PRATT] MODES OF OCCURRENCE. 35 
continuously for nearly a mile. There arc al least two of these corun- 
dum-bearing bands which are parallel to each other and about 2 miles 
apart. The only variation that has been observed in them is in the 
percentage of corundum and garnet; otherwise they are identical. 
The amount of corundum is never Large, and from determinations 
made on samples from various parts of I he deposits ii will not average 
over 4 or 5 per cent. 
The corundum occurs for the mosl pari in small particles and frag- 
ments thai have no regular shape and are of a gray, white, and 
bluish-white color or almost colorless. It is also in crystals which 
vary in size from some that are very minute to some thai are 2\ inches 
long and about one-hall' inch in diameter, and which are usually fairly 
well developed in the prism /one. 
It is probable t hat I hese schists arc t he result of t he metamorphism 
of sandstones and shales formed from alluvial deposits man} thou- 
sand feet- in thickness that were once the bed of the ocean. By lat- 
eral compression these have been folded and raised into the mountain 
ranges of this region. Thai these have been much higher than al 
the present time is very evidenl from the granitic dikes, which are of 
deep-seated origin. By decomposition and erosion the mountains 
have been worn down to their present condition, thus exposing the 
schists in contact with the granitic dikes which have aided in their 
thorough metamorphism. The shales were rich in alumina, and dur- 
ing their metamorphism the excess of the alumina crystallized as 
corundum along the planes of Lamination, so thai during the subse- 
quent weathering the corundum has been left in knotty nod u les, si lid- 
ding the surface of t he rock and giving it 1 he appearance of containing 
a high percentage of the mineral. 
Genth ' has described an occurrence of corundum in I 'at rick County, 
Ya., about 2 miles from Stuart, where it has been found in the mica- 
schists on a knob of Bull Mountain. These schists are talcose and 
ehloritic in character and are intersected by a number of granitic 
dikes. The portions of the schists in which the corundum occurs are 
gneissoid in character. This occurrence is decidedly different from 
that in Clay County, N. C, and more like the corundum-bearing 
schists near the headwaters of Caney Fork of Tuckasegee River, in 
Jackson County. The schists are in rather narrow bands that can 
be followed for some distance across the county. They are not true 
chlorite-schists like those described on page 21, but are made up 
largely of an elastic mica (probably muscovite) with some chlorite. 
The corundum occurs in rough crystals and nodules up to 1 inch in 
length and half an inch in diameter, of a grayish-white to white color 
and colorless. It is readily cleaned, and tests made upon the cleaned 
product show that it is well adapted for the manufacture of the vitri- 
fied wheel. 
i Am. Jour. Sci., 3d series, Vol. XXXIX, 1890, p. 47. 
