388 REVIEWS 
that has produced considerable tonnages of ore. The investigation 
covers an area of approximately 550 square miles, including parts of 
Charlotte, Halifax, and Mecklenburg counties, Virginia, and parts of 
Granville and Person counties, North Carolina. 
The area is made up almost wholly of igneous and highly meta- 
morphosed rocks. They include ancient metamorphic gneisses and 
schists, the origin of which is unknown; a sequence of volcanic rocks, 
both basic and acidic, and volcanic clastics of each type, together with 
much volcano-sedimentary material; intrusive rocks of both basic and 
acid types, such as gabbro, diorite, granite, and syenite; and different 
varieties of dike rock, especially diabase. There is a small area of red 
or brown sandstone of Triassic-Newark age. Except the intrusives, 
the sandstones, and the dikes the rocks are all highly schistose and 
gneissoid in texture. 
This prominent schistosity of the rocks is probably the most obvious 
structural phenomenon of the district, although jointing is prominent 
and there is conclusive evidence of folding. There is little direct evidence 
of faulting, but the intense dynamic metamorphism of the district 
could hardly have occurred without causing a certain degree of faulting. 
With the exception of a few mineralized areas in more or less 
epidotized zones of the true basic schist, where deposits of native copper 
or of cuprite occur, the ore deposits are found in well-defined fissure veins, 
which occupy fractures in the rocks—in some instances possibly fault 
planes. The rock in which the veins occur is basic in character—the 
Virgilina greenstone—having the mineralogical and chemical nature of 
andesite; but it is thought that the vein material, both ore and gangue, 
was derived from the granitic magma of the region. 
The gangue minerals, exclusive of included fragments of schist, 
named in the approximate order of their abundance, are: quartz, 
calcite, epidote, chlorite, hematite, sericite, albite, and possibly other 
plagioclase feldspars in small amount, and pink orthoclase. 
The ore minerals, named in the approximate order of their abundance 
are: bornite, chalcocite, native copper, malachite, azurite, cuprite, 
chalcopyrite, chrysocolla, klaprothite (?), pyrite, argentite, silver, and 
gold. Of these minerals, bornite (in part), chalcocite (in part), chalco- 
pyrite (in part), pyrite, klaprothite, argentite, native copper, and gold 
are regarded as hypogene or primary; while a part of the chalcocite, 
bornite, and chalcopyrite, and all the native silver, cuprite, malachite, 
azurite, and chrysocolla are held to be supergene or secondary. 
