﻿268 
  F. 
  B. 
  Taylor 
  — 
  Niagara 
  and 
  the 
  Great 
  Lakes. 
  

  

  ical 
  structure, 
  this 
  feature 
  is 
  explicable 
  only 
  on 
  the 
  supposi- 
  

   tion 
  that 
  the 
  great 
  cataract 
  was 
  not 
  then 
  active, 
  but 
  was 
  

   replaced 
  by 
  a 
  much 
  smaller 
  one. 
  That 
  was 
  the 
  Erigan 
  cataract. 
  

  

  In 
  the 
  lakes, 
  the 
  Nipissing 
  beach, 
  which 
  is 
  the 
  latest 
  aban- 
  

   doned 
  shore 
  line 
  marking 
  a 
  critical 
  stage, 
  connects 
  the 
  St. 
  Clair 
  

   and 
  Nipissing 
  outlets, 
  and 
  was 
  evidently 
  made 
  when 
  both 
  were 
  

   flowing. 
  But 
  the 
  Nipissing 
  outlet 
  is 
  now 
  160 
  feet 
  above 
  Lake 
  

   Huron, 
  so 
  that 
  ever 
  since 
  that 
  outlet 
  was 
  abandoned 
  Niagara 
  

   has 
  had 
  all 
  the 
  discharge 
  of 
  the 
  upper 
  lakes. 
  The 
  position 
  of 
  

   the 
  Nipissing 
  beach 
  is 
  such 
  that 
  the 
  Chicago 
  and 
  Trent 
  valley 
  

   outlets 
  are 
  absolutely 
  excluded. 
  The 
  Nipissing 
  beach 
  marks 
  

   the 
  activity 
  of 
  the 
  St. 
  Clair 
  outlet 
  and 
  also 
  that 
  of 
  the 
  Nipis- 
  

   sing 
  outlet, 
  but 
  not 
  of 
  any 
  other. 
  In 
  tracing 
  back 
  the 
  order 
  of 
  

   changes 
  we 
  are 
  therefore 
  compelled 
  to 
  pass 
  from 
  the 
  St. 
  Clair 
  

   to 
  the 
  Nipissing 
  outlet, 
  and 
  so 
  from 
  the 
  present 
  lakes 
  to 
  the 
  

   second 
  Lake 
  Algonquin. 
  There 
  is 
  no 
  escape 
  from 
  this 
  step. 
  

   This 
  brings 
  us 
  to 
  a 
  time 
  when 
  Niagara 
  did 
  not 
  receive 
  the 
  

   waters 
  of 
  the 
  upper 
  lakes, 
  — 
  the 
  perfect 
  correlative 
  of 
  the 
  

   Erigan 
  section 
  of 
  the 
  Niagara 
  gorge. 
  But 
  before 
  the 
  second 
  

   Lake 
  Algonquin 
  there 
  was 
  Warren 
  Gulf 
  with 
  its 
  marine 
  

   straits. 
  The 
  Erigan 
  Fall 
  replaced 
  Niagara 
  during 
  that 
  

   time 
  also. 
  The 
  simplest 
  possible 
  supposition 
  as 
  to 
  the 
  cause 
  

   of 
  these 
  changes, 
  and 
  it 
  is 
  the 
  only 
  cause 
  which 
  is 
  indicated 
  

   by 
  the 
  facts, 
  is, 
  that 
  there 
  has 
  been 
  going 
  on 
  throughout 
  the 
  

   whole 
  period 
  a 
  very 
  gradual 
  differential 
  elevation, 
  greater 
  

   always 
  at 
  the 
  north 
  than 
  at 
  the 
  south. 
  This 
  elevation 
  covers 
  

   all 
  the 
  changes 
  which 
  have 
  taken 
  place 
  since 
  the 
  Chippewa 
  

   beach 
  was 
  at 
  sea 
  level, 
  and 
  tallies, 
  we 
  may 
  say, 
  with 
  half 
  the 
  

   work 
  done 
  in 
  the 
  post-glacial 
  Niagara 
  gorge. 
  That 
  part 
  of 
  the 
  

   gorge 
  below 
  the 
  Whirlpool 
  is 
  similar 
  to 
  the 
  part 
  above 
  the 
  

   bridge, 
  and 
  suggests 
  the 
  existence 
  of 
  a 
  pre-Erigan 
  great 
  cata- 
  

   ract, 
  substantially 
  like 
  the 
  present 
  one, 
  which 
  again 
  suggests 
  a 
  

   pre-Warren 
  lake 
  stage, 
  substantially 
  like 
  the 
  present. 
  

  

  And 
  for 
  this 
  we 
  have 
  only 
  to 
  suppose 
  an 
  immediately 
  post- 
  

   glacial 
  condition 
  of 
  elevation 
  at 
  the 
  north 
  similar 
  in 
  a 
  general 
  

   way 
  to 
  the 
  present 
  land 
  attitude 
  and 
  a 
  progressive 
  pre-Warren 
  

   depression, 
  to 
  introduce 
  in 
  reverse 
  order 
  all 
  the 
  post-Warren 
  

   changes. 
  While 
  that 
  elevation 
  existed 
  the 
  gorge 
  was 
  cut 
  out 
  

   from 
  Lewiston 
  to 
  the 
  whirlpool. 
  The 
  first 
  marked 
  change 
  

   produced 
  by 
  the 
  depression 
  was 
  the 
  opening 
  of 
  the 
  Nipissing 
  

   outlet, 
  at 
  which 
  the 
  Niagara 
  cataract 
  began 
  to 
  weaken. 
  

   Further 
  progress 
  of 
  the 
  depression 
  closed 
  the 
  St. 
  Clair 
  outlet, 
  

   and 
  the 
  erosion 
  of 
  the 
  Erigan 
  gorge 
  began. 
  The 
  continuing 
  

   depression 
  next 
  transformed 
  the 
  Nipissing 
  outlet 
  into 
  a 
  strait, 
  

   and 
  Warren 
  Gulf 
  was 
  established. 
  At 
  the 
  maximum 
  of 
  the 
  

   depression 
  the 
  Chippewa 
  marine 
  beach 
  was 
  formed. 
  The 
  ero- 
  

  

  