﻿Iron Ores of the Lake Superior region. 267 



been destroyed by fire. A number of the thin sections made 

 from these specimens before the fire have, however, been 

 saved, and these, with the field notes, and with the aid of a 

 number of specimens for which we are indebted to the kindness 

 of Dr. C. Kominger, suffice to establish the general identity of 

 the Marquette ferruginous schists with those of the districts pre- 

 viously described, and to enable us to recognize the various stages 

 in the process of silicification. While there are certain portions 

 of the district from which our material is very scanty, or, indeed, 

 wanting altogether, and while we think that there can in the 

 main be no question as to most of the developments of ferrug- 

 inous material, there are certain kinds, as for instance some 

 of the coarser-grained actinolitic schists, as to whose rela- 

 tion to the other ferruginous materials we feel now unwilling 

 to speak. We feel also that our knowledge as to the structural 

 relations of certain of the ore beds, more particularly some of 

 the magnetite bodies, is insufficient to allow us to speak too 

 confidently as to their origin. A good many of the ore bodies, 

 and more particularly some of the so-called soft hematites, ap- 

 pear to have resulted, partly at least, from a direct oxidation 

 of the iron carbonate of some of the cherty schists. In other 

 cases the ore bodies owe their origin and general shape, we 

 think, to processes of infiltration and replacement. 



The iron ores and associated ferruginous schists of the Ver- 

 milion Lake country occur in a belt of schistose rocks which, 

 bounded north and south by belts of granite and gneiss, emerges 

 from the general drift-covering of northeastern Minnesota not 

 many miles west of Vermilion Lake and pursues thence, a general 

 northwesterly course to the national boundary line in the vicin- 

 ity of Knife Lake. The schistose rocks of this belt have, as a 

 rule, an approximately vertical position, the folding having 

 been close to a degree unparalleled in the iron-bearing rocks 

 south of Lake Superior. Small portions of this belt, including 

 the ferruginous schists and iron ores, present characters which 

 are practically identical with those of portions of the iron- 

 bearing formations of the several other regions already passed 

 in review. On account of this identity, and because also there 

 are some strong reasons for suspecting an unconformity between 

 them and the larger part of the schistose rocks of this belt, 

 which are quite different in character, the iron-bearing portions 

 of the belt are supposed to belong with the other iron-bearing 

 formations of the Lake Superior country. 



The ferruginous materials are exposed at a number of places 

 along the course of the schistose belt, but so far as is now 

 known, they reach their greatest development in the vicinity of 

 the south shore of Vermilion Lake. Here are immense expo- 



