DISCUSSION OF CORRELATION 711 



through the Red Rock mine and southward, the iron formation is 

 correlated with the Vulcan or Upper Huronian notwithstanding the 

 facts (i) of similar position with reference to the underlying Hem- 

 lock volcanics, (2) that the strike of the magnetic line north of the 

 Red Rock mine indicates a continuity of the Vulcan iron forma- 

 tion there with the Xegaunee a httle farther north, and (3) that 

 there is no evidence whatever beyond some difference in degree 

 of metamorphism to show that the iron formations in section 

 27, T. 46 N., R. 33 W., and at the Red Rock mine are not one and 

 the same. 



The reason why the iron-bearing series (VulcanJ of the Crystal 

 Falls-Iron River-Florence district was not correlated with the 

 Xegaunee by the United States Geological Survey is a simple one. 

 In the Menominee Range, Van Hise and Bayley found that the 

 iron-bearing series is unconformably above a quartzite-dolomite 

 succession similar to the Lower Huronian of the Marquette Range 

 and, under the dual classification, therefore Upper Huronian. 

 Since the Negaunee formation (prior to 1904) had been correlated 

 with the Lower Huronian, the question arose as to the position of 

 the iron-bearing series in the interv^ening districts. It was reasoned 

 that (i) because the iron-bearing series of the Crystal Falls district 

 was at that time inseparable from the great Upper Huronian slate 

 area opening out south and west from the Marquette district, and 

 (2) because the Hanbury slate of the iron-bearing series of the 

 Menominee Range seems to have areal connections with the slates 

 of the Florence-Crystal Falls district, therefore the iron-bearing 

 series in the latter district must be considered Upper Huronian. 

 This conclusion was preferred, notwithstanding the evidence of 

 continuity of the Vulcan and Xegaunee formations in the northern 

 part of the Crystal Falls district, and, as we shall see, became a 

 source of considerable difi&culty in applying the dual classification 

 to the facts of succession in the Felch Mountain and Florence 

 districts. 



Recent developments in the Hemlock and Michigan mines at 

 Amasa have fortunately determined conclusively that the Vulcan 

 iron formation there which had been correlated as Upper Huronian 

 is in realitv Xegaunee or :Middle Huronian. On the thirteenth 



