THE PENOKEE IRON -BEARING SERIES OF 

 MICHIGAN AND WISCONSIN. 



By R. D. Irving and C. R. Van Hise. 



INTRODUCTION. 



In a previous publication of the Survey' one of the writers of this 

 memoir lias provisionally mapped under a common color all of the various 

 areas in the lake Superior region, the rocks of which are now regarded by 

 any authority as the equivalent of the Huronian series of the Canadian 

 geologists. The provisional mapping was preliminary to a thorough study 

 of each of these areas in the United States, with the object of determining 

 not only its own strxicture and stratigraphy and the genesis of its rocks, 

 but also the general stratigrapliy of the pre-Cambrian formations in the 

 northwestern states. This map, with corrections uj) to date, is repro- 

 duced in this volume (PI. i). The areas there included are: 



The Original Huronian (H). 



The Marfpiette-Menominee Iron-bearing schists (H2). 



The Wisconsin valley slates (II3). 



The Penokee Iron-bearing .series (H4). 



The St. Louis slates (H5). 



The Chippewa valley (piartzites (Hg). 



The 151ack river Iron-bearing schists (H7). 



The Baraboo quartzites (Hg). 



' Preliminary Paper on an Investigation of the Archean Rooks of the Northwestern States, by 

 R. D. IrvinR. U. S. Gcol. Survey, Fifth Annual Report, pp. lSl-241. PI. XXH. 



WON XIX 1 1 



