﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  59 
  

  

  As 
  the 
  ice 
  front 
  continued 
  to 
  melt 
  away, 
  retreating 
  northeastward, 
  

   drainage 
  at 
  a 
  lower 
  level 
  was 
  permitted 
  along 
  the 
  ice 
  front 
  to 
  the 
  

   Hudson 
  valley, 
  and 
  the 
  sea. 
  As 
  a 
  result, 
  the 
  water 
  level 
  sank, 
  the 
  

   Chicago 
  outlet 
  was 
  abandoned, 
  and 
  Lake 
  Warren 
  became 
  much 
  

   contracted 
  and 
  in 
  part 
  cut 
  up 
  and 
  merged 
  into 
  new 
  bodies 
  of 
  water. 
  

   The 
  largest 
  of 
  these 
  was 
  glacial 
  Lake 
  Algonquin,, 
  which 
  occupied 
  

   the 
  basins 
  of 
  the 
  three 
  upper 
  Great 
  lakes, 
  and 
  seems 
  to 
  have 
  been 
  

   for 
  a 
  long 
  time 
  independent 
  of 
  Lake 
  Erie, 
  which 
  after 
  the 
  division 
  

   of 
  Lake 
  Warren 
  was 
  for 
  a 
  time 
  much 
  smaller 
  than 
  it 
  now 
  is. 
  (Fig. 
  

   II 
  and 
  13) 
  

  

  The 
  critical 
  period 
  in 
  the 
  development 
  of 
  the 
  lakes, 
  with 
  reference 
  

   to 
  the 
  birth 
  of 
  Niagara, 
  was 
  the 
  uncovering 
  of 
  the 
  divide 
  at 
  Rome 
  

   (N. 
  Y.) 
  and 
  the 
  consequent 
  diversion 
  of 
  the 
  drainage 
  into 
  the 
  

   present 
  Mohawk 
  valley. 
  This 
  brought 
  with 
  it 
  a 
  subsidence 
  of 
  the 
  

   waters 
  north 
  of 
  the 
  Niagara 
  escarpment 
  to 
  the 
  level 
  of 
  this 
  outlet, 
  

   which 
  was 
  considerably 
  below 
  that 
  to 
  which 
  the 
  other 
  lakes 
  could 
  

   subside, 
  owing 
  to 
  the 
  rocky 
  barriers 
  which 
  kept 
  them 
  at 
  greater 
  

   altitudes. 
  As 
  a 
  result 
  Niagara 
  river 
  came 
  into 
  existence, 
  though 
  at 
  

   first 
  it 
  was 
  only 
  a 
  connecting 
  strait 
  between 
  Lake 
  Erie 
  and 
  the 
  

   subsiding 
  predecessor 
  of 
  Lake 
  Ontario. 
  The 
  overflow 
  from 
  Lake 
  

   Erie 
  occurred 
  at 
  the 
  present 
  site 
  of 
  Blackrock, 
  because 
  there 
  hap- 
  

   pened 
  to 
  be 
  the 
  lowest 
  point 
  in 
  the 
  margin 
  of 
  the 
  lake. 
  It 
  is 
  not 
  

   improbable 
  that 
  a 
  small 
  preglacial 
  stream 
  had 
  predetermined 
  this 
  

   point, 
  either 
  flowing 
  southward 
  into 
  the 
  river 
  occupying 
  the 
  Erie 
  

   basin^ 
  or 
  ^northward 
  as 
  an 
  obsequent 
  stream 
  into 
  the 
  Tonawanda. 
  

   The 
  course 
  of 
  the 
  river 
  below 
  Blackrock 
  was 
  determined 
  by 
  the 
  

   directions 
  of 
  steepest 
  descent 
  of 
  the 
  land 
  surface, 
  which 
  was 
  prob- 
  

   ably 
  predetermined 
  to 
  some 
  extent 
  by 
  preglacial 
  streams. 
  As 
  soon, 
  

   however, 
  as 
  the 
  level 
  of 
  the 
  waters 
  of 
  the 
  Ontario 
  valley 
  sank 
  below 
  

   the 
  edge 
  of 
  the 
  Niagara 
  escarpment 
  at 
  Lewiston, 
  a 
  fall 
  came 
  into 
  

   existence, 
  which 
  daily 
  increased 
  in 
  hight 
  as 
  the 
  level 
  of 
  the 
  northern 
  

   lake 
  was 
  lowered. 
  From 
  that 
  time 
  to 
  the 
  present, 
  Niagara 
  has 
  

   worked 
  at 
  its 
  task 
  of 
  gorge-cutting, 
  the 
  present 
  length 
  of 
  the 
  gorge, 
  

   from 
  Lewiston 
  to 
  the 
  falls, 
  marking 
  the 
  amount 
  of 
  work 
  accom- 
  

   plished. 
  

  

  