﻿6 
  W. 
  Upham 
  — 
  Champlain 
  Subsidence 
  and 
  

  

  beach 
  at 
  30 
  feet 
  was 
  formed 
  after 
  that 
  at 
  15 
  feet 
  is 
  shown 
  by 
  

   the 
  occurrence 
  in 
  some 
  places 
  of 
  a 
  peat 
  deposit, 
  described 
  by 
  

   Andrews 
  and 
  Leverett, 
  which 
  passes 
  underneath 
  the 
  30 
  feet 
  

   beach 
  and 
  is 
  continuous 
  from 
  its 
  upper 
  side 
  down 
  to 
  the 
  lower 
  

   beach. 
  The 
  peat 
  marks 
  a 
  land 
  surface 
  over 
  which 
  the 
  lake 
  

   rose 
  to 
  form 
  the 
  middle 
  or 
  third 
  beach, 
  after 
  having 
  stood 
  

   at 
  the 
  lower 
  or 
  second 
  beach 
  for 
  some 
  time. 
  Still 
  later, 
  

   however, 
  it 
  probably 
  again 
  stood 
  at 
  the 
  lower 
  level, 
  corre- 
  

   sponding 
  to 
  the 
  present 
  watershed 
  in 
  the 
  abandoned 
  outlet. 
  

   This 
  old 
  channel 
  of 
  outflow, 
  at 
  its 
  summit, 
  as 
  I 
  am 
  informed 
  

   by 
  Mr. 
  Ossian 
  Guthrie 
  from 
  the 
  canal 
  survey, 
  is 
  now 
  11 
  feet 
  

   above 
  the 
  mean 
  level 
  of 
  Lake 
  Michigan, 
  but 
  the 
  surface 
  there 
  

   is 
  postglacial 
  silt 
  ; 
  at 
  another 
  point, 
  where 
  the 
  channel 
  bed 
  

   consists 
  of 
  till, 
  and 
  at 
  a 
  third 
  place 
  where 
  the 
  bed 
  is 
  rock, 
  

   its 
  height 
  in 
  each 
  case 
  is 
  only 
  eight 
  feet 
  above 
  the 
  present 
  

   lake, 
  or 
  590 
  feet 
  above 
  the 
  sea. 
  The 
  mouth 
  of 
  Lake 
  Warren 
  

   appears 
  to 
  have 
  been 
  at 
  first 
  near 
  Lemont, 
  on 
  the 
  Des 
  Plaines 
  

   river 
  about 
  25 
  miles 
  from 
  the 
  lake, 
  where 
  the 
  river 
  valley 
  

   was 
  obstructed 
  by 
  drift 
  which 
  suffered 
  erosion, 
  allowing 
  the 
  

   mouth 
  of 
  the 
  lake 
  to 
  be 
  transferred 
  gradually 
  upstream, 
  at 
  

   the 
  same 
  time 
  being 
  lowered, 
  to 
  its 
  final 
  position 
  ten 
  miles 
  

   from 
  the 
  lake 
  shore 
  in 
  Chicago. 
  Epeirogenic 
  movements, 
  

   between 
  the 
  times 
  of 
  formation 
  of 
  the 
  second 
  and 
  third 
  

   beaches, 
  slightly 
  lifted 
  the 
  outlet 
  and 
  adjacent 
  portion 
  of 
  the 
  

   course 
  of 
  the 
  Des 
  Plaines 
  river, 
  as 
  compared 
  with 
  the 
  southern 
  

   and 
  southwestern 
  part 
  of 
  the 
  Lake 
  Michigan 
  basin, 
  causing 
  the 
  

   old 
  lake 
  to 
  extend 
  a 
  little 
  farther 
  on 
  that 
  side 
  than 
  before. 
  

   Toward 
  the 
  north 
  and 
  east, 
  however, 
  this 
  change 
  was 
  doubt- 
  

   less 
  more 
  than 
  counteracted 
  by 
  the 
  rapid 
  differential 
  rise 
  of 
  

   the 
  land. 
  

  

  Fresh-water 
  shells 
  are 
  found 
  abundant 
  in 
  the 
  15 
  feet 
  beach 
  

   at 
  Evanston 
  and 
  elsewhere 
  southward 
  through 
  Chicago. 
  All 
  

   the 
  species 
  obtained, 
  representing 
  ten 
  or 
  more 
  genera, 
  are 
  still 
  

   living 
  in 
  this 
  region. 
  Wood 
  of 
  oak 
  and 
  cedar, 
  and 
  the 
  thigh 
  

   bone 
  of 
  a 
  deer, 
  have 
  been 
  also 
  found 
  in 
  the 
  same 
  beach 
  at 
  

   Evanston.* 
  

  

  For 
  the 
  distance 
  of 
  about 
  185 
  miles 
  from 
  Chicago 
  north 
  

   to 
  the 
  south 
  end 
  of 
  Green 
  bay, 
  the 
  highest 
  shore 
  of 
  Lake 
  

   Warren 
  appears 
  to 
  be 
  now 
  nearly 
  level, 
  for 
  Mr. 
  Taylor 
  finds 
  

   evidence 
  of 
  submergence 
  only 
  to 
  a 
  height 
  of 
  some 
  20 
  feet 
  

   above 
  that 
  part 
  of 
  Green 
  bay 
  and 
  the 
  neighboring 
  lake 
  shore. 
  

   Thence 
  northward, 
  however, 
  the 
  beach 
  rises 
  about 
  14 
  feet 
  per 
  

   mile 
  for 
  110 
  miles 
  to 
  Cook's 
  Hill, 
  near 
  the 
  north 
  end 
  of 
  this 
  

   bay 
  ; 
  in 
  60 
  miles 
  from 
  that 
  latitude 
  north 
  to 
  Houghton, 
  it 
  has 
  

   an 
  ascent 
  of 
  260 
  feet, 
  or 
  4-J 
  feet 
  per 
  mile 
  ; 
  but 
  in 
  about 
  90 
  

  

  * 
  H. 
  M. 
  Bannister, 
  Geology 
  of 
  Illinois, 
  vol. 
  iii, 
  1868, 
  pp. 
  241, 
  242. 
  F. 
  Leverett, 
  

   " 
  Eaised 
  Beaches 
  of 
  Lake 
  Michigan," 
  before 
  cited, 
  p. 
  189. 
  

  

  