UNIVERSITY OF MINNESOTA Minnesota Geological Survey PAUL K. SIMS, DIRECTOR BULLETIN 37 PHOTOGRAPH BY KENNETH M. WRIGHT MINNESOTA'S ROCKS AND WATERS A Geological Story by GEORGE 1\1. SCHWARTZ and GEORGE A. THIEL with the assistance of Peggy Harding Love The University of Minnesota Press, MinncajJolis Copyright 195.4,19138 by the UNIVERSITY OF MINNESOTA All rights resen'ed PRINTED AT THE JONES PRESS, INC., MINNEAPOLIS 3~2 Revised edition Library of Congress Catalog Card Number; 54-6370 PUBLISHED IN GREAT BRITAIN, INDIA, AND PAKISTAN BY GEOFFREY CUl\lBERLEGE: OXFORD UNIVERSITY PRESS, LONDON. BOMBAY, AND KARACHI TO THE MEMORY OF JUNIOR F. HAYDEN enthw;iastic naturalist and benefactor of the Departments of Botany and Geology of the UniveTsity of "Minnesota Preface THIS volume has been prepared in an attempt to make available to the citizens of Minnesota a general summary of the major geologi­ cal features of the state and to stimulate a greater interest in, and appreciation of, their natural surroundings. Ability to interpret the landscape requires knowledge of the forces that produced it. One may admire the beauty of a waterfall or marvel at its grandeur, but to appreciate it fully, one must know how it was formed. Man draws from the earth many materials which are necessary for life and happiness, and he deals with geological conditions in many of his daily activities. For example, he plows the soil, which is composed largely of weathered rock materials, and cuts the sur­ face rocks as he grades roads and railroads and excavates founda­ tion places for his skyscrapers and his great plants in which to exploit the earth's resources. Yet how many of the thousands of citizens of Minnesota employed in these enterprises understand the geological relationships of the materials with which they labor? How much greater would be their interest in their assigned tasks if they knew more about the formation of the materials which occupy their attention? An understanding of geological processes guides us in the search for mineral resources and aids us in understanding the forces which produced them. Soil erosion, one of our most important prob­ lems, is closely related to the geology of the area involved. V11 V111 MINNESOTA'S ROCKS AND WATERS The resources of any region determine to a marked degree the activity of its inhabitants. They are the foundation of our well­ being, the hope of our future. JYIinnesota, though known as an agri­ cultural state, has great mineral wealth, and many of its citizens are engaged in mineral industries. All of the mineral substances pro­ duced from the rocks of the state may be classified as industrial minerals eyen though some are metals and others nonmetals. JYletal mining is restricted to the iron ranges, but the nonmetals include a great variety of materials - such as limestone for agricultural lime, marl, sand and grayel, clays and shales, wool rock, and structural and architectural stone - which are excavated and processed at many places in the state. The authors of this book have had many years of experience in educational work in JYlinnesota. It is their opinion, based upon ob­ servation and experience, that in the curriculums in our schools not enough time is devoted to a study of our own state and its re­ sources. It is hoped that this volume will furnish science teachers with accurate information which they can in turn pass on to their students at the appropriate time, and that citizens at large will find it a source of information regarding their state. Technical terms have been held to a minimum in order to make the text intelligible to those unfamiliar with detailed geological terminology. The authors know that this method inevitably results in generalities that may not always take into account all detailed scientific infor­ mation available to the geologist. We hope, however, that geologists 'will recommend the book to their friends and that they will not hesitate to explain some of the exceptions that are bound to appear 'where such broad generalizations are employed for the sake of sim­ plicity. Geology is the science that weaves all the other natural sciences together into a cornprehensive whole and this results in great complexity. The authors, with full awareness of the magni­ tude of the task, have attempted to resolve complex geological details by employing a nonscientific assistant who screened out much of the detail and obtained a residue that is sufficiently free of technicalities to be comprehensible to the general reader. GEORGE JVI. SCHWARTZ GEORGE A. THIEL Acknowledg17lents THIS bulletin is an attempt to summarize the most important aspects of the geology of ]\iinnesota. It follows, therefore, that the authors have called on every available source of information, together with their own knowledge gained in over thirty years of geological work and teaching within the state. Because this is a nontechnical publication it was decided to omit footnote references to sources of information. All sources published before 1951 will be found in the Bibliography of Minnesota Geology, which appeared as Bulletin 34 of the Minnesota Geological Survey. A complete list of the publications of the Geological and Natural History Survey of lVlinnesota and its successor, the lVIinnesota Geological Survey, is reproduced as Appendix 2 of this bulletin. Other principal sources of data are the following: C. W. Hall. The geography and geology of Minnesota. Minne­ apolis. 1903. C. K. Leith. The Mesabi iron-bearing district of Minnesota: U.S.G.S. Mon. 43, 1903. J. M. Clements. The Vermilion iron-bearing district of Minnesota. U.S.G.S. Mon. 45, 1903. C. R. Van Hise and C. K. Leith. The geology of the Lake Superior region. U.S.G.S. Mon. 52, 1911. D. E. Willard. The story of the North Star State. St. Paul. 1922. IX x MINNESOTA'S ROCKS AND WATERS J. ·W. Gruner. The mineralogy and geology of the taconites and iron ores of the Mesabi range, Minnesota. St. Paul, Office of the Commissioner of Iron Range Resources and Rehabilitation. 1946. F. F. Grout. The titaniferous magnetites of lVIinnesota. St. Paul, Office of the Commissioner of Iron Range Resources and Rehabili­ tation. 1949-1950. The authors acknowledge their debt to these sources. They also owe much to their colleagues past and present in the Department of Geology at the University of Minnesota. We are indebted to Dr. N. Prokopovich for many of the line drawings. lVIany of the illustrations have been taken from previous publi­ cations of the lVIinnesota Geological Survey; others originated through the activity of the Survey personnel. These have not been separately acknowledged. Illustrations from outside the Survey have been credited to the proper source. The book is illustrated profusely, and the cost of the illustrations was covered by funds from the generous bequest of Junior F. Hayden to the Department of Geology. It was Mr. Hayden's hope to join with the authors in preparing the illustrations, but his un­ timely death deprived him of that pleasure. It is, therefore, with a deep sense of gratitude that we have dedicated this volume to his melnory. Contents PART 1. THE STORY OF THE ROCKS 1 The Face of the Land 3 2 RiveTs and Lakes 25 3 .1Ylinerals and Rocks 53 4 Clues to the Span of Geological Time 93 5 The 1vlost Ancient Rocks in 1vlinnesota 104 6 .11linnesota undeT Paleozoic Seas 118 7 The Age of Reptiles 142 8 The Great Ice Age 150 9 1vlinnesota's 111ineml ResmlTces 172 PART II. GEOLOGICAL EXCURSIONS THROUGH MINNESOTA 10 N oTtheasteTn lJ,I innesota 191 11 N oTthwestem 111 innesota 252 12 N mth and TVest Central .Minnesota 259 13 The Minnesota River Valley 271 14 Southwestem 111 innesota 284 15 Southeastem ~Minnesota 291 16 The St. C1'oix River Valley 329 A List of the Minerals of Minnesota 341 .Minnesota Geological SUTvey Publications 344 Glossary 347 index 357 Xl IllustJ'ations Frontispiece. Winter view of typical coast line of Lake Superior, formed by erosion of lava flows. The cove and spur pattern is a result of different rates of erosion of the tops and bottoms of successive flows. 1. Map showing location of Minnesota 4 2. Map of drainage basins of Minnesota 6 3. Map of counties of Minnesota 7 4. Photograph of relief model of Minnesota 8 5. Aerial photograph of fields partly dissected by gullies 10 6. Tributary valley of Mississippi River near Dakota 10 7. View of Mississippi Valley near Red Wing 11 8. Map of major physiographic divisions of Minnesota 13 9. Map of former major glacial lakes and rivers of Minnesota 15 10. Diagram showing formation of an outwash plain and a terminal morame 21 11. Manitou Falls, North Shore of Lake Superior 27 12. Left. Block diagrams showing stream piracy. Right. Maps show- ing drainage changes of St. Louis and Mississippi rivers 29 13. Aerial view of Lac La Croix 30 14. Painted Rocks, Lac La Croix 31 15. Mica Bay, Lake Namekan, St. Louis County 32 16. Map showing many irregular lakes in terminal moraine, Otter Tail County 34 17. Diagrams showing origin of different kinds of glacial lakes 37 18. Oxbow lakes along Mississippi River 38 19. Saucer lakes, Minnesota River Valley 39 20 . .Junction of St. Croix and Mississippi rivers 41 XII ILLUSTRATIONS Xlll ~1. Underwater sand bars, Pelican Lake 43 ~~. Ice rampart, Leech Lake 44 ~3. Muskeg swamp 46 ~4. Diagrams of stages in the filling of a lake basin by peat 47 ~5. Bog succession zones 48 ~6. Diagrams showing structural positions of springs 49 ~7. A large spring, Lanesboro. Above: spring pool in valley. Below: spring discharging from valley w·all 51 ~8.