156 



GEOLOGY OF THE NAKBAGANSETT BASIN. 



the phenomena of the Wamsutta series in North Attleboro and the under- 

 lying terrane of schists with intrusive granite-porphyries in Cumberland into 

 an interpretable relation. On the one hand, we have the effusive products 

 of volcanic action; on the other hand, the underground conduits and rents 

 filled with their equivalent portions of the magma. 



The same story is fairly derived from the Blue Hill region on the 

 north side of the Norfolk County Basin. The beginning of sedimentation 

 in this part of the Carboniferous land area appears clearly to have been 

 accompanied by extensive acid eruptions. It is probable, as above noted, 

 that the large felsite area about Boston was formed also in Wamsutta time. 

 How much later the action continued can not be readily determined. The 

 intrusion of pegmatitic granites in the southern arm of the Narragansett 

 Basin, in the vicinity of "Watsons Pier, together with the marked local meta- 

 morphism of all the Carboniferous strata in that portion of the area, shows 

 that volcanic action held on there later than in the northern fields, if it did 



M/7/ers ft/Ver Abbots Run 



Hoppin ///// 



Fig. 15.— < leolou-iral wen 



not altogether take place later than the deposition of the Carboniferous 

 strata in this part of the continent. 



FOLDING OF THE "WAMSTTTA GROUP. 



The folds of the strata of the red Wamsutta series in North Attleboro 

 are the most complicated that have been found in the Narragansett Basin. 

 The large horseshoe-shaped area of red rocks above described wraps 

 around the older granitite and Cambrian rock of Hoppin Hill, so that 

 the general structure is anticlinal; but the dips of the beds are now 

 in many places inward toward the center, giving rise to an apparent 

 synclinal structure. On the east, from the village of North Attleboro 

 southward to South Attleboro, the dips of the red beds are mainly inward 

 toward the Hoppin Hill area, until at the latter place they become very 



