HURONIAN ROCKS OF LAKE SUPERIOE. 65 



In regard to the Lake Superior region, it seems to me an easy matter to prove the 

 unconformability of the Animikie formation with the Huronian system, as laid down by 

 Dr. Eel], and with the folded schists of Prof. Irving. The latter gentleman, in his 

 interesting and excellent report on the Archtean formations of the North-western States 

 for 1885, admits that the folded schists of the Marquette and Menominee districts, as 

 well as those of the north shore of Lake Superior, or a great part of them, are Huronian. 

 He then tries to show that thej are the equivalents of the Animikie formation. He states 

 (p. 206) in reference to the Lake Superior Huronian of Dr. Bell : — 



" Accepting, for the time, some of them as Huronian, we are immediately confronted 

 with a structural problem of a good deal of difficulty, i.e. the relation of these folded 

 schists to the unfolded Animikie series. G-enerally, as the Animikie series is traced 

 towa.rds its northern border, it is found to lie against a belt of granite and gneiss. This 

 is so along the shore of Thunder Bay and thence westward to Grunfliut Lake, is true 

 again at the Mesabi Range and Pokegoma Falls district, in Minnesota. North of this 

 belt of granite again come the belts of folded schists. The appearance thus presented is at 

 first sight one of general unconformity between the flat-lying Animikie and an older 

 series, including the gneiss and folded schists. But a close study of the folded schists 

 indicates, as has already been shown by Bell, Chester, "Winchell, and myself, much litho- 

 logical similarity between portions of them and the Animikie series, so that a different 

 structural hypothesis at once presents itself to the mind. This is the one that I have 

 elsev/here illustrated and explained. The hypothesis is, briefly, that the Animikie rocks 

 were once continuous with the folded schists to the north of them, and that they are now 

 separated, merely because of the erosion of the crowns of the folds between them, the 

 close folding of the folded schists being supposed on this view to have been produced 

 concomitantly with the broad, simpler bend which forms the trough of Lake Superior. 

 On this hypothesis, the unfolded schists of the north shore are compared with the unfolded 

 Penokee of the south shore, and the folded schists of the national boundary with the 

 folded schists of the Marquette and Menominee region. All are supposed to represent a 

 great sheet of Huronian depo.sit, once continuously spread upon a floor of far older 

 gneisses and schists which has since been brought to view by folding and denudation." 



It appears from this, as from his whole report, that the professor rests his hypothesis 

 mainly upon the lithological similarity of portions of the two formations to one another 

 and it is not claimed, I believe, anywhere, that stratigraphical structure favours it, but 

 decidedly the contrary. Yet, in the case of contiguous formations like these, stratigraph- 

 ical evidence is the strongest that can be produced ; and, in the present one, as I shall 

 endeavor to show further on, it is clear and decisive against the equivalency of the two 

 formations. It is true that he shows, in regard to the Kingfisher and Knife Lakes dis- 

 tricts, that Prof Winchell saw appearances that indicated a transition of the Animikie 

 flat beds to the folded schists, and that the extensive examination of the same locality by 

 the Assistant Greologist, Ohauvenet, showed a correspondence. Irving says (p. 207) : " His 

 work thus far, as also the results of our microscopic study of the specimens gathered, 

 have tended to show that the Knife Lake schists ar# actually the Animikie slates in a 

 folded condition." If so, they must have been folded by local agencies, and I feel con- 

 fident that they can have no unbroken connection with the folded schists of the Huronian 

 system. I have not been in the locality referred to, but a little to the east I haA'e exam- 

 Sec, iv, 1887. 9. 



