﻿dt3Jr 
  P. 
  A. 
  Daly 
  — 
  Geology 
  of 
  Pigeon 
  Point, 
  Minnesota. 
  

  

  probably 
  less 
  than 
  30 
  meters 
  in 
  thickness 
  ; 
  it 
  is 
  hard 
  to 
  believe 
  

   that 
  its 
  original 
  content 
  of 
  heat 
  could 
  have 
  sufficed 
  to 
  melt 
  and 
  

   impregnate 
  the 
  gabbro 
  to 
  the 
  extent 
  demanded 
  by 
  the 
  hypoth- 
  

   esis. 
  The 
  contact 
  of 
  the 
  two 
  chief 
  phases 
  has 
  not 
  the 
  char- 
  

   acter 
  of 
  that 
  between 
  two 
  members 
  of 
  the 
  normal 
  composite 
  

   sill 
  in 
  other 
  parts 
  of 
  the 
  world. 
  This 
  hypothesis 
  also 
  fails 
  to. 
  

   account 
  for 
  the 
  practical 
  restriction 
  of 
  the 
  red 
  rock, 
  except 
  for 
  

   the 
  small 
  dikes 
  above 
  noted, 
  to 
  the 
  upper 
  contact 
  of 
  the 
  

   gabbro. 
  It 
  fails 
  to 
  explain 
  the 
  micropegmatitic 
  (red-rock) 
  

   material 
  often 
  seen, 
  under 
  the 
  microscope, 
  to 
  fill 
  the 
  interstices 
  

   of 
  the 
  feldspar-pyroxene 
  fabric 
  in 
  the 
  gabbro, 
  scores 
  of 
  meters 
  

   stratigraphically 
  below 
  any 
  level 
  which 
  could 
  have 
  been 
  

   seriously 
  affected 
  by 
  the 
  hypothetical 
  red-rock 
  injection. 
  

   Finally, 
  this 
  hypothesis 
  fails 
  to 
  account 
  for 
  the 
  local 
  develop- 
  

   ment 
  of 
  the 
  intermediate 
  rock 
  between 
  the 
  main 
  gabbro 
  and 
  

   the 
  roof 
  quartzites, 
  with 
  no 
  red 
  rock 
  present 
  in 
  the 
  cross-sec- 
  

   tion 
  at 
  all 
  ; 
  the 
  intermediate 
  rock, 
  here 
  as 
  usual, 
  passing 
  

   gradually 
  into 
  the 
  gabbro. 
  

  

  These 
  objections 
  have 
  great 
  cumulative 
  • 
  weight. 
  One 
  is 
  

   compelled 
  to 
  assume 
  that 
  at 
  one 
  stage 
  much 
  of 
  the 
  gabbro 
  and 
  

   much 
  or 
  all 
  of 
  the 
  red 
  rock 
  were 
  simultaneously 
  molten 
  ; 
  that 
  

   the 
  gabbro 
  froze 
  first 
  and 
  the 
  red 
  rock 
  froze 
  last, 
  so 
  as 
  to 
  be 
  

   capable 
  of 
  diking 
  both 
  gabbro 
  and 
  intermediate 
  rock. 
  

  

  In 
  summary, 
  the 
  writer 
  considers 
  the 
  main 
  body 
  of 
  eruptive 
  

   rock 
  in 
  the 
  peninsula 
  to 
  be 
  a 
  unit, 
  a 
  sill 
  which 
  has 
  been 
  dif- 
  

   ferentiated 
  under 
  gravity. 
  The 
  intermediate 
  rock 
  represents 
  a 
  

   shallow 
  layer 
  marking 
  incomplete 
  differentiation 
  between 
  the 
  

   gabbro 
  below 
  and 
  the 
  red 
  rock 
  above. 
  Because 
  of 
  special 
  

   concentration 
  of 
  gas 
  in 
  the 
  red 
  rock, 
  its 
  temperature 
  of 
  con- 
  

   solidation 
  was 
  relatively 
  low, 
  and 
  small 
  tongues 
  of 
  its 
  magma 
  

   were 
  driven 
  down, 
  into 
  the 
  gabbro, 
  as 
  well 
  as 
  upwards, 
  into 
  

   the 
  sedimentary 
  roof, 
  because 
  of 
  the 
  abnormally 
  high 
  gas- 
  

   tension. 
  

  

  Differentiation 
  necessarily 
  Postulated. 
  — 
  At 
  the 
  close 
  of 
  

   his 
  paper 
  (p. 
  118), 
  Bayley 
  stated 
  that 
  the 
  red 
  rock 
  " 
  is 
  only 
  the 
  

   final 
  stage 
  in 
  the 
  alteration 
  of 
  the 
  slates 
  and 
  quartzites 
  by 
  the 
  

   gabbro.'' 
  In 
  other 
  words, 
  he 
  regards 
  the 
  red 
  rock 
  as 
  the 
  

   crystallized 
  product 
  of 
  a 
  secondary 
  magma. 
  Apparently 
  he 
  

   nowhere 
  mentions 
  the 
  principle 
  of 
  differentiation 
  in 
  connection 
  

   with 
  the 
  problem, 
  but 
  considers 
  the 
  red 
  rock 
  as 
  sedimentary- 
  

   rock 
  material 
  which 
  has 
  been 
  fused 
  in 
  situ. 
  Yet 
  his 
  average 
  

   analyses 
  of 
  red 
  rock 
  and 
  sedimentaries 
  are 
  systematically 
  con- 
  

   trasted, 
  as 
  shown 
  in 
  the 
  accompanying 
  Table 
  I, 
  taken 
  from 
  

   p. 
  113 
  of 
  his 
  paper. 
  The 
  red 
  rock 
  is 
  poorer 
  in 
  iron 
  and 
  

   magnesia, 
  and, 
  as 
  distinctly, 
  richer 
  in 
  soda 
  and 
  potash. 
  

  

  