246 GEOLOC^Y OF THE NARRAGANSETT BASIN. 



in the chapter on the arkoses and conglomerates of the Narragansett Bay- 

 region (Chapter X). 



WEST OF THE COVE AND PATTAQUAMSCOTT RIVER. 



Pattaqnamscott River and the cove toward the southwest were once 

 probably occupied by the Carboniferous series, now removed by erosion, 

 excepting along the western side of the valley formed by the 'eastern side 

 of Tower Hill At the southern end of this hill, north of the railroad, 

 the rock is very quartziferous and schistose. The schistosity strikes 

 N. 80° E. and dips 60° N. In certain layers the rock is full of pebbles, 

 chiefly quartzitic, bu.t with also some granitic ones. The pebbles are very 

 much elongated and flattened, as at the pier exposure. Farther northeast 

 the conglomerate pebbles are still more drawn out. The pebbles usually 

 are white, bordered by a greater accumulation of black mica than is found 

 in the general mass. As the lengthening of the pebbles continues, a point 

 comes where there appears an alternation of whiter and darker thin bands, 

 in which only a person familiar with such studies would still recognize 

 the pebble. This limit has here been reached. Farther down the hillside 

 some of the larger quartzitic and granitic pebbles are less drawn out, and 

 can easily be recognized. Some of the larger ones are 1| to 2 inches long. 

 Below the hotel, farther northeast, the rock is well exposed. From the 

 southern end of Tower Hill, as far as the hotel, the Carboniferous rocks are 

 frequently cut along the schistosity by dikes of ordinary granite, and also 

 by the pegmatite phase of the same, into which it merges in some places, 

 while at others the contrast is sharp. The result is a rapid alternation of 

 clastic Carboniferous rock with these granitic and pegmatitic dikes, espe- 

 cially well shown below the hotel. The alternation of Carboniferous rocks 

 and the pegmatitic granite occurs for a distance of 2 miles along the east 

 side of Tower Hill. The schistosity dips westward. Groing northward no 

 more Carboniferous rocks are encountered until the old plumbago mine, a 

 little over half a mile south of Bridgetown, is reached. Above the mine is 

 a good exposure of a dark, very micaceous, and probably graphitic schist. 

 The strike of the schistosity here is N. 5° E. and the dip 70° E. Farther 

 down the hillside a great quartz vein includes scattered and brecciated rem- 

 nants of the Carboniferous series; among others, fragments of genuine 

 black plumbago, unctuous to the touch. The main body of Tower Hill, 



