POSTGLACIAL FAULTS OF EASTERN NEW YORK 25 



Postglacial faults in New England 



Two instances at least of these movements are now known. 



Postglacial faults at Attleboro, Mass. Postglacial faults of 

 the class described in this paper are now known to exist in 

 southern Massachusetts. In April 1905 I found them well 

 developed in vertical Carboniferous sandstones and shales with- 

 out slaty cleavage on the south side of the axis of the Attleboro 

 syncline at. a locality a little over a mile southwest of Attleboro, 

 Mass. The outcrops are near the point where the Thatcher 

 road bridge spans the railroad from Boston to Providence. The 

 principal ledge is illustrated in a report on the geology of the 



Fig. 7 Diagrammatic cross-section of supposed fissure near the top of Mt St John, looking 

 west by north 



Narragansett basin, 1 but these faults were not particularly noted 

 at the time the field work was done. At the outcrop near the 

 railroad track I measured a downthrow to the south of 3 inches 

 distributed over five small faults. The largest throw measured 

 was 1.07 inches and the smallest measured was .24 inches. These 

 were widely distributed over a space nearly 100 feet wide meas- 

 ured across the strike of the beds. The faults occur in the plane 

 of the bedding. The strike of the beds at this locality is n. 52 e. 

 The rock surfaces are usually well glaciated and the detection 

 of postglacial slips is accordingly readily made. In an outcrop 

 in the field near by there is an apparent downthrow of 1 foot to 

 the north but weathering has somewhat obscured the evidence. 



x See U. S. Geol. Sur. Monograph 33. i8qq. pi. 7, p. 175-76. 



