 
near Pelham, Mass." A lenticular mass of hai-zhurgite (saxonite) 
about 40 feet in width of outcrop and about '200 feet long is inclosed 
by gneisses. A zone of bronze-colored biotite, usuall^^ 4 by 8 inches 
thick, which incloses the coriuulum is developed along i)ortions of 
the peridotite boundary. (See page 53.) 
CORUNDUiVr IN PYROXENITE. 
At many of the corundum-bearing peridotite localities in North 
Carolina, such as those of Macon, Jackson, and Transylvania counties, 
a pyroxenite composed of interlocking, coarse-bladed, gray enstatite 
constitutes an important part of the outcrop; and at a number of 
places the pyroxenite alone forms oval and lenticular masses in 
every way similar to those composed of peridotite. In Ijoth cases 
corundum-bearing zones of secondary minerals are frequently formed 
along the borders of the pyroxenite and intersect the mass of tlie 
rock in exactly the same manner as described above for peridotite. 
Enstatite rocks are somewhat connnon in North Carolina, but acces- 
sory minerals in them are rare, and the most common one observed 
is chromite, in small grains. In a few instances corundum has been 
found in them. 
Corundum has also been observed sparingly in the enstatolite 
variety of pyroxenite itself in at least two localities, namely, at the 
Rattlesnake mine, near Sapphire, Jackson County, and at a locality 
on the West Fork of French Broad River, in Transylvania County. 
Corundum is also intimately associated with a hy})erstheQite 
(pyroxenite) dike cutting the gneisses on Thumping Creek, Clay 
County, where it occurs in a zone of fine, scaly, broAvn mica developed 
along the plane of contact between the dike and the gneiss. It is also 
found in a very small amount in the hypersthenite itself. The dike 
is a very dark, fine-grained rock, which the microscoi)e shoAvs to be 
composed of strongly pleochroic hypersthene about half altered to 
a green amphibole. 
CORUNDUM IN AMPHIBOLITE. 
Associated with the peridotite rocks of Clay County, N. C, and of 
the adjoining Towns County, Ga., are dikes of amphibolite, which 
are for the most part between the peridotite and the gneiss, although 
in some places they cut the peridotite formation close to the (contact 
of that rock with the gneiss. These dikes vary in width from 25 to 
over 300 feet, their average width being from 75 to 100 feet. The 
relation of these amphibolite dikes to the peridotite formation at 
Buck Creek, Clay County, N. C, is shown in fig. 9. 
«Mon. U. S. Geol. Survey, vol. 29, 1898, pp. 47-54. 
