144 GEOLOGY OF THE NARRAGANSETT BASIN. 



The relative paucity of granitic pebbles in the Wamsutta conglomer- 

 ates along the northern border is evidently due to the previously mentioned 

 condition of the granitite at the time deposition set in. Nowhere is there a 

 sharper contrast between the arkose beds and the red shales than on the 

 southern face of Foolish Hill. Bands of red shale here alternate with the 

 arkose in a manner to show that the small particles of the shale brought 

 with them their coloring matter from the seat of denudation, as Russell has 

 argued in the case of the red beds of the Juratrias. 1 The importation of the 

 oxide of iron subsequent to deposition would have colored the arkoses and 

 the shales alike. 



About a mile southwest of Whiteville, shown on the Dedham sheet, 

 conglomerates occur dipping gently southward. The quartzite pebbles of 

 this rock are locally brecciated, and their surfaces exhibit a kneaded appear- 

 ance on the matched faces, showing clearly that brecciation has taken place 

 since deposition. The waterworn rounded surface of the original pebble 

 can be readily traced. These dynamic phenomena indicate that the strata 

 along this northern margin have never been under the pressure which has 

 so profoundly acted upon the elongated conglomerate pebbles near Newport, 

 Rhode Island. 



The shallowness of the waters — if indeed the deposits were made in a 

 permanent water basin — over this area in Wamsutta time is shown by the 

 current marks on sandstone layers between Whiteville and Easton, and by 

 the coarseness of the sediments. 



The structure of the beds is everywhere comparatively simple, their 

 dip being southerly beneath the carbonaceous strata which begin the Rhode 

 Island Coal Measures. Their continuity is frequently interrupted by faults 

 in the manner explained in the discussion of the boundary line from Burnt 

 Swamp Corner eastward. 



Gray sandstones of the northern border. — In the small hill near the border northwest 

 of the Shepardville reservoir, in Wrentham, there are exposures of a brown- 

 ish, sometimes greenish, fme-gTained, rather massive rock, which under the 

 microscope is seen to be composed of grains of clastic quartz and feldspar. 

 This rock is at present considered as a member of the Wamsutta series, and, 

 on account of its more extensive development a few miles southward, in 

 North Attleboro, may be called the Attleboro sandstone. The outcrops 



1 Subaerial decay of rocks, by I. C. Kussell : Bull. U. S. Geol. Survey No. 52, 1889, p. 56. 



