6 CONTENTS. 



Chapter VI. — The Intrusives — Contiuned. 

 Sectiou I. — Unrelated intrusives — Continued. Page. 



Basic intrusives - 198 



iMetadoleiite 199 



Geographical distribution 199 



Petrographical characters 199 



Macroscopical 199 



Microscopical 200 



Relations to ndjacent rooks 203 



Relations to Lower Huronian Mansfield slates .'. 203 



Relations to Lower Huronian Hemlock voloanios 204 



Relations to Upper Huronian 204 



Relations to other intrusives 204 



Contact metamorphism of Mansfield slates by the dolerite 204 



Spilosites 206 



Analyses of spilosites 207 



Desmosites - 207 



Adinoles 208 



Analyses of adinoles 208 



Comparison of analyses of normal Mansfield clay slates and the contact prod- 

 ucts 209 



No endomorphic efteots of dolerite intrusion 211 



Metabasalt 211 



Ultrabasic intrusives 212 



Picrite-porphyry (porphyritic limbiirgite) 212 



Geographical distribution and exposures 212 



Petrographical characters 212 



Gray tremolitized picrite-porphyry 213 



. Dark serpentinized picrite-porphyry 217 



Classification 220 



Section II. — A study of a rock series ranging from rocks of intermediate acidity through 



those of basic composition to ultrabasic kinds 221 



Diorite 222 



Nomenclature 222 



Distribution and exposures 223 



Petrographical characters 223 



Description of interesting variations 226 



Sec. 1-5, T.42N.,R. 31W 226 



Across river from Crystal Falls '. 227 



Southeast of Crystal Falls 227 



Analysis of diorite 231 



Gabbro and norite 233 



Petrographical characters 233 



Description of interesting kinds of gabbro 240 



Hornbleude-gabbro in sec. 15, T. 42 N., R. 31 W 240 



Sees. 15,22,28, and 29, T. 42 N.,R. 31 W 241 



Hornblende gabbro dikes 243 



Bronzitenorite dike 244 



Sec. 29, T. 42 N., R. 31 W., 1200 N., 200 W 245 



Dynamically altered gabbro 247 



Relative ages of gabbros 249 



Peridotites 249 



Distribution, exposures, and relations 249 



Petrographical characters 249 



