SCHIST-CONGLOMERATE IN GEORGIA A77 
joints into two or more divisions. The surface of the bowlders is 
generally more or less roughened and occasionally pitted, as if having 
been attacked by some dissolvent agent. Striations, corresponding 
in direction to the long axis of the bowlders, are sometimes noticed, 
but such markings are not common. 
A microscopical examination of thin sections shows that the 
-bowlders and the pebbles consist almost entirely of interlocking 
grains of quartz, the chief accessory mineral being mica, which makes 
Fic 4—Schist-conglomerate, showing joint structure, Lumpkin County, Georgia 
up, apparently, only a fractional part of 1 per cent. of the entire m:ss. 
The quartz grains in some cases are slightly elongated in the direction 
of the longer axis of the bowlders, but the extent of the deformation 
is by no means sufficient to account for the elongation of the bowlders 
themselves. The matrix, binding the bowlders and pebbles together, 
is made up chiefly of biotite and quartz, the former mineral being the 
more abundant. Magnetite also occurs in more or less abundance 
in the matrix in the form of crystals arranged along certain well- 
defined lines. 
