218 // L. Smyth — Lower Menominee and 



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 chert} 7 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. 



Iron ores occur at three horizons in the lower Menominee. 

 The lowest and least important is found in the upper portion 

 of the quartzite near its junction with the limestone. While 

 lean (usually martite) ores are of wide distribution, only one 

 workable deposit of rich ore has as yet been discovered in this 

 position in the series. The slate member contains the great 

 majority of the rich ore deposits. These occur as local con- 

 centrations in a ferruginous rock, composed of banded jasper 

 and iron ore, which perhaps is the modified representative of 

 portions of the slates carrying a large proportion of non-clastic 

 material of original deposition. The banded jasper is not con- 

 tinuous, and it occurs at different horizons in the slates. The 

 third horizon is the Michigamme jasper, which up to the 

 present time has yielded only a few small bodies of rich ore. 



Lower Marquette. 



The lower Marquette series in the western part of the Mar- 

 quette 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 gruenerite),* 

 magnetite, and silica, one or two of which may locally pre- 

 dominate over the rest, and an upper member, usually 

 but not invariably, characterized by bands of red jasper 

 and specular hematite. The iron-bearing member has a maxi- 

 mum thickness of more than 1000 feet, but usually it has 

 been cut down greatly or, with the lower quartzite, entirely, 

 by the Animikief transgression. 



The Marquette iron ores, except those in the Upper Mar- 

 quette series, occur, as Yan Ilise has shown,:}: either (#) at the 



* A. C. Lane and F. P. Sharpless. this Journal. Dec, 1891, p. 505. Report of 

 the State Board of Geol. Survey, Michigan, Lansing, 1893, p. 183. 



f Animikie is here used as a general term, covering the time of deposition of 

 the Upper FTuronian. Upper Marquette, Upper Menominee, Penokee-Gogebic, 

 and the Animikie of Northern Minnesota and Cauada. all of which are regarded 

 as generally equivalent. 



% This Journal, Feb.. 1892. 



