PRUDENCE TSLAND. 237 



the lower beds of the small section here exposed. These shales are every- 

 where filled with dark minerals, which in some cases resemble, macroscop- 

 ically, ottrelite, and in other cases may be some other dark micaceous 

 mineral. The pebbles of the conglomerate are uniformly small, usually 

 not over li inches in diameter. Many of them are distinctly quartzitic or 

 granitic; in the latter case of medium grain, of bluish tint, and without 

 phenocrysts. 



There has been no flattening of pebbles or considerable shearing, 

 metamorphism being, however, abundantly shown by the frequent presence 

 cf black mica in the sandstone and of ottrelite in the black shales. 



A continuation of the strikes along the entire western margin of 

 Conanicut would carry the series there exposed to Hope Island. The 

 form of the sea bottom between these two islands also suggests a general 

 continuity of strata, and the rocks exposed on Hope Island are believed 

 to belong to the same general series as those exposed on Conanicut, although 

 possibly just beneath that series, as is indicated by the more quartzitic 

 phase and the general absence of the more argillaceous or slaty pebbles, 

 the latter being more frequently quartzitic and granitic. At Hope Island, 

 however, the strikes are much more toward the northeast, averaging N. 30°E. 



A continuation of the strike would carry these rocks toward Johnsons 

 and Pine Hill ledges south of Pine Hill Point, on the western shore of 

 Prudence Island. Whether they occur there could not be determined. 



PRUDENCE ISLAND. 



The lowest rocks exposed on the west side of the island are found 

 north of Prudence Park wharf, and continue thence northward, forming 

 the shore for a little over a mile, with an average strike of N. 20° E. 

 and a dip of 25° to 45°, at one place 60° E. The average dip is about 

 35°. At the wharf the sandstone is bluish, with a few thin conglomerate 

 layers. The pebbles are elongated, but much less than at Hope Island, 

 and the general metamorphism is evidently less. The sandstone series 

 appears again about a quarter of a mile northward, at the end of a long 

 inward curve of the shore, where it contains thin conglomerate layers. 

 Thence it follows the shore northward, the shale series often appearing in 

 contact with the sandstones on the eastern line of outcrop, on the top of 

 the bank. Black carbonaceous streaks often band the sandstones. At some 



