Metamorphic Sediments in Southwestern Rhode Island. 455 



Kingstown area have not been exhaustively studied, but it is 

 very evident, from the field work done, that vertical dips and 

 the most complete recrystallization of the sediments are found 

 where granitic intrusions are most abundant. There seems, 

 then, no reason for doubting that in the Kingstown area, as 

 well as in southeastern Connecticut, the granite intrusion 

 accompanied metamorphism and folding. As the Kingstown 

 sediments have been determined to be of Carboniferous age,* 

 the time of granite intrusion and folding may be correlated 

 with the Appalachian Revolution. 



The Kingstown Sediments. — As the Kingstown sediments 

 have heretofore been regarded as resting uncomformably upon 

 the granite, a study of their composition is necessary for a 

 complete solution of the problem here considered, and as a 

 check on the conclusions already reached. Detailed descrip- 

 tions of outcrops have been made by Foerste,f and only petro- 

 graphic evidence is considered here. 



The sediments comprise chiefly an alternating series of light 

 to dark gray arkose, conglomerate and phyllite beds, with at 

 least one highly graphitic bed. Metamorphism effects are 

 every where distinct, varying from moderate around Hamilton, 

 the northernmost point studied, to extreme in close proximity 

 to granite contacts. In the latter case traces of clastic struc- 

 ture are nearly, or quite, obliterated, and the rocks are typical 

 gray gneisses and schists, penetrated by the reddish granite. 



The pebbles of the less metamorphosed conglomerate com- 

 prise quartzite , quartz-sericite schist, black very line-grained 

 slaty schist, vein-quartz, f el site-porphyry, a fine even-grained 

 granite. The granite pebbles, which do not resemble the 

 Sterling or Westerly granite, will be separately described below 

 In the highly metamorphosed conglomerate, the pebbles appear 

 as flattened lenses and even linear streaks . Only the less 

 severely mashed are clearly recognizable. The arkose and the 

 matrix of conglomerate consist of quartz, feldspar, biotite, and 

 muscovite in varying amounts. The most metamorphosed expo- 

 sures present the same general megascopic characters and varia- 

 tions as the quartz-biotite schist of southeastern Connecticut. 

 Thin sections prove the feldspars to be mostly plagioclase with 

 a few of poorly defined microperthite and, possibly, of ortho- 

 clase. Not a feldspar grain was noted with the well-developed 

 microcline twinning so characteristic of the feldspar in the 

 Sterling and Westerly granite, save in the one instance , \\ 

 miles south of E"arragansett Pier, of a schist inclusion which 

 is thoroughly injected with dikelets and stringers from the 

 granite. 



* Mon. XXXIII, U. S. G. S., plate xxxi. 

 f Op. cit., pp. 215 et seq. 



