1 1 Bulletin of Laboratories of Denisun University. [Voi xii 



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 hornblende 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 chernical laboratory of Denison 

 University.^ 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 

 (analyses IX and XII) and Maine (analysis XI). 



A cursory examination of the analyses is sufficient to indi- 

 cate the andesitic character of the rocks, with an advanced 

 stage of alteration shown in IV, V, VI, and VII. Further- 

 more, the ratio of the SiO^ to the base-forming elements in I 

 and II, the least altered material, suggests an intermediate 

 rather than an acid or basic andesite. The prevailingly low 

 SiOj in the remaining analyses (IV, V, VI, and VII) is ex- 

 plained on the basis of advanced alteration, since the rocks 

 yielding these results were the most altered and were highly 

 schistose in structure. Other apparent irregularities in the 

 analyses are likewise explained on the same basis, since the 

 greatest irregularities are indicated in the analysis of the most 



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 nf an andesite 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 Car- 

 olina rocks] are very similar to the greenstones which iorm so important a part 

 of the Archaean and Algonkian of the Lake Superior region." 



' I am indebted to Professor W, Blair Clark, of Denison University, for 

 kindly placing at my disposal the facilities for making the analyses. 



