CONTENTS. VII 



Chapter IV.— The Lower Huronian series— Continued. 



Section 3. — Tlie Hemlock formation— Continuecl. Page. 



Normal sedimentaries of the Hemlock formation 152 



Economic products lO'' 



Buildiug and ornamental stones 153 



Road materials - 154 



Chapter V. — The Upper Huroxian series - 155 



Distribution, exposures, and topography , 155 



Magnetic lines 156 



' Thickness 157 



Folding - 158 



Crystal Falls syncline - 158 



Time of folding of the Upper Huronian 161 



Relations to other series 162 



Relations to intrusi ves 164 



Correlation , - 161 



Petrographical characters 165 



Sedimentary rocks - - 165 



Microscopical description of certain of the sedimentaries 169 



Igneous rocks 1"* 



Ore deposits 1''' 



History of opening of the district 1''5 



Distribution 1''5 



Western half of sec. 34, T. 46 N., R. 33 W 176 



Sec. 20, T. 45 N., R. 33 W 176 



The Amasa area 177 



The Crystal Falls area 178 



Character of the ore 1<50 



Relations to adj acent rocks 182 



Origin 183 



Size of the ore bodies 184 



Methods of mining 184 



Prospecting 185 



Production of ore from the Crystal Falls area 186 



Chapter VI. — The Intrusives - 187 



Order of treatment 188 



Age of the intrusives 188 



Relations of folding and the distribution of the intrusives 189 



Section I. — Unrelated intrusives 190 



Classification 190 



Acid intrusives 190 



Geographical distribution and exposures of granites 190 



Biotite-granite 191 



Micropegmatites 192 



Muscovite-biotite-granite 193 



Relations of granites to other intrusives 194 



Dynamic action in granites 194 



Contact of granites and sedimentaries 194 



Evidence of intrusion 195 



Basic intrusives 198 



Metadolerite 199 



Geographical distribution 199 



Petrographical characters 199 



Macroscopical 199 



Microscopical 200 



