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The Influence of Geologic Structure on the Drainage Pattern in Northeastern Minnesota

Karl ver Steeg
The Journal of Geology
Vol. 55, No. 4 (Jul., 1947), pp. 353-361
Stable URL: http://www.jstor.org/stable/30058852
Page Count: 12
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The Influence of Geologic Structure on the Drainage Pattern in Northeastern Minnesota
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Abstract

The region is especially interesting from the standpoint of geomorphology. Erosion of monoclinal structure of the Animikie and Keweenawan formations has developed ridges with an asymmetrical profile, known as "sawtooth mountains." The ridge and valley topography in the area underlain by the Rove slate and associated intrusives (dikes, and sills) resembles that of the folded Appalachians. The preglacial drainage pattern was trellised. The Duluth gabbro is banded; those zones composed of minerals less resistant to weathering and erosive agencies underlie the valleys, and the more resistant rocks, such as the "red rock," make up the ridges. The lakes located on the Saganaga granite are irregular in outline and are not oriented in any particular direction. The Pleistocene ice sheets produced noteworthy changes in the drainage lines. Numerous glacial lakes now occupy depressions which show striking east-west alignment. Many of the streams are new or have been forced to find new channels. Waterfalls and rapids and postglacial gorges are common.

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