48 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. Nov. 19, 



Many years ago I published in the ' American Journal of Science ' 

 a coloured representation of these capricious mutual infoldings on 

 the east of the mouth of the Thessalon River (Lake Huron). In 

 the middle, too, of a naked islet in Lake Huron, opposite the river 

 just mentioned, but three miles off, a boss of granite pushes its bare 

 red mass from beneath a paste-like envelope of fine-grained green- 

 stone, just as occurs in Carp River, on the south side of Lake 

 Superior*, but the mode of contact is not stated. 



III. Huronian of various districts. — a. South shore of Lake 

 Superior. — With respect to the Azoic Series of the south shore of 

 Lake Superior, already alluded to, I beg to refer the Society to 

 columns 8, 9, and 10 of Table III., and here quote Poster and Whit- 

 ney t as saying that this series " is in alternating beds, of great 

 thickness, of gneiss, of chloritic, talcose, argillaceous, and siliceous 

 slate, of quartz, of saccharoid and crystalline limestones, and ser- 

 pentines — all much contorted, highly inclined — nowhere having a 

 sedimentary aspect, and most nJetamorphic near the lines of igneous 

 outburst," so powerful and numerous hereabouts. 



I look upon the Huronian or Azoic Rocks, here spoken of, as 

 belonging to the Huronian of the north of Lake Huron and Lake 

 Superior, for the following stratigraphical and mineralogical reasons : 



1. The transgressive relation of the Potsdam Sandstone to both. 



2. The same strike East and West in both ; dip high. 



3. The great prevalence in both of chloritic, dioritic, and horn- 

 blendic slates. 



4. The abundance of trappcan and hornblendic rock, sometimes 

 in brecciated masses composed of jasper, slate, felspar, and horn- 

 blende. 



5. The extraordinary and extensive intermixture of the beds of 

 greenstone and granite, which defy description and classification. 



6. The same quartzites, occasionally becoming a conglomerate, 

 with red jasper and other pebbles. 



7. The occasional bands of white, grey, and red crystalline lime- 

 stone. 



8. The presence in both of greenstone-dykes. 



9. The absence of organic remains in both. 



The quartzite of the country south of Lake Superior, unlike that 

 of Lake Huron, contains vast beds of magnetic iron-ore. 



Besides the Huronian beds, as already treated of, Sir W. E. Logan 

 has described with great care a new formation, which he calls " the 

 copper-bearing rocks." They are of great interest, and their more 

 prominent characters may be best seen in columns 10, 11, 12 of the 

 Synoptical Table III. They repose on the Huronian, unconformably 

 to the crystalline rock below and to the Potsdam Sandstone above. 

 This subformation occupies about 250 miles of the north shore of 

 Lake Superior — that is, from Michipicoton to Pigeon River. It is 

 very naturally divided into a lower and an upper group; the lower 

 group, consisting of bluish slates or shales, with sandstones and 

 intcrstratified columnar trap, extends from Thunder Head to Pigeon 

 * Oj). cit, p. 14. f Op. cif. p. 14. 



