CONTENTS. 11 



Chapter V. — The Upper Huronian (Animikie) — Continued. Page. 

 Section II. Rove slate — Continued. 



Relation to adjacent formations 395 



Relations to the Keweenawan dolerite 395 



Relations to the Keweenawan (Duluth) gabbro 395 



Age 395 



Thickness 395 



Chapter VI. — The Keweenawan 397 



Section I. Duluth gabbro and Logan sills 397 



Distribution, exposures, and topography 398 



Distribution 398 



Exposures 399 



Topograph}' , . . . 399 



Petrographic characters of the gabbro 401 



Macroscopic characters 401 



Microscopic charactei's 404 



Petrographic characters of the Logan sills 405 



Macroscopic characters 405 



Microscopic characters 406 



Constituents 406 



Relations of the gabbro to adjacent formations 406 



Relations to the Ely greenstone 406 



Relations to the Lower Huronian sediments 407 



Relations to the Giants Range granite 407 



Relations to the Snowbank and Cacaquabic granites 407 



Relations to the Ujiper Huronian sediments 407 



Relations to the Keweenawan ' 407 



Relations of the Logan sills to adjacent formations 408 



Relations to the Upper Huronian (Animikie) 408 



Relations to the Keweenawan 410 



Relations of the gabbro to the Logan sills 410 



Conclusions as to age and relation of the gabbro and sills 417 



Metamorphic effect of gabbro and sills 418 



Archean (Ely) greenstone ^ 418 



Lower Huronian 419 



Upper Huronian (Gunflint formation) 419 



Rove slates 419 



Endomorphic action : 419 



Iron-oxide bodies in the gabbro 420 



Character, occurrence, and origin ot the iron-oxide bodies 420 



Section II. Acid dikes younger than the Duluth gabbro 422 



Section III. Basic intrusives younger than the Duluth gabbro 422 



Petrographic characters 423 



Macroscopic characters 423 



Microscopic characters 423 



Relations to adjacent formations, and age 424 



Metamorphic effects 424 



Chapter VII. — The drift 425 



Chapter VIII. — Topography op the district in its relations to geologic structure 431 



Chapter IX. — Geologic history of the Vermilion district 437 



Index 449 



