440 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



ends abruptly in a vertical, northward-facing wall 165 feet west of the tei*- 

 mination of the northern portion already noted, and on the other side of 

 Fall River. 



We notice that the sandstone resting on the trap near the northern 

 terminus of the west ridge is exactly the same soft, deep-red shale, and that 

 it rests upon a trap with the same amygdaloidal texture and the same min- 

 eral contents as at the south terminus of the east ridge. At the same dis- 

 tance from this contact in either ridge the rock becomes suddenly filled with 

 the same chopped-straw-like forms, which may be fucoids, or indusia of the 

 insect found farther east in the sandstone, or, more probably, concretions; 

 and measui-ing a second distance we find a thin bed of gray conglomerate 

 interposed in the sandstones in both cases. The sandstone series thus agrees 

 minutely on either side the line, and with the traps must have been faulted 

 with the dip about 165 feet. 



The rock is intercalated in the sandstone and dips eastward with it. It 

 would seem to follow this direction only a little way Ijefore coming to the 

 Fall River fault, as an artesian well sunk on the east bank of the river by 

 the Montague Paper Company (see "Artesian wells," Chapter XII) went 

 down 900 feet below the level of the dam, while immediately opposite on 

 the west, and separated only by the width of the river (about 1,430 feet), 

 the trap dips toward the well with an angle of 32°, which would make it 

 ap]iear in the well at 894 feet below the surface, whereas it does appear 

 at 585 feet, making an upthrow on the east of the fault plane of 209 feet. 



THE UNITY OF THE SHEET. 



From its noi'th end to a point just below the lower suspension bridge 

 at Turners Falls, the trap ridge is an inconspicuous object seen from the 

 surface of the high sands on the west, and here it is for a distance entirely 

 covered by them. When it reemerges it has a greater width and has 

 changed its direction to southerly. This is my interpretation of the facts 

 at this point, and I find myself here again at variance with the conclusions 

 of Professor Davis, cited above. It is certain tliat there is no proof that the 

 trap from the south runs by the northern strip on the west, so that the latter 

 could be called a posterior range to it. There is also no conclusive proof 

 that the two parts of the dike are united under the sands. I tliink it most 

 probable that they are. The two are lithologically identical, as are the 

 sandstones above them, and the region abounds in faults. 



