Savage and Boss — Age of Iron Ore. 187 



Art. VIII. — The Age of the Iron Ore in Eastern Wis- 

 consin; by T. E. Savage and C. S. Ross. 



It has long; been known that a bed of oolitic iron ore occurs 

 in several isolated lenses or patches in southeastern Wisconsin, 

 occupying a position immediately above the Maquoketa (Rich- 

 mond) shale, and below a limestone of Silurian age. This ore 

 bed is best exposed about 4 miles south of Mayville, near the 

 village of Neda, where its maximum thickness is about 30 feet. 

 From this place it continues north towards Mayville and south 

 towards Iron Junction. Another lens is known to be present 

 a few miles farther southeast, in the vicinity of Hartford. 

 North of Mayville an outcrop of the iron ore occurs about 5 

 miles east of DePere, in Brown County, and still farther north 

 the iron deposit is known in a few places southwest of the 

 town of Sturgeon Bay. The distribution of this iron ore 

 in Wisconsin has been recently described in a paper by F. T. 

 Thwaites,* to which the reader is referred for a detailed descrip- 

 tion of the distribution of the deposit. 



Many years ago this iron ore bed was well described by 

 Chamberlin,f who correlated it with the Clinton iron ore of 

 the Appalachian region as follows : 



" As yet there seems no authentic instance of organic remains 

 having been found in this deposit, although I was shown fossils, 

 said, with undoubted truth, to have been taken from the ore, but 

 they were probably found in the disturbed drift ore, as they were 

 Cincinnati species, specimens of which were ascertained to have 

 been driven up by glacial forces into the mixed mass overlying 

 the Mayville ore bed. We are left, then, without the valuable 

 criterion which fossils afford for determining the age of this 

 important formation. But there is, nevertheless, no occasion for 

 doubt on this subject. Its stratigraphic position fixes its age 

 within very narrow limits. The limestone above belongs to a 

 very low horizon in the Niagara group, and, indeed, it has been 

 regarded by some eminent geologists as belonging to the Clinton 

 epoch, and it probably is the approximate equivalent of the upper 

 portion of the Clinton beds of New York, but as will be seen 

 hereafter, there is no good reason for separating this limestone 

 from the great mass of the Niagara group, with which it is in- 

 timately connected. There is a sharp line of demarcation between 

 the ore and the limestone at most points, so that there is no reason 

 for assigning the ore a higher position than the Clinton epoch." 



" While, as already stated, the clay below mingles somewhat 

 with the lower layers of the iron deposit, the ore ' takes on ' layers 



•Frediik T. Thwaites, Bull. No. 540, U. S. Geol. Survey, 1912, pp. 

 o38— 342. 



fT. C. Chamberlin, Geology of Wisconsin, vol. ii, 1877, pp. 327-335. 



