96 COKUNDUM^ ITS OCCURRENCE AND DISTRIBUTION. 
with staiirolite and rutile, muscovite, and biotite as accessory minerals. 
The labradorite of this rock is often broken, exhibiting rolling extinc- 
tions, and the albite lamellse are curved and bent, strongly indicating 
a shearing movement in the rock. The corundum does not occur in 
crystals, but in small fragments and in elongated nodules, which are 
cracked and seamed, as if they had been drawn out during the shear- 
ing process. The staurolite is in rather broad irregular grains, and 
the rutile in small irregular grains and well-crystallized prisms. 
From the character and structure of this rock, as noted above, it is 
very probably a metamorphosed igneous rock of the gabbroid family. 
During metamorj^hism the augite of the gabbro would be converted 
into the brown hornblende. Any iron ore that was present would be 
taken up by the hornblende and garnet. The rutile would have 
resulted from the titanic acid that is a regular component of the iron 
ores in these gabbro or diabase rocks. Staurolite is a mineral that is 
rather naturally expected, as it is usually a mineral of met amor phism, , 
and its natural home is in the schistose rocks. The feldspar has suf- 
fered the least chemically (except the corundum), and shows only 
the shearing of dynamic processes. The general character and shape 
of the corundums would indicate that they were original constitu- 
ents of the igneous rock and were not formed during its meta- 
morphism. 
ORIGIN OF CORUNDUM IN QUARTZ-SCHIST. 
These rocks, which are found in Clay County, N. C., and in Rabun 
County, Ga., are described at length on pages 55-56. They vary 
from those that are a normal gneiss to those that contain little or no» 
feldspar, and they can be best designated as quartz-schist. 
The corundum occurs for the most part in small particles and frag- 
ments that have no definite shape, and are of a gray, wdiite, and 
bluish-white color to almost colorless. It is also in crystals varying 
in size from minute ones to some that are 2^ inches long and about 
one-half an inch in diameter, Avhich are usually fairly well developed I 
in the prismatic zone. 
It is probable that these schists are the result of the metamorphism 
of sandstones and shales formed from alluvial deposits of many 
thousand feet in thickness, that were formerly the bed of the ocean. 
By lateral compression these have been folded and raised into the 
mountain ranges of this section. That these were much higher than 
at the present time is very evident from the granitic dikes that are oil 
deep-seated origin. By decomposition and erosion the mountainf^ 
liaA^e been worn down to their present condition, thus exposing tht 
schists in contact with granitic dikes which have aided in their thor- 
ough metamorphism. The shales were rich in alumina, which pos- 
sibly w^as in the form of bauxite, and during their metamorphisir 
