CONTENTS 



Letter of transmittal 17 



Outline of monograph 19 



Chapter I. — General description of'the district 29 



Introduction 29 



Previous geologic work in the district 29 



Scope of the paper 31 



Geographic hmits 32 



Stratigraphy 33 



Physiography , 34 



Rehef 34 



Mesabi or Giants range 35 



Area north and northwest of Giants range 36 



The gabbro plateau 37 



Gunflint Lake area 38 



Drainage 39 



Hydrographic basin 39 



Streams 40 



Lakes 41 



Differences in water level 42 



Water power , : 43 



Origin of the lakes 43 



Plankton 46 



Exposures 46 



Forests 47 



Soil 50 



Game and fish 50 



Culture 52 



Indian reservation 54 



Chapter II. — Resume op literature 55 



History of exploration and character of the routes 56 



Geological literature 64 



Chapter III. — The Archean 129 



Section I. Definition and subdivisions 129 



Section II. Ely greenstone 130 



Features of the greenstone 130 



Occurrence and character 131 



Distribution 131 



Exposures 134 



Topography 134 



Structure 135 



Petrographic characters ^ 136 



The amygdaloidal structure 139 



The spherulitic structure 141 



The ellipsoidal structure 144 



5 



