Art. VII. I Watson, Virgilina Copper Disttict. 117 



confirm their igneous character. When compared with similar 

 analyses of well known igneous rocks of a certain type from 

 widely separated localities, fairly close agreement is shown in 

 the essential chemical features. Knowing, therefore, the 

 greatly altered condition of the bulk of the rocks in the area, 

 such differences as are brought out in the table of analyses are 

 readily explained on the basis of chemical and physical meta- 

 morphism. 



Chemical Evidetice. 



The chemical analyses of these rocks have been previously 

 discussed in this paper — pages 112-113. The close conformity 

 in composition of the rocks (the least altered ones), as there 

 indicated, with that of andesites from well known but widely 

 separated localities is certainly indicative of igneous origin. 

 Their uniform composition is in contrast with that of a series of 

 clastic rocks, where, as shown by Rosenbusch,^ the chemical 

 proportions are largely accidental. The microscopical study 

 fully confirms the chemical evidence favoring the igneous origin 

 of these rocks. 



Comparison ivitJi other Areas. 



Scattered areas of ancient volcanic rocks have been recog- 

 nized at various localities along the Atlantic coast by geologists, 

 extending from New Brunswick through Maine, New Hamp- 

 shire, Massachusetts, Pennsylvania, and Maryland into northern 

 Virginia, the Carolinas, Georgia'" and Alabama. Some of the 

 so-called sedimentary areas of the northern Atlantic coast of 

 the earlier geologists are now regarded as altered volcanic 

 rocks. ^ 



Areas of such volcanics have been described from eastern 



1 Zur Auffassung der Chemischen Natur des Grundgebirges, Tschermak's 

 Min. u. Petrog. Mitth. 1891, Vol. XII, pp. 49-61. 



* G. H. Williams discusses this subject in the 15th Ann. Report, U. S. 

 Geol. Survey, 1895, pp. 663-664. 



' For a statement of the distribution of the volcanic rocks on the Atlantic 

 coast, see Williams, Jour. Geology, 1894, II, 1-3 1. 



