PREVIOUS INVESTIGATIONS 357 



paper on the distribution of the ancient volcanic rocks along the Atlantic 

 Coast region. Attention is directed in the paper to the area immediately 

 southwest of the Virgilina district, in which occur both acid and basic 

 eruptives, mostly acid, of pre-Cambrian age. 



Mr W. H. Weed* recently published a valuable paper treating in 

 some detail the type of ore deposits in this belt and the important eco- 

 nomic features. He refers to the rocks of the district as follows : 



"The country- rock is schist, in few places massive enough to be called 

 gneiss. . . . The rocks are all of igneous origin— even the softest and most 

 shaly show this character in thin sections under the microscope. But in a few 

 instances only is the igneous nature of the schists recognizable to the eye. This 

 was observed at the Thomas mine, where a purplish rock is clearly a porphyritic 

 meta-andesite. These schists are cut by dikes of later igneous rock (diabase). The 

 only one seen by the writer was that exposed in the Blue Wing mine; . . . 

 Apart from the dikes, however, I would say, on the strength of field-observations 

 alone, that the rocks are of igneous origin, and belong to the various porphyries 

 which have been discovered in the Appalachian belt. This conclusion is con- 

 firmed by the microscopic examination of thin sections, which has shown the 

 rocks to be altered andesites, that is meta-andesites and andesite tuffs." 



General Field Characters and Occurrence 



As seen from the accompanying map, the area is located near the 

 eastern border of the Piedmont plain, in Halifax county, Virginia, and 

 Person and Granville counties, in North Carolina, 47 miles east of Dan- 

 ville. The belt occupies a low, flat-topped, though somewhat conspicu- 

 ous, ridge, which trends a few degrees west of south and slopes very 

 gradually both to the east and west. It will average 100 to 200 feet 

 in elevation above the neighboring stream valleys. The cross-drain- 

 ages are all small, but the ridge is flanked by several large ones on the 

 west and northwest sides. The ridge is traced northward to the Dan 

 River valley, in Virginia, some 10 miles north of the state line. In 

 North Carolina its southward extension is estimated by Hanna f to be 

 about 30 miles, reaching nearly to Durham. Prospecting is confined, 

 however, to an approximate north-south distance of 18 miles along the 

 ridge and to an average cross-distance of from 2 to 3 miles. Although 

 of no conspicuous height, the ridge forms a somewhat prominent feature 

 in the landscape. 



Natural outcrops of the rock are by no means common and are seldom 

 more than 3 feet high, forming sharp and narrow spurs or reefs, which 

 persist for only short distances. The numerous shafts sunk over the 



* Types of Copper Deposits in the Southern United States, Trans. Amer. Inst. Min. Engrs., 

 1901, vol. xxx, pp. 453, 454. 



fOres of North Carolina, Raleigh, 1888, p. 215. 



