370 T. L. WATSON — VIRGILINA COPPER DISTRICT 



Areas of such volcanics have been described from eastern Canada,* 

 by Bailey, Matthew, Ells, and Bell. In New England t Wads worth, 

 Diller, Shaler, Bayley, G. 0. Smith, H. S. Williams, and Gregory have 

 described similar areas in Massachusetts and Maine. Other similar 

 areas are well known in Pennsylvania, Maryland, and Virginia through 

 the investigations of G. H. Williams, X Keith, § and Bascom.|| In the 

 Lake Superior regional they have been long known through the contri- 

 butions principally of Irving, Van Hise, the Winchells, Clements, Bay- 

 ley, Wadsworth, Williams, and Grant. 



Through the studies of Clements and Brooks areas of greenstone 

 schists, similar to those of the Lake Superior region, and derived from an 

 original basic igneous rock of pre-Cambrian age, have been identified in 

 the crystalline area of Alabama.** 



The rock types indicated in these areas vary from acid to basic vol- 

 canics in composition, according to locality, and are represented princi- 

 pally by such rocks as rhyolite, andesite, diabase, diorite, gabbro, and 

 their associated tuff deposits. 



From the descriptions, the rocks of the Virgilina district are closety 

 similar in many essential features to the corresponding altered phases of 

 the Catoctin and South Mountain areas in Virginia, Maryland, and 

 Pennsylvania, and certain ones of the famous greenstones from the 

 Lake Superior region. When the altered rocks, greenstones, of the va- 

 rious areas are traced by means of chemical and microscopical study to 

 the original rock type, the differences become more apparent. This dif- 

 ference is that which distinguishes in the original rock an andesite from 

 a diabase, diorite, gabbro, etcetera ; but, as already stated, the altered 

 rock derived from these several types is closely similar. 



Sufficient study of the ancient volcanic rocks occurring to the south- 

 west of the Virgilina area, in North Carolina, is lacking on which to 

 base specific comparisons. That they are altered volcanic rocks of great 

 age, comprising both acid and basic types, is established, but the exact 

 mineral and chemical composition, denoting the original rock types 

 from which they are derived, is yet to be investigated. Megascopic 

 descriptions and the field relations of many of the basic types indicate 

 their striking similarity to those of the Virgilina district. 



* Ann. Report Canadian Geol. Survey, 1877-'8 D D, 1879-'80 D, 1889-'90 F, 1891. 



f Mus. Comp. Zool. Bull., vol. v, p. 282 ; ibid., vol. vii, pp. 166-187, 1881 ; A. J. S., 1886, vol. 32, p. 40 ; 

 8th Ann. Rept. U. S. G. S., pt. 2, p. 1043 ; A. J. S., 1899, vol. viii, p. 359 ; Bull. no. 165, U. S. G. S., 1900, 

 212 pp. 



J A. J. S., 1892, xliv, 482-496; Jour. Geology, 1894, ii, 1-31. 



g 14th Ann. Rept. U. S. G. S., 1894, pp. 285-395 ; Am. Geol., 1892, x, 365 ; Bull. G. S. A., ii, 156, 163. 



|| Bull. no. 136, U. S. G. S., 1896, 124 pp. 



TJThe literature is scattered through annual reports, monographs, and bulletins of the U. S. 

 Geological Survey and the state reports of the surveys of Minnesota, Wisconsin, and Michigan. 



**Geol. Survey of Alabama, Bulletin no. 5, 1896, pp. 84-96, 120-197. 



