The Iron Ores of the Lake Superior Region. 
219 
THE IRON ORES OF THE LAKE SUPERIOR REGION. 
By C. E. VAN HISE. 
The object of the present article is to bring together in a single paper 
the more important conclusions as to the iron ores of the Lake Superior 
region, which have been reached in recent years by the Lake Superior 
Division of the United States Geological Survey. 
The iron ores are all associated with peculiar nonfragmental rocks 
which have great variety, but which have the common feature of con¬ 
taining a considerable content of iron. The varieties include ferrugin¬ 
ous cherts, ferruginous slates, sideritic slates, actinolitic schists, magneti- 
tic schists, hematitic schists and intermediate phases. At different times 
in the past it has been suggested that the Lake Superior iron ores, like 
many of those of later age, are derived from carbonate of iron. How¬ 
ever, Irving was the first to definitely prove this by showing that in this 
region there is abundant residual iron carbonate, and that there are 
actual transitions between this and other phases of the iron formations.* 
Since this conclusion was announced, the evidence that these and also 
the ores are derived directly or indirectly from a lean cherty and often 
calcareous and magnesian siderite has been greatly augmented. 
The manner of the transformation of the iron carbonates into the 
other phases of rock of the iron formation have been traced out in de¬ 
tail in the Penokee and Animikie districts.! The work of the past two 
years has given a large amount of evidence that exactly similar trans¬ 
formations have taken place in the Marquette, Vermilion, and Kaminis- 
tiquia districts. As yet the Menominee proper and Felch Mountain 
districts have not been sufficiently studied to furnish this evidence; but 
the ferruginous rocks here occurring are exactly like those in the other 
districts and there is no doubt as to their equivalent age, so that it is. 
highly probable that the same is true. 
The iron ores now mined occur in two geological series, separated by 
a physical break.J These are the Lower Huronian and Upper Huronian. 
* Irving, R. D., Origin of the Ferruginous Schists and Iron Ores of the Lake Superior 
region: Am. Jour. Sci., 3rd ser., vol. 32, 1886, pp. 255-272. 
t Irving, R. D. and Van Hise, C. R.: The Penokee Iron-Bearing Series of Michigan and 
Wisconsin: Tenth Ann. Rept. U. S. Geol. Survey, 1890, pp. 380-422. 
t Van Hise, C. R.: An attempt to harmonize some apparently conflicting Views of Lake 
Superior Stratigraphy. Am. Jour. Sci., 3rd ser., vol. 41, 1891, pp. 117-137. 
