98 Bullethi of Laboratories of Denis on University [Voi. xii 



The rocks have been designated slates by the earlier work- 

 ers, which, according to present usage, would imply a meta- 

 morphosed sediment. 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 sub- 

 sequent alteration developed a schistose structure and an abund- 

 ance 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" and Nitze^ 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 composi- 

 tion. I have not visited these areas, but the descriptions of the 

 basic rocks denote similarity to the Virgilina greenstones. 



This paper discusses the evidence for regarding the Virgi- 

 lina area as one of greatly altered pre-Cambrian volcanic rocks, 

 closely allied to similar 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 attention. No detailed work with respect to the dif- 



1 Trans. Amer. Inst. Min. Engrs.,Vol. XXX, p. 453 et seq. 

 * Journal of Geology, 1894, Vol. II, pp. 1-31. 



3 Bulletin No. 3, N. C, Geol. Survey, 1896, pp. 37-43 ; Bulletin No. 10 

 ibid, 1897, pp. 15, 16 



