128 GEOLOGY OF THE NAREAGANSETT BASIN. 



of points as far east as Brockton. The basal series of the Carboniferous 

 may be seen within a few feet of contact with tlie granitite in Wrentham, 

 in the low hill half a mile north of the Shepardville reservoir. So far as 

 can be observed, the strata are simply downfolded without faulting. Along 

 this line there is little topographic expression to the contact. The Carbon- 

 iferous area is covered by a low, gently undulating drift plain, while the 

 gi^anitic rocks rise into rounded knobs having elevations of from 100 to 

 200 feet above the plain on the south. 



poohsh Hiu fault — Midway between Foxboro and Mansfield the boundary 

 line makes a rectangular turn along the western face of Foolish Hill. 

 This side of the hill presents a long, smooth wall, inclined steeply westward. 

 The basal beds of the Carboniferous rise up on the southeni face of this 

 granitic hill, with steep dips to the southward, and reappear on the low 

 ground to the westward with an offset of 2,000 feet or more to the north. 

 The railroad from Mansfield to Foxboro follows approximately the line of 

 this fault. 



From Foohsh Hill to Brockton — ^Eastward to Eastou tho coutact can be traced 

 with less certainty. The attitude of the basal Carboniferous beds on the 

 south varies a-s regards angle of dip from point to point, but is generally 

 much steeper as the contact is approached. This change of dip is so 

 marked in some cases as to suggest unconformity between the red basal 

 series and the overlying gray carbonaceous beds. While, as before noted, 

 no actual faulting can be shown in these cases, it may be questioned 

 whether the steeper dips along the border do not express the upward drag 

 of the edges of strata from downfaulting of the rocks in the basin. 



Between Easton and Brockton there are positive indications of small 

 faults along the boundary, shown in actual exposures, but the precise nature 

 of the disturbances and their bearing upon the form of the basin in this 

 region are not clear on account of the drift coating. 



A mile northeast of the last-named locality is a very considerable 

 irregularity in the boundary, by which, according to Messrs. Grriswold and 

 Ma^l^ut, th^ red beds in vertical positions are let into the granitite floor. 

 Still nearer Brockton the sudden disappearance of red sandstone in the 

 dtift for a space indicates a displacement or disappearance of the beds by 

 erosion. The fact is worth noting here that the coarse pink granite just 

 muth of Montello railroad station is faulted along NE.-SW. planes. 



