﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  I7I 
  

  

  with 
  apparently 
  identical 
  physical 
  conditions 
  have 
  lost 
  all 
  traces 
  

   of 
  recent 
  glaciation. 
  

  

  Weak 
  erosion 
  of 
  the 
  Wisconsin 
  ice 
  sheet. 
  It 
  will 
  be 
  seen 
  that 
  

   the 
  critical 
  point 
  in 
  this 
  study 
  is 
  the 
  erosional 
  impotence 
  of 
  the 
  

   latest 
  ice 
  sheet. 
  With 
  this 
  established 
  then 
  at 
  least 
  dual 
  glacia- 
  

   tion 
  of 
  the 
  region 
  must 
  be 
  accepted. 
  

  

  The 
  principle 
  is 
  recognized 
  by 
  glacialists 
  that 
  intensity 
  of 
  ice 
  

   erosion 
  depends 
  on 
  pressure, 
  velocity 
  of 
  the 
  bottom 
  ice, 
  and 
  its 
  

   armament 
  or 
  tools. 
  The 
  glacier 
  can 
  do 
  its 
  most 
  effective 
  work 
  of 
  

   abrasion 
  when 
  the 
  basal 
  ice 
  is 
  only 
  moderately 
  charged 
  with 
  rock 
  

   rubbish, 
  and 
  that 
  of 
  hard 
  texture. 
  A 
  heavy 
  burden 
  of 
  subglacial 
  

   drift 
  serves 
  to 
  diminish 
  the 
  plasticity 
  of 
  the 
  ice 
  and 
  so 
  reduce 
  the 
  

   velocity 
  of 
  flow 
  ; 
  while 
  at 
  the 
  same 
  time 
  it 
  acts 
  as 
  protection 
  or 
  a 
  

   buffer 
  for 
  the 
  subadjacent 
  rock. 
  For 
  this 
  reason 
  rapid 
  corrasion 
  is 
  

   a 
  self-checking 
  process.^ 
  On 
  the 
  other 
  hand 
  it 
  is 
  certain 
  that 
  clear 
  

   ice 
  can 
  not 
  abrade 
  the 
  bed 
  rock 
  at 
  all. 
  A 
  moderate 
  load 
  of 
  hard 
  

   tools 
  is 
  the 
  most 
  effective 
  for 
  abrasion. 
  

  

  The 
  first 
  ice 
  sheet 
  that 
  transgressed 
  our 
  region 
  found 
  it 
  deeply 
  

   covered 
  with 
  the 
  residual 
  product 
  of 
  millions 
  of 
  years 
  of 
  weather- 
  

   ing, 
  and 
  could 
  do 
  no 
  effective 
  erosion 
  until 
  not 
  only 
  the 
  sheet 
  of 
  

   geest 
  (regolith) 
  on 
  our 
  area 
  had 
  been 
  removed 
  but 
  also 
  that 
  lying 
  

   on 
  the 
  region 
  northward 
  into 
  Labrador 
  and 
  Canada 
  which 
  was 
  

   swept 
  by 
  the 
  southward 
  ice 
  flow. 
  The 
  theoretical 
  stages 
  would 
  

   be 
  as 
  follows 
  : 
  ( 
  i 
  ) 
  the 
  scraping 
  away 
  of 
  the 
  decay 
  product 
  and 
  

   bearing 
  it 
  far 
  southward, 
  as 
  no 
  very 
  heavy 
  moraines 
  lie 
  near 
  our 
  

   area; 
  (2) 
  vigorous 
  erosion 
  during 
  the 
  phase 
  of 
  favorable 
  load, 
  

   with 
  harder 
  tools 
  from 
  the 
  plucking 
  of 
  the 
  fresher 
  rocks; 
  (3) 
  

   weak 
  abrasion 
  by 
  the 
  clearer 
  ice 
  after 
  the 
  glacier 
  had 
  swept 
  its 
  

   floor 
  arid 
  reduced 
  the 
  asperities 
  in 
  its 
  path. 
  

  

  On 
  the 
  postulate 
  of 
  a 
  single 
  ice 
  invasion 
  of 
  the 
  Thousand 
  Islands 
  

   region 
  it 
  is 
  necessary 
  to 
  assume 
  that 
  after 
  the 
  ice 
  had 
  removed 
  

   the 
  abundant 
  product 
  of 
  Prepleistocene 
  weathering 
  it 
  used 
  its 
  

   medium 
  load 
  of 
  debris 
  to 
  plane 
  the 
  hard 
  Potsdam 
  and 
  to 
  plane 
  and 
  

   deeply 
  flute 
  the 
  limestone, 
  but 
  at 
  the 
  same 
  time 
  failed 
  to 
  rub 
  down 
  

   the 
  scores 
  of 
  comparatively 
  abrupt 
  cliffs 
  and 
  scarps 
  which 
  opposed 
  

   its 
  motion. 
  Here 
  we 
  find 
  another 
  inconsistency. 
  Without 
  further 
  

   discussion 
  it 
  will 
  be 
  understood 
  that 
  the 
  assumption 
  of 
  a 
  single 
  

   glacial 
  epoch 
  involves 
  serious 
  contradictions 
  and 
  difficulties 
  in 
  the 
  

   explanation 
  of 
  the 
  phenomena 
  of 
  the 
  region. 
  

  

  Assuming 
  dual 
  or 
  multiple 
  glacial 
  epochs 
  the 
  features 
  and 
  history 
  

   are 
  fairly 
  clear. 
  The 
  accumulations 
  of 
  long 
  eras 
  of 
  rock 
  weathering 
  

  

  1 
  Geol. 
  Soc. 
  Am. 
  Bui. 
  16:26. 
  

  

  