Art. VII.] Watson, Virgilina Copper District. 125 



ported to be rather numerous in parts of Granville county, and 

 in several instances are observed cutting the rocks of this area. 

 To the east, south, and west massive granites and granitic 

 gneisses of approximately the same mineral composition are of 

 frequent occurrence. Sufficient work has not yet been done, 

 however, to definitely determine the exact origin of the gneisses, 

 but in many cases their close mineralogical resemblance to the 

 granites is suggestive of igneous origin. Indeed, a chemical 

 analysis quoted by Kerr^ of a similar granitic gneiss taken from 

 the Raleigh quarries would strongly indicate, in connection 

 with the mineral components, an original massive granite sub- 

 sequently rendered schistose by pressure. 



The occurrence of similar ancient volcanic rocks in the ad- 

 joining counties to the southeast of the Virgilina area, described 

 by Williams" and others'^ as closely resembling those of the 

 South Mountain area, are grouped as pre-Cambrian in age, and 

 can be most likely correlated with the rocks of the Virgilina 

 district. 



The rocks of this district are shown to be quite similar in 

 many respects to the volcanics farther north in Virginia and 

 Maryland of the Catoctin belt and of South mountain, a con- 

 tinuation of the Catoctin belt in Pennsylvania. Keith^ has 

 shown the rocks of the Catoctin belt to be pre-Cambrian — 

 Algonkian — in age. Likewise Williams^ and Bascom^ have 

 shown the series of both acid and basic volcanics of South 

 mountain in Pennsylvania to be of the same age — Algonkian. 



' Geology of North Carolina, Geol. Survey of N. C, 1875, vol. i, p. 122. 

 ' Jour, of Geology, 1894, vol. ii, pp. 1-31. 



^ Gold Deposits of North Carolina, Geol. Survey of N. C, Bulletin no. 3, 

 1896, pp. 37-43; ibid., Bulletin No. 10, 1897, pp. 15, 16. 



* Geology of the Catoctin Belt, 14th Ann. Rept., U. S. Geol. Survey, 1894, 

 p. 319. See map, plate xxii, opposite p. 308. 



^ Volcanic Rocks of South Mountain in Pennsylvania and Maryland, Am. 

 Jour. Sci., i8q2, vol. xliv, pp. 493, 494; Jour, of Geology, 1894, vol. ii, pp. 1-31. 



® The Ancient Volcanic Rocks of South Mountain, Pennsylvania, Bulletin 

 No. 136, U. S. Geol. Survey, 1896, p. 30. 



^ Jour, of Geology, 1893, vol. i, pp. 813-832. 



