﻿the 
  Pre- 
  Cambrian 
  Era. 
  47 
  

  

  the 
  Grenville 
  — 
  Kona 
  dolomite, 
  Randville 
  dolomite, 
  Bad 
  River 
  

   limestone, 
  which 
  may 
  be 
  a 
  witness 
  to 
  the 
  dominance 
  of 
  forms 
  

   of 
  vegetation 
  not 
  higher 
  than 
  the 
  Chara. 
  

  

  But 
  this 
  vegetation 
  might 
  rapidly 
  change 
  the 
  atmosphere 
  

   from 
  one 
  of 
  C0 
  2 
  to 
  one 
  containing 
  largely 
  oxygen. 
  There 
  is 
  

   no 
  little 
  graphite 
  in 
  the 
  Grenville, 
  the 
  thickness 
  frequently 
  

   assigned 
  to 
  it 
  is 
  almost 
  incredible, 
  and 
  the 
  carbon 
  in 
  100 
  feet 
  

   of 
  a 
  limestone 
  with 
  3 
  per 
  cent 
  of 
  C 
  would 
  turn 
  our 
  whole 
  

   atmosphere 
  back 
  into 
  C0 
  2 
  . 
  

  

  Not 
  until 
  we 
  get 
  above 
  the 
  "Urkalk" 
  do 
  we 
  find 
  really 
  red 
  

   quartzite 
  or 
  red 
  rocks 
  that 
  seem 
  to 
  have 
  been 
  originally 
  such 
  

   or 
  an 
  iron 
  formation 
  that 
  seems 
  to 
  be 
  no 
  leached 
  carbonate 
  or 
  

   secondary 
  thing, 
  but 
  a. 
  primary 
  precipitate 
  formed 
  as 
  suggested 
  

   by 
  Leith 
  and 
  Mead's 
  experiments 
  when 
  iron 
  chloride 
  or 
  sulphate 
  

   was 
  broken 
  up 
  by 
  sodium 
  silicate 
  or 
  carbonate 
  and 
  oxygen 
  into 
  

   Fe 
  2 
  3 
  , 
  Si0 
  2 
  and 
  NaCl, 
  etc. 
  In 
  the 
  typical 
  jaspilite 
  or 
  banded 
  

   iron 
  formation 
  the 
  ratio 
  of 
  Fe 
  2 
  3 
  to 
  Si0 
  2 
  is 
  just 
  about 
  that 
  

   required 
  by 
  such 
  reactions 
  between 
  water-glass 
  and 
  ferrous 
  

   chloride. 
  But 
  as 
  this 
  reaction 
  went 
  on, 
  the 
  iron 
  accumulated 
  

   under 
  a 
  non-oxidizing 
  atmosphere 
  would 
  be 
  disposed 
  of, 
  and 
  

   would 
  be 
  very 
  unlikely 
  to 
  accumulate 
  in 
  such 
  quantities 
  again. 
  

   The 
  Huronian 
  is 
  as 
  widely 
  associated 
  with 
  iron 
  ore 
  as 
  the 
  

   Carboniferous 
  with 
  coal. 
  Never 
  again 
  was 
  there 
  an 
  iron 
  ore 
  

   formation 
  on 
  a 
  world-wide 
  scale. 
  

  

  Not 
  until 
  the 
  air 
  was 
  cleared 
  of 
  most 
  of 
  its 
  C0 
  2 
  (as 
  the 
  

   reel 
  character 
  of 
  the 
  Keweenawan 
  shows 
  it 
  then 
  certainly 
  was) 
  

   and 
  not 
  until 
  the 
  sea 
  was 
  cleared 
  of 
  its 
  ferrous 
  salts, 
  was 
  the 
  

   world 
  ready 
  for 
  a 
  wide 
  spread 
  of 
  those 
  living 
  forms 
  which 
  

   may 
  have 
  existed 
  and 
  evolved 
  in 
  nooks 
  and 
  corners, 
  in 
  lakes 
  

   and 
  rivers, 
  devoid 
  of 
  the 
  hard 
  parts, 
  which 
  were 
  simultaneously 
  

   evolved 
  in 
  many 
  lines, 
  when 
  the 
  salinity 
  of 
  mother 
  ocean 
  

   became 
  such 
  as 
  to 
  produce 
  them 
  as 
  a 
  physiological 
  reaction. 
  

  

  Have 
  we 
  not 
  in 
  the 
  correlation 
  of 
  : 
  (1) 
  The 
  ferrous 
  uncon- 
  

   centrated 
  Azoic 
  ; 
  (2) 
  The 
  calcareous 
  concentration 
  and 
  pre- 
  

   cipitation 
  by 
  the 
  first 
  vegetable 
  life 
  ; 
  (3) 
  The 
  precipitation 
  of 
  

   the 
  iron 
  by 
  the 
  oxygenated 
  atmosphere 
  produced 
  by 
  the 
  first 
  

   vegetable 
  life 
  ; 
  (4) 
  The 
  precipitation 
  of 
  skeleton 
  and 
  shell 
  by 
  

   protoplasm 
  when 
  oceanic 
  concentration 
  reached 
  the 
  point 
  when 
  

   it 
  became 
  physiologically 
  and 
  chemically 
  necessary, 
  — 
  criteria 
  

   for 
  Pre-Cambrian 
  or 
  Collozoic 
  Correlation 
  which 
  are 
  more 
  

   rational 
  a 
  priori 
  and 
  fit 
  the 
  facts 
  full 
  as 
  well 
  as 
  the 
  hypothesis 
  

   of 
  two 
  and 
  only 
  two 
  granite 
  invasions 
  % 
  

  

  I 
  do 
  not 
  wish 
  to 
  slur 
  over 
  the 
  fact 
  that 
  iron-bearing 
  forma- 
  

   tions 
  have 
  been 
  found 
  in 
  rocks 
  assigned 
  to 
  the 
  Keewatin 
  and 
  

   that 
  other 
  objections 
  may 
  be 
  raised, 
  one 
  by 
  one 
  writer 
  one 
  by 
  

   another. 
  I 
  would 
  only 
  say 
  that 
  they 
  seem 
  to 
  me 
  less 
  difficult 
  

   to 
  surmount 
  than 
  Lawson's 
  difficulties. 
  

  

  