CONTENTS. IX 



Chapter VI. — The Intrusives — Continued. 

 Section II. — A study of a root series, etc. — Continued. 

 Peridoti tes- — C on tinned . 



Peridotite varieties — Continued. Page. 



Peridotite from sec. 22, T. 42 N., R. 31 W., 1990 N., 150 W 260 



Relations of peridotites to other rocks 261 



Age of peridotites 262 



General observations on the above series ' 262 



Textural characters of the series 262 



Chemical composition of the series 263 



Relative ages of rocks of the series 265 



Part II. — The eastern part of the Crystal Falls district, including the Felch 

 Mountain range, by Henry Lloyd Smyth. 



Chapter I. — Geographical limits and ph y'siography 329 



Introduction 329 



Preliminary sketch of geology 331 



Character of surface 331 



Drainage 334 



Chapter II. — Magnetic observations in geological mapping 336 



Section I. — Introduction 336 



Section II. — Description of the magnetic rocks 338 



Section III. — Distribution of magnetism in the magnetic rocks 339 



Section IV. — Instruments and methods of work 341 



Section V. — Facts of observation and general principles 344 



(1) Observed deflections when the strike is north and south and the dip vertical 844 



(2) Deflections of the horizontal needle 345 



(3) Deflections of the dip needle 347 



(4) Horizontal and vertical components when the magnetic rock dips vertically ,349 



(5) Horizontal and vertical components when the magnetic rock dips at any angle 350 



(6) Determination of depth 354 



(7) Summary 356 



Section VI.^Apjjlications to special cases 356 



(1) The magnetic rock strikes east or west of north and dips vertically -.... 357 



(2) The magnetic rock strikes east and west 359 



(3) Two parallel magnetic formations 361 



Section VII. — The interpretation of more complex structures 366 



(1) Pitching synclines 367 



(2) Pitching anticlines 370 



(3) Formations sjjlit by intrusives 371 



(4) Summary 372 



Chapter III. — The Felch Mountain range 374 



Section I. — Position, extent, and previous work 374 



Section II. — General sketch of the geology 383 



Section III. — The Archean 385 



Topography 386 



Petrographical characters 387 



Section IV. — The Sturgeon quartzite 398 



Distribution, exposures, and topography 398 



Folding and thickness 399 



Petrographical characters 401 



Section V. — The Eandville dolomite 406 



Distribution, exposures, and topography 406 



Petrographical characters 408 



