﻿426 
  R. 
  A. 
  Daly 
  — 
  Geology 
  of 
  Pigeon 
  Point, 
  Minnesota. 
  

  

  to 
  the 
  eastward 
  thereof. 
  The 
  red 
  rock 
  of 
  the 
  isthmus 
  has 
  

   throughout 
  a 
  general 
  east-west 
  contact 
  with 
  the 
  mass 
  of 
  the 
  

   intermediate 
  rock 
  and 
  gabbro, 
  and 
  not 
  a 
  north-south 
  contact, 
  

   as 
  indicated 
  on 
  Bayley's 
  map. 
  The 
  patch 
  of 
  red 
  rock 
  and 
  

   intermediate 
  rock 
  mapped 
  by 
  him, 
  in 
  a 
  narrow 
  band 
  stretching 
  

   south 
  toward 
  " 
  D 
  " 
  from 
  the 
  little 
  bay 
  at 
  " 
  B" 
  fig. 
  1, 
  does 
  not 
  

   exist. 
  Finally, 
  the 
  southern 
  edge 
  of 
  the 
  gabbro 
  locally 
  extends 
  

   farther 
  south, 
  both 
  to 
  east 
  and 
  west 
  of 
  Little 
  Portage 
  Bay, 
  than 
  

   as 
  drawn 
  on 
  Bayley's 
  map. 
  Special 
  care 
  was 
  taken 
  to 
  be 
  sure 
  

   of 
  these 
  necessary 
  changes 
  and, 
  in 
  general, 
  fig. 
  1 
  is 
  believed 
  to 
  

   be 
  essentially 
  correct, 
  in 
  spite 
  of 
  the 
  fact 
  that 
  the 
  upper 
  part 
  

   of 
  the 
  gabbro 
  carries 
  some 
  interstitial 
  micropegmatite 
  and 
  is 
  

   thus 
  not 
  always 
  to 
  be 
  distinguished 
  with 
  ease 
  from 
  the 
  inter- 
  

   mediate 
  rock. 
  

  

  It 
  is 
  seen 
  that 
  the 
  map 
  is 
  distinctly 
  simplified 
  by 
  these 
  

   changes. 
  The 
  main 
  gabbro 
  is 
  continuous 
  and 
  not 
  cut 
  across 
  by 
  

   any 
  large 
  body 
  of 
  red 
  rock. 
  The 
  red 
  rock 
  is 
  nearly 
  continuous, 
  

   lying 
  between 
  the 
  main 
  gabbro 
  on 
  the 
  north 
  and 
  the 
  quartz- 
  

   ite-metargillite 
  series 
  of 
  the 
  south. 
  The 
  intermediate 
  rock 
  is 
  

   nearly 
  as 
  continuous 
  ; 
  it 
  lies 
  between 
  the 
  gabbro 
  and 
  the 
  red 
  

   rock, 
  again 
  with 
  persistent 
  trend 
  of 
  outcrop 
  directed 
  nearly 
  

   east 
  and 
  west. 
  

  

  Main 
  Intrusive 
  a 
  Sill. 
  — 
  R. 
  D. 
  Irving 
  andBayley 
  considered 
  

   the 
  main 
  intrusive 
  to 
  be 
  a 
  dike. 
  In 
  a 
  letter 
  ]S 
  T 
  . 
  H. 
  Winchell 
  

   has 
  stated 
  his 
  belief 
  that 
  it 
  is 
  a 
  sill.* 
  The 
  decision 
  between 
  

   the 
  two 
  views 
  is 
  not 
  obvious, 
  on 
  account 
  of 
  the 
  few 
  exposures 
  

   of 
  the 
  Animikie 
  sediments 
  along 
  the 
  northern 
  side 
  of 
  the 
  erup- 
  

   tive 
  mass. 
  So 
  far 
  as 
  the 
  evidence 
  goes, 
  however, 
  the 
  sill 
  

   hypothesis 
  should 
  be 
  preferred. 
  The 
  matter 
  is 
  so 
  important 
  

   that 
  some 
  of 
  the 
  detailed 
  field 
  observations 
  are 
  worth 
  stating. 
  

  

  Harrow 
  dikes 
  of 
  red 
  rock 
  respectively 
  cut 
  the 
  sediments, 
  the 
  

   main 
  gabbro, 
  the 
  intermediate 
  rock, 
  and 
  even 
  rock 
  phases 
  

   which 
  themselves 
  closely 
  approximate 
  red 
  rock 
  in 
  composition; 
  

   nevertheless, 
  every 
  one 
  must 
  agree 
  with 
  Bayley 
  and 
  TTinchell 
  

   that 
  the 
  main 
  gabbro, 
  the 
  intermediate 
  rock, 
  and 
  the 
  main 
  

   body 
  of 
  red 
  rock 
  are 
  transitional 
  into 
  one 
  another, 
  forming 
  a 
  

   single 
  geological 
  unit. 
  The 
  case 
  is 
  strikingly 
  parallel 
  to 
  the 
  

   associations 
  of 
  silicic, 
  mediosilicic, 
  and 
  subsilicic 
  rocks 
  in 
  the 
  

   intrusive 
  sheet 
  at 
  Sudbury, 
  Ontario, 
  in 
  the 
  (Moyie) 
  sills 
  of 
  

   the 
  Purcell 
  mountains 
  of 
  British 
  Columbia, 
  and 
  in 
  several 
  sills 
  

   and 
  laccoliths 
  of 
  South 
  Africa. 
  Since 
  the 
  red 
  rock 
  and 
  the 
  

   gabbro 
  belong 
  to 
  one 
  rock 
  body, 
  the 
  contact 
  of 
  each 
  with 
  the 
  

   Animikie 
  sediments 
  should 
  be 
  questioned 
  concerning 
  the 
  struc- 
  

   tural 
  relation 
  of 
  the 
  intrusive. 
  

  

  The 
  actual 
  contact 
  of 
  the 
  gabbro 
  with 
  the 
  sediments 
  is 
  

   exposed 
  at 
  very 
  few 
  places. 
  One 
  of 
  these 
  is 
  described 
  by 
  

  

  * 
  See 
  this 
  Journal, 
  vol. 
  xx, 
  page 
  200, 
  1905. 
  

  

  