IRVING ON THE ANIMIKE AND HURONIAN. Ill 



whether more than a small proportion of these folded schists be referred to the Huro- 

 nian, although in the present state of our knowledge it seems probable enough that a 

 large part of them should be so referred." 



Before proceediug with this quotation one cannot help remarking that the 

 diminution of the volume of vertical schists hardly facilitates the demonstra- 

 tion of their structural and petrographic continuity with horizontal schists 

 not only contiguous, but actually overlying. But Irving proceeds: 



" 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 Animike series. Generally, as the Animike series is traced 

 towards its western 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 Gunflint lake [*], and is 

 true again at the Nesabi range and Fokegama falls district in Minnesota. North of 

 the belt of granite again come the belts of folded schists [f]. The appearance thus pre- 

 sented is at first sight one of general unconformity between the flat-lying Animike and 

 an older series, including the gneisses and folded schists. But a closer study of the 

 folded schists indicates, as has already been shown by Bell, Chester, [N. H.] Win- 

 chell and myself, much lithological similarity between portions of them and the 

 Animike series, so that a different structural hypothesis at once presents itself to the 

 mind. This is the one that I have elsewhere illustrated and explained. The hypoth- 

 esis is, briefly, that the Animike rocks were once continuous with the folded schists to 

 the north of them, and that they were 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, simple 

 bend which forms the trough of Lake Superior. On this hypothesis the folded 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 regions. All are supposed to represent a great sheet of Huronian 

 deposits continuously spread upon a floor of far older gneisses and schists which have 

 since been brought to view by folding and denudation." J 



Objections to Irving's Hypothesis. — The nature of this hypothesis involves 

 no action mechanically impossible ; but we must test its validity by its 

 adaptation to the })articular case rather than by its abstract possibility. We 

 deny, therefore, that any evidence exists that it represents the actual mech- 

 anism which wrought out the Archaean geology of the northwest. 



1. The structural relations now existing between the Animike and the 

 '* folded schists " are evidence excluding the hypothesis. Professor Irving 

 claims the flat-lying Animike of Thunder bay as Huronian, and he claims 

 as Huronian the vertical schists on which this Animike rests. Now, we 

 hold it as impossible to conceive of a method of common folding and denu- 

 dation which would result in such a mode of superposition. Such super- 



* North of Gunflint lake, however, the vertical (" folded ") schists intervene between the Animike 

 and the granite. 



t''"Vje an exposition of the distribution of the schists in the author's memoir in Bull. Geol. Soc. 

 Am^, vol. I, 1890, pp. 300-367. 



X Fifth Ann. Rep. U. S. Geol. Surv.. 1883, pp. 206, 207. 



