Page:The Journal of geology (IA journalofgeology21894univers).pdf/41

of the geology of South Mountain, and has for many years invested it with a reputation for complexity which it in no way deserves.^[1]

In Maryland and Virginia the acid and basic lavas and tuffs of South Mountain are extended southward as an important element 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.^[2] 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 summer 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 command was inadequate for the thorough exploration of the volcanic 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 encountered. On the road from Sanford to Pittsboro purple felsites and porphyries showing spherulites and beautiful flow-structures, and accompanied by pyroclastic 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