pratt] MODES OF OCCURRENCE. 31 
composed essentially of orthoclase feldspar, corundum, and biotite, 
with the feldspar predominating. This would classify the rock as a 
corundum-bearing biotite-syenite. The rock, for the most part, has 
a somewhat gneissoid structure, and in these portions the corundum 
is more or less finely divided, being in fine grains and small crystals. 
In other portions, where the corundum is coarsely crystallized, the 
rock has something of a pegmatitic character, and the corundum is 
surrounded by the orthoclase. The crystals of corundum vary in size; 
the Largest ones are TJ- inches long and from a quarter to a half an 
inch in diameter. They are fairly well developed in the prismatic 
zone, but many of them, especially the larger ones, are rounded. In 
color they vary from bluish gray to almost colorless. The percentage 
of the corundum in the rock is large, and from a superficial examina- 
tion it could be compared to the percentage of quartz in an average 
granite. The biotite is in small tablets, without definite crystal out- 
line, and the tablets are often so arranged as to give the mass of the 
rock its gneissic appearance. The orthoclase did not show any crystal 
outline even in the larger fragments. 
This occurrence of corundum was discovered by Prof. F. W. 
Traphagen, of Bozeman, Mont., to whom I am indebted for the 
specimens. 
From the appearance of the hand specimens, this occurrence of 
corundum is similar to thai in the syenite of Ontario, Canada, recently 
described by Blue 1 and Miller. 2 
CORUNDUM IN AMPHIBOLE-SCHIST. 
At the Sheffield mine, in Cowee Township, Macon County, X. ('., 
corundum has been mined in a saprolitic rock at various times for a 
number of years. In a shaft sunk to determine the depth of the 
corundum-bearing saprolite, solid, unaltered rock was encountered. 
The shaft, which was 87 feet deep, passed through the following rocks: 
The first L2 feet (a) was through the saprolite, in which there were 
seams of kaolin; the next 2 feet (1>) were corundum bearing. From 
14 to 28 feet (c) the same saprolite was encountered; the next 2 feet 
(d) were corundum bearing, followed by 10 feet (e, 30 to 40 feet) of 
the saprolite, and 2 more feel (/) that were corundum bearing. From 
42 to 63 feet (<j) the rock began to be less decomposed, ami from 63 to 
•'»<; feet (//) another seam of corundum-bearing rock was encountered. 
From this point to the bottom of the shaft the rock became more and 
more solid, until at 77 feet (i) the fresh rock was encountered. These 
various seams in the rock are very pronounced. They dip 30 fJ toward 
the west near the top, but become nearly horizontal near the bottom 
1 Trans. Am. Inst. Min. Eng., Vol. XXVIU, 1898, p. 565, and Rept. Bureau of Mines, Ontario, Vol. 
VIII, Part II, L899,p. 240. 
2 Rept. Bureau of Mines, Ontario, Vol. VII, Part III, 1898, p. 238, and Vol. VIII, Part II, 1899, 
p. 305. 
