the Structural Relations of the Iluronian. 225 



glomerate was not sufficiently large to enable one to determine 

 strike or clip. 



Passing now a few paces south of the main limestone ledge, 

 i. e., geologically upward, the actual contact between it and 

 the upper slate-conglomerate is seen, although for no great dis- 

 tance. This contact is perfectly sharp. Upon one side of the 

 line is the typical limestone ; upon the other is the coarse con- 

 glomerate. The bedding of the latter is not sufficiently dis- 

 tinct to determine whether between the two formations there 

 is a discordance. Above the contact occurs a good sized 

 exposure of upper slate-conglomerate. This contains innu- 

 merable characteristic fragments of this formation, including 

 besides various granitic fragments those of basic eruptives, of 

 quartzite and of jasper. The distinctive feature of the ex- 

 posure is, however, the presence of very numerous fragments 

 of limestone, which sometimes reach a foot or more in diameter 

 These fragments have precisely the appearance of the strongly 

 laminated underlying limestone. The bandings of the frag- 

 ments lie in various directions, showing that this structure ex- 

 isted in the original rock at the time of the deposition of the 

 conglomerate. 



About 40 rods east, while the typical upper slate-conglomer- 

 ate was not found, at the extreme southernmost part of the 

 limestone bluff is a limestone-conglomerate or recomposed 

 limestone, which is regarded at this point as the base of the 

 upper slate-conglomerate. 



A large exposure of lower slate-conglomerate some distance 

 to the west of the locality above described shows the bedding 

 to be vertical. It also has a cleavage in several directions so 

 that large fragments under slight blows break into polygonal 

 blocks. As compared with the upper slate-conglomerate it is 

 much more crystalline. Its finer grained phases pass into a 

 siliceous schist. The outcrop of lower slate-conglomerate adja- 

 cent to and north of the limestone has the same lithological 

 •character as the large bluff to the west. 



It is concluded from the above observations that bearing in 

 favor of a considerable break between the Upper and Lower 

 Huronian are the following points : — There is (1) a difference in 

 degree of metamorphism. The Lower Huronian has been so 

 much altered as to have become semi-crystalline and to take on 

 various cleavages, while the upper slate-conglomerate has no 

 such characters. (2) Blocks of limestone in the upper slate-con- 

 glomerate are in exactly the same condition as in the original 

 ledge. (3) Also the jasper fragments here contained were prob- 

 ably derived from the hetnatitic jaspery formation which is 

 known to occur in the Lower Huronian. This sedimentary 

 formation, like the limestone, belongs to one series, while the 



