WAMSUTTA GROUP. 143 



THE AREA ALONG THE NORTHERN BORDER. 



The area of reddish and chocolate-colored strata along the northern 

 margin of the basin, from near Burnt Swamp Corner eastward, is consid- 

 ered first for the reason that along this line there is indubitable evidence of 

 the relative positions of the red and gray rocks. Throughout the extent of 

 this northern margin the red conglomerates, sandstones, and slates occur at 

 or near the base of the Carboniferous formation, or are separated from it 

 by beds of arkose and gray quartzose conglomerates. The beds can be 

 studied along the border in Wrentham about three-quarters of a mile north 

 of the Shepardville reservoir, in two small hills lying west of the stream 

 which comes in from the north. Immediately south of a small contact 

 valley between the granitite and the Carboniferous beds of the border 

 appear red sandstones and slates. The rock is pervaded by two sets of 

 cleavage planes striking about in the line of the border, the dip of one 

 being nearly vertical and that of the other into the granitic terrane at an 

 angle of 70°. The attitude of the sedimentary beds is not very plainly 

 exhibited. Limited exposures of banding indicate a strike parallel with 

 the border and a southerly dip of from 25° to 30°. The outcrops in the 

 western knoll show red sandstones succeeded by greenish sandstone, which 

 in turn is succeeded by more red sandstone. Near this locality an old mill- 

 stone made out of a reddish conglomerate with small quartz pebbles was 

 seen in 1894 built into the fence. The greenish sandstones just mentioned 

 have a more extensive development in the North Attleboro area (p. 151). 



The red beds are well exposed on the soiithern face of Foolish Hill in 

 Foxboro. They here dip steeply southward. The cleavage dips steeply 

 northward. Thin bands of red slate may be seen intercalated between 

 beds of whitish arkose. Red conglomerates with quartzite pebbles also 

 occur. The thickness of the beds is difficult to obtain with accuracy, but 

 it may be estimated at this point as upward of 1,000 feet. 



Red beds appear to the east near the contact, at some points conglomer- 

 ates prevailing over sandstones. The thickness evidently diminishes toward 

 the east, but exact measurements are wanting. The red color of the basal 

 rocks also declines and becomes of a chocolate hue. The strata are rarely 

 deep red east of Brockton, though deep-red slates occur northeast of 

 Abington. In the eastern part of the field red conglomerates are no longer 

 recognized. 



