io6 Bulletin of Laboratories of Denison University. [Voi. xii 



opening (Cornfield) is made, showing the massive rock in its 

 least altered condition (analysis I). The rock is porphyritic in 

 structure and the color is a medium dark-purplish shade, which 

 contrasts with the surrounding more altered green schistose 

 rock. 



Epidote of the usual pistachio-green color enters largely in 

 places into the composition of the rocks, and it is mixed locally 

 in considerable proportion with white quartz as a vein mineral. 

 The schistose greenstone is easily scratched with the knife, and 

 suggests approximately the same degree of hardness as that of 

 ordinary clay slate. 



At the Copper World mine, 6^ miles south of Virgilina, 

 in the Carolina portion of the belt, a partially loose-textured, 

 fine-grained, purple rock is mixed with the surrounding green 

 schists. The material bears every resemblance to a tuff, ^ and 

 is streaked in places by the characteristic actinolite shade of 

 green due to alteration, and contains inclosures of a dark- 

 colored massive material, usually of small but varying dimen- 

 sions and partially rounded in outline. The fragmental or 

 clastic nature of the mass is plainly visible. The microscope 

 confirms the clastic nature of this rock and shows that it is com- 

 posed of fragments of igneous rocks of the same character and 

 composition as the igneous rocks of the district. Micro- 

 scopic study also indicates the presence of similar clastic ma- 

 terial at a number of other points in the district. 



No trace of the amygdaloidal structure, so characteristic of 

 the South Mountain and Lake Superior basic greenstone areas, 

 has been observed in the Virgilina rock. 



Microscopy of the Rocks. 



The rocks vary in texture from dense aphanitic to medium 

 fine-grained, with the porphyritic structure shown usually in the 

 massive types. The original minerals are entirely altered to 

 secondary minerals in many of the sections, but, with few ex- 

 ceptions, some trace of the original outline of the feldspar con- 



• See Weed, W. H., op. cit. 



