﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  9I 
  

  

  Ice 
  erosion. 
  Ice, 
  like 
  flowing 
  water, 
  has 
  very 
  little 
  erosive 
  effect 
  

   upon 
  rocks 
  unless 
  it 
  is 
  properly 
  supplied 
  with 
  tools. 
  When 
  flowing 
  

   ice 
  is 
  shod 
  with 
  hard 
  rock 
  fragments 
  the 
  power 
  to 
  erode 
  is 
  often 
  

   pronounced 
  because 
  the 
  work 
  of 
  abrasion 
  is 
  mostly 
  accomplished 
  

   by 
  the 
  rock 
  fragments 
  rather 
  than 
  by 
  the 
  soft 
  ice 
  itself. 
  For 
  in- 
  

   stance, 
  when 
  the 
  great 
  ice 
  lobe 
  moved 
  up 
  the 
  St 
  Lawrence 
  valley 
  it 
  

   was 
  shod 
  with 
  many 
  pieces 
  of 
  hard 
  Precambric 
  rocks, 
  and 
  the 
  effects 
  

   of 
  erosion 
  are 
  remarkably 
  well 
  shown 
  in 
  the 
  Thousand 
  Islands 
  

   region. 
  Thus, 
  about 
  two 
  miles 
  due 
  south 
  of 
  Clayton 
  the 
  writer 
  

   has 
  seen 
  a 
  succession 
  of 
  great 
  grooves, 
  covering 
  an 
  area 
  of 
  several 
  

   acres, 
  and 
  cut 
  into 
  the 
  hard, 
  fresh 
  Potsdam 
  sandstone 
  on 
  top 
  of 
  a 
  

   low 
  hill. 
  A 
  little 
  search 
  will 
  reveal 
  polished 
  and 
  scratched 
  or 
  

   grooved 
  rock 
  surfaces 
  in 
  almost 
  any 
  part 
  of 
  the 
  State. 
  Granite 
  

   ledges 
  in 
  the 
  Adirondacks 
  are 
  often 
  glaciated, 
  and 
  the 
  freshness 
  

   and 
  hardness 
  of 
  the 
  surface 
  rock 
  proves 
  that 
  the 
  ice 
  eroded 
  all 
  the 
  

   deep 
  preglacial 
  soil 
  as 
  well 
  as 
  the 
  zone 
  of 
  rotten 
  rock, 
  and 
  an 
  

   unknown 
  amount 
  of 
  live 
  or 
  fresh 
  rock. 
  

  

  In 
  former 
  years 
  a 
  very 
  great 
  erosive 
  power 
  was 
  ascribed 
  to 
  flow- 
  

   ing 
  ice, 
  but 
  today 
  some 
  glacialists 
  consider 
  ice 
  erosion 
  to 
  be 
  almost 
  

   negligible, 
  while 
  many 
  others 
  maintain 
  that, 
  under 
  favorable 
  con- 
  

   ditions, 
  flowing 
  ice 
  has 
  a 
  very 
  considerable 
  erosive 
  effect. 
  During 
  

   the 
  very 
  long 
  preglacial 
  time, 
  rock 
  decomposition 
  must 
  have 
  pro- 
  

   gressed 
  so 
  far 
  that 
  rotten 
  rock, 
  including 
  soils, 
  had 
  accumulated 
  to 
  

   considerable 
  depths, 
  as 
  today 
  in 
  the 
  southern 
  states. 
  Such 
  soils 
  are 
  

   called 
  " 
  residual 
  " 
  because 
  they 
  are 
  derived 
  by 
  the 
  decomposition 
  

   of 
  the 
  very 
  rocks 
  on 
  which 
  they 
  rest. 
  But 
  now 
  one 
  rarely 
  ever 
  

   sees 
  rotten 
  rock 
  or 
  soil 
  in 
  its 
  original 
  place 
  in 
  New 
  York 
  because 
  

   such 
  materials 
  were 
  nearly 
  all 
  scoured 
  off 
  by 
  the 
  passage 
  of 
  the 
  

   great 
  ice 
  sheet, 
  mixed 
  with 
  other 
  soils 
  and 
  ground 
  up 
  rock 
  frag- 
  

   ments 
  and 
  deposited 
  elsewhere. 
  Such 
  are 
  called 
  transported 
  soils. 
  

   Along 
  the 
  southern 
  side 
  of 
  the 
  State, 
  where 
  the 
  erosive 
  power 
  of 
  

   the 
  ice 
  was 
  least, 
  rotten 
  rock 
  is 
  not 
  so 
  uncommonly 
  seen. 
  

  

  Ice, 
  shod 
  with 
  hard 
  rock 
  fragments 
  and 
  flowing 
  through 
  a 
  deep, 
  

   comparatively 
  narrow 
  valley 
  of 
  soft 
  rock, 
  is 
  especially 
  powerful 
  as 
  

   an 
  erosive 
  agent 
  because 
  the 
  abrasive 
  tools 
  are 
  supplied 
  ; 
  the 
  work 
  

   to 
  be 
  done 
  is 
  easy 
  ; 
  and 
  the 
  increased 
  depth 
  of 
  the 
  ice 
  where 
  

   crowded 
  into 
  a 
  deep, 
  narrow 
  valley 
  causes 
  greater 
  pressure 
  on 
  the 
  

   bottom 
  and 
  sides 
  of 
  the 
  valley. 
  Many 
  of 
  the 
  valleys 
  of 
  northern 
  

   New 
  York 
  were 
  thus 
  very 
  favorably 
  situated 
  for 
  ice 
  erosion, 
  as 
  

   for 
  example, 
  the 
  Cbamplain, 
  St 
  Lawrence, 
  Black 
  river, 
  and 
  Finger 
  

   lakes 
  valleys, 
  as 
  well 
  as 
  many 
  of 
  the 
  nearly 
  north-south 
  valleys 
  of 
  

   the 
  Adirondacks. 
  The 
  writer 
  has 
  made 
  a 
  special 
  study 
  of 
  ice 
  

  

  