﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  1 
  69 
  

  

  the 
  hollow 
  being 
  produced 
  partly 
  by 
  the 
  washing 
  of 
  the 
  clay 
  cover 
  

   down 
  the 
  wide 
  solution 
  joints, 
  On 
  the 
  sides 
  of 
  the 
  hollow 
  the 
  ribs 
  

   are 
  being 
  newly 
  uncovered 
  by 
  the 
  storm 
  wash 
  and 
  the 
  tramping 
  

   of 
  cattle, 
  but 
  no 
  trace 
  of 
  glacial 
  polish 
  was 
  seen, 
  the 
  new 
  surfaces 
  

   being 
  similar 
  to 
  the 
  longer 
  exposed 
  surfaces 
  of 
  the 
  middle 
  of 
  the 
  

   ribs. 
  Masses 
  of 
  chert 
  standing 
  2 
  or 
  3 
  inches 
  above 
  the 
  limestone 
  

   surface 
  prove 
  a 
  long 
  period 
  of 
  solution 
  of 
  the 
  rock 
  surface, 
  which 
  

   seems 
  impossible 
  beneath 
  the 
  -present 
  clays 
  in 
  the 
  short 
  time 
  in- 
  

   volved. 
  Enforcing 
  this 
  conclusion 
  is 
  the 
  fact 
  that 
  only 
  a 
  number 
  

   of 
  rods 
  distant, 
  in 
  the 
  gutters 
  of 
  the 
  electric 
  road 
  under 
  similar 
  clay 
  

   cover 
  the 
  same 
  limestone 
  shows 
  elegant 
  glaciation. 
  But 
  while 
  the 
  

   ribbing 
  is 
  s. 
  40° 
  w. 
  the 
  preserved 
  glacial 
  scorings 
  are 
  variable, 
  rang- 
  

   ing 
  from 
  s. 
  50° 
  w. 
  to 
  s. 
  10° 
  e. 
  

  

  These 
  two 
  examples 
  of 
  the 
  ribbing, 
  which 
  can 
  be 
  multiplied, 
  will 
  

   give 
  illustration 
  of 
  the 
  quality 
  of 
  the 
  evidence 
  they 
  offer 
  in 
  favor 
  

   of 
  at 
  least 
  dual 
  glaciation 
  in 
  recent 
  time. 
  These 
  flutings 
  are 
  wide- 
  

   spread, 
  remarkably 
  uniform 
  in 
  direction 
  (generally 
  s. 
  42-45° 
  w.), 
  

   symmetrical 
  and 
  true 
  in. 
  form. 
  They 
  can 
  not 
  be 
  attributed 
  to 
  

   weathering, 
  nor 
  jointing, 
  nor 
  wave 
  work, 
  nor 
  water 
  corrosion, 
  all 
  

   of 
  which 
  have 
  left 
  conspicuous 
  records 
  in 
  the 
  district. 
  Undoubtedly 
  

   the 
  ribbing 
  is 
  old 
  glacial, 
  and 
  it 
  represents 
  a 
  glacial 
  abrasion 
  vastly 
  

   more 
  energetic 
  than 
  the 
  similar 
  work 
  of 
  the 
  latest 
  ice 
  sheet. 
  

  

  Weathered 
  surfaces. 
  The 
  considerable 
  weathering 
  which 
  the 
  

   limestones 
  have 
  suffered 
  is 
  shown 
  in 
  plates 
  23, 
  26, 
  27 
  and 
  63. 
  

   Doubtless 
  some 
  part 
  of 
  this 
  corrosion 
  is 
  postglacial, 
  specially 
  on 
  

   the 
  more 
  exposed 
  patches 
  and 
  on 
  cliff 
  edges 
  where 
  the 
  rock 
  was 
  

   not 
  buried 
  by 
  the 
  drift; 
  but 
  it 
  must 
  not 
  be 
  assumed 
  that 
  these 
  

   etched, 
  corroded 
  and 
  open-jointed 
  surfaces 
  were 
  all 
  left 
  smooth 
  

   and 
  glaciated 
  by 
  the 
  latest 
  ice 
  sheet, 
  as 
  that 
  is 
  the 
  question 
  under 
  

   discussion. 
  

  

  The 
  uncovering 
  of 
  corroded 
  surfaces 
  which 
  have 
  been 
  under 
  

   clay 
  that 
  would 
  seem 
  to 
  have 
  been 
  sufficient 
  protection 
  from 
  the 
  

   postglacial 
  weathering, 
  as 
  jllustrated 
  in 
  plates 
  61 
  and 
  62, 
  argues 
  

   strongly 
  for 
  nonglaciation 
  of 
  such 
  surfaces. 
  The 
  conditions 
  shown 
  

   in 
  plate 
  60 
  seems 
  to 
  prove 
  that 
  great 
  open 
  joints 
  existed 
  in 
  the 
  

   limestones 
  previous 
  to 
  the 
  deposition 
  of 
  the 
  glacial 
  clays. 
  

  

  Probably 
  many 
  of 
  the 
  deeply 
  corroded 
  surfaces 
  were 
  recently 
  

   buried 
  under 
  ice 
  or 
  lake 
  deposits 
  which 
  have 
  been 
  swept 
  off 
  by 
  

   the 
  wave 
  erosion 
  of 
  the 
  standing 
  waters 
  and 
  the 
  subsequent 
  and 
  

   now 
  acting 
  storm 
  wash. 
  Without 
  more 
  special 
  study 
  on 
  the 
  ground 
  

   it 
  is 
  impossible 
  to 
  estimate 
  the 
  amount 
  of 
  postglacial 
  weathering. 
  

   In 
  some 
  places 
  it 
  seems 
  very 
  small, 
  and 
  where 
  slightly 
  covered 
  prac- 
  

  

  