CHAPTER IV. 

 THE CARBONIFEROUS BASIN. 



The rocks referred to the Carboniferous period in the Narragansett 

 Basin are grouped together, either for the reason that they are known to 

 contain the fossils peculiar to this period or because they are stratigraph- 

 ically united with those which are thus fossiliferous. The members of the 

 formation are arkoses, conglomerates, sandstones, shales, and coals, with a 

 great variety of secondary structures. The strata are almost everywhere 

 bent into steep-sicled folds. Limestones and rocks of igneous origin are 

 conspicuous only in certain parts of the area. The beds are nonmarine, 

 and present no signs of equivalency in their lower strata with the lower 

 Carboniferous or Mississippian series. 



In a general way the strata of the basin exist under two phases: One 

 is a belt of much metamorphism, beginning near Pawtucket and extending 

 southward and widening to the sea in Narragansett Bay, but most pronounced 

 along the western boundary (see fig. 6, p. 120). The second phase is char- 

 acteristic of the greater portion of the remainder of the area, or about two- 

 thirds of the whole, extending eastward and north into the Norfolk County 

 Basin. In this field the effects of metamorphism are rarely so great as 

 seem commonly to be believed by geologists. The transition between the 

 two fields is often very abrupt. The geologist who should pass from the 

 nearly vertical metamorphic strata of the East Side in the city of Provi- 

 dence, Rhode Island, to the slightly folded and unaltered sandstone and 

 shale beds of East Providence, would, from a comparison of the rocks 

 alone, be led to infer that there was in this field a set of" very ancient tilted 

 rocks flanked on the east by strata of much less antiquity. So short is the 

 space between the two rock phases at this point, being the width of the 

 Seekonk River only, that one is led to believe that an intermediate zone 

 of considerable width has been concealed by a fault. 



In the less metamorphosed area, with which this part of the report has 



