﻿R. 
  A. 
  Daly 
  — 
  Geology 
  of 
  Pigeon 
  Point, 
  Minnesota. 
  435 
  

  

  

  

  

  Table 
  I. 
  

  

  

  

  

  1 
  

  

  2 
  

  

  3 
  

  

  4 
  

  

  5 
  

  

  Si0 
  2 
  

  

  74-00 
  

  

  72-42 
  

  

  70-31 
  

  

  73-64-74-22 
  

  

  59-71 
  

  

  Ti0 
  2 
  

  

  •34 
  

  

  •40 
  

  

  tr. 
  

  

  

  tr. 
  

  

  Al.O, 
  

  

  12-04 
  

  

  13-04 
  

  

  12-81 
  

  

  10-61-11-25 
  

  

  18-32 
  

  

  Fe 
  2 
  3 
  

  

  '78 
  

  

  •68 
  

  

  7-26 
  

  

  6-24- 
  7-45 
  

  

  8-11 
  

  

  FeO 
  

  

  2-61 
  

  

  2'49 
  

  

  •88 
  

  

  •77- 
  1-04 
  

  

  •85 
  

  

  MnO 
  

  

  •05 
  

  

  •09 
  

  

  

  

  

  none 
  

  

  MgO 
  

  

  •42 
  

  

  •58 
  

  

  2-03 
  

  

  1-48- 
  1-57 
  

  

  3-54 
  

  

  CaO 
  

  

  •85 
  

  

  •66 
  

  

  •60 
  

  

  •36- 
  '56 
  

  

  1-05 
  

  

  BaO 
  

  

  •12 
  

  

  •15 
  

  

  

  

  

  SrO 
  

  

  tr. 
  

  

  tr. 
  

  

  

  

  

  _ 
  . 
  . 
  . 
  

  

  Na,0 
  

  

  3-47 
  

  

  3-44 
  

  

  2-19 
  

  

  1-67- 
  3-04 
  

  

  1-93 
  

  

  K 
  2 
  

  

  4-33 
  

  

  4-97 
  

  

  1-90 
  

  

  1-08- 
  1-65 
  

  

  3-43 
  

  

  Li 
  2 
  

  

  tr.? 
  

  

  tr. 
  

  

  _ 
  _ 
  _ 
  _ 
  

  

  

  - 
  _ 
  _ 
  - 
  

  

  H 
  2 
  

  

  •86 
  

  

  1-21 
  

  

  2'22 
  

  

  

  3*24 
  

  

  *.<>. 
  

  

  •06 
  

  

  •20 
  

  

  

  

  

  ...... 
  

  

  CI 
  

  

  tr. 
  

  

  tr. 
  

  

  

  

  

  

  

  9993 
  100-33 
  100*20 
  100*18 
  

  

  1. 
  — 
  Analysis 
  of 
  the 
  powder 
  of 
  three 
  specimens 
  of 
  porphyritic 
  red 
  rock. 
  

   2. 
  — 
  Analysis 
  of 
  the 
  powder 
  of 
  seven 
  specimens 
  of 
  granular 
  red 
  rock. 
  

   3. 
  — 
  Mean 
  of 
  the 
  analyses 
  of 
  three 
  unaltered 
  quartzites 
  and 
  one, 
  slightly 
  

   altered, 
  metargillite. 
  

  

  4. 
  — 
  Eange 
  of 
  oxides 
  in 
  three 
  quartzites 
  free 
  from 
  contact 
  metamorphism. 
  

   5. 
  — 
  Analysis 
  of 
  one 
  specimen 
  of 
  unaltered 
  metargillite. 
  

  

  The 
  present 
  writer's 
  field 
  and 
  microscopic 
  study 
  has 
  led 
  to 
  

   the 
  belief 
  that 
  the 
  systematic 
  differences 
  are 
  typical 
  of 
  red 
  rock 
  

   and 
  sedimentary 
  rock 
  throughout 
  practically 
  the 
  whole 
  outcrop 
  

   of 
  the 
  sill 
  roof. 
  Hence 
  the 
  mere 
  fusion 
  of 
  the 
  sediments 
  by 
  

   the 
  heat 
  of 
  the 
  gabbro 
  magma 
  probably 
  cannot 
  explain 
  the 
  red 
  

   rock 
  as 
  now 
  constituted. 
  If 
  part 
  of 
  the 
  quartzite-metargillite 
  

   roof 
  has 
  been 
  simply 
  fused 
  in 
  situ, 
  without 
  being 
  dissolved 
  in 
  

   the 
  gabbro, 
  the 
  red-rock 
  magma 
  could 
  have 
  originated 
  from 
  

   the 
  fused 
  product 
  only 
  if 
  the 
  latter 
  had 
  undergone 
  some 
  differ- 
  

   entiation. 
  Still 
  more 
  clearly, 
  the 
  red 
  rock 
  cannot 
  be 
  assumed 
  

   to 
  have 
  originated 
  from 
  a 
  solution 
  of 
  sediments 
  in 
  the 
  gabbroid 
  

   magma, 
  unless 
  the 
  resulting 
  hybrid 
  magma 
  has 
  been 
  differen- 
  

   tiated. 
  Competing 
  with 
  both 
  of 
  these 
  hypotheses 
  is 
  a 
  third 
  : 
  

   that 
  the 
  red 
  rock 
  and 
  gabbro 
  are 
  the 
  two 
  poles 
  of 
  differentia- 
  

   tion 
  in 
  a 
  primary 
  magma, 
  which 
  has 
  never 
  been 
  affected 
  by 
  

   assimilation. 
  In 
  any 
  case 
  differentiation 
  has 
  to 
  be 
  reckoned 
  

   with 
  and 
  it 
  is 
  this 
  feature 
  that, 
  more 
  than 
  anything 
  else, 
  makes 
  

   the 
  genetic 
  problem 
  difficult. 
  

  

  As 
  a 
  preparation 
  for 
  further 
  discussion 
  it 
  is 
  well 
  to 
  note 
  the 
  

   approximate 
  relative 
  amounts 
  of 
  red 
  rock 
  and 
  gabbro 
  in 
  the 
  

   sill. 
  Taking 
  15° 
  as 
  the 
  average 
  dip, 
  the 
  thickness 
  of 
  the 
  

   exposed 
  part 
  of 
  the 
  sill 
  varies 
  from 
  125 
  meters 
  to 
  200 
  meters 
  

  

  