CHAPTER V. 



THE UPPER HURONIAN (ANIMIKIE). 



In the eastern portion of the Vermilion district there has been found 

 overlying the Knife Lake slates and the Ogishke conglomerate where these 

 are present and, where they are wanting, lying immediately upon the Ely 

 greenstone or the granite of Saganaga Lake, a series of sedimentary rocks, 

 of which a considerable thickness is exposed. These rocks belong to tlie 

 great sedimentary series which is best developed in a very wide area lying 

 along the northwest and north shores of Lake Superior and extending well 

 up into Canada, but which is also well developed in the Mesabi district on 

 the southern slope of the Giants range in Minnesota. To this series the 

 name Animikie, the Ojibway word for thunder, has been given by Hunt" 

 from the fact that these rocks are typically developed in the vicinity of the 

 two well-known topograpliic features of the north shore of Lake Superior, 

 namely Thunder Bay and Thunder Cape. 



The Upper Huronian series of the Vermilion district may be readily 

 divided into two facies of rocks which are quite different petrographically. 

 At the bottom of the series occurs an iron-bearing formation, known 

 as the Gunflint formation, consisting of bands of ferruginous carbonates, 

 quartz, magnetitic quartz, magnetitic ore, and augite, hypersthene, horn- 

 blende, olivine, griinerite, and magnetite rocks. All of these apparently 

 represent altered forms of some original ferruginous rocks. Above these 

 iron-bearing rocks there occurs a great slate-graywacke formation, known 

 as the Rove slate. 



SECTION I.— GUNFLINT FOBISIATION. 



The rocks of this formation are well developed on the north shore of 

 Gunflint Lake, from which their name has been derived. They extend in 

 a belt, shown on the maps in the accompanying atlas, for a number of 



«The geognostical history of the metals, by T. Sterry Hunt: Trans. Am. Inst. Min. Eng., Vol. I, 

 pp. 331-395; Vol. II, pp. 58-59. 

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