442 Hawkins — Notes on the Geology of Rhode Island. 



Table I. 

 Analyses of Carboniferous Sediments from Bhode Island. 



No. 24 25 



Si0 2 79-77% 61-70% 



A1 2 3 13-99 27-18 



Fe 2 3 -64 8-02 



MgO -37 -4Y 



CaO -30 -50 



Na 2 2-40 



K 2 2-54 Igni- 



H 2 -38 tion 



C0 2 ■ -06 Loss = 2-90 



S None 



MnO Tr. 



100-45% 100-77% 



Sp. Gr. 2-690 (porous). 



24. Arkose, Summit of Snake Hill, Harmony, E. I.; Woonsocket Basin. 

 A. C. Hawkins. 



25. Shale, Windmill Hill, Providence, K. I.; Narragansett Basin. A. F. 

 Buddington. (Composite sample every 2 feet across quarry, exclud- 

 ing ottrelitic shales on west wall.) 



The Milford granite gneiss also, together with its 

 included quartzites and basic rocks, is clearly pre-Car- 

 boniferous. At Nautaconkanut Hill, southwest of Prov- 

 idence, for instance, a basal Carboniferous conglomerate, 

 exposed along the east side of the hill, contains pebbles of 

 granite gneiss, green schist, and quartzite, plainly derived 

 from adjacent outcrops of the latter rocks in the immedi- 

 ate vicinity. On the east side of Narragansett Bay, 

 arkosic gradations of Carboniferous sediments into the 

 bordering granite gneiss are very plainly exposed, as at 

 Steep Brook, north of Fall Eiver, and in the railroad cut 

 at Tiverton. On Conanicut Island similar conditions 

 are found. 



The Sterling granite gneiss is at first much more diffi- 

 cult to place as to age relations to the Carboniferous, 

 whereas all the contacts along the Narragansett Bay 

 front appear to be obscured, largely by a long tidal 

 estuary (Pattaquamscott River) which occupies the con- 

 tact line. Loughlin 7 has maintained that certain coarse 

 pegmatites and granites which intrude the Carboniferous 

 sediments at Tower Hill and elsewhere in that vicinity are 

 probably connected with the Sterling granite gneiss and 

 seem to indicate the post-Carboniferous age of the latter. 



7 Loughlin, G. F., this Journal, 29, 450-455, 1910. 



