256 R. D. Irving — Is there a Huronian Group f 



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ning thence north of west into Wisconsin, is the 

 most extensive. The accompanying section is 

 designed to represent the general relations of the 

 two formations and the nature of the folding of 

 the strata in this region. As in the case of the 

 sections of the Marquette region, this one also 

 has been drawn to a scale after a careful study 

 of all the facts hitherto published, and of those 

 gathered by ourselves. The two formations con- 

 cerned are manifestly identical with those of the 

 Marquette region. We have here again to do 

 with an upper, relatively little altered, iron-bear- 

 ing series, and a lower, deeply altered series of 

 gneiss and schists with immense areas of intru- 

 sive granite. The principal point of difference 

 between the two regions lies in the much closer 

 folding that the Menominee rocks have received. 

 Had the section been made farther west, a 

 larger thickness o'f the Huronian strata would 

 have been shown, and other folds would -present 

 themselves. 



All the arguments that applied in the Mar- 

 quette region in favor of the existence of a dis- 

 cordance between the two formations, apply here 

 again. The basal conglomerates of this series 

 are particularly finely developed, and may be 

 seen on a grand scale at the contact of the 

 basal quartzite with the granite at the falls of 

 the Sturgeon Eiver. 



The several belts that intervene between the 

 one just described and that of the Marquette 

 region, are much narrower, but nevertheless seem 

 to contain as great a thickness of the iron- 

 bearing formation. In the case of the Felch 

 Mountain belt, which does not exceed a mile 

 in width, all of the strata are described by Dr. 

 Rominger as dipping at a high angle to the 

 northward, and in crossing the belt from the 

 south to the north, after passing the middle, one 

 traverses a repetition of the belts crossed farther 

 south, but in an inverted order. It would seem 

 that we have to do here with a case of a syn- 

 clinal whose sides are folded close together. Fig. 

 6 shows in a general way the supposed relations 

 between the older rocks and the several belts of 

 the newer series in the relatively little known 

 area between the Marquette region and the 

 Menominee Eiver. 



