﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  53 
  

  

  The 
  valley 
  of 
  Georgian 
  bay 
  is 
  continued 
  northwestward 
  in 
  the 
  

   channel 
  known 
  as 
  North 
  passage, 
  a 
  narrow 
  body 
  of 
  water 
  lying 
  

   between 
  the 
  Manitoulin 
  islands 
  and 
  the 
  Canadian 
  old-land. 
  The 
  

   southward 
  continuation 
  of 
  the 
  lowland 
  is 
  blocked 
  by 
  drift; 
  but 
  a 
  

   number 
  of 
  borings, 
  between 
  the 
  southern 
  end 
  of 
  Georgian 
  bay 
  and 
  

   Lake 
  Ontario, 
  east 
  of 
  Toronto, 
  have 
  developed 
  the 
  existence 
  of 
  a 
  

   buried 
  channel, 
  which 
  connects 
  these 
  two 
  valleys. 
  This 
  channel 
  is 
  

   considered 
  by 
  Spencer 
  to 
  mark 
  the 
  pathway 
  of 
  his 
  former 
  Laurei- 
  

   tian 
  river. 
  It 
  is 
  clear 
  however 
  that 
  this 
  valley 
  is 
  merely 
  the 
  buried 
  

   connecting 
  part 
  of 
  the 
  inner 
  lowland 
  which 
  extends 
  along 
  the 
  base 
  

   of 
  the 
  entire 
  Niagara 
  escarpment. 
  This 
  portion 
  of 
  the 
  lowland 
  

   was 
  originally 
  occupied 
  by 
  two 
  streams 
  flowing, 
  the 
  one 
  northwest- 
  

   erly 
  into 
  the 
  ancient 
  Saginaw, 
  the 
  other 
  southeasterly 
  into 
  the 
  Dun- 
  

   das. 
  The 
  divide 
  between 
  the 
  two 
  may 
  have 
  been 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  Lake 
  Simcoe. 
  It 
  is 
  however 
  not 
  at 
  all 
  improbable 
  that 
  

   the 
  tributary 
  of 
  the 
  Dundas 
  may 
  have, 
  owing 
  to 
  favorable 
  condi- 
  

   tions, 
  gained 
  an 
  advantage 
  over 
  that 
  of 
  the 
  Saginaw, 
  and 
  pushed 
  

   the 
  divide 
  northward. 
  Such 
  a 
  migration 
  of 
  the 
  divide 
  might 
  have 
  

   resulted 
  in 
  the 
  diversion 
  of 
  the 
  upper 
  waters 
  of 
  the 
  Saginaw 
  by 
  cap- 
  

   ture, 
  so 
  that 
  they 
  eventually 
  became 
  tributary 
  to 
  the 
  Dundas. 
  This 
  

   would 
  account 
  for 
  the 
  greater 
  depth 
  of 
  the 
  Georgian 
  bay 
  lowland, 
  

   which, 
  after 
  the 
  capture 
  of 
  the 
  upper 
  Saginaw 
  waters, 
  could 
  be 
  

   deepened 
  independently 
  of 
  the 
  notch 
  in 
  the 
  cuesta 
  through 
  which 
  

   its 
  waters 
  were 
  formerly 
  carried 
  out. 
  This 
  of 
  course 
  is 
  merely 
  sup- 
  

   positional, 
  and 
  the 
  truth 
  can 
  be 
  established 
  only 
  by 
  more 
  detailed 
  

   study 
  of 
  the 
  ground. 
  It 
  is 
  however 
  what 
  we 
  might 
  expect 
  to 
  hap- 
  

   pen 
  in 
  the 
  normal 
  adjustment 
  of 
  a 
  coastal 
  plain 
  drainage. 
  This 
  

   hypothetic 
  relation 
  is 
  illustrated 
  in*fig. 
  6. 
  

  

  The 
  Huron 
  lowland 
  and 
  the 
  Chippewa 
  and 
  Tonawanda 
  valleys. 
  

   On 
  the 
  yielding 
  strata 
  of 
  the 
  SaHna 
  group 
  a 
  second 
  lowland 
  was 
  

   carved 
  out 
  by 
  subsequent 
  streams, 
  leaving 
  an 
  escarpment 
  capped 
  

   by 
  the 
  Devonic 
  limestones 
  on 
  the 
  south. 
  This, 
  as 
  we 
  have 
  seen, 
  

   becomes 
  prominent 
  eastward 
  in 
  the 
  Helderberg 
  range, 
  where 
  the 
  

   third 
  upper 
  Devonic 
  escarpment 
  unites 
  with 
  it. 
  In 
  the 
  Niagara 
  

   region 
  it 
  faces 
  the 
  Tonawanda 
  and 
  Chippewa 
  lowlands, 
  which 
  were 
  

   probably 
  opened 
  out 
  by 
  a 
  subsequent 
  stream 
  tributary 
  to 
  the 
  an- 
  

  

  