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Item Bulletin No. 28. The Geology of the Anorthosites of the Minnesota Coast of Lake Superior(Minnesota Geological Survey, 1939) Grout, Frank F.; Schwartz, George M.The northeast corner of Minnesota, lying north of Lake Superior and comprising Cook and Lake counties and part of St. Louis County, is underlain by Keweenawan rocks except for a narrow strip along the Canadian border. Early studies of these rocks were made principally by Winchell and by Irving, as shown by the list of publications given below. Because of the size and inaccessibility of much of the region, these early studies were confined to a narrow strip along the shore of Lake Superior. Later Grout and other members of the Minnesota Geological Survey made detailed studies of the Duluth gabbro. Between the areas covered by these workers lies a region in which only reconnaissance work had been done previous to the mapping presented in this report. It is planned eventually to map in detail this entire area, but as it embraces approximately 4,000 square miles of forested or brushy country, much of it not easily accessible for detailed work, it will take many field seasons to complete the task. The particular region mapped in this survey was selected because of unusual plagioclase feldspar masses of very high purity, for which it is hoped uses may be found, but the results are also significant as an example of the geology of a great Keweenawan area. The Keweenawan of this region consists almost entirely of igneous rocks. and even the few sedimentary rocks known are closely connected with extrusive igneous activity. It is about centrally located in the Keweenawan area of the north shore of Lake Superior and lies above the thickest part of the Duluth gabbro, but probably is not connected with it by continuous intrusive masses below the drift.Item Bulletin No. 8. I. The Anorthosytes of the Minnesota Coast of Lake Superior; II. The Laccolitic Sills of the North-west coast of Lake Superior(Minnesota Geological Survey, 1893) Lawson, AndrewAmong the problems which were named in instructions given to Dr. Lawson when he entered upon the season's work for the Minnesota. Geological and Natural History Survey along the northern coast of lake Superior, one was the following. To determine if possible the date and stratigraphic relations of the gabbro invasion. How well he has answered that question his report on the "Anorthosytes of the Minnesota coast of lake Superior" bears ample testimony. In order, however, that the important bearing which his results have on the geology of the northeastern part of the state, may be made more apparent, it is deemed best to preface this publication with a short exposition of the history of the investigation, and a few paragraphs on the extent of the gabbro rocks and on the significance of the term gabbro.