﻿264 jR. D. Irving — Ferruginous Schists and 



In the easternmost portion of this iron belt, the ferruginous 

 schists composing it are largely actinolitic magnetite-slates, 

 and the same is true of all of its western portion, that is to say, 

 of all that portion west of the Potato River, though occasion- 

 ally a jaspery tendency is noticed. In the interval between 

 these two portions, however, the rocks of the belt are of some- 

 what different character, although belonging to the same hori- 

 zon with, and being actually continuous with, the actinolitic 

 magnetite-schists. This intervening portion, along a distance of 

 some thirty miles between the Potato River in Wisconsin and 

 a point about four miles west of the Little Presqu' Isle River in 

 Michigan, shows as the prevailing rock a stratiform cherty 

 material, portions of which are magnetitic but without actino- 

 lite, so far as our sections have yet revealed. Other portions 

 show jaspery layers in considerable developments, while at a 

 number of points on both sides of the Michigan-Wisconsin 

 boundary workable deposits of a rich hematite ore have been 

 opened. But the most interesting feature of this belt lies in the 

 occurrence within it, and grading into the other materials con- 

 stituting it, of an iron carbonate, closely analogous to that above 

 described as occurring at a similar low horizon in the Animike 

 series. Like the carbonates of the Animike series also, it is 

 manifestly the least altered of the rocks of the belt and the 

 nearest to the original condition. Its gradations into the vari- 

 ous cherty and jaspery portions of the belt, and also into the 

 hematite beds mentioned above, render it evident that these 

 are derivatives from it, a conclusion which is wholly borne out 

 by the appearances presented by the thin sections. With this 

 unaltered carbonate are at times small quantities of magnetite, 

 which is mingled so intimately with the mass that its original 

 character seems possible ; but, as in the case of the Animike 

 iron horizon, the main part of the magnetite here seems also to 

 be secondary. It should be said also that here, as in the 

 case of the Animike, gradations are observable into a frag- 

 mental black slate both from the actinolitic and magnetitic 

 kinds and from the cherty carbonates. It should also be said 

 that at one place on the Penokee range, near the passage of Bad 

 River, there is, forming part of and grading into the actinolitic 

 magnetitic slates, a garnetiferous slate composed mainly of 

 actinolite, garnet, quartz and magnetite. The relation here is 

 so intimate as to render evident a community of origin between 

 the garnetiferous and non-gat netiferous kinds. 



It will thus be seen that the occurrences in the Penokee 

 region are strikingly like those of the Animike iron horizon 

 and that here as there there is strong evidence that all of these 

 ferruginous rocks have been derived from original carbonates 

 by metasomatic processes ; the only differences being the greater 



