376 T. L. WATSGN VIRGILINA COPPER DISTRICT 



indicates that the area has been subject to long-continued dynamo-meta- 

 morphism. In view of these facts and in the absence of contradictory 

 field evidence, the rocks are placed as pre- Cambrian in age. This is in 

 accord with the work of Kerr and Holmes, who agree in assigning the 

 rocks of this area to the Huronian (Algonkian),* and with that of 

 Keith,f Williams, J and Bascom § for somewhat similar volcanics occur- 

 ring to the north in Virginia, Maryland, and Pennsylvania. 



It further harmonizes with the work of Williams || and Nitze^f in 

 the adjoining counties to the southwest of the Virgilina district, where 

 similar rocks are described and classified as pre-Cambrian in age. Sub- 

 sequent work will probably establish the contemporaneous origin of the 

 rocks for the several scattered areas. 



Conclusions 



The principal points developed in this study may be summarized as 

 follows : 



1. The rocks of the area here described have been greatly altered 

 through pressure and chemical metamorphism, as indicated in the pre- 

 vailing secondary schistose structure and the abundant development of 

 the secondary minerals — chlorite, epidote, and hornblende — and small 

 amounts of others. The alteration has advanced sufficiently far in the 

 schistose phases to destroy in most cases the original structure and 

 minerals of the rock. 



2. From structural, petrographic, and chemical evidences the rocks 

 are shown to have been derived from an original andesite, but in their 

 present much altered state they are, according to present usage, more 

 properly designated meta-andesites ; that these are intimately asso- 

 ciated with the corresponding volcanic elastics. Furthermore, the pop- 

 ular name greenstone applied to many areas of greatly altered massive 

 and schistose rocks along the Atlantic Coast and Lake Superior regions, 

 shown to have been derived from an original basic eruptive rock type, 

 has equal application to the existing rocks of the Virgilina district. 



3. The rocks are pre-Cambrian in age and represent an area of 

 ancient volcanics similar to others described as occurring along the 

 Atlantic Coast region from eastern Canada to Georgia and Alabama and 

 in the Lake Superior region. 



4. The rocks are cut by numerous approximately parallel quartz 

 veins which contain workable copper deposits. The veins have been 

 described as true fissure veins, and the ore is glance and bornite, with- 

 out chalcopyrite and pyrite. 



*Van Hise, C R.: Correlation Papers, Bulletin no. 86, U. S. Geol. Survey. 



f Op. cit. J Op. cit. § Op. eit. || Op. cit. fl Op. cit. 



