in the Xarragansett Basin. 51 



able at present, and reliable structural data pointing to their 

 separation or correlation is lacking. Certain distinctions in age 

 have been made, but the structural evidence for these distinc- 

 tions, some of which is cited in this paper, does not appear 

 convincing, and it remains for future work to determine the 

 structural and age relations of these granites to one another. 

 Until this is done, some of the statements here presented must 

 be regarded as tentative. Further attention will be called to 

 the granite problem on later pages. 



Sedi^textaet Rocks. 



Xarragansett Basin. 



The sedimentary rocks of the Xarragansett Basin are grouped 

 by TVood worth as follows :* 



4. Dighton conglomerate group 



3. Rhode Island Coal Measures 



•2. Wamsutta group 



1. Pondville group (conglomerates with basal arkose) 



As the Pondville and Wamsutta formations are limited to 

 the northern part of the Xarragansett aud to the adjoining 

 Norfolk County Basins, and as the evidence at hand regarding 

 them is scant, they will not be considered until after the 

 " Coal Measures " and the Dighton conglomerate. 



The " Coal Measures-' — The 4i Coal Measures " are the 

 most extensive formation of the Xarragansett Basin, and in 

 their southern part include what Foerste has called the Kings- 

 town series (fig. 1), which is cut by apophyses of the Sterling 

 granite gneiss. The part of Foerste ? s Kingstown series studied 

 by the senior authorf is limited to the southwest part of the 

 Basin nearby the granite contact. It consists of an alternating 

 series of light to dark gray arkose, conglomerate, and phyllite, 

 and one or more graphitic beds. The conglomerate pebbles, 

 besides Cambrian quartzite, and schists, include white-weather- 

 ing quartz felsite-porphyry and granite of "the East Greenwich 

 type. The arkose and the conglomerate matrix consist of 

 quartz, plagioclase, some microcline of the East Greenwich 

 granite type, biotite, and muscovite. There is a total absence 

 of pebbles or mineral grains characteristic of any of the other 

 granites involved in the problem — notably the Milford and 

 Dedham types. 



At Xatick. R. I., north of the area visited by the writer, 

 Foerste;}; describes the basal conglomerate beds of the " Coal 



*U. S. Geol. Survey Mon. 33, p. 134. 



f This Journal (4), vol. xxix, p. 455. 1910. JOp. c it. } p . 054 



