46 Van IHse — Iron Ores of the Penokee-Gogebic Series. 



tinue for a considerable depth. "While they may extend in 

 unimpaired richness and magnitude to a depth as great as 

 can be penetrated by workings, it is certain that they do not 

 continue to an indefinite distance. There is also a possibility 

 that the deposits may become poorer than at the surface at 

 comparatively small depths ; for it may be that percolating 

 waters, since the termination of the Glacial epoch, have been 

 able to remove from the upper parts of the deposits a small 

 percentage of silica. Such a removal, even to the extent of 

 live per cent, or less, would have an important influence upon 

 the value of the deposits. 



Emmons on Ore-deposits. — It is of interest to compare the- 

 conclusions reached, to those of Emmons* as to the origin of the 

 silver-lead-deposits of Leadville, Colorado. He finds that the 

 ore did not form in pre-existing cavities, but by a gradual 

 replacement of the rock materials by substances brought in 

 solutions ; and also that these solutions did not come up from 

 below, but have reached their "immediate locus" by pass- 

 ing downward through the rocks above. In his discussion 

 upon ore-deposits in general, he maintains that a like origin 

 is much more common than has been believed. It will be 

 seen that my conclusions as to the origin of the iron ore 

 of the Penokee-Gogebic Series, arrived at independently of 

 Mr. Emmons's work, are in exact harmony with his general 

 conclusions. 



Iron ores in other parts of the Lake Superior country. — 

 Before closing this paper, some allusions must be made to the 

 nature and origin of the iron ores which are found in other 

 regions in the Lake Superior country. Large deposits of ore 

 are found in rocks remarkably like those of the Penokee- 

 Gogebic series, in the Vermilion Lake, Marquette and Meno- 

 monee regions. These ores are associated in almost every 

 mine with a somewhat varying peculiar rock, universally 

 known as soapstone. The connection between the ore and 

 these soapstones is so constant that the appearance of this 

 peculiar greasy altered material is considered as a very favor- 

 able indication in prospecting. It is true that the rock which 

 miners denominate soapstone, in different localities has quite 

 different appearances, and frequently schists are called soap- 

 stones which have no essential likeness to the material with 

 which the ore is found associated. These so-called soapstones, 

 in the regions referred to, are at times peculiar green banded 

 schists, at other times are compact strongly foliated sericite- 

 schists, and only occasionally do they retain the structure of 



* U. S. G-eol. Survey; Monograph XII; Geology and Mining Industry of Lead- 

 ville; Samuel Franklin Emmons, pp. 375-879. Trans. Am. Inst. Min. Eug., vol. 

 xvi, pp. 804-839. Structural Relations of Ore Deposits, S. F. Emmons. 



