CONTENTS. 



Page. 



Chapter 1. — GeoiJraphical limits and physiographv 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 344 



(2) Deflections of the horizontal needle 345 



(3) Deflections of the dip needle 347 



(4) Horizontal and vertical components when the magnetic rook 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. — Applications 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 37O 



(3) Formations split by intrusives 37I 



(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 



Section VI. — The Mansfield schists 41I 



Distribution, exposures, and topography 411 



Petrographical characters 412 



325 



