﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  I49 
  

  

  tude, 
  which 
  very 
  Hkely 
  was 
  partly 
  controlled 
  by 
  early 
  glaciation, 
  

   yet 
  a 
  significant 
  number 
  are 
  transverse. 
  Some 
  basins 
  in 
  the 
  vicinity 
  

   of 
  Alexandria 
  Bay 
  [pi. 
  47] 
  and 
  others 
  south 
  of 
  Clayton 
  [pi. 
  46] 
  

   do 
  not 
  conform 
  to 
  the 
  prevailing 
  direction, 
  and 
  the 
  basins 
  of 
  the 
  

   Redwood 
  lakes 
  are 
  so 
  irregular 
  in 
  form 
  as 
  to 
  rule 
  out 
  ice 
  erosion 
  

   as 
  the 
  dominant 
  agent. 
  It 
  seems 
  certain 
  that 
  these 
  basins, 
  like 
  the 
  

   scarp 
  borders 
  of 
  the 
  plateaus, 
  are 
  due 
  to 
  atmospheric 
  agencies 
  

   with 
  only 
  small 
  and 
  indeterminate 
  glacial 
  effects 
  ; 
  or 
  that 
  they 
  cer- 
  

   tainly 
  antedate 
  the 
  latest 
  ice 
  invasion. 
  One 
  would 
  naturally 
  sup- 
  

   pose 
  that 
  the 
  scraping 
  ice 
  sheet 
  would 
  have 
  rubbed 
  the 
  transverse 
  

   valleys 
  full 
  of 
  drift. 
  In 
  some 
  valleys 
  and 
  against 
  some 
  scarps 
  the 
  

   amount 
  of 
  drift 
  is 
  sufficient 
  to 
  be 
  noticeable, 
  but 
  it 
  only 
  masks 
  the 
  

   foot 
  of 
  the 
  cliffs. 
  In 
  many 
  relatively 
  deep 
  depressions 
  -the 
  drift 
  

   is 
  scarcely 
  perceptible, 
  though 
  some 
  may 
  be 
  buried 
  under 
  the 
  lake 
  

   silts 
  which 
  occupy 
  the 
  valley 
  bottoms. 
  

  

  Besides 
  the 
  lack 
  of 
  drift 
  filling 
  is 
  to 
  be 
  noted 
  the 
  absence 
  of 
  pre- 
  

   glacial 
  talus 
  accumulations. 
  In 
  places 
  the 
  Potsdam 
  is 
  so 
  freely 
  

   jointed 
  that 
  the 
  cliffs 
  break 
  down 
  under 
  the 
  frost 
  quite 
  rapidly 
  and 
  

   heavy 
  block 
  taluses 
  occur 
  which 
  are 
  evidently 
  postglacial; 
  but 
  in 
  

   most 
  cases 
  there 
  is 
  little 
  or 
  no 
  talus, 
  specially 
  outside 
  the 
  Potsdam 
  

   rocks. 
  In 
  the 
  case 
  of 
  the 
  limestone 
  walls 
  solution 
  might 
  be 
  suffi- 
  

   cient 
  agency 
  to 
  remove 
  the 
  products 
  of 
  weathering, 
  and 
  this 
  might 
  

   also 
  apply 
  to 
  the 
  Precambric 
  Grenville 
  limestones 
  which 
  form 
  some 
  

   part 
  of 
  the 
  basins 
  of 
  the 
  Redwood 
  lakes 
  ; 
  but 
  such 
  removal 
  can 
  

   not 
  apply 
  to 
  the 
  almost 
  imperishable 
  Potsdam 
  sandstone. 
  The 
  

   older 
  fragmental 
  deposits 
  produced 
  by 
  the 
  recession 
  of 
  the 
  cliffs 
  

   have 
  been 
  removed, 
  most 
  likely 
  by 
  the 
  glacial 
  ice, 
  but 
  without 
  

   leaving 
  much 
  drift 
  in 
  their 
  place. 
  

  

  The 
  lack 
  of 
  drift 
  in 
  the 
  basins 
  and 
  over 
  the 
  plains 
  clearly 
  implies 
  

   a 
  lack 
  of 
  drift 
  burden 
  in 
  the 
  latest 
  ice 
  sheet. 
  The 
  cause 
  of 
  this 
  

   will 
  be 
  discussed 
  later 
  [page 
  172]. 
  The 
  small 
  abrading 
  power 
  of 
  

   the 
  ice 
  was 
  probably 
  due 
  to 
  its 
  lack 
  of 
  tools, 
  and 
  evidently 
  it 
  did 
  

   not 
  have 
  sufficient 
  power 
  of 
  " 
  plucking 
  " 
  or 
  removing 
  blocks 
  in 
  

   mass 
  to 
  destroy 
  or 
  even 
  seriously 
  cut 
  the 
  steep 
  ledges 
  and 
  scarps 
  

   which 
  stood 
  across 
  its 
  path. 
  

  

  One 
  suggestion 
  in 
  partial 
  explanation 
  of 
  the 
  somewhat 
  contradic- 
  

   tory 
  features, 
  is 
  that 
  stagnant 
  ice 
  occupied 
  the 
  strong 
  depressions 
  

   ever 
  which 
  the 
  upper 
  ice 
  moved 
  by 
  shearing. 
  This 
  would 
  fairly 
  

   account 
  for 
  the 
  absence 
  of 
  heavy 
  drift 
  in 
  the 
  basins 
  and 
  valleys 
  

   and 
  the 
  protection 
  of 
  the 
  walls. 
  Another 
  suggestion 
  takes 
  account 
  

   of 
  the 
  fact 
  that 
  when 
  the 
  latest 
  ice 
  sheet 
  disappeared 
  from 
  this 
  

  

  