92 PROCEEDINGS OF THE PHILADELPHIA MEETING 



slow creeping: of soil and trees down the slopes might well account for the 

 phenomena shown. 



Prof. D. W. Johnson analyzed the evidence presented by Doctor Davis and 

 concluded that it could not properly be regarded as supporting the theory of 

 recent coastal subsidence, for the reason that all the phenonjena described by 

 the author are frequently produced by normal retrogression of a vertically 

 stable shoreline under wave attack and ma.v be observed on lake shores where 

 no changes of level are involved. 



Fiii'ilicr rcmai-ks were made )iy Messrs. H. Ami and Joseph Barrell. 



BASIC ROCKS OF RHODE ISLAND: THEIR CORRELATION AND RELATIONSHIPS 



BY A. C. HAWKINS AND C. W. BROWN 



(Absti-act) 



Rhode Island as a whole is underlain by a great granite batholith, now 

 sheared, of uncertain age, but of high antiquity, together with other sheared 

 granite types lying to the east and west, of alleged different ages. In these 

 stocks are found remnants of metamorphosed rocks, quartzites, quartzitic horn- 

 blende, and biotite schists of so-called sedimentary or comliined sedimentary 

 and igneous origin. In addition there appear several gabbroid stocks, more 

 ()!• less changed, but rather basic in type, which may in part be pre-granitio. 

 IMoreover, there appear trappean intrusions of four distinct types, such differ- 

 ent ones as minette and Triassic diabase dikes. Of these four types, two are 

 perhaps rather closely associated in age, but the others are more remote from 

 each other. 



From the field relations and from analyses of similar rocks, which show 

 silica too low and lime and magnesia too high for sediments, it would seem 

 that the so-called sedimentary biotite schists are distinctly of igneous contact 

 origin, resulting from the intrusion of granites into earlier basic rocks more, 

 or less schistose. From the evidence along the borders of the new Carbonif- 

 erous basin, the Woonsocket basin, extending southward from the Norfolk, 

 it would appear that some of the granitic stocks asserted to be post-Carbonif- 

 erous are really pre-Carboniferous in age. 



Read in full from manuscript. 



Discussion 



Mr. Sidney Powers asked why the authors thought the Sterling to be pre- 

 Carboniferous. 



Mr. Hawkins replied that they had found that the Woonsocket basin sedi- 

 ments (presumably Carboniferous) rested unconformably on granites of Mil- 

 ford age on its borders and contained blue quartz grains evidently derived 

 from the latter. Tliey also found that the structure of the granite gneisses 

 on the borders indicated a possible anticline on whose eroded crest the sedi- 

 ments were deposited. In response to Mr, Powers's request for proof of the 

 intrusive nature of Westerly granites into Sterling granite gneiss, Mr. Haw- 

 kins stated that such contacts had been exposed in quarries at Bradford, 

 Rhode Island. 



