﻿Geology 
  and 
  Natural 
  History. 
  151 
  

  

  Lower 
  Keewatin, 
  so 
  that 
  the 
  pre-Keewatin 
  basement 
  is 
  nowhere 
  

   observable, 
  except 
  for 
  the 
  above 
  mentioned 
  suggestions 
  of 
  a 
  quite 
  

   cold 
  original 
  crust 
  of 
  the 
  earth. 
  The 
  base 
  of 
  the 
  Upper 
  Kee- 
  

   watin 
  is 
  marked 
  by 
  a 
  well 
  developed 
  pebble-and-bowlder 
  con- 
  

   glomerate 
  which 
  lies 
  indifferently 
  upon 
  the 
  Lower 
  Keewatin 
  and 
  

   upon 
  some 
  of 
  the 
  granite 
  which 
  is 
  intrusive 
  in 
  it. 
  

  

  The 
  failure 
  to 
  recognize 
  the 
  Coutchiching 
  as 
  a 
  series 
  of 
  meta- 
  

   morphic 
  clastic 
  strata 
  of 
  great 
  volume 
  distinct 
  from 
  the 
  Keewatin 
  

   is 
  worthy 
  of 
  note, 
  and 
  arises 
  from 
  the 
  difficulty, 
  the 
  great 
  inhe- 
  

   rent 
  difficulty 
  of 
  Archean 
  Geology, 
  of 
  correlating 
  formations 
  on 
  

   the 
  basis 
  of 
  petrographical 
  characters. 
  The 
  particular 
  phase 
  of 
  

   that 
  difficulty 
  in 
  the 
  present 
  instance 
  is 
  that 
  schists 
  similar 
  to 
  

   those 
  of 
  the 
  Coutchiching, 
  i. 
  e., 
  mica 
  schists 
  and 
  feldspathic 
  mica 
  

   schists 
  (gneisses 
  so 
  called), 
  occur 
  also 
  in 
  the 
  Keewatin 
  and 
  the 
  

   criteria 
  for 
  discriminating 
  between 
  the 
  two 
  have 
  not 
  yet 
  been 
  

   established. 
  The 
  mica 
  schists 
  are 
  regarded 
  simply 
  as 
  a 
  result 
  of 
  

   the 
  more 
  intense 
  metamorphism 
  of 
  the 
  Keewatin. 
  This 
  view 
  is 
  

   advanced 
  without 
  attempt 
  to 
  explain 
  the 
  nature 
  of 
  the 
  metamor- 
  

   phism 
  which 
  would 
  convert 
  the 
  basic 
  eruptives 
  so 
  characteristic 
  of 
  

   the 
  Lower 
  Keewatin 
  into 
  the 
  very 
  acid 
  schists 
  with 
  which 
  we 
  are 
  

   here 
  concerned. 
  The 
  interesting 
  fact 
  comes 
  out 
  very 
  clearly 
  on 
  

   nearly 
  all 
  the 
  plates 
  mapping 
  the 
  Archean, 
  that 
  there 
  is 
  a 
  body 
  of 
  

   mica 
  schists 
  of 
  very 
  considerable 
  volume 
  intervening 
  quite 
  regu- 
  

   larly 
  between 
  the 
  greenish 
  rocks 
  of 
  the 
  Keewatin 
  and 
  the 
  intru- 
  

   sive 
  granites, 
  just 
  as 
  is 
  the 
  case 
  on 
  Rainy 
  Lake, 
  where 
  they 
  were 
  

   discriminated 
  as 
  a 
  series 
  of 
  metamorphic 
  sediments, 
  which 
  could 
  

   be 
  mapped 
  and 
  discussed 
  as 
  a 
  constituent 
  of 
  the 
  complex 
  distinct 
  

   from 
  the 
  Keewatin. 
  The 
  schists 
  thus 
  intervening 
  between 
  the 
  

   greenstone 
  of 
  the 
  Keewatin 
  and 
  the 
  granite, 
  although 
  embraced 
  

   in 
  the 
  Keewatin, 
  are 
  mapped 
  in 
  a 
  distinct 
  color 
  which 
  has, 
  on 
  

   many 
  of 
  the 
  plates, 
  a 
  large 
  breadth 
  relatively 
  to 
  the 
  greenstones 
  

   and 
  other 
  constituents 
  of 
  the 
  Keewatin. 
  The 
  fact 
  that 
  they 
  are 
  

   thus 
  mapped 
  where 
  only 
  the 
  broadest 
  kind 
  of 
  discrimination 
  is 
  

   attempted 
  bespeaks 
  for 
  the 
  mica 
  schist 
  formation 
  an 
  individuality 
  

   and 
  separateness 
  such 
  as 
  were 
  recognized 
  on 
  Rainy 
  Lake. 
  The 
  

   fact, 
  moreover, 
  that 
  the 
  granite 
  in 
  several 
  of 
  the 
  areas 
  mapped 
  

   comes 
  directly 
  against 
  the 
  greenstones 
  of 
  the 
  Keewatin 
  does 
  not 
  

   harmonize 
  with 
  the 
  view 
  that 
  the 
  mica 
  schists 
  are 
  only 
  more 
  

   intensely 
  altered 
  portions 
  of 
  the 
  Keewatin. 
  It 
  may 
  be 
  asked 
  very 
  

   pertinently, 
  also, 
  of 
  the 
  advocates 
  of 
  the 
  new 
  hypothesis 
  whether 
  

   the 
  normal 
  Keewatin 
  is 
  notably 
  reduced 
  in 
  volume 
  by 
  the 
  conver- 
  

   sion 
  of 
  such 
  a 
  large 
  fraction 
  ot 
  it. 
  into 
  mica 
  schist? 
  

  

  It 
  is 
  but 
  fair 
  to 
  state 
  that 
  Dr. 
  Grant 
  recognizes 
  the 
  Coutchiching 
  

   as 
  an 
  individual 
  series 
  of 
  the 
  Archean 
  complex 
  though 
  he 
  com- 
  

   plains 
  of 
  the 
  difficulty 
  of 
  discriminating 
  between 
  it 
  and 
  the 
  mica 
  

   schists 
  of 
  the 
  Keewatin. 
  Mr. 
  Winchell 
  on 
  the 
  other 
  hand 
  de- 
  

   clares 
  that 
  " 
  under 
  the 
  term 
  Keewatin 
  are 
  included 
  all 
  the 
  elastics 
  

   of 
  the 
  Archean." 
  It 
  seems 
  to 
  the 
  writer 
  that 
  there 
  is 
  more 
  to 
  be 
  

   gained 
  for 
  Archean 
  geology 
  in 
  the 
  present 
  stage 
  of 
  investigation 
  

   by 
  discriminating 
  as 
  much 
  as 
  possible 
  under 
  as 
  many 
  names 
  as 
  

   may 
  be 
  needful 
  for 
  the 
  purpose. 
  It 
  will 
  be 
  time 
  enough 
  to 
  drop 
  

  

  