34 CORUNDUM IN THE UNITED STATES. [bull. 180. 
are much more coarsely crystallized, especially the biotite. It is a 
hornblende-gneiss, showing but little mica except where associated 
with the corundum. 
The corundum occurs in nodules and crystals, half an inch and 
smaller in diameter, sometimes wrapped with muscovite in a manner 
similar to that described for the corundum in the chlorite-schists 
(p. 21). The crystals are prismatic, with the length of the prism 
usualty two or three times its diameter. Occasionally they are very 
flat, with the prism not over a quarter of an inch in length and half 
an inch in diameter, and from their appearance these crystals are 
known locally as "button" corundum. 
This occurrence of corundum in gneiss is in no way associated with 
the peridotite rocks of this section of the country. It is, however, 
very similar to the occurrence of corundum in quartz-schist described 
below. None of the peridotite rocks in which the corundum is so 
commonly found in this section of North Carolina have been found 
associated with these bands of gneiss. 
CORUNDUM IN MICA-SCHIST. 
It has recently been observed that portions or bands of the crystal- 
line rocks of the southwestern part of North Carolina and the north- 
eastern part of Georgia are corundum bearing. The composition of 
these rocks varies from those that are a normal gneiss to those that 
contain no feldspar and can best be described as quartz-schist com- 
posed of biotite, mica, and quartz. Some portions of the rock are 
rich in garnet, others are almost entirely free from this mineral, and 
occasionally there are also small bands of white quartzite. The rocks 
are distinctly laminated and are frequently intersected by granitic 
dikes, some of which are coarsely crystallized and of a pegmatitic 
character. These dikes are often parallel with the bedding of the 
schists, although many of them cut irregularly through them. Where 
these dikes are parallel to the bedding of the schists, the laminated 
structure of the latter is much more apparent. The general strike of 
these crystalline rocks is about northeast to southwest and the dip is 
about 30° NW. 
Portions or bands of these schists are corundum bearing, but they 
are irregularly defined and gradually merge into the normal rock. 
They have a similar relation to the normal schists as the garnet-bearing 
bands of a gneiss to the normal gneiss in which they occur. These 
bands are not veins in any sense of the word, but are simply por- 
tions of the same mass of crystalline rocks in which corundum occurs 
as a constituent of the rock. They vary in width from a foot or 
two to 12 or 15 feet, but in these wider ones the corundum-bearing 
portion is not continuous and is intercepted by streaks of barren rock 
and granitic dikes. The bands can be traced for a distance of 5 or 
(j miles in a northeast-southwest direction, sometimes outcropping 
