Haiukins — Notes on the Geology of Rhode Island. 437 



Aet. XV. — Notes on the Geology of Rhode Island; by 

 A. C. Hawkins. 



Introduction. 



The recent paper by B. K. Emerson, 1 covering the 

 geology of Massachusetts and Rhode Island, with its 

 geologic map, sets forth in a somewhat generalized way 

 that of the area included in western Rhode Island. The 

 material herewith submitted, largely the results of inves- 

 tigations in the latter area by the present writer during 

 the years 1912-1916, is in accord in many important 

 respects with Professor Emerson's conclusions, and may 

 serve to furnish certain of the geologic details not 

 hitherto available. 



Acid Igneous Rocks. 



The State of Rhode Island is underlain by a great 

 granitic batholith, whose members, now all more or less 

 badly sheared, are represented by three principal types, 

 the Milford, Northbridge, and Sterling granite gneisses. 

 These are biotite granite gneisses of closely similar 

 composition, 2 each with its distinguishing characteristics 

 (although certain phases of each resemble the others very 

 closely at times), and together or separately they have 

 invaded all of the older rocks of this region. The part 

 of the granitic mass exposed to the west of the Car- 

 boniferous sediments of the Narragansett Basin is in its 

 arrangement about as follows : In the northwestern por- 

 tion of the State, as far south as the vicinity of Moosup 

 Valley, and from thence southeastward toward East 

 Greenwich, is found the Northbridge granite gneiss, 

 covering the western half of Providence County and a 

 portion of Kent County; northwest and west of Provi- 

 dence, in the eastern half of Providence County, as far 

 west as the. general vicinity of "Woonsocket, and perhaps 

 somewhat farther westward (compare Emerson, op. cit.), 

 occurs the Milford granite gneiss ; and farther south, 

 from East Greenwich southward toward Point Judith and 



1 TJ. S. Geol. Survey, Bull. 597, 1917. 



2 Emerson, B. K., and Perry, J. H., U. S. Geol. Surv., Bull. 311, 9-10, 

 45-47, 1907; Loughlin, G. F., this Journal, 29, 447-457, 1910; U. S. Geol. 

 Surv., Bull. 492, 35-38, 1912. 



