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



The covering of loose, decayed surface rock and soil is 

 very thin, and the moderately fresh and firm rock is encoun- 

 tered at slight depths beneath the surface. 



At the mine openings some alteration in the vein constitu- 

 ents is indicated to the entire depth of the workings, 400 to 

 500 feet. This is shown in the case of the sulphide ores, which 

 in several places are slightly changed by the percolating car- 

 bonated waters to the green copper carbonate (malachite) found 

 slightly staining the vein material and the unaltered ores. The 

 rocks taken at these depths are of the same characteristic green 

 color, and the thin-sections indicate the same amounts 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, hav- 

 ing 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 weath- 

 ering. The mineral products resulting from the alteration are 

 strongly in evidence. Epidotization and chloritization are mani- 

 fested on a considerable scale. 



The greenstones are cut in several places by diabase dikes 

 of later geological age. One of these dikes, 1 2 feet wide, is 

 exposed m the Blue Wing mine at the 1 00-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 coun- 



