6 CONTENTS. 



Chapter III. — The Aechean — Continued. Page. 

 Section II. Ely greenstone— Continued. 



Occurrence and cliaracter — Continued. • 



Microscopic characters 150 



Texture - 151 



Schistose greenstones 153 



General characters 153 



Origin 154 



Contact metamorphism 155 



Contact effect of granite on the greenstone 155 



Mineralogic composition of the metamorphosed rocks 157 



Contact effect of gabbro on greenstone 161 



Relation to adjacent formations - 162 



Economic value 163 



Interesting localities 165 



Possible tuffs associated with the greenstones 166 



Evidences of volcanic character 166 



Metamorphism of the greenstones / 169 



Section III. Soudan formation 172 



Occurrence and character 172 



Distribution 172 



Exposures 173 



Topograph}'- 175 



Structure 175 



Petrographic characters 179 



Macroscopic characters of the fragmental portion of the Soudan formation 179 



Microscopic characters of the fragmental portion of the Soudan formation 180 



Macroscopic characters of the iron-bearing formation proper 181 



The iron ores 183 



Microscopic characters of the iron-bearing formation proper 185 



Origin 188 



Relations to adjacent formations 191 



Relations to the Ely greenstones 191 



R6sum6 of relations to Ely greenstones 198 



Relations to the Archean acid intrusives 199 



Relations to the overlying sediments 199 



Relations to basic erupti ves 200 



Age 200 



Thickness 200 



Interesting localities 200 



Intricate folding of the Soudan formation 210 



elastics associated with the iron-bearing formation 212 



The iron-ore deposits 213 



Historical sketch 213 



Ore horizons 215 



, The Ely iron-ore deposits 216 



Deposits occurring at the bottom of the iron formation 216 



The Tower and Soudan deposits 222 



Deposits occurring at bottom of the iron formation 223 



Deposits occurring within the iron formation 224 



Origin of the ore deposits 227 



Methods of mining in the Vermilion district 234. 



Production and shipments of iron ore from the Vermilion district 241 



Prospecting 243 



