CLINTON IRON ORE DEPOSIT. 327 



CHAPTER YIEL 



UPPER SILUBIAN. 



CLINTON IRON ORE DEPOSIT. 



It has already been incidentally stated, that, at certain points, the 

 Cincinnati shales were overlaid by an iron ore deposit, while much 

 more frequently it was observed, that the Niagara limestone rested 

 directly upon them. "Wherever the iron ore occurs, it is found to be 

 capped by Niagara limestone. The phenomenon presented, then, is 

 that of a separation of the shales and limestone, at some points, by a 

 bed of iron ore, coming in between them, and growing thicker till its 

 maximum is reached, and then thinning out and disappearing again, 

 forming an irregular lens-like mass. 



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 pro- 

 bably 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 stratigraph- 

 ical 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 intimately con- 

 nected. There is a sharp line of demarkation 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 at the 

 bottom, so that its beds are in a slight degree unconformable to those 



