2 THE PENOKEE lEON-BEARING SERIES. 



The Sioux quartzites (Hg). 



The Aniinikie series, which inchides the Mesalji range (Hio)- 



Folded schists of Canada, iiichiding VeriuiHou hike series (Hn). 



This classification has reference not only to a certain geographical 

 separateness of the various areas, but also to certain peculiar geological 

 characteristics which each area or group of areas displays. 



In the six and a half years that have elaj)sed since the beginning of 

 our present study of the older formations of the Northwest, work has been 

 done in a number of these areas, much new matei'ial has been collected, 

 and many interesting new conclusions have been reached. In the case 

 of the Penokee area, this study has been completed. An account 

 of this region is particularly called for, because of the absence of folds 

 and of the accompanying changes due to pressure — which so greatly 

 increase the difficulties of study in the Marquette-Menominee region, for 

 instance — and because of the clear and unmistakaljle nature of it.s relations 

 to adjoining formations. Our design, then, is to publi.sh at the present time 

 a full account of the area, showing in detail the processes by which the 

 jirincipal results are reached, and to use these results in future in the study 

 of other areas of the Northwest. 



The general geograpliical position of the Penokee belt will be best 

 understood by reference to PI. i. The larger scale map of PI. ii will serve 

 to show more definitely the extent and position (jf the area the geology of 

 which is to be discussed. This belt stretches from lake Gogebic, Michigan, 

 to lake Numakagon, in Wisconsin, a distance t>f about 80 miles. Its. 

 course from lake Gogebic to the Montreal river is about Avest, and from the 

 Montreal to" lake Numakagon about 20° south of west. Our more detailed 

 investigations have extended over an average width of F) miles. Of this 

 width, the iron-bearing series, which particularly forms the subject of the 

 present volume, occupies from a f(uarter of a mile to about 3 miles, the 

 remainder being occupied to the south by granites, gneisses, and schists, 

 and to the north by the interbedded eruptives and fragmentals of the 

 Keweenaw series. 



Whatever the relations of the schist, gneiss and granite mapped in PI. ii 

 to one another and to the rocks adjacent, they are sharply separated in surface 



