﻿16 
  W. 
  Ujpham 
  — 
  Champlain 
  Subsidence 
  and 
  

  

  mum 
  height 
  at 
  Montreal 
  somewhat 
  exceeding 
  500 
  feet 
  above 
  

   the 
  present 
  sea 
  level. 
  Earlier 
  than 
  that 
  time 
  of 
  occupa- 
  

   tion 
  of 
  the 
  depressed 
  broad 
  valley 
  by 
  the 
  sea, 
  it 
  was 
  filled 
  

   from 
  Lake 
  Ontario 
  to 
  near 
  Quebec, 
  by 
  a 
  great 
  glacial 
  lake, 
  

   held 
  on 
  its 
  northeast 
  side 
  by 
  the 
  receding 
  continental 
  

   ice-sheet. 
  The 
  directions 
  of 
  the 
  glacial 
  striae 
  and 
  transporta- 
  

   tion 
  of 
  the 
  drift 
  in 
  the 
  St. 
  Lawrence 
  valley, 
  running 
  south- 
  

   westward 
  at 
  Montreal 
  and 
  onward 
  to 
  the 
  great 
  lakes, 
  but 
  east- 
  

   ward 
  from 
  Quebec 
  down 
  the 
  shores 
  of 
  the 
  Gulf 
  of 
  St. 
  Law- 
  

   rence, 
  and 
  southeast 
  across 
  Nova 
  Scotia 
  and 
  New 
  Brunswick, 
  

   show 
  that 
  the 
  latest 
  remnant 
  of 
  the 
  ice 
  barrier 
  blockading 
  this 
  

   valley 
  was 
  melted 
  away 
  in 
  the 
  neighborhood 
  of 
  Quebec, 
  then 
  

   admitting 
  the 
  sea 
  to 
  a 
  large, 
  low 
  region 
  westward. 
  Until 
  this 
  

   barrier 
  was 
  removed, 
  a 
  glacial 
  lake, 
  which 
  here 
  for 
  convenience 
  

   of 
  description 
  and 
  citation 
  is 
  designated 
  as 
  the 
  Lake 
  St. 
  Law- 
  

   rence, 
  dating 
  from 
  the 
  confluence 
  of 
  Lakes 
  Iroquois 
  and 
  Hud- 
  

   son-Champlain 
  and 
  growing 
  northward 
  and 
  eastward, 
  spread 
  

   over 
  the 
  Ottawa 
  valley 
  probably 
  to 
  the 
  mouth 
  of 
  the 
  Mattawa, 
  

   and 
  down 
  the 
  St. 
  Lawrence, 
  as 
  fast 
  as 
  the 
  ice-front 
  was 
  melted 
  

   back. 
  

  

  When 
  Lake 
  Iroquois 
  ceased 
  to 
  outflow 
  at 
  Eome 
  and, 
  after 
  

   intervening 
  stages 
  of 
  outlets 
  existing 
  for 
  a 
  short 
  time 
  at 
  suc- 
  

   cessively 
  lower 
  levels 
  north 
  of 
  the 
  Adirondacks, 
  began 
  to 
  oc- 
  

   cupy 
  the 
  Champlain 
  basin 
  and 
  the 
  St. 
  Lawrence 
  valley 
  north- 
  

   ward, 
  changing 
  thus 
  to 
  the 
  Lake 
  St. 
  Lawrence, 
  its 
  surface 
  fell 
  

   by 
  these 
  stages 
  about 
  250 
  feet 
  to 
  the 
  glacial 
  Lake 
  Hudson- 
  

   Champlain, 
  which 
  had 
  doubtless 
  reached 
  northward 
  nearly 
  to 
  

   the 
  St. 
  Lawrence. 
  After 
  this 
  reduction 
  of 
  the 
  water 
  body 
  in 
  

   the 
  Ontario 
  basin, 
  it 
  still 
  had 
  a 
  dqpth 
  of 
  about 
  150 
  feet 
  over 
  

   the 
  present 
  mouth 
  of 
  Lake 
  Ontario, 
  as 
  shown 
  by 
  a 
  beach 
  traced 
  

   by 
  Gilbert, 
  which 
  thence 
  rises 
  northeastward 
  but 
  declines 
  

   toward 
  the 
  south 
  and 
  southwest. 
  Its 
  plane, 
  which 
  is 
  nearly 
  

   parallel 
  with 
  the 
  higher 
  Iroquois 
  beaches, 
  sinks 
  to 
  the 
  present 
  

   lake 
  level 
  near 
  Oswego, 
  N. 
  Y. 
  Farther 
  southwestward 
  the 
  shore 
  

   of 
  the 
  glacial 
  lake 
  at 
  this 
  lower 
  stage 
  has 
  been 
  since 
  submerged 
  

   by 
  Lake 
  Ontario. 
  The 
  Niagara 
  river 
  was 
  then 
  longer 
  than 
  

   now, 
  and 
  the 
  lower 
  part 
  of 
  its 
  extent 
  has 
  become 
  covered 
  by 
  

   the 
  present 
  lake. 
  From 
  the 
  time 
  of 
  the 
  union 
  of 
  Lakes 
  Iroquois 
  

   and 
  Hudson-Champlain, 
  a 
  strait, 
  at 
  first 
  about 
  150 
  feet 
  deep, 
  

   but 
  later 
  probably 
  diminished 
  on 
  account 
  of 
  the 
  rise 
  of 
  the 
  

   land 
  to 
  a 
  depth 
  of 
  about 
  50 
  feet, 
  joined 
  the 
  broad 
  expanse 
  

   of 
  water 
  in 
  the 
  Ontario 
  basin 
  with 
  the 
  larger 
  expanse 
  in 
  the 
  

   St. 
  Lawrence 
  and 
  Ottawa 
  valleys 
  and 
  the 
  basin 
  of 
  Lake 
  Cham- 
  

   plain. 
  At 
  the 
  subsequent 
  time 
  of 
  ingress 
  of 
  the 
  sea 
  past 
  Que- 
  

   bec 
  the 
  level 
  of 
  Lake 
  St. 
  Lawrence 
  fell 
  probably 
  50 
  feet 
  or 
  

   less 
  to 
  the 
  ocean 
  level. 
  The 
  place 
  of 
  the 
  glacial 
  lake 
  so 
  far 
  

   westward 
  as 
  the 
  Thousand 
  Islands 
  was 
  then 
  taken 
  by 
  the 
  sea, 
  

  

  