File:Preliminary report on the geology of east central Minnesota including the Cuyuna iron-ore district (1918) (14577582459).jpg

Identifier: preliminaryrepor00hard (find matches)
Title: Preliminary report on the geology of east central Minnesota including the Cuyuna iron-ore district
Year: 1918 (1910s)
Authors: Harder, Edmund Cecil, 1882- Johnston, A. Walfred, author Geological Survey (U.S.)
Subjects: Geology Iron mines and mining
Publisher: Minneapolis, University of Minnesota
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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. Metamorphosed sedimentary rocks of lower-middle Huronian age arenot very extensively distributed in northern Minnesota. In the Ver-milion district this series is represented by the Ogishke conglomerate,iron-bearing Agawa formation, and Knife Lake slate. The conglomerateoccurs at the base, and is overlain locally by Agawa iron-bearing forma-tion, and above this is the Knife Lake slate. The Ogishke conglomerate varies extremely in thickness in differentparts of the district. It has been thoroughly indurated and locally pro-nounced metamorphism has resulted in the development of schistosephases while intense folding has brought about complex relations betweenit and the underlying Archean. The materials composing the conglom- 50 Van Hise, C. R., and Leith, C. K., op. cit., pp. 118-210. Leith, C. K., The Mesabi iron-bearing district of Minnesota. U. S. Geo!. Survey, Mott.43- 1903. Clements, J. M., The Vermilion iron-bearing district of Minnesota. U. S. Geo!. Survey,Mon. 45. 1903. PLATE I
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LIEF MAP OF THE LAKE SUPERIOR DISTRICT SHOWING THE LOCATION OF THE IRON-ORE DISTRICTS, AFTER VAN HISE AND LEITH SCALE, I INCH TO ABOUT 60 MILES GENERAL GEOLOGY OF MINNESOTA ii erate have been derived from the underlying Keewatin and Laurentianrocks, pebbles of greenstone, granite, porphyry and jasper being foundin it. The Knife Lake slate covers considerable areas and is of great thick-ness. It includes many different phases such as argillaceous slate, biotitic,amphibolitic, quartzitic, and sericitic schists, graywacke, and conglomer-ate. Its metamorphism has been intense, and complex folding has re-sulted in the development of secondary structures, such as cleavage andschistosity, throughout the formation. The iron-bearing Agawa formation occurs as thin lenses or layersbelow the Knife Lake slate and above the Ogishke conglomerate. Itconsists of ferruginous chert, jasper, and other iron-bearing rocks inter-bedded with layers of slate. In the Mesabi district the lower-middle Huronian ipreliminaryrepor00hard

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