249 



and, iilthoiigh the ledges on either side locate it closely enough for 

 mapping, it is nowhere exactly or satisfiictorily exposed. We 

 now learn for the first time that the full breadth of this bed of 

 slate does not exceed 100 feet, equal to a thickness of about 

 80 feet, and also that it is conformably overlain on the west by 

 a heavy bed of conglomerate, which forms the shore for a 

 distance of 400 feet. The exposed breadth of the conglomerate 

 is, at first, only 30 feet ; but it increases northward to a 

 maximum of 70 feet, equal to a thickness of nearly 60 feet. 

 This is probably not the entire thickness of the conglomerate ; 

 at any rate there are no indications on this part of the shore 

 of its being overlain by slate. It is, for the most part, a 

 rusty and readily disintegrating rock. At some points it is quite 

 ochery in appearance ; and it is, doubtless, owing to the lack of 

 an efficient cement and its consequent friable or crumbling 

 character that it fails to outcrop farther south on the shore. 

 Although mainly of medium and uniform texture, a portion of 

 the bed, as exposed on the shore, is extremely coarse and 

 irregular. The pebbles ai'e of all sizes up to a yard or more in 

 diameter, the largest observed being a bowlder of coarse granite 

 over five feet in length. Furthermox-e, the various sizes are 

 jumbled together promiscuously, without evident assorting or 

 stratification, looking not unlike an indurated till or bowlder 

 clay. 



On account of its I'elations to the slate, the composition of 

 this conglomerate possesses unusual interest. The conglom- 

 erate is not only underlain, but, as will be seen later, it is 

 overlain by slate, the overlying bed embracing a thickness 

 of a thousand feet or more. It is clear that, in the absence 

 of fossils in the slate, the key to its geological age is to be 

 sought in this intercalated conglomerate, proceeding on the 

 principle that every rock of this region represented among the 

 pebbles of the conglomerate must be older than both the con- 

 glomerate and the great overlying slate. We are able to prove 

 in this way that the slate is newer than most, at least, of the 



