﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  1 
  65 
  

  

  eastern 
  region. 
  The 
  drift 
  of 
  northwestern 
  Pennsylvania 
  lying 
  in 
  

   advance 
  of 
  the 
  Wisconsin 
  drift, 
  is 
  believed 
  to 
  be 
  as 
  old 
  at 
  least 
  as 
  

   the 
  Kansan. 
  For 
  an 
  ice 
  sheet 
  to 
  so 
  expand 
  as 
  to 
  reach 
  either 
  

   northwest 
  or 
  southeast 
  Pennsylvania 
  without 
  trespassing 
  on 
  New 
  

   York 
  seems 
  impossible. 
  Hence 
  we 
  are 
  forced 
  to 
  the 
  belief, 
  apart 
  

   from 
  any 
  evidences 
  on 
  the 
  ground, 
  that 
  the 
  State 
  has 
  been 
  more 
  

   than 
  once 
  in 
  the 
  climatic 
  condition 
  of 
  Greenland 
  at 
  the 
  present 
  

   time. 
  

  

  If 
  the 
  State 
  has 
  been 
  overrun 
  by 
  ice 
  sheets 
  more 
  than 
  once 
  it 
  

   seems 
  rather 
  strange 
  that 
  geologists 
  have 
  not 
  recognized 
  the 
  phe- 
  

   nomena 
  and 
  discriminated 
  the 
  records. 
  It 
  must 
  be 
  admitted 
  that 
  we 
  

   now 
  lack 
  the 
  evidence 
  afforded 
  by 
  multiple 
  till 
  sheets, 
  separated 
  by 
  

   temperate 
  climate 
  deposits 
  such 
  as 
  are 
  found 
  in 
  the 
  Western 
  States. 
  

   With 
  attention 
  directed 
  to 
  this 
  subject 
  it 
  is 
  probable 
  that 
  some 
  con- 
  

   clusive 
  proofs 
  will 
  be 
  discovered. 
  

  

  But 
  while 
  no 
  single 
  fact 
  or 
  class 
  of 
  phenomena 
  yet 
  found 
  fur- 
  

   nishes 
  conclusive 
  proof 
  of 
  more 
  than 
  one 
  ice 
  epoch, 
  we 
  have 
  a 
  

   variety 
  of 
  indirect 
  evidences, 
  and 
  many 
  features 
  are 
  well 
  ex- 
  

   plained 
  only 
  on 
  that 
  supposition, 
  and 
  several 
  lines 
  of 
  study 
  converge 
  

   toward 
  that 
  conclusion. 
  Moreover, 
  to 
  attribute 
  all 
  the 
  glacial 
  

   phenomena 
  .to 
  a 
  single 
  ice 
  sheet 
  involves 
  inconsistencies, 
  such 
  as 
  

   the 
  evidence 
  of 
  impotence 
  in 
  erosion 
  of 
  the 
  latest 
  ice, 
  with 
  indica- 
  

   tion 
  of 
  vigorous 
  erosion 
  formerly; 
  and 
  the 
  lack 
  of 
  glaciation 
  sur- 
  

   faces 
  on 
  ice-shaped 
  rock 
  as 
  well 
  protected 
  as 
  places 
  showing 
  hairline 
  

   striae 
  and 
  polish. 
  

  

  The 
  glacial 
  features 
  of 
  the 
  Thousand 
  Islands 
  region 
  which 
  are 
  

   not 
  satisfactorily 
  referred 
  to 
  the 
  latest 
  ice 
  work 
  probably 
  can 
  not 
  

   be 
  attributed 
  to 
  an 
  ice 
  sheet 
  as 
  ancient 
  as 
  the 
  Kansan, 
  but 
  would 
  

   seem 
  to 
  be 
  the 
  effect 
  of 
  some 
  recent 
  ice 
  epoch. 
  Whether 
  it 
  was 
  

   one 
  of 
  the 
  later 
  Prewisconsin 
  invasions 
  or 
  only 
  an 
  early 
  Wis- 
  

   consin 
  episode 
  we 
  may 
  not 
  now 
  decide. 
  

  

  Anomalous 
  physiography. 
  South 
  of 
  our 
  area, 
  in 
  the 
  central 
  

   part 
  of 
  the 
  State, 
  many 
  channels 
  of 
  ancient 
  drainage 
  are 
  found 
  

   which 
  are 
  not 
  Postwisconsin. 
  In 
  the 
  area 
  under 
  discussion 
  these 
  

   features 
  do 
  not 
  occur 
  because 
  the 
  whole 
  region 
  was 
  drowned 
  in 
  

   deep 
  water 
  during 
  the 
  ice 
  recession. 
  But 
  the 
  region 
  has 
  its 
  own 
  

   peculiar 
  topographic 
  features 
  that 
  are 
  difficult 
  of 
  full 
  explanation 
  

   under 
  the 
  conception 
  of 
  a 
  single 
  ice 
  transgression. 
  The 
  valley, 
  

   basin 
  and 
  scarp 
  topography 
  has 
  already 
  been 
  briefly 
  discussed 
  

   [p. 
  146]. 
  Other 
  points 
  will 
  be 
  touched 
  on 
  below, 
  but 
  a 
  full 
  dis- 
  

   cussion 
  of 
  the 
  difficult 
  problem 
  requires 
  more 
  fieldwork 
  specially 
  

   directed 
  to 
  the 
  particular 
  features. 
  

  

  