176 



GEOLOGY OF THE NAERAGANSETT BASIN. 



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conglomerate dipping 70° N. About 60 feet of beds are exposed, showing 

 alternations with sandstone and slate. The pebbles of the conglomerate 

 are granitite, quartzite, and quartz, and range up to 5 inches in diameter. 

 This bed occupies a stratigraphic position on the north side of the Perrins 

 anticline roughly corresponding to that of the Seekonk conglomerate on 

 the south side of the axis, and raises the question whether the Seekonk 



conglomerate is the coarse con- 

 glomerate elsewhere found at 

 the base of the Dighton group 

 or a lower conglomerate com- 

 prised within the Seekonk beds 

 proper. Westward and east- 

 ward for many miles no rocks 

 are exposed along this northern 

 strike line. 



Somewhat higher up in the 

 section, and over a mile north- 

 east of the last-named outcrop, 

 there are exposed, along the 

 Old Colony Railroad tracks at 

 Thatcher road bridge, 1 mile 

 south- southwest of Attleboro 

 station, about 40 feet of coarse, 

 gray, gritty, and often con- 

 glomeratic sandstones exhibit- 

 ing cross bedding and marked 

 local or contemporaneous ero- 

 sion. A bed of fine sandstone 

 20 feet thick was excavated, 

 evidently by a river, to the un- 

 derlying coarse pebbly beds, and then the area was covered up with 

 coarse sands. This feature can be relied upon to show that the northern 

 face of the strata was originally uppermost. The beds stand at high angles, 

 dipping north. 



Contact of red and gray beds, with local unconformity. Cl'OSSmg llOrtllWai'd OVei' a few 



feet of covered beds, we find a glaciated exposure by the roadside exhib- 



rig. 24. — Contemporaneous erosion, with unconformity, in the Car- 

 boniferous at Attleboro, Massachusetts. The pebbles shown in 

 the upper part of the diagram are identical with the red slate in 

 the lower part. 



