PETROGRAPHY OB 1 THE ROCKS 363 



The remaining minerals occurring in the rocks present no noteworthy 

 features. 



In the thin-sections of the purple-colored slaty rocks of the Copper 

 World, Durgy, and Yancey mines and the " Slate Vein," in the Carolina 

 portion of the belt, and probably the fissile greenstone from the Halifax 

 Copper mine, in Virginia, there is strong evidence for regarding the 

 rocks as clastic volcanics. The evidence is less plain in some sections 

 than in others, on account of the extreme alteration having destroyed 

 nearly all trace of the rock structure. When "the texture is not entirely 

 destroyed the microscope shows a clastic composed of igneous fragments 

 similar in all respects to the true igneous rocks of the district.* 



The clastic nature of the rock at the Copper World mine is visible to 

 the unaided eye and is described elsewhere in this paper. At no other 

 point in the belt was the writer able to detect with certainty the clastic 

 nature of any part of the volcanics. 



The microscopic study entirely fails to indicate what the original 

 characterizing bisilicate component was in these rocks — whether augite 

 or hornblende, or both, with possible biotite and olivine. We are in 

 doubt, therefore, as to whether the rocks were originally augite or horn- 

 blende andesites. 



Chemical Analyses 



Six analyses of the Virgilina greenstones, four complete (analyses I-V, 

 inclusive) and two partial (VI and VII), were made by the writer in the 

 chemical laboratory of Denison University .f These are compared with 

 analyses of so-called greenstones (Catoctin schist) of the Catoctin belt of 

 northern Virginia (analysis VIII) and with those of the well known 

 Marquette and Negaunee districts of Michigan (analyses XIII and XIV). 

 Also analyses I and II, representing the freshest material, are compared 

 with analyses of andesites from Colorado (anal} r ses IX and XII) and 

 Maine (analysis XI). 



* Through the kindness of Professor J. Morgan Clements, of the University of Wisconsin, I have 

 been able to examine and compare the slides of the similar volcanic rocks of th6 Lake Superior 

 region, and the similarity, as remarked by Professor Clements, is strikingly close to the rocks of 

 the Virgilina district. 



Professor Clements very kindly examined the thin-sections of the Virginia-North Carolina 

 rocks and the accompanying hand specimens here described, and in a personal memorandum to 

 the writer stated that the rocks were igneous and of an andesitic character, confirming the writer's 

 study of the material ; further, that the evidence was strong for regarding some of the volcanics 

 as elastics composed of fragments of basic or intermediate igneous rocks similar to the igneous 

 rocks of the district. He says : " I find they [Virginia-North Carolina rocks] are very similar to 

 the greenstones which form so important a part of the Archaean and Algonkian of the Lake Supe- 

 rior region." 



fl am indebted to Professor W. Blair Clark, of Denison University, for kindly placing at my 

 disposal the facilities for making the analyses. 



