CHAPTER XI. 



THE PRE-CARBONIFEROUS ROCKS. 



The pre-Carboniferous rocks of the basin usually consist of granite, 

 often rendered gneissoid by shearing. In a number of localities undoubted 

 clastic rocks appear. This is true, for instance, of the western third of 

 Newport Neck, from Brentons Point to Brentons Cove, of all of the New- 

 port Harbor Islands, and of some of the shore exposures along the southern 

 margin of the harbor. The shales here are often purplish and sometimes 

 contain thin layers of limestone. At various points along the southern 

 Newport Harbor region rather thick layers of limestone occur, in striking- 

 contrast to the absence of limestones in the Carboniferous series. 1 The 

 purplish or greenish shales are frequently interbedded with a more quartz- 

 itic greenish or whitish rock, sometimes shaly, but usually more like argillite. 



Similar rocks are found along the eastern shore of Sakonnet River 

 from Browns Point to the granite area a mile north of Sakonnet Breakwater. 

 The same purplish-colored shales, with occasional very thin limestone 

 layers, and the same greenish argillitic or quartzitic rocks are seen here. 



The purplish shales, with their thin interbedded limestones just men- 

 tioned, remind the observer of the Olenellus Cambrian rocks found in 

 eastern Massachusetts. While not identifying these more southern expo- 

 sures with the same precise horizon northward, the writer is of the opinion 

 that eventually the purple shales of Newport Neck and Little Compton may 

 prove to be Cambrian rocks. 



Farther inland, eastward, the exposures consist of rock varying between 

 quartzite and argillite, with abundant parallel shearing planes, often show- 

 ing the effects of subsequent folding. The Cambrian beds in Little Comp- 

 ton, east of the shore exposures, are often decidedly quartzitic. So are 

 also some of the shore exposures. It is not unlikely that these exposures 

 include more than one horizon, paleontologically considered. 



1 Prof. T. N. Dale saw, April 25, 1883, in the possession of Mr. Coggeshall, a blacksmith at New- 

 port, carbonaceous shales with fragments of 10 specimens of Avieulopecten, said to have come from 

 Portsmouth mine. Sketches of these fossils were submitted to Professor Von Zittel. Their impor- 

 tance lies in the fact that, if authentic, they are the first known evidence favoring the presence of 

 salt water during Carboniferous times in New England. 



