ÏÏURONIAN EOCKS OF LAKE SUPERIOR. 69 



Marquette and westward across the Wisconsin boundary. On the north, they are bounded 

 by coarse granites which occupy the north slope of the range and on the south, in Town 

 45, they pass into micaceous and hornblendic gneiss that carries gold in the inclosed 

 quarz veins. No doubt these schists are a continuation of the Marc[uette and Meno- 

 menee schists. But I should be greatly surprised if they can be shown to be the con- 

 tinuation of the Penokee-Grogebic flat slates, as would appear by the arguments and the 

 map of Prof. Irving. I mean by the Peuokee-Gogebic belt, the Gogebic belt of slates 

 in which the Colby Iron Mine is situated. Before seeing Prof Irving's report, I was 

 under the impression that the rocks of the Penokee Iron Eange were like those of Mar- 

 quette, and those of the Gogebic Iron Eange like the Aniraikie rocks. 



From all the known facts, it seems certain that the Auimikie and Keweenian groups 

 together, form the bottom of the great geological basin of Lake Superior, which covers 

 an area of about 30,000 square miles. These strata show a moderately low dip towards 

 the middle of the lake, but become steeper on the south side than they are on the north. 

 They cover nearly the whole bed of Lake Superior, as may be seen by the exposures on the 

 inlands and main shore. From the broad part or middle of the lake — say, from the 

 meridian of Passage Island, they strike inland one both shores, and with a breadth of one 

 hundred and fifty miles, they continue west-south-westward for more than two hundred 

 and fifty miles — or nearly, if not cjuite to Mississipf)i River — leaving a tongue of the old 

 rocks, from the west, to penetrate between them to the end of the lake at Duluth, as will be 

 seen by Irving's map. The Archaean rocks, named the " Laurentian gneiss " and " Huronian 

 folded schists," wherever seen on either side of this great basin are almost invariably 

 highly inclined and unconformable to the comparatively undisturbed strata referred to. 

 But, as would naturally be the case, with a basin or depression such as this, the strike of 

 these two sets of strata (though not the angles of the dip) along the sides would be 

 likely to ngree very nearly, which is the actual condition presented, as may be seen on 

 the south side along the South and Gogebic Ranges, and on the north side along the 

 line of contact from Thunder Bay westward. This apparent agreement of the strike of 

 the two sets of strata would render it the more difficult to detect unconformability 

 between them, especially as an unstratified member of the Archœan rocks almost inva- 

 riably presents itself next the flat strata of the Animikie series. These conditions exist in 

 the only portions of the contact examined by Prof. Irving. But from Thunder Bay 

 eastward, this conformability of strike no longer continues, as may be seen north-east 

 of Thunder Bay and at Black and Nipigon Bays, where the flat-lying strata of the great 

 basin referred to make a deep impression northward across the general strike of the nearly 

 A'ertical folded schists and gneisses. This general want of conformity may be again 

 seen along the north shore, south-eastward and diagonally across the strike of the Archœan 

 rocks, from Nipigon Bay to Sault Ste. Marie. Along this part of the coast, great belts — 

 miles in width — of the Hitronian folded schists, standing on edge, stiike into the lake 

 towards the flat basin referred to, and presumably they continue underneath the Animikie 

 group. As for instance, the schists of Michipicoten River, Homer Township, Pic and 

 Steel Rivers, Nij^igou and Thunder Bays, all of which strike into the flat geological 

 basin referred to. 



The Slate Islands are situated ten miles from the shore, opposite to Steel River. 

 These islands are occupied by folded Huronian schists, standing on edge, running east 



