﻿THE 
  

  

  AMERICAN 
  JOURNAL 
  OF 
  SCIENCE 
  

  

  [FOURTH 
  SERIES.] 
  

  

  Art. 
  XXXIX. 
  — 
  The 
  Geology 
  of 
  Pigeon 
  Point, 
  Minnesota 
  ; 
  

   Reginald 
  A. 
  Daly, 
  Harvard 
  University. 
  

  

  Contents. 
  

  

  Introduction. 
  

  

  Revised 
  map. 
  

  

  Main 
  intrusive 
  a 
  sill. 
  

  

  Tilting 
  after 
  injection 
  of 
  the 
  sill. 
  

  

  Stratiform 
  structure 
  of 
  the 
  sill. 
  

  

  Segregation 
  of 
  red 
  rock 
  through 
  gas 
  tension. 
  

  

  Ribbon 
  injections. 
  

  

  Time 
  relations 
  of 
  the 
  magmatic 
  phases. 
  

  

  Differentiation 
  necessarily 
  postulated. 
  

  

  Nature 
  of 
  the 
  magma 
  differentiated. 
  

  

  Evidences 
  of 
  assimilation. 
  

  

  Red-rock 
  shells 
  surrounding 
  xenoliths. 
  

  

  Magmatic 
  stoping. 
  

  

  Capacity 
  of 
  the 
  original 
  magma 
  for 
  assimilation 
  and 
  contact 
  fusion. 
  

  

  Assimilation 
  in 
  the 
  sill 
  conduit. 
  

  

  Summary 
  on 
  the 
  origin 
  of 
  the 
  red 
  rock. 
  

  

  Introduction. 
  — 
  During 
  the 
  summer 
  of 
  1916 
  the 
  writer, 
  in 
  

   company 
  with 
  Professor 
  Charles 
  Pal 
  ache 
  of 
  Harvard 
  Univer- 
  

   sity, 
  spent 
  six 
  days 
  in 
  a 
  field 
  examination 
  of 
  the 
  intrusive 
  body 
  

   which 
  has 
  become 
  celebrated 
  through 
  the 
  able 
  memoir 
  by 
  Bay- 
  

   ley, 
  entitled 
  " 
  The 
  Eruptive 
  and 
  Sedimentary 
  Rocks 
  of 
  Pigeon 
  

   Point, 
  Minnesota, 
  and 
  Their 
  Contact 
  Phenomena."* 
  With 
  

   the 
  kind 
  assistance 
  and 
  personal 
  guidance 
  of 
  Professor 
  F. 
  P. 
  

   Grout 
  of 
  the 
  University 
  of 
  Minnesota, 
  the 
  point 
  was 
  found 
  to 
  

   be 
  easily 
  accessible. 
  Leaving 
  the 
  regular 
  steamer 
  from 
  Duluth 
  

   to 
  Port 
  Arthur 
  at 
  Grand 
  Portage, 
  six 
  miles 
  west 
  of 
  the 
  point, 
  

   the 
  party 
  there 
  boarded 
  the 
  motor-boat 
  of 
  Mr. 
  P. 
  Gagnon 
  and 
  

   were 
  soon 
  comfortably 
  camped 
  in 
  Little 
  Portage 
  Bay, 
  an 
  excel- 
  

   lent 
  center 
  for 
  the 
  study 
  of 
  the 
  whole 
  eruptive 
  area, 
  especially 
  

  

  * 
  W. 
  S. 
  Bayley, 
  Bulletin 
  109, 
  United 
  States 
  Geological 
  Survey, 
  1893. 
  

  

  Am. 
  Jour. 
  Sci. 
  — 
  Fourth 
  Series, 
  Vol. 
  XLIII, 
  No. 
  258. 
  — 
  June, 
  1917. 
  

   29 
  

  

  