﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  23 
  

  

  The 
  Pleistocene^ 
  

  

  During 
  the 
  geologic 
  periods 
  of 
  the 
  Devonic, 
  Carbonic 
  and 
  

   Permic, 
  and 
  the 
  Mesozoic 
  and 
  Cenozoic 
  eras, 
  each 
  millions 
  of 
  

   years 
  in 
  length, 
  our 
  area 
  was 
  doubtless 
  always 
  above 
  the 
  sea 
  and 
  

   subjected 
  to 
  the 
  wasting 
  processes 
  of 
  atmospheric 
  erosion. 
  

  

  Closing 
  the 
  immensely 
  long 
  time 
  of 
  erosion 
  and 
  bringing 
  the 
  

   history 
  down 
  to 
  the 
  present 
  time, 
  three 
  geologic 
  episodes 
  are 
  

   conspicuously 
  recorded 
  in 
  the 
  existing 
  surface 
  features. 
  The 
  

   first 
  of 
  these 
  episodes 
  was 
  the 
  burial 
  of 
  the 
  entire 
  area 
  for 
  some 
  

   scores 
  of 
  thousands 
  of 
  years 
  under 
  the 
  Labradorian 
  ice 
  sheet 
  with 
  

   its 
  grinding 
  flow. 
  The 
  second 
  was 
  the 
  burial 
  for 
  further 
  thou- 
  

   sands 
  of 
  years 
  under 
  glacial 
  and- 
  marine 
  waters 
  that 
  immediately 
  

   succeeded 
  the 
  latest 
  of 
  the 
  ice 
  bodies. 
  The 
  third 
  episode 
  is 
  the 
  

   present 
  time, 
  a 
  restoration 
  of 
  the 
  subatmospheric 
  conditions 
  of 
  

   erosion, 
  which 
  has 
  endured, 
  probably, 
  some 
  10,000 
  or 
  20,000 
  

   years. 
  

  

  It 
  is 
  now 
  comparatively 
  certain 
  that 
  during 
  the 
  long 
  geologic 
  

   history 
  great 
  changes 
  of 
  climate 
  have 
  occurred. 
  The 
  idea, 
  once 
  

   prevalent, 
  that 
  there 
  had 
  been 
  during 
  all 
  geologic 
  time 
  a 
  steady 
  

   lowering 
  of 
  temperature 
  and 
  refrigeration 
  of 
  climate 
  from 
  a 
  

   primitive 
  condition 
  of 
  excessive 
  heat 
  and 
  moisture 
  is 
  wholly 
  an 
  

   error. 
  The 
  oldest 
  rocks 
  of 
  sedimentary 
  origin 
  contain 
  records 
  of 
  

   glaciation. 
  In 
  the 
  Permic, 
  ice 
  work 
  was 
  great 
  and 
  wide-spread, 
  

   and 
  glaciation 
  was 
  probably 
  frequent 
  during 
  past 
  time 
  in 
  elevated 
  

   regions 
  now 
  eroded. 
  The 
  warm 
  climate 
  of 
  the 
  middle 
  Tertiary 
  was 
  

   followed 
  by 
  glacial 
  cold 
  in 
  northern 
  lands, 
  and 
  all 
  of 
  New^ 
  England, 
  

   New 
  -York 
  State 
  and 
  the 
  basiin 
  of 
  the 
  Great 
  Lakes 
  was 
  deeply 
  

   buried 
  under 
  successive 
  sheets 
  of 
  ice 
  which 
  had 
  their 
  origin 
  or 
  

   centers 
  of 
  accumulation 
  in 
  Canada 
  and 
  Labrador. 
  The 
  peculiar 
  

   effects 
  of 
  the 
  glacial 
  invasions 
  will 
  be 
  described 
  in 
  a 
  later 
  chapter. 
  

  

  Following 
  at 
  least 
  the 
  latest 
  of 
  the 
  ice 
  sheets 
  the 
  entire 
  area 
  

   under 
  description 
  was 
  buried 
  for 
  some 
  thousands 
  of 
  years 
  be- 
  

   neath 
  waters 
  held 
  up 
  to 
  high 
  levels 
  by 
  the 
  glacier 
  acting 
  as 
  a 
  

   barrier 
  across 
  the 
  St 
  Lawrence 
  valley. 
  The 
  shore 
  features 
  and 
  

   deposits 
  characteristic 
  of 
  lake 
  action 
  are 
  found 
  over 
  the 
  region. 
  

  

  During 
  the 
  time 
  of 
  the 
  ice 
  retreat 
  this 
  portion 
  of 
  the 
  continent 
  

   was 
  lower, 
  or 
  nearer 
  ocean 
  level, 
  than 
  at 
  present, 
  and 
  when 
  the 
  

   ice 
  barrier 
  melted 
  away 
  in 
  the 
  St 
  Lawrence 
  valley, 
  the 
  glacial 
  

   Avaters 
  (Lake 
  Iroquois) 
  were 
  drained 
  down 
  to 
  sea 
  level, 
  and 
  the 
  

   north 
  and 
  west 
  sections 
  of 
  our 
  area 
  were 
  long 
  swept 
  by 
  oceanic 
  

   waters, 
  a 
  branch 
  of 
  the 
  Champlain 
  (Hochelagan) 
  sea 
  called 
  

  

  1 
  By 
  H. 
  L. 
  Fairchild. 
  

  

  