GENERAL FEATURES. 9 



along the eastern border, from near the southern end of Aquidneck Island 

 to Freetown, Massachusetts, a distance of 35 miles, a granitic area of 

 considerable extent had already risen above the surface of the sea and 

 was the seat of no little erosion. This is shown by the fact that along 

 this line the rocks at the base of the Carboniferous section are made up 

 mainly of granitic debris, the mass forming a characteristic arkose, at 

 points so resembling the material from which it was derived that it appears 

 at first sight to be the product of simple decay in place. Its' age is suffi- 

 ciently indicated by the numerous Carboniferous fossils disclosed by the 

 pits which have been made in the mass in the search for fire clays. It is 

 likely — though the evidence is less indicative than that just noted — that 

 the eastern wall of the basin was in Carboniferous time continued north- 

 ward as far as the neighborhood of Cohasset. The evidence is to a great 

 extent from the drift, and is therefore subject to much doubt. 



The condition of this basin in the beginning of Carboniferous time Avas 

 apparently that of a broad trough jDenetrating far into the land and 

 perhaps, though probably not, extending westward so as to include with- 

 out break what is now the separated basin extending through the central 

 part of Worcester County southward into Connecticut and northward to 

 New Hampshire. The very coarse nature of the pebbly — or, indeed, we 

 may term it cobbly — waste which occurs in the upper part of the Carbon- 

 iferous, appears to indicate that the trough must have been shallow. This 

 conclusion is affirmed by the tolerably uniform distribution of the pebbles, 

 some of them a foot or more in diameter, across the basin on the line from 

 Fall River to Attleboro. 



On the assumption that the Narragansett Basin was shallow at the 

 beginning of the Carboniferous period, and on the supposition that in the 

 center of the field these beds attain a depth of several thousand feet, it 

 seems necessary to assume that the orogenic work was in part accomplished 

 during that time. The history of the basin can be best explained by the 

 hvpothesis of an extensive subsidence of the land within the limits of the 

 trough as the beds which it contains were laid down, and a corresponding 

 overlap invasion of the sediments, which constantly removed the shore 

 lines farther away from the center of the basin. 



After the close of the Carboniferous period the Narragansett district 

 was evidently the seat of yet further mountain-building actions, which led 



