CHARACTER AND MODE OE OCCURRENCE OF ROCKS 359 



of chlorite and epidote as those from the shallow depths. As developed, 

 both macroscopically and microscopically, the rocks collected at the 

 Various depths are indistinguishable. This is also shown in the dumps 

 at the mine openings. 



The microscope reveals, as elsewhere shown, the igneous origin of the 

 rocks ; but, with few exceptions, the rocks do not entirely indicate their 

 true igneous nature in the field. They are prevailingly finely laminated 

 and schistose in structure, having the general characteristic features of a 

 soft, green to purple colored schist. A number of sections showed the 

 prevailing strike of the schistosity to be north 10 to 20 degrees east and 

 an eastward dip of 70 to 80 degrees. 



The change in these rocks is clearly the result primarily of the 

 processes of metamorphism active while the rocks were deeply buried. 

 At a subsequent date, when the rocks were brought near the surface, they 

 were further changed by weathering. The mineral products resulting 

 from the alteration are strongly in evidence. Epidotization and chlorit- 

 ization are manifested on a considerable scale. 



The greenstones are cut in several places by diabase dikes of later geo- 

 logical age. One of these dikes, 12 feet wide, is exposed in the Blue 

 Wing mine at the 100-foot level, where it is observed to cut across the 

 schistosity of the rocks. These dikes are described in the reports of the 

 North Carolina Survey as being quite numerous in parts of Granville 

 and Person counties. Faulted and slickensided surfaces are in evidence 

 at some of the mine openings. 



The rocks are further cut by numerous irregular quartz veins, which 

 contain the workable copper ores. The veins are traced for a mile or 

 more in length on the surface, and in most cases they are more or less 

 parallel, partially overlapping at the ends, and trending north 5 to 10 

 degrees east. They are grouped by Weed* as true fissure veins, lentic- 

 ular in shape, though connecting, crossing at times the schistosity of 

 the rocks and at others parallel to it. The surface over most of the 

 district is much littered with white quartz fragments derived from the 

 disintegration of the veins. 



Petrography 



macroscopic descriptions 



A pronounced schistose structure prevails, and only in a few places do 

 the rocks appear like massive eruptives in the field. The degree of schis- 

 tosity varies from the thin banding of a gneiss to the typical foliation of 

 micaceous schists. The very finely banded structure is more character- 



* Trans. Amer. Inst. Min. Engrs., 1901, vol. xxx, p. 452. 



