﻿Iron Ores of the Lake Superior region. 265 



extent to which the alteration in the Penokee series has been 

 carried out, and the occurrence in it of a garnetiferous rock not 

 met with as yet in the Animike series. 



The iron-bearing series of the Menominee region, which lies 

 on both sides of the Menominee Eiver, the boundary between 

 northeastern Wisconsin and Michigan, is folded so as to place 

 the rock belts for the most part in an approximately vertical 

 position. There does not seem, however, to have been the 

 closeness of folding so noticeable in the Yermilion Lake region 

 of Minnesota. The most abundant of the ferruginous rocks of 

 the Menominee region are cherty schists charged in varying 

 quantities with, magnetite, or hematite, or both, and even with 

 the brown oxide of iron, and containing varying quantities of 

 an iron carbonate. These schists graduate into and include 

 carbonaceous and graphitic slates, just as in the Penokee and 

 Animike formations, and when studied in the thin sections are 

 seen plainly to be merely a repetition of those met with on a 

 large scale in the eastern portion of the Penokee range, from 

 which they differ chiefly in the highly contorted condition 

 which they show in places, while in others they are relatively 

 free from such contortions. These contortions have no parallel 

 in the adjoining layers, and often seem to have little relation, 

 in axial directions, to the general system of folding of the 

 strata. They are taken to indicate the relatively great resist- 

 ance to folding offered by these schists, on account of the 

 silicious induration they received prior to the folding process. 

 When these contortions are wanting, the similarity between 

 much of the Menominee ferruginous schist, and the Grunflint 

 beds of the Animike series amounts to an identity of charac- 

 ters. The iron carbonate, whose presence in these schists is 

 often indicated by the rusty brown weathering, occurs in very 

 varying proportions, but is manifestly an original ingredient. 

 Actinolite is present, in some kinds, and the thin sections dem- 

 onstrate the derivation of all phases from an original carbonate. 

 The siliceous matter of these schists is more commonly cherty* 

 or flinty than jaspery, but at times it takes on a jaspery aspect 

 for considerable areas. Although we do not here meet with 

 such extensive masses of jaspery material as are found in the 

 Vermilion Lake and Marquette regions, nevertheless, the com- 

 munity of origin of the jaspers of the Menominee region with 

 those of the two latter regions is sufficiently manifest, although 

 there are some peculiarities in structure and arrangement 

 among the Marquette and Vermilion Lake jaspery schists 



* The term " chert " is used iu this article to cover colorless, white, or grayish 

 hornstone-like silica, which under the microscope is either wholly crystalline, or 

 partly crystalline and partly chalcedonic, or even amorphous. 



