252 GEOLOGY OF THE NAREAGANSETT BASIN. 



black, carbonaceous type, especially along the northwestern side of the 

 exposure, interstratified with which is coarser white sandstone. Both rocks 

 contain garnets, and the shaly rock is ottrelitic. Strike N. 23° E., dip 

 about 45° W. 



Toward the western end of Potowomut Neck, near a residence north 

 of the road, are numerous exposures of sandstone with strike N. 50° E., 

 dip 35° N., on the western end of the exposures. Toward the eastern end 

 of the neck a series of exposures extend from the Potowomut Rocks directly 

 southward nearly to the Potowomut River. The general trend of the rocks 

 is northeasterly, but it is evident that considerable irregular flexuring or 

 folding has taken j)lace, so that the strikes are very irregular, and the dips are 

 both northerly and southerly, according to the particular locality observed. 

 While therefore unsatisfactory for purposes of stratigraphy, these exposures 

 are still worthy of close examination, because they show some very inter- 

 esting phenomena connected with the shearing of these rocks more or less 

 perpendicular to the bedding and the consequent interpenetration of the 

 frayed surfaces of the adjoining layers. The more carbonaceous layers in 

 the exposures west of the house north of the road show garnets and other 

 minerals, the products of metamorphism ; one of these minerals occurring 

 in the rock is columnar, black, with frayed expanded ends. While a large 

 part of the rock exposures are coarse white sandstone or finer-grained black 

 shaly rocks, as in the rest of the series described in this area and south- 

 ward, yet there is a very large exposure, west of the buildings north of the 

 road, of a greenish shaly rock, spotted with the stained marks caused by 

 the weathering of some pyritiferous mineral, which is very unusual in the 

 series. The strike at the Potowomut Rocks seems to be N. 50° E., dip 

 apparently steep northwest. 



WESTERN BORDER OF THE CARBONIFEROUS BASIN, FROM EAST 

 GREENWICH TO NATICK AND NORTHWARD INTO CRANSTON. 



The present western border of the Carboniferous basin of the Narra- 

 gansett region extends from East Greenwich southwesterly, west of Davis- 

 ville and Wickford Junction. At East Greenwich the pre-Carboniferous 

 rocks form the steep hillside above the town. At a road corner near the 

 top of the hill, in a line almost directly west of the Potowomut Rocks, 

 these more ancient rocks are well exposed in a quarry. The rock here is 



