﻿98 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  from 
  the 
  region. 
  To 
  summarize, 
  we 
  may 
  say 
  that 
  the 
  present 
  

   Great 
  Lakes 
  basins 
  are 
  due 
  to 
  a 
  combination 
  of 
  factors, 
  the 
  more 
  

   important 
  of 
  which 
  were: 
  the 
  formation 
  of 
  preglacial 
  valleys 
  by 
  

   stream 
  erosion; 
  a 
  more 
  or 
  less 
  deepening 
  of 
  these 
  valleys 
  by 
  ice 
  

   erosion 
  ; 
  the 
  great 
  accumulation 
  of 
  glacial 
  debris 
  along 
  the 
  southern 
  

   side 
  of 
  the 
  Great 
  Lakes 
  region 
  ; 
  and 
  the 
  tilting 
  of 
  the 
  land 
  down- 
  

   ward 
  toward 
  the 
  north. 
  

  

  We 
  are 
  now 
  ready 
  to 
  trace 
  out 
  the 
  principal 
  stages 
  in 
  the 
  history 
  

   of 
  the 
  Great 
  Lakes 
  during 
  the 
  final 
  retreat 
  of 
  the 
  ice 
  sheet. 
  When 
  

   the 
  ice 
  front 
  had 
  receded 
  far 
  enough 
  northward 
  to 
  uncover 
  the 
  

   western 
  end 
  of 
  Lake 
  Superior, 
  the 
  southern 
  end 
  of 
  Lake 
  Michigan, 
  

   and 
  an 
  area 
  west 
  of 
  the 
  present 
  end 
  of 
  Lake 
  Erie, 
  small 
  lakes 
  

   were 
  formed 
  against 
  the 
  ice 
  walls 
  (see 
  figure 
  30). 
  One 
  of 
  these 
  

   has 
  been 
  called 
  Lake 
  Duluth 
  which 
  drained 
  southward 
  into 
  the 
  

   Mississippi 
  ; 
  the 
  second 
  Lake 
  Chicago 
  which 
  drained 
  past 
  Chicago 
  

   through 
  the 
  Illinois 
  river 
  and 
  into 
  the 
  Mississippi 
  ; 
  and 
  the 
  third 
  

   Lake 
  Maumee 
  which 
  drained 
  southwestward 
  past 
  Fort 
  W^ayne 
  

   through 
  the 
  Wabash 
  river 
  and 
  into 
  the 
  Ohio 
  and 
  Mississippi. 
  

  

  At 
  a 
  still 
  later 
  stage 
  the 
  conditions 
  shown 
  on 
  the 
  map 
  (figure 
  31) 
  

   existed. 
  Lake 
  Chicago 
  was 
  then 
  much 
  larger, 
  and 
  Lake 
  Maumee 
  

  

  

  Fig. 
  31 
  A 
  later 
  stage 
  of 
  Great 
  Lakes 
  history, 
  showing 
  how 
  

   the 
  eastern 
  and 
  western 
  ice 
  margin 
  lakes 
  combined 
  with 
  outlet 
  

   past 
  Chicago. 
  

  

  After 
  Taylor 
  

  

  had 
  expanded 
  into 
  the 
  extensive 
  Lake 
  Whittlesey 
  which 
  covered 
  

   nearly 
  all 
  of 
  Lake 
  Erie 
  as 
  well 
  as 
  the 
  immediately 
  surrounding 
  

   country. 
  Lake 
  Whittlesey 
  was 
  at 
  a 
  lower 
  level 
  than 
  the 
  former 
  

   Maumee 
  and 
  the 
  outlet 
  past 
  Fort 
  Wayne 
  ceased, 
  but 
  the 
  drainage 
  

  

  