THE IRON SERIES, CONTINUED. 101 



schistose and metamorphic rocks overlying what was conceived to 

 be the basal, gneissic Laurentiau. The later and more careful 

 work has essentially modified such grouping. The reorganization 

 has been brought about by the brothers N. H. and Alexander Win- 

 chell, by R. D. Irving, C. R. Van Hise, and the Canadian geolo- 

 gists, especially A. C. Cawfon, who has worked in the Rainy Lake 

 region. The definite introduction of Huronian in the classification 



O 



is especially due to Logan (1857). Previously Foster and Whitney 

 had merely called all the metamorphic rocks concerned with the 

 iron ores in the Lake Superior regions "Azoic." T. B. Brooks in 

 the Marquette district distinguished twenty members (1873), but, 

 as Major Brooks frankly states, the classification was chiefly in- 

 tended to aid explorations for ores. Rominger made the classi- 

 fication much simpler (1884), and many others have since written 

 on the subject. 1 



2.02.17. As now viewed, the Laurentian is regarded as con- 

 sisting of granites and gneisses and a higher series of gneisses and 

 schists. They are grouped under the name of " Fundamental Com- 

 plex" by Irving and Van Hise (Cascade Formation of Wads- 

 worth, 1892), but the upper series is called Coutchiching in the 

 Rainy Lake Region by Lawson. The unconformity is an eruptive 

 one. Above these, after an unconformity not always clearly 

 marked, comes the succession of schistose rocks, which are grouped 

 together under the name Algonkian. They consist of a lower 

 series, called by various names in the different regions, but which 

 in the Marquette, Menominee, afcd Yermilion Lake districts contains 

 some of the most important mines. It is variously denominated 

 Lower Huronian, Lower Marquette, Keewatin, Lower Vermilion, 

 and Menominee proper in the different exposures, and probably 

 the great cherty limestone of the Penokee-Gogebic series is its 

 local equivalent. In the Marquette district Wadsworth has re- 

 cently divided it still further into the Republic and Mesnard forma- 

 tions. The upper part follows an unconformity and is called in the 

 different regions Upper Huronian, Animikie, Upper Yermilion, L^p- 

 per Marquette, Western Menominee, and Penokee-Gogebic proper. 



1 See M. E. Wadsworth, Notes on the Geology of the Iron and Copper 

 Districts, 1880 ; N. H. Wmchell, " A Last Word with the Huronian,'* 

 Geol Soc. Amer., Vol. II., p. 85 ; C. R. Van Hise, "An Attempt to Har- 

 monize some apparently conflicting Views of Lake Superior Strati- 

 graphy," Amer. Jour. Sci., ii., XLI. 117 ; and Tenth Ann. Rep. Director 

 U. S. Geol. Survey. The papers give many references. 



