124 BULLETIN OF THE ESSEX INSTITUTE. 



hundred feet obliquely along the side of the gulch. On 

 the uphill side, at least, the dike is very much branched, 

 surrounding and enclosing many large masses of granite ; 

 and there appear also to be large dikes of sandstone 

 extending southwest into the granite. The sandstone 

 is mostly fine, but some of it is decidedly coarse ; and 

 in general it is much mottled. Traces of a true bedding 

 are indicated at various points in alternating layers of 

 coarse and fine material. The numerous shear planes 

 show a strong southwest hade. On the east side of 

 the gulch the sandstone outcrops strongly about one 

 hundred yards below its southern limit on the west side ; 

 and extends thence eastward along the steep slope (13) 

 above the more gently sloping bench of the Fountain 

 series. The dike sandstone seems to extend to the 

 bottom of the slope, and its lower edge is concealeil by 

 drift ; but on the uphill side the boundary can be traced 

 at intervals, although the fine grained dark brown sranite 

 occurring here is easily mistaken for the sandstone. If 

 all the sandstone on this slope is to be referred to one 

 dike, it must be from two hundred to three hundred feet 

 wide. A quarry-like excavation afibrds a good exposure 

 of the sandstone, whicn is of entirely normal character. 

 The distribution of sandstone in the slide material indi- 

 cates branching along the upper edge of the dike ; and 

 one dike four feet thick is clearly exposed, hading south- 

 west about 45°. Near this is a dikelet two to four inches 

 wide of a very dark brown sandstone which is not easily 

 distinguished from the inclosing granite ; and this is 

 but one of many instances where the brown color of the 

 sandstone is most marked next the granite ; suggesting 

 the biotite of the granite as a source of a part at least of 

 the cementing and coloring iron oxide of the sandstone. 

 In its eastern extension this great dike appears to split 



