DISTEIBUTION OF THE GRANITES 365 



Several narrow dikes of minette accompany the granite, which are, so 

 far as known to the writer, the only basic dikes yet discovered along the 

 Rhode Island and Connecticut coast east of the Triassic traps and ex- 

 clusive of the peridotite of Iron Mine hill, Cumberland. 



Almost exactly the same area and phenomena as those described by 

 Pirsson formed the subject-matter of a paper by Collie,* which, how- 

 ever, makes no reference to Pirsson's observations or those of any pre- 

 vious writer. Collie differs from Pirsson in concluding that the granite 

 was intruded before the Carboniferous. He shows that the minettes are 

 later than the granite, as one dike of them cuts the granite. Crosby f 

 has recently examined the same area, and also the related one at New- 

 port neck. He reaches the same conclusion as Collie as to the age of 

 the granite, and refers it in particular to the Cambrian. 



Granites similar to the above occur on the west shore of Narragansett 

 bay, between the Bonnet and the Pier. They are extensively accom-, 

 panied by pegmatite dikes. 



Between Narragansett bay and Niantic, where the first granite quarries 

 are met, there are occasional outcrops of massive granites in the gneisses, 

 but they have not been opened up by any quarry industry and present 

 no features differing essentially from the more significant exposures fur- 

 ther west. About a mile south of the railway station at Niantic, Rhode 

 Island, on a hill in the midst of woods, quarries have been opened in a 

 finely crystalline gray granite, practically like that at Westerly. Con- 

 tacts with the gneissic walls are well shown, as are pegmatites and other 

 phenomena characteristic of the granite intrusions. 



About 5 miles south of Niantic, over a drift-buried area, is the small 

 summer resort known as Quonochontaug beach. It is located immedi- 

 ately on the seabeach, in the neighborhood of some ledges of coarse 

 biotite-granite. In a scattered group of boulders on the shore is the 

 large one of orbicular or spheroidal granite, which was described and 

 figured by the writer some years ago.| 



The granites are most extensively opened up for study in the vicinity 

 of Westerly, in the extreme southwestern corner of the state. Two hills 

 respectively south and north of the railway have furnished large amounts 

 of stone, especiall}^ for monumental work. There are two contrasted 

 varieties of granite. One is a finely crystalline gray variety and is the 

 only one present in the southern hill, where it is quarried by the Smith 



*G. L. Collie: The geology of Conaoieut Island, Rhode Island. Trans. Wis. Aead. of Sei., Arts 

 and Letters, vol. x, March, 1895, p. 199. 



t W. O. Crosby: Contribution to the Geology of Newport neck and Conanicut island. Amer. 

 Jour. Sci., March, 1897, p. 2:50. Crosby gives a good bibliography and resume of previous work. 



JJ. F.Kemp: .\n orbicular granite from Quonochontaug beach, Rhode Island. Trans. New 

 York Acad. Sci., vol. xiii, 1894, p. 140. 



