ABSTRACTS 



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GEOLOGY. — Notes on the geology and iron ores of the Cuyuna district, 

 Minnesota. E. C. Harder and A. W. Johnston. U. S. Geo- 

 logical Survey Bulletin 660-A. Pp. 26, with maps, sections, and 

 illustrations. 1917. 



The Cuyuna iron-ore district is near the geographic center of Minne- 

 sota, about 90 miles west of Duluth and 55 miles southwest of the 

 western part of the Mesabi district. In contrast with some of the 

 other Lake Superior iron-ore districts, it is without marked topographic 

 relief. It is mainly a region of low, irregular morainic hills interspersed 

 with lakes and extensive swamps and marshes. 



The productive part of the Cuyuna district is commonly divided 

 into two ranges — the north range, including the part lying north of 

 the Northern Pacific Railway, and the south range, including the belt 

 lying south of the railway. The discovery of iron ore in the Cuyuna 

 district was entirely due to the existence of abnormal magnetic attrac- 

 tions in the region. 



The bedrock in the district and adjacent region is largely concealed 

 by a mantle of glacial drift that varies in thickness from 15 feet to 

 about 400 feet. No rock exposures are known in Crow Wing County, 

 in which most of the district is situated. The rocks that have been 

 found up to the present time in the district can all be grouped under 

 three classes: (1) sedimentary and igneous metamorphosed rocks 

 interlayered with each other in beds and lenses and usually having 

 steep dips due to extensive folding, (2) igneous rocks intruded into the 

 metamorphosed rocks subsequent to their metamorphism and deforma- 

 tion, and (3) younger rocks which lie horizontally on the eroded sur- 

 faces of the rocks of the other two classes. The age of the various rocks 



is not definitely known. 



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