118 BULLETIN OF THE ESSEX INSTITUTE. 



Opposite the middle of the second hill, a few feet 

 southwest of the trail (6), is a small prospect shaft about 

 fifteen feet deep on a sandstone dike three to four feet 

 wide. It trends northwest-southeast, approximately, and 

 hades southwest about 5°. The rock is much crushed, 

 with evidences of shearing along the walls. On the 

 trail, opposite the northwest end of the second hill, a 

 dike at least six or eight feet wide is exposed between 

 disintegrated granite walls. The sandstone of the dike 

 is white on the northeast side and red (highly ferruginous) 

 on the southwest. These two outcrops make the sand- 

 stone dikes unquestionable for this locality ; and the 

 appearances suggest their origin in the sheeting of the 

 formations along the great fault-line. 



On the second spur of granite opposite the third hill, 

 and several hundred feet southwest of the probable line 

 of the fault, are two large sandstone dikes ( 7 ) . The 

 southwest dike is fifty to one hundred feet wide and 

 separated by about twenty feet of granite from the nar- 

 rower northeast dike. The larger dike gives ofl' a branch 

 one to two feet wide on the southwest side. Toward the 

 northwest end of the third hill the granite appears 

 beneath the Potsdam beds, the downthrow being no longer 

 sufficient to conceal the base of the Potsdam ; and it is clear 

 that from this point northwest the fault now lies wholly 

 in the granite. The Potsdam sandstone is non-glauconitic 

 here and not unlike that of the dikes, except that it is, 

 in the main, rather coarser. Some of it is blotched and 

 spotted with white in the manner so characteristic of the 

 dike rock. 



From this point and the last sedimentary outcrops 

 northwestward an occasional small fragment of sand- 

 stone in the disintegrated granite shows that the dikes are 

 not wholly wanting. About half way to Cascade (8) 



