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Prelimi?iary Report on the Marquette Iron-Beari7ig District of Michigan. 

 By Charles Richard Van Hise and William Shirley 

 Bayley. With a Chapter 071 the Republic Trough. By Henry 

 Lloyd Smyth. U. S. Geological Survey, 15th Ann. Rept., 

 pp. 477-650, pis. 13-26, figs. 9-20; 1895. 



The Marquette district, the oldest important iron district in the 

 Lake Superior region, is well known to students of pre-Cambrian 

 geology, and while it has been studied in detail before, the present 

 report represents the first systematic and successful attempt to unravel 

 the structure of the region and to determine the sequence and relations 

 of the various rock bodies. The key to the structure of this district, 

 which is in general the key to the structure of much of the Lake 

 Superior region, has been known for several years ; it is that below 

 the Keweenawan are three unconformable rock series, frequently so 

 closely folded together that their separation is very difficult. These 

 three series are the Archean, the Lower Huronian, and the Upper 

 Huronian, or, as termed in this report, the Basement Complex, the 

 Lower Marquette, and the Upper Marquette. 



The district studied extends from the Lake Superior shore just 

 south of Marquette westward to Michigamme, a distance of over thirty- 

 five miles; it is nine miles in width, but in places much more than 

 half of this distance is occupied by rocks of the Basement Complex, 

 and has not been studied in detail. The Lower and Upper Marquette 

 rocks occur in a basin flanked on either side (north and south) by the 

 Basement Complex, which is composed of an intricate mixture of 

 granites, gneisses, schists, and surface volcanics, all thoroughly crystal- 

 line, and cut by basic and acid dikes. 



The Lower Marquette is separated into six conformable formations 

 as follows, in ascending order : Mesnard quartzite, Kona dolomite, 

 Wewe slate, Ajibik quartzite, Siamo slate, and Negaunee formation. 

 During Lower Marquette time the transgression of the ocean was from 

 the east, so that the lower formations are represented only in the east- 

 ern part of the district, and on going westward higher and higher 

 strata are found, resting directly on the underlying Basement Com- 

 plex, between which and the Lower Marquette there is a marked uncon- 

 formity. The Negaunee is the Lower Marquette iron-bearing forma- 

 tion, and is composed of sideritic slates, griinerite-magnetite schists, 

 ferruginous slates, ferruginous cherts and jaspilite, all of which are 



