WARREN. 



ALKALI-GRANITES AND PORPHYRIES. 



289 



igneous rocks so far as the writer is informed. In the present series 

 of rocks its presence is perhaps not remarkable because lime, to form 

 the more usual calcite, is present in very small amount, Avhile iron 

 oxide is relatively abundant. 



To determine the chemical composition of the aporhyolite a speci- 

 men of rock showing a few small feldspar phenocrysts was secured from 

 some fresh excavations made along the road just south of Wampatuck 

 Hill. The results of an analysis of this specimen yielded the results 

 given below (18). With it are given the results (19) of some determina- 

 tions made for Professor Crosby b}' students and also analyses of 

 aporhyolite fll & 20) from the nearby Xeponset Valley intrusion. 



18. Aporhyolite, Wampatuck Hill, Blue Hill Reservation, Mass. Analyst, 

 C. H. Warren. 



11. Rhyolitic faces of Neponset Valley, Mass., granite. Analyst, W. H. 

 Hall. F. Bascom, op. cit., p. 138. 



19. Average of several determinations quoted by Crosby (op. cit., p. 380) 

 of aporhyolite from Pine Hill. 



20. Aporhyolite (flow) Neponset Valley, Mass. Analyst, W. H. Walker. 

 F. Bascom, op. cit., p. 144. 



