THE DISTRIBUTION OF ANCIENT VOLCANIC ROCKS. 27 



of the geology of South Mountain, and has for many years 

 invested it with a reputation for complexity which it in no way 

 deserves.^ 



In Maryland and Virginia the acid and basic lavas and tuffs 

 of South Mountain are extended southward as an important ele- 

 ment in the composition of the Blue Ridge. They have been 

 somewhat studied by the writer in this region and have been 

 mapped and described by Keith.^ This author mentions two 

 quartz-porphyry areas showing flow-structure and tuffs, the 

 larger between Catoctin and Blue mountains in Maryland, and 

 the smaller near Front Royal in Virginia. He says that the 

 diabase shows many indications of being a surface flow, and that 

 it extends along the Blue Ridge from Maryland half way across 

 Virginia, with an average width of twenty miles. 



Southern States. — Volcanic rocks are largely developed in the 

 central portion of both the Carolinas, as may be gathered from 

 the old reports of Emmons and Lieber. During the past sum- 

 mer the writer had the opportunity of examining the belt in 

 Chatham and Orange counties. North Carolina, in company with 

 the State Geologist, Professor J. A. Holmes. The time at com- 

 mand was inadequate for the thorough exploration of the vol- 

 canic belt which skirts the western edge of the Triassic sandstone, 

 but in a drive from Sanford to Chapel Hill an abundance of the 

 most typical ancient lavas, mostly of the acid type, was encoun- 

 tered. On the road from Sanford to Pittsboro purple felsites 

 and porphyries showing spherulites and beautiful flow-structures, 

 and accompanied bypyroclastic breccias and tuffs, were met with 

 two miles north of Deep river and were almost continuously 

 exposed to Rocky river. Here devitrified acid glasses with 

 chains of spherulites and eutaxitic structure were collected, while 

 beyond as far as Bynum on Haw river, four miles northeast of 



^See J. P.Lesley: Summary Final Report, Penn. Geol. Survey, Vol. i, p. 151, 

 1892. 



^^ American Geologist, Vol. 10, pp. 366-68, December, 1892. Geologic Atlas of 

 the U. S., Harper's Ferry Sheet {in press). For their distribution in Maryland see the 

 Geological Map of the State, edited by G. H. Williams, and published in the 

 World's Fair Book "Maryland," Baltimore, 1893. 



