354 T. L. WATSON — VIRGILINA COPPER DISTRICT 



In many instances the characteristic field appearance of the rocks is 

 that of slate or schist, but in their altered phases they are shown, by 

 structural, chemical, and petrographic evidence, to be igneous in origin. 

 Their subsequent alteration developed a schistose structure and an 

 abundance of chlorite, epidote, and a limited quantity of hornblende. 

 These impart to the rock its uniform green color and give the popular 

 name "greenstone." 



Recent workers are agreed as to the igneous origin of these rocks, and 

 in a recent paper discussing the type of metalliferous deposits of the 

 area Weed * has correctly named the rocks. 



Scattered areas of ancient volcanic acid and basic rocks are described 

 by Williams f and Nitze J immediately to the southwest of the Virgilina 

 district. The rock areas are found in Orange, Chatham, Montgomery, 

 Randolph, and Stanly counties, North Carolina. Nitze describes the 

 basic rocks as being dark green in color, partly massive and partly 

 schistose in structure, and perhaps pyroxenic and at times propylitic 

 in mineral composition. I have not visited these areas, but the descrip- 

 tions of the basic rocks denote similarity to the Virgilina greenstones. 



This paper discusses the evidence for regarding the Virgilina area as 

 one of greatly altered pre-Cambrian volcanic rocks, closely allied to sim- 

 ilar areas of ancient volcanics distributed along the Atlantic coast from 

 eastern Canada to Georgia, and certain altered basic rocks in the Lake 

 Superior region. The time which the writer was able to give to this 

 investigation was insufficient to map and define the exact limits of the 

 area. 



Previous Work 



The rocks of this immediate area have hitherto received but little atten- 

 tion. No detailed work with respect to the differentiation and classifica- 

 tion of the rocks of the Virgilina district has yet been undertaken. Brief 

 references of a general character dating as far back as the Emmons Sur- 

 vey (1856) are found in numerous reports on economic subjects issued 

 by the North Carolina Geological Survey. Such references as bear 

 directly on the area in question are here reviewed : 



After describing the Gillis copper mine in Person county, North Caro- 

 lina, the earliest discovered one in the belt, Doctor Emmons § refers to 

 the rock as follows: "The rock immediately investing the mine is the 

 altered slate belonging to the Taconic system." Emmons first thought 

 the rock was talcose, but later regarded it as argillaceous. 



* Trans. Amer. Inst. Min. Engrs., 1901, vol. xxx, p. 453 et seq. 



t Journal of Geology, 1894, vol. ii, pp. 1-31. 



t Bulletin no. 3, N. C. Geol. Survey, 1896, pp. 37-43; Bulletin no. 10, ibid., 1897, pp. 15, 16. 



g Geology of the Midland Counties of North Carolina, 1856, p. 344. 



