﻿I/O 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  tically 
  nothing. 
  Such 
  cases 
  give 
  the 
  impression 
  of 
  slight 
  corrosion 
  

   since 
  the 
  ice 
  removal. 
  On 
  the 
  other 
  hand 
  the 
  existence 
  of 
  broad 
  

   surfaces 
  of 
  exceedingly 
  rough 
  and 
  open-jointed 
  rock, 
  from 
  which 
  

   the 
  farmers 
  have 
  to 
  fence 
  their 
  cattle, 
  and 
  the 
  location 
  of 
  which 
  

   would 
  seem 
  to 
  have 
  been 
  favorable 
  to 
  gladation^ 
  give 
  the 
  suggestion 
  

   of 
  large 
  pos^Iacial 
  weathering. 
  The 
  critical 
  question 
  is, 
  were 
  the 
  

   l2"er 
  surfaces 
  glaciated 
  by 
  the 
  latest 
  ice 
  sheet? 
  It 
  would 
  appear 
  

   tha: 
  ?- 
  i.:r:.: 
  ::: 
  :.rA 
  intensity 
  of 
  postglacial 
  weathering 
  which 
  has 
  

   net 
  dei:rc.ei 
  zlit 
  glacial 
  polish 
  on 
  the 
  limestone 
  ribs 
  shown 
  in 
  

   plate 
  6i 
  could 
  not 
  justly 
  be 
  held 
  responsible 
  for 
  the 
  open 
  joints 
  

   and 
  rough 
  surfaces 
  shown 
  in 
  plate 
  60, 
  where 
  a 
  deep 
  clay 
  cover 
  has 
  

   been 
  removed 
  chiefly 
  by 
  washing 
  down 
  into 
  the 
  open 
  joints 
  and 
  

   being 
  carried 
  away 
  by 
  subterranean 
  flow. 
  

  

  The 
  amount 
  of 
  recent 
  weathering 
  is 
  conspicuously 
  greater 
  in 
  

   locations 
  where 
  the 
  surfaces 
  have 
  been 
  subjected 
  to 
  wave 
  wash 
  of 
  

   the 
  Iroquois 
  and 
  Gilbert 
  waters, 
  this 
  being 
  specially 
  effective 
  in 
  

   both 
  solution 
  and 
  mechanical 
  removal 
  of 
  the 
  limestone. 
  

  

  Old 
  planation 
  surfaces. 
  If 
  the 
  ribbing 
  on 
  the 
  limestone 
  was 
  

   in 
  existence 
  before 
  the 
  last 
  ice 
  invasion 
  then, 
  of 
  course, 
  the 
  lime- 
  

   s::r.e 
  p.?. 
  ins 
  and 
  plateaus 
  were 
  formed 
  previously; 
  and 
  it 
  has 
  ai- 
  

   res:; 
  -te:: 
  stated 
  that 
  the 
  broader 
  topographic 
  features 
  are 
  con- 
  

   fir::! 
  ;Tl:r 
  ed 
  to 
  antedate 
  Wisconsin 
  gladation. 
  An 
  ice 
  sheet 
  

   with 
  sufficient 
  vigor 
  to 
  do 
  the 
  plucking 
  and 
  planing 
  necessary 
  to 
  

   give 
  the 
  limestones 
  and 
  Potsdam 
  sandstones 
  their 
  breadth 
  of 
  flat- 
  

   ness 
  should 
  leave 
  abundant 
  evidence 
  in 
  glaciated 
  surfaces 
  ; 
  and 
  the 
  

   limestone 
  ribbing 
  is 
  a 
  relic 
  of 
  such 
  e^e:::ve 
  erosion. 
  Again, 
  the 
  

   general 
  lack 
  of 
  glacial 
  polish 
  is 
  the 
  fact 
  which 
  re::::res 
  explanation. 
  

  

  The 
  plains 
  of 
  Potsdam 
  sandstone 
  present 
  tiie 
  same 
  question. 
  

   Over 
  broad 
  surfaces 
  of 
  the 
  ver\- 
  firm, 
  hard, 
  insoluble 
  sandstone. 
  

   ei::::: 
  ::re 
  or 
  practically 
  unprotected 
  by 
  any 
  impervious 
  cover, 
  only 
  

   a 
  n 
  :: 
  :: 
  part 
  exhibits 
  striae 
  or 
  polish. 
  Certainly 
  it 
  was 
  once 
  all 
  

   vig 
  r: 
  : 
  ' 
  ~ 
  ::iated, 
  for 
  in 
  no 
  other 
  way 
  could 
  the 
  level, 
  even, 
  firm 
  

   surfaces 
  be 
  ;r: 
  :v:ed. 
  From 
  hasty 
  examination 
  it 
  is 
  impossible 
  to 
  

   confidently 
  : 
  :• 
  :: 
  "h 
  ether 
  the 
  patchy 
  scoring 
  and 
  polishing 
  is 
  due 
  

   to 
  weak 
  re: 
  : 
  r 
  : 
  ::on 
  on 
  an 
  old 
  weathered 
  surface, 
  or 
  to 
  reten- 
  

   tion 
  of 
  ptii: 
  vrrr 
  : 
  resent 
  weathering. 
  The 
  former 
  alternative, 
  

   recent 
  panial 
  sniscthm^ 
  en 
  an 
  old 
  weathered 
  surface, 
  is 
  more 
  in 
  

   harmony 
  with 
  the 
  general 
  body 
  of 
  fact; 
  and 
  it 
  seems 
  more 
  prob- 
  

   able 
  that 
  the 
  recent 
  ice 
  sheet 
  failed 
  to 
  generally 
  polish 
  the 
  c\i 
  

   weathered 
  surface 
  than 
  that 
  patches 
  with 
  finest 
  polish 
  and 
  hairline 
  

   striae 
  should 
  be 
  so 
  perfectly 
  preserved 
  while 
  surrounding 
  surfaces 
  

  

  A 
  

  

  