M. D. Irving — Is there a Hcronian Group ? 367 



longer distinct, the close folding having brought the strati- 

 form members of both groups to too great a uniformity of 

 inclination. Finally, in the Vermillion Lake region the ex- 

 treme pressure to which the rocks have been subjected has 

 not only brought about a general community of inclination 

 between the rocks of the two groups, v but has developed in 

 the lower group, and among the eruptives of the upper group, 

 so complete a schistose structure as to render the separation 

 of the two series often exceedingly difficult. Nevertheless, 

 that the two groups are there actually represented the facts 

 above presented seem to me clearly to demonstrate ; while such 

 a state of affairs as there obtains is certainly no theoretical im- 

 possibility on the hypothesis that these schists include two en- 

 tirely distinct series of rocks. Imagine, for instance, the region 

 of the Alps of southern Europe planed off by denudation to a 

 level surface. Here Archsean crystalline schists and various 

 fossiliferous formations are intricately folded together; and the 

 appearances resulting from such a planing off would not be so 

 far different from those obtaining in those portions of the Lake 

 Superior region, where Archaean schists and newer detrital 

 rocks are folded together, save that the newer formations would 

 now be fossiliferous. 



There must be cases, however, where it will long remain 

 very difficult, if not impossible, to separate the Huronian from 

 older schists, or to determine if any Huronian be present. 

 This I suspect will be the case with some of the Canadian belts 

 north and northeast of Lake Superior, which have been called 

 Huronian. A large part of the schists of these belts are plainly 

 not Huronian ; but it remains to be seen whether any of the 

 belts contain any true Huronian, and whether there may not 

 be some further division possible of the pre-Huronian schists; 

 a view maintained vigorously by Mr. Lawson, of the Canadian 

 Survey. As to this I do not care to express, now, any very 

 definite opinion. However, it seems plain that no such facts as 

 those here presented to substantiate the complete separation 

 that obtains between the Huronian and the pre-Huronian rocks 

 have been yet advanced to establish a separability of the latter 

 rocks themselves. 



Throughout the region then which stretches from the north 

 shore of Lake Huron to the Mississippi River, we find evidence 

 of the existence of this same discordance between the Huro- 

 nian, and the older basement rocks — a discordance due to one 

 and the same orographic disturbance. Bearing in mind the 

 discordance between the Huronian and the overlying Kewee- 

 naw series, and that between the Keweenaw series and Pots- 

 dam sandstone, we reach the conclusion that throughout this 

 great region the following succession obtains, in ascending 

 order : 



