VIII CONTENTS. 



Chapter VI. — The Intrusives— Continueil. 

 Section I. — Unrelated intrusives — Continued. 

 Basic intrusives — Continued. 



Jletadolerite — Continued. P.ige. 



Relations to adjacent rocks 203^ 



Relations to Lower Huronian Mansfield slates 203 



Relations to Lower Huronian Hemlock volcanios 204 



Relations to Upper Huronian 204 



Relations to other intrusives 204 



Contact metaniorphism 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 effects of dolerite intrusion 211 



Metabasalt 211 



Ultrabasic intrusives 212 



Picrite-porphyry (porphyritic limburgite) 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 rook series ranging from rockq 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 interestiug variations 226 



Sec. 15, T. 42 N., R. 31 W 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 



Bronzite-norite dike 244 



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



Dy nauiically altered gabbro 247 



Relative ages of gabbros 249 



Peridotites 249 



Distribution, exposures, and relations 249 



Petrographical characters 249 



Peridoti te varieties 252 



Wehrli te 253 



Amphibole-iieridotite 253 



Gradations of amphibole-peridotite to wehrlite and olivine-giibbro 254 



Process of crystallization 257 



Analysis of peridoti te 25& 



