in the Narragansett Basin. 47 



The unconformity separates the " Coal Measures " below from 

 the Dighton conglomerate above, and the latter is assigned by 

 the authors to the Permian. There is some indication that the 

 Wamsutta formation and Pondville conglomerate are also Per- 

 mian, but present evidence on this point is very meager, and 

 the tentative assignment of these rocks to the Permian should 

 be regarded as a working hypothesis rather than a final conclu- 

 sion. In the light of the new data here presented a tentative 

 correlation table is given, correlating the upper conglomerate 

 of the Norfolk County Basin and the upper part of the Pox- 

 bury conglomerate with the Dighton conglomerate. The dis- 

 cussion of the stratigraphic problem necessarily involves some 

 discussion of the present state of the granite problem, and it 

 is suggested that the different biotite granites in the region 

 may be parts of one extensive and complex batholith, rather 

 than representatives of two or more batholiths of widely sepa- 

 rated geologic ages, as has been supposed by several who have 

 worked in the region. The evidence, however, on this point 

 is also so meager that no final conclusion, only a suggestion, 

 can be offered. 



Summary of Areal Geology. 



The positions of the three sedimentary basins are shown in 

 fig. 1. The rocks in them are practically all conglomerates, 

 sandstones (or arkoses), and slates, showing varying degrees of 

 dynamic metamorphism. As these rocks have all been derived 

 from rocks in the immediately surrounding areas, their differ- 

 ence in composition can best be noted after the surrounding 

 rocks have been described. The surrounding rocks are largely 

 granites and closely related rocks. Cambrian quartzites, slates, 

 schists, and limestones are also present and have furnished 

 material to the strata in all of the three basins ; but only the 

 granites are of sufficiently critical importance to need descrip- 

 tion here. 



Granites. 



East Gr< enwich granite group* — The East Greenwich gran- 

 ite group occupies a comparatively small area, along the west 

 border of the Narragansett Basin at East Greenwich. It com- 

 prises four principal varieties: granite and granite porphyry, 

 a basic phase of the granite porphyry, a blue quartz-microcline 

 porphyry, and a microgranite. A micrographic texture is a 

 character common to all these varieties, and is especially well 

 developed in a large part of the microgranite. Microcline is 



* The data given here are abstracted from Emerson and Perry's description. 

 See U. S. Geo!. Survey, Bull. 311, pp. 58-65, 1907. 



