GEOLOGY OF NORTHERX WISCOXSIX. 5o 



degrees, which is that of the sandstones on the St. Croix, the thick- 

 ness is not far from 40,000 feet. 



The dimensions of the Lake Superior S3^uclinal, as thus made out, 

 are simpl3^ enormous. It is over 300 miles in length, and from 30 

 to 50 miles in width. Over 4,000 square miles of territory are oc- 

 cupied in Wisconsin alone, hy rocks belonging to its northern or 

 southern edge. It can only be compared to an extensive, inverted 

 range of mountains. 



Westward extension of the Penohie range. — The Penokie sj'stem 

 lies directly below, or geographically, south, from the Copper-Bear- 

 ing series. The two formations are intimately connected, the strike 

 and dip conforming throughout. The eastern end of the Penokie 

 Range is near Lake Gogebic, in Michigan, nearly 100 miles from 

 the famous Marquette iron region. It extends westerly without 

 break to a point seven miles west from Penokie Gap. In Ashland 

 county it forms a bold, high ridge, over thirty miles in length, and 

 never more than two miles in width. In the western part of the 

 county the range appears to break down and become lost for a dis- 

 tance of ten miles, when it appears again at two localities near At- 

 kins Lake. The question of its westward extension from Atkins 

 Lake, is one of great economic as well as of scientific importance. 

 The country between the supposed end of the range and the St. 

 Croix River has never been visited by a geologist. On account of 

 its poverty in pine, it is comparatively unknown to woodsmen and 

 explorers. That the formation does extend westward, probably to 

 the vicinity of the St. Croix, I have strong presumptive evidence, 

 but of course not absolute proof. I do not intend to assert that the 

 Huronian belt extends uninterruptedly from the Penokie Range to 

 the St. Croix. On the contrary, it has doubtless been subjected to 

 extensive denudation, and large portions of it may no longer re- 

 main. Large sections of it are probably buried deep beneath accu- 

 mulations of drift. The space of ten miles between the western 

 end of the main range and the outcrops near Atkins' Lake, has 

 been largely removed by erosion, but it is more than probable that 

 below the deposits of drift the downward extension of the members 

 of the system may still be found. The arguments in favor of the 

 westward continuation of the Huronian schists in a more or less in- 

 terrupted belt, are the following: 



