File:Preliminary report on the geology of east central Minnesota including the Cuyuna iron-ore district (1918) (14577601918).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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cke beds being thicker. The slaty layers show fine micadeveloped along cleavage planes. Lenses and stringers of quartz occurparallel to the bedding. The rock lies on the crest of a large anticlinewith small anticlines and synclines on either limb. The axial line of theanticline strikes about east and pitches about io°E. About a quarter of a mile to the north of this exposure, in the NWJ4of SWJ4 of the section, is a ridge of dark gray slate trending northwest.The ridge rises only a few feet above the surrounding flat, swampy coun-try. It is about 500 feet long and about 200 feet wide. The rock isuniform, dark gray slate with fine mica developed locally along cleavageplanes. Thin laminae and specks of limonite lie parallel to the cleavageand also occur as small spots throughout the rock. In the fresher phasespyrite is abundant, indicating that the limonite is derived from pyriteby weathering. The slate forms a synclinal trough that pitches a littlesouth of east at a low angle. PLATE IX
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B. OUTCROPS OF SLATE AT THE NORTHERN PACIFIC RAILROAD BRIDGE OVER ST. LOUISRIVER BELOW THOMSON DAM, CARLTON COUNTY. LOOKING SOUTH WESTWARD ROCKS OF EAST CENTRAL MINNESOTA 87 West of these two ridges in the western part of the SWJ4 of section31, and extending into the SE^ of section 36, T. 48N., R. 18W., aresmall, low, badly broken exposures of dark gray slate. No outcrop show-ing the attitude of the rock was found. About a quarter of a mile east of the outcrops described above inthe NW34 of SE)4 of section 31, several small exposures of light gray,medium-grained graywacke are found along Black Hoof River. Therock is hard and siliceous and shows no cleavage. The next group of exposures northeast of the Atkinson-Park Lakeregion are those in the vicinity of Otter Creek in sections 16, 17, and 20,T. 48N., R. 17W. Most of these exposures occur along the NorthernPacific Railway which runs northeastward from Atkinson to Carlton.Some are found along Otter Creek. A short distance northeast of

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