160 
AMERICAN GEOLOGY. 
fracture: it has sharp and translucent edges, and is usually 
very tough. When mixed with a small proportion of argilla¬ 
ceous matter, it forms also a hard tough rock, which appears 
above the surface of the ground in hatchet-shaped projections. 
Sometimes these rise, with rounded, sharp edges, seven or eight 
feet high, and extending as many feet in the direction of their 
strike, and then disappear in the soil. A succession of such 
outcrops continue for miles, forming a peculiar feature in the 
geology of the district. 
2. A quartzite porphyry. This rock is quite common. Its 
porphyritic character is obscure; and it happens not unfre- 
quently that it takes on the character of a breccia. Fig. 22 is 
designed to illustrate its porphyritic character; but it is often 
more obscure, and I am well convinced that I have found a few 
rolled quartz pebbles imbedded in the mass. 
The quartzite or chert is in beds, and in one or two, and 
probably more districts, composes the largest part of the rock 
in a belt half a mile wide. It appears homogeneous in the 
protected part of the mass, while the weathered surface consists 
of a white or gray fine granular substance, similar in its con¬ 
dition to tripoli. This change extends several inches into the 
rock, and forms a well defined border around the unchanged 
parts within the mass. Although the slates bear strongly the 
indications of sediments, no fossils have as yet been found in 
them. In their general features they bear a strong resemblance 
to the slates of the lower half of the Taconic system. I do not 
propose to attempt to give a full and minute description of this 
formation of slates of North Carolina, and of the adjacent states, 
at this time. I shall proceed to the consideration of certain 
questions relating to the gold as it occurs in veins, and other 
relations to the rocks which contain it. 
