DISCUSSION OF CORRELATION 713 



CORRELATION OF THE NEGAUNEE (iRON-BEARING) SERIES WITH THE 

 VULCAN (iron-bearing) SERIES OP THE STURGEON TROUGH, 

 EELCH MOUNTAIN DISTRICT, CALUMET TROUGH, AND MENOM- 

 INEE RANGE 



These ranges lie south of the Marquette district and east of the 

 Iron River-Crystal Falls-Florence district and form eastward- 

 projecting tongues of the Huronian of this great area (see Fig. 3). 



1. Sturgeon River syncline. — -The Negaunee formation has been 

 traced by outcrops, exploration, and magnetic surveys from the 

 Marquette Range into the north limb of the Sturgeon River syn- 

 cHne. From near Witch Lake, about 8 miles south of Republic, 

 the Negaunee formation is shown by the mapping of the United 

 States Geological Survey to rest directly on the Archean. In the 

 Sturgeon syncline, however, the Archean is overlain by the Rand- 

 ville dolomite and Sturgeon quartzite, equivalent to the Kona and 

 Mesnard of the Lower Huronian in the Marquette Range. On the 

 south limb of this synchne the iron formation reappears above the 

 Randville dolomite and has naturally been correlated with the 

 Negaunee of the north hmb. 



2. Fetch Mountain district. — The Felch Mountain district is a 

 narrow syncHne of Huronian rocks downfolded in the Archean, 

 from one to two miles wide, trending east-west, and, like the Sturgeon 

 trough, opening out westward into the great slate area of the Crystal 

 Falls district, wherein the structure is obscured. It is separated 

 from the Sturgeon trough north of it by an anticline on which the 

 Archean appears as a belt of granite about 2^ to 3 miles wide. In 

 the Felch syncline there is an iron formation (Groveland) similar 

 to that in the Sturgeon trough, separated from the quartzite- 

 dolomite below by conformably underlying sedimentary schist 

 (Felch schist) which has not been observed in the Sturgeon trough, 

 although it may be present there also. Bayley makes no mention 

 of the Negaunee formation of the Sturgeon trough in 1899,' al- 

 though it was subsequently discovered through exploration and is 

 shown on the maps of the United States Geological Survey pubHshed 

 in 191 1. ^ On these maps the iron formation in the Sturgeon trough 

 is called Negaunee (Middle Huronian) and in the Felch syncline 



' Monograph 36, U.S. Geol. Survey. " Monograph 52. 



