7IO C. K. LEITH AND R. C. ALLEN 



had been then available. There could then have been little if 

 any reason for assigning these two iron-bearing series to different 

 positions in the Huronian group and there is even less reason for 

 such assignment today, because there is substantial evidence for 

 the correlation of the Ironwood and the Negaunee series on other 

 grounds, which will be discussed below. 



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

 NEGAUNEE (iRON-BEARING) SERIES 



Marquette and Crystal Falls districts. — -The basis of correlation 

 of the formations of the Marquette and Crystal Falls districts is 

 afforded by an indicated practical continuity of the Negaunee and 

 Vulcan iron-bearing formations. In 1903 H. L. Smyth traced 

 the Negaunee iron formation from the Repubhc trough southwest 

 around two major anticlines to the northeast side of the great oval 

 anticline in the northern part of the Crystal Falls district.' The 

 relation of the Negaunee formation in this area to a persistent 

 magnetic line may be seen on Fig. 3. From the vicinity of 

 Michigamme Mountain, T. 44 N., R. 31 W., where the Negaunee 

 formation is exposed, a magnetic line extends north through the 

 Sholdice and Doan explorations, where the Negaunee is again 

 exposed, and thence, north, northwest, west, and southwest around 

 the great oval anticline into section 27, T. 46 N., R. 33 W., where it 

 still coincides with the position of the iron formation. A short 

 distance beyond the latter locality the line is broken, but it 

 reappears after an interval of about 2 miles and passes through 

 the Red Rock and Hemlock mines at Amasa and beyond, connect- 

 ing with the iron formation which has been mapped as Vulcan or 

 Upper Huronian. 



The United States Geological Survey in 1911^ accepted the 

 conclusion that the magnetic line, exposures, explorations, and 

 drift bowlders prove the practical continuity of the Negaunee 

 formation from Michigamme Mountain for a distance of 25 miles 

 around the great anticline to a point about a mile south of section 

 27, T. 46 N., R. 33 W., but from a point about 2 miles farther on, 



' See Smyth's discussion in Monograph 36, U.S. Geol. Survey, pp. 452-55. 

 2 Monograph 52. 



