WAMSUTTA GROUP. 149 



angles. While the section at Pondville indicates simple downfolding of 

 the margin, the form of the basin and the distribution of beds along the 

 border, particularly on the north, are suggestive of downfaulting of the 

 beds in most parts of the basin. The strata are usually not so much meta- 

 morphosed as those south of Pawtucket in the main basin. The occurrence 

 of locally metamorphosed conglomerates at Morrills Station (see fig. 6, 

 p. 120), on the Walpole and Wrentham Railroad, illustrates the effect of 

 great pressure in producing the elongation of pebbles and in inducing 

 secondary minerals. In this instance the rock has become very markedly 

 sericitic and disintegrates rapidly. 



SOUTH ATTLEBORO LIMESTONE BED. 



This name has been chosen for the occurrence of nodular aggregations 

 of calcite and amorphous carbonate of lime which are associated with the 

 red shales of the Wamsutta or red rocks, and which are particularly well 

 displayed in South Attleboro, in the southern base of the hill at the foot oi 

 which the town is situated. 



A section from the road northward up the hill is as follows: 



Section of the Wamsutta formation in South Attleboro, Massachusetts. 



Feet. In. 



Red shales, concealed southward 6 



Fine conglomerate 1 2 



Red shale 6 



Limestone bed 6 



Shales, red 10 



Conglomerate 5 



Shales, red, partly covered 119 



Sandstone, red 24 8 



Shales, red, partly concealed 99 2 



(Felsite, reddish and irregular in thickness, exhibiting flow structure, 25 ft.) 



Shales, red 2S 4 



Red conglomerate, coarse pebbles 60 



Shales, red 60 



(Diabase, amygdalar cavities on northern aspect, 15 ft.) 



Red shales, concealed northward, measured 175 



The limestone occupies irregular kidney-shaped cavities in the red 

 shale, or is for a few inches of its thickness in the form of rude layers. 

 Another mode of occurrence is as isolated nodular masses half an inch in 

 diameter. These nodules are frequently elongated in the direction of the 



