160 



GEOLOGY OP' THE NARRAGANSETT BASIN. 



stone beds than in the shales, the latter being very much crumpled and 

 often striking east and west. 



The metamorphism of this belt allies it petrographically with the area 

 southward in the lower part of Narragansett Bay. The sandy and pebbly 

 beds, however, exhibit less dynamic metamorphism, but the shales above 

 exhibit in a marked degree the development of new minerals which has 

 resulted from this change. 



There are three well-marked north-south troughs about Providence 

 in which the softer argillaceous beds occur, separated by more resistant 

 arenaceous strata standing out as ridges. Beginning on the west, and next 



\Seekonk River 



I East Providence 



\ [Ten Mile River 



Fig. 17.— Hypothetical geological section east and west through Providence, Khode Island, showing supposed relations of 

 Cranston and Tenmile River heda. 



the escarpment which marks the crystalline and igneous border, there is 

 the depression between it and Sockanosset, Rocky, Sky High, Bradley, 

 and Windmill hills. The structure and character of the strata occupying 

 this depression can be inferred only from isolated observations, mainly in 

 the "dugway" in the southwestern part of Cranston, where the basal beds 

 of the Carboniferous cling to the escarpment in a recess. The next trough 

 on the east, which opens out into the bay south of Providence, is very 

 thoroughly filled in with glacial sand plains. The occurrence of conglom- 

 erates toward the south and the evidence from borings in the vicinity of 

 Providence are the sole indications of the stratigraphy. 



