•±56 Loughlin — Granites and Metamorphic Sediments. 



Granite Pebbles. — The granite pebbles in the conglomerate 

 are light gray to pink, fine even-grained to sub-porphyritic, 

 and consist of finely intergrown quartz and feldspar with a lit- 

 tle biotite and muscovite. Three thin sections were studied; 

 one of a pebble from an outcrop 1J miles west of Wickford 

 Junction (fig. 1), one from an outcrop \ mile southeast of 

 Hamilton, and one from a bowlder south of McSparren Hill. 

 The three thin sections present the same characters. The tex- 

 ture is conspicuously micrograph ic. The primary minerals are 

 plagioclase and micro perthite in about equal amounts, quartz, 

 biotite , and the usual minor accessories ; the chief secondary 

 minerals are muscovite, replacing feldspars, and chlorite replac- 

 ing biotite. The microperthite is the same type as that noted 

 in the arkose and conglomerate matrix. The plagioclase mostly 

 corresponds to oligoclase-andesine, though some grains appear 

 more basic. These characters suffice to point out the decided 

 lack of resemblance to the Sterling granite. 



Derivation and Correlation of the Kingstown Sediments. — 

 The composition of the Kingstown sediments thus verifies the 

 conclusions already stated, and no evidence whatever remains 

 to indicate that the Sterling granite is not the younger rock. 

 The Kingstown sediments were derived from a series of quartz - 

 ites and black slaty schists, felsite-porphyry, and igneous rocks 

 containing considerable plagioclase. The plagioclase may come 

 wholly or in part from the fine-grained granite and possibly in 

 part from more basic igneous rocks, no pebbles of which have 

 yet been found. None of these rocks are found within the area 

 studied, but they may be represented in the Cambrian forma- 

 tions and the granite-porphyries to the north.* 



The general similarity in mineral composition between the 

 Kingstown sediments and the quartz-biotite schists of the south- 

 eastern Connecticut and the Westerly-Niantic, R. I., districts 

 favors the correlation of these rocks as parts of one extensive 

 formation. Fossil evidence in the areas studied is wholly lack- 

 ing, but structural and petrographic evidence favors this provi- 

 sional conclusion. 



Summary. 



The principal conclusions reached in this paper are as follows: 



1. The Westerly granite is closely related to the Sterling 

 granite in general character and mineral composition, and is 

 considered the latest exposed phase of the Sterling batholith. 



2. The Sterling granite batholith is continuous from east- 

 ern Connecticut to Narragansett Bay, R. L, and includes 

 granite formerly thought to be pre-Cambrian. There are no 



* Emerson and Perry, op. cit., pi. 1. 



