576 THE MARQUETTE lEON-BEAEING DISTRICT. 



Smyth has recently mapped in detail an area between and nearly 

 connecting the Marqnette and Menominee districts. He has made also a 

 general stndy of the latter district. As the results of his studies, he sum- 

 marizes the Lower Menominee succession as follows:^ 



Avoiding minute subdivisions, the Lower Menominee consists of — 



(1) A basal quartzite, rarely cous'lomeratic. The tliicliuess may reach a maxi- 

 mum of about 1,000 feet, and over large areas is at least 700 feet. 



(2) A crystalline limestone which averages about 700 to 1,000 feet in thickness. 

 On the Fence River, in Ts. 44 and 45 N"., R. 31 W., where it largely if not entirely 

 replaces the lower quartzite, the thickness attained, if there are no subordinate folds, 

 is from 1,500 to 2,000 feet. 



(3) Red, black, and green slates that are not known to exceed 200 to 300 feet in 

 thickness. The slates here and thei-e contain the iron formation that affords the rich 

 ores of Iron Mountain and Norway. In the southern part of T. 44 N., R. 31 W., the 

 horizon of the slates is in part occupied by altered eruptives that rapidly increase in 

 thickness towards the north, the whole attaining a maximum of nearly 2,000 feet on 

 the Fence River, in T. 45 N., R. 31 W. 



(4) The highest member, except volcanics, yet recognized in the Felch Mountain 

 and Fence River divisions of the Lower Menominee is typically developed at Michi- 

 gamme Mountain, sec. 4, T.43 N., R. 31 W., and sec. 33, T. 44 N., R. 31 W., and has been 

 called the Michigamme jasper. This is a greatly altered ferruginous rock usually 

 carrying apparently fragmental quartz grains. Various stages in the alteration permit 

 two or three types to be recognized. The least modified seems to indicate that the 

 rock was originally, in part at least, a clastic sediment. The alteration appears to 

 have been effected by the infiltration of iron salts, the formation of cherty silica, and 

 the replacement of the original constituents to varying degrees. The most highly 

 altered type bears the closest possible resemblance in the hand specimen to the 

 banded specular jasper seen on the Republic bluff. 



Smyth then makes the following statement as to the Marquette district: 



The Lower Marquette series, in the western part of the Marquette area, where it 

 most nearly approaches the Menominee region, consists, when exposed, of — 



(1) A basal conglomerate — quartzite — quartz-schist, probably less than 100 feet 

 thick. North of the Michigamme mine the quartzite passes upward into a slate. 



(2) An iron-bearing formation which may be divided further into a lower member, 

 composed of actinolite (or griinerite), magnetite, and silica, one or two of which may 

 locally predominate over the rest, and an upper member usually, but not invariably, 



■The Lower Menominee and Lower Marquette series in Michigan, by H. L. Smyth; Am. Jour. 

 Sci., 3rd series, VoL XLVII, 1894, pp. 216-223. 



