514 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



nished a metallographic microscope and equipped it with an improved 

 lighting device especially for this work, and the photomicrographs 

 illustrating the paper were made in the photographic laboratory of 

 the Museum by Thomas W. Smillie. 



The specimens herein described are the property of the U. S. 

 National Museum. 



GEOGRAPHY AND GEOLOGY. 



Before entering upon a description of the ores a brief sketch of the 

 geology of the district will be given. 



Location. — The Virgilina copper district is located near the eastern 

 border of the Piedmont Plateau in Person and Granville counties, 

 North Carolina, and .Halifax and Charlotte counties, Virginia, each 

 State including approximately one-half of the ore-bearing area. It 

 takes its name from the village of Virgilina, a station on the Southern 

 Railway situated on the State line near the center of the district, and 

 about 160 miles west of Norfolk and 45 miles east of Danville. The 

 most important ore deposits occur on two approximately parallel 

 flat- topped, though somewhat conspicuous, ridges which trend from 

 15 to 20° east of north, and which have very gradual slopes. The 

 maximum elevation is at Virgilina, 540 feet above sea level. The 

 relief is not pronounced, varying from about 300 feet up to the maxi- 

 mum above stated, but the country is decidedly hilly. Rainfall is 

 rather heavy, especially during the winter and spring, and streams are 

 numerous. 



Geology. — The rocks of the district are highly schistose, and are 

 popularly known as slates. They are of two distinct types — green- 

 stone schists, and quartzose sericitic schists or gneisses. Into these 

 schistose rocks have been intruded large masses of granite, and less 

 important bodies of more basic material, probably gabbro. Also 

 here and there throughout the area occur small diabase dikes. The 

 intrusive rocks are not schistose, but are closely jointed. 



A close examination of these schists reveals their character — a 

 great series of volcano-sedimentary rocks of two types — a basic rock, 

 andesite, and one highly acid in character, a quartz porphyry. Of the 

 andesite there are three types — porphyritic, amygdaloidal, and tuf- 

 faceous, and of the quartz porphyry only two — porphyritic and tuffa- 

 ceous. Closely associated with the greenstone schists and grading 

 directly into them, are heavy beds of highly schistose greenish rocks 

 differing from the tuffaceous portions of the andesite only in that 

 they contain varying amounts of land waste intermixed with the 

 basic volcanic material. These range from fairly well-marked sand- 

 stone and fine conglomerate on the one hand to typical andesitic tuffs 

 entirely free from terrigenous material on the other. The relative 

 position of these two phases of the greenstone indicates that at the 



