﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  105 
  

  

  ridge 
  on 
  which 
  it 
  is 
  located. 
  It 
  is 
  almost 
  completely 
  surrounded 
  by 
  

   walls 
  of 
  hard 
  Shawangunk 
  conglomerate, 
  while 
  the 
  lake 
  basin 
  itself 
  

   is 
  in 
  the 
  soft 
  underlying 
  Ordovicic 
  shales. 
  This 
  lake 
  does 
  not 
  appear 
  

   to 
  owe 
  its 
  origin 
  to 
  a 
  dam 
  of 
  glacial 
  drift, 
  but 
  rather 
  to 
  ice 
  erosion 
  

   in 
  the 
  soft 
  shales 
  at 
  a 
  place 
  where 
  they 
  had 
  already 
  been 
  exposed 
  

   to 
  view 
  before 
  the 
  oncoming 
  of 
  the 
  ice. 
  Such 
  patches 
  of 
  shale 
  

   occur 
  at 
  several 
  places 
  on 
  the 
  mountain. 
  

  

  Near 
  the 
  very 
  western 
  end 
  of 
  the 
  State 
  lies 
  another 
  lake 
  remark- 
  

   ably 
  situated. 
  This 
  is 
  Lake 
  Chautauqua, 
  famous 
  as 
  the 
  great 
  center 
  

   of 
  Chautauqua 
  assemblies. 
  The 
  altitude 
  of 
  the 
  lake 
  is 
  1338 
  feet, 
  

   and 
  its 
  northern 
  end 
  is 
  near 
  the 
  edge 
  of 
  the 
  steep 
  front 
  of 
  the 
  

   Southwestern 
  plateau 
  province 
  where 
  it 
  overlooks 
  the 
  low 
  Erie 
  

   plain. 
  The 
  drainage 
  is 
  southward 
  into 
  the 
  Allegheny 
  river, 
  but 
  the 
  

   narrow 
  place 
  near 
  the 
  middle 
  of 
  the 
  lake 
  strongly 
  suggests 
  a 
  pre- 
  

   glacial 
  divide 
  there. 
  As 
  Tarr 
  says 
  : 
  " 
  If 
  this 
  view 
  be 
  true, 
  Chau- 
  

   tauqua 
  lake 
  is 
  made 
  up 
  of 
  parts 
  of 
  two 
  valleys, 
  one 
  north-sloping, 
  

   the 
  other 
  south-sloping, 
  and 
  each 
  dammed 
  by 
  heavy 
  morainic 
  

   accumulations." 
  * 
  

  

  Extinct 
  glacial 
  lakes. 
  Hundreds 
  of 
  extinct 
  glacial 
  lakes 
  are 
  

   known 
  to 
  be 
  scattered 
  over 
  the 
  State. 
  Some 
  of 
  these 
  existed 
  only 
  

   during 
  the 
  time 
  of 
  the 
  ice 
  retreat, 
  while 
  others 
  persisted 
  for 
  a 
  

   greater 
  or 
  lesser 
  length 
  of 
  time 
  after 
  the 
  Ice 
  age. 
  Lakes 
  Warren, 
  

   Iroquois 
  etc., 
  already 
  described, 
  were 
  fine 
  examples 
  of 
  the 
  first 
  type. 
  

   North-sloping 
  valleys 
  were 
  particularly 
  favorable 
  for 
  the 
  develop- 
  

   ment 
  of 
  glacial 
  lakes 
  during 
  the 
  retreat 
  of 
  the 
  ice 
  because 
  the 
  ice 
  

   front 
  always 
  acted 
  as 
  a 
  dam 
  across 
  such 
  valleys, 
  thus 
  allowing 
  the 
  

   waters 
  to 
  become 
  ponded. 
  When 
  the 
  ice 
  front 
  stood 
  across 
  the 
  

   northern 
  ends 
  of 
  the 
  Finger 
  Lakes 
  valleys, 
  the 
  waters 
  in 
  those 
  

   valleys 
  were 
  ponded 
  at 
  much 
  higher 
  levels 
  than 
  they 
  now 
  are, 
  and 
  

   the 
  ancient 
  water 
  levels 
  are 
  more 
  or 
  less 
  clearly 
  marked 
  by 
  the 
  

   old 
  beach 
  lines. 
  

  

  Perhaps 
  the 
  finest 
  example 
  of 
  a 
  large, 
  wholly 
  extinct 
  glacial 
  lake 
  

   is 
  Black 
  lake, 
  which 
  occupied 
  a 
  good 
  portion 
  of 
  the 
  Black 
  river 
  

   valley 
  on 
  the 
  western 
  side 
  of 
  the 
  Adirondacks. 
  This 
  lake, 
  small 
  at 
  

   first, 
  was 
  formed 
  by 
  ponding 
  the 
  waters 
  in 
  the 
  upper 
  Black 
  river 
  

   valley 
  around 
  Forestport, 
  Oneida 
  county, 
  in 
  front 
  of 
  the 
  waning 
  

   (northward 
  retreating) 
  ice 
  lobe 
  in 
  the 
  Black 
  river 
  valley. 
  Its 
  first 
  

   discharge 
  was 
  probably 
  southward 
  past 
  Remsen. 
  Further 
  retreat 
  

   of 
  the 
  ice 
  lobe 
  permitted 
  an 
  enlargement 
  of 
  the 
  lake 
  to' 
  the 
  region 
  

   around 
  Boonville, 
  and 
  the 
  discharge 
  was 
  then 
  southward 
  along 
  the 
  

   channel 
  of 
  the 
  present 
  Lansing 
  kill. 
  The 
  deep, 
  narrow 
  gorge 
  a 
  

  

  1 
  Tarr's 
  Physical 
  Geography 
  of 
  New 
  York 
  State, 
  p. 
  205. 
  

  

  