Metamorphic Sediments in Southwestern Rhode Island. 449 



Evidence at Westerly and Niantic, M. I. 



The writer during the past six years has made several visits 

 to the Westerly, R. I., granite quarry district along the south- 

 ern part of the Connecticut boundary, and one visit to the 

 neighboring and similar district of Niantic, R. I. (fig. 1 ) 

 He finds at these places the above summarized evidence dupli- 

 cated and supplemented by a later intrusion — that of the Wes- 

 terly granite. Metamorphic sediments here appear only as 

 isolated inclusions in granite. Both the sediments and the 

 Sterling granite series are cut by dikes of the fine-grained 

 Westerly granite ( quartz-monzonite according to Dale ). * 

 The latter rock has the same mineralogic characters as the 

 Sterling granite, differing only in containing a higher percent- 

 age of plagioclase. Its contact phase and apophyses are 

 medium-grained to pegmatitic, and cannot be distinguished 

 in the specimen from the Sterling granite series. The contacts 

 of the Westerly with the Sterling granite are sharp, but the 

 close petrographic resemblance between the two rocks and the 

 absence of any evidence indicative of widely different age 

 favor the interpretation that the Westerly granite is not a type 

 independent of the Sterling granite series, but the latest 

 exposed phase of the same batholith. 



Reconnaissance Eastward to the Kingstown Area. 



Two reconnaissance traverses have been made across south- 

 western Rhode Island, one extending from the southeastern 

 Connecticut area .eastward to Wickford Junction, the other from 

 Hope Yalley southward to JSTiantic and thence eastward, in a 

 zigzag course, to Wakefield (fig. 1). The outcrops visited 

 are plotted on the map. Those along the first, or northern, 

 traverse are identical in character with the normal gneissoid 

 Sterling granite, save one outcrop of the porphyritic type a 

 mile west of Millville. The normal type is disintegrated to 

 a considerable extent, a characteristic feature in parts of south- 

 eastern Connecticut, and some outcrops are completely reduced 

 to a coarsely granular soil to a depth of six feet or more. 



Short veins of pegmatite and pegmatitic quartz, from less 

 than an inch to one foot in width, are commonly present, most 

 of them cutting across the schistosity of the granite. One small 

 dike of fine-grained granite, similar to the Westerly type, was 

 noted on the southward sloping ridge 1-J- miles east of Pine 

 Hill. No inclusions of the metamorphic sediments were found. 



A glance at the map will show that no outcrops were found 

 along the eastern three miles of the traverse ; but over 99 per 



* Dale, T. N., The Chief Commercial Granites of Mass., N. H. and 

 E. I. Bull.. U. S. G. S., No. 354, 1908, pp. 190 et seq. The reader is referred 

 to this Bulletin for structural and petrographic details. 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 173.— May, 1910. 

 30 



