448 Hatvhins — Notes on the Geology of Rhode Island. 



"pre-Cambrian" Northbridge gneiss is mapped by 

 Emerson and Perry as an intrusive one, the East Green- 

 wich granites being the younger. Relations with the 

 Milford granite gneiss are not discussed by them. The 

 field relations are obscure, but dikes of aplitic and gran- 

 itic material which cut the granite gneisses in the vicinity 

 of Riverpoint and Arctic might perhaps be referred to 

 the East Greenwich group. 



Felsites are not prominent in this State, and yet small 

 occurrences are present in at least two places. In the 

 adjacent area of South Attleboro, Massachusetts, they 

 are extensively developed, being associated with Carbon- 

 iferous sediments and diabase. At Diamond Hill, Cum- 

 berland, R. I., a considerable mass of dense felsite has 

 been largely replaced by vein quartz, 19 but fragments of 

 it are still plainly visible. There is also present on the 

 crest of this quartz mass a small area of unknown extent 

 underlain by a coarse biotite granite similar in appear- 

 ance to that exposed in the quarries a mile farther west ; 

 relations of granite and vein quartz are not exposed. 

 Again on the northwest slope of Bald Hill, in Scituate, in 

 local drift, are found narrow red felsite dikes cutting a 

 granite gneiss. This latter occurrence extends the zone 

 of rhyolite occurrences in Rhode Island southward a 

 little farther toward the far-away field of similar rocks 

 at South Mountain, Pennsylvania. 



A very well-defined zone extending from Wakefield 

 through Newport to Sakonnet Point is occupied by pre- 

 Carboniferous green schist, quartzite, limestone, and 

 granite, cut by prominent intrusions of pegmatite, 

 granite, diabase, gabbro, and minette, and bordered on 

 the north and possibly also on the south by sediments of 

 Carboniferous age. The writer suggests that this zone 

 of ancient rocks may represent an elevated block or 

 horst, separated by fault zones of nearly east-west strike 

 (probably pre-Carboniferous in age) from adjacent 

 blocks which have fallen away on the north and south. 

 Within this zone of disturbance, at various times, the 

 numerous intrusions have found their way upward. It 

 is in line with the Westerly granites and pegmatites, also 

 parallel to the coast line. 



19 Warren, C. H., and Powers, S., Bull. Geol. Soc. Am., 25, 472, 1914. 



