﻿4 
  MUSSEL 
  RESOUECES 
  OF 
  THE 
  ILLINOIS 
  RIVER. 
  

  

  PHYSICAL 
  CONDITIONS. 
  

  

  The 
  Illinois 
  River 
  is 
  one 
  of 
  the 
  most 
  important 
  tributaries 
  of 
  the 
  

   upper 
  Mississippi, 
  not 
  only 
  on 
  account 
  of 
  the 
  volume 
  of 
  water 
  it 
  

   dischai^es 
  and 
  its 
  excellent 
  transportation 
  facilities, 
  but 
  because 
  of 
  

   its 
  extensive 
  fisheries 
  and 
  large 
  mussel 
  resources. 
  The 
  Illinois, 
  

   formed 
  by 
  the 
  junction 
  of 
  the 
  Kankakee 
  and 
  Des 
  Plaines 
  Rivers 
  

   and 
  emptying 
  into 
  the 
  Mississippi 
  at 
  Grafton, 
  111,, 
  is 
  about 
  273 
  miles 
  

   in 
  length. 
  Its 
  drainage 
  basin 
  comprises 
  about 
  29,000 
  square 
  miles 
  

   of 
  fine 
  farm 
  land 
  in 
  Illinois, 
  Indiana, 
  and 
  Wisconsin. 
  Besides 
  re- 
  

   ceiving 
  many 
  important 
  natural 
  tributari^, 
  it 
  is 
  the 
  outlet 
  of 
  the 
  

   Chicago 
  Drainage 
  Canal, 
  having 
  a 
  discharge 
  of 
  several 
  thousand 
  

   cubic 
  feet 
  per 
  second 
  of 
  water 
  from 
  Lake 
  Mchigan, 
  and 
  with 
  an 
  

   equivalent 
  drainage 
  area 
  of 
  6,000 
  square 
  miles. 
  The 
  river 
  conse- 
  

   quently 
  carries 
  an 
  enormoiis 
  amount 
  of 
  sewage 
  from 
  Chicago, 
  as 
  

   well 
  as 
  from 
  the 
  various 
  cities 
  and 
  manufacturing 
  plants 
  along 
  its 
  

   course. 
  

  

  The 
  greater 
  part 
  of 
  Illinois 
  is 
  covered 
  by 
  glacial 
  drift 
  of 
  varying 
  

   thickness, 
  brought 
  down 
  from 
  the 
  Northeast 
  during 
  the 
  ice 
  age, 
  and 
  

   as 
  a 
  consequence 
  many 
  of 
  the 
  old 
  river 
  beds 
  were 
  filled 
  with 
  sand 
  and 
  

   gravel 
  and 
  the 
  streams 
  were 
  forced 
  to 
  cut 
  new 
  channels, 
  in 
  some 
  

   places 
  completely 
  changing 
  the 
  course 
  for 
  all 
  or 
  a 
  part 
  of 
  the 
  way. 
  

   Such 
  is 
  the 
  case 
  with 
  the 
  Illinois 
  River. 
  In 
  the 
  upper 
  part 
  the 
  river 
  

   has 
  cut 
  its 
  way 
  through 
  the 
  Wisconsin 
  drift 
  down 
  into 
  solid 
  rock, 
  

   while 
  in 
  the 
  lower 
  portion, 
  although 
  still 
  in 
  its 
  old 
  course, 
  it 
  is 
  often 
  

   as 
  much 
  as 
  100 
  feet 
  above 
  solid 
  rock. 
  

  

  The 
  watershed 
  of 
  the 
  Illinois 
  River 
  extends 
  in 
  a 
  broad 
  band, 
  averaging 
  100 
  miles 
  

   in 
  width, 
  ia 
  a 
  northeast-southwest 
  direction 
  directly 
  across 
  the 
  center 
  of 
  Illinois. 
  

   The 
  western 
  side 
  of 
  the 
  watershed 
  is 
  20 
  to 
  40 
  miles 
  in 
  width, 
  while 
  the 
  width 
  of 
  the 
  

   eastern 
  side 
  is 
  60 
  to 
  80 
  miles. 
  From 
  the 
  jimction 
  westward 
  for 
  50 
  miles, 
  being 
  in 
  a 
  

   new 
  course, 
  its 
  bed 
  is 
  usually 
  on 
  the 
  rock 
  and 
  it 
  has 
  an 
  average 
  fall 
  of 
  about 
  1 
  foot 
  

   per 
  mile, 
  but 
  in 
  the 
  remainder 
  of 
  its 
  course 
  it 
  is 
  in 
  a 
  preglacial 
  channel 
  and 
  has 
  a 
  

   very 
  slight 
  fall. 
  From 
  the 
  jimction 
  to 
  Utica, 
  its 
  com-se 
  is 
  independent 
  of 
  preglacial 
  

   drainage 
  lines. 
  About 
  midway 
  of 
  its 
  westward 
  course 
  it 
  crosses 
  the 
  Marseilles 
  moraine. 
  

   This, 
  no 
  doubt, 
  for 
  a 
  considerable 
  period 
  held 
  a 
  lake 
  in 
  the 
  basin 
  at 
  the 
  head 
  of 
  the 
  

   river 
  (the 
  Morris 
  Basin), 
  but 
  was 
  eventually 
  cut 
  down 
  to 
  the 
  level 
  of 
  the 
  low 
  part 
  of 
  

   the 
  basin. 
  From 
  the 
  Marseilles 
  moraine 
  westward 
  the 
  channel 
  found 
  no 
  prominent 
  

   drift 
  barriers 
  to 
  remove, 
  but 
  has 
  been 
  compelled 
  to 
  cut 
  down 
  50 
  to 
  75 
  feet 
  into 
  the 
  

   rock 
  in 
  opening 
  an 
  outlet 
  from 
  the 
  Morris 
  Basin 
  into 
  the 
  valley 
  of 
  the 
  lower 
  Illinois. 
  

   The 
  lower 
  Illinois 
  seems 
  to 
  have 
  been 
  so 
  imperfectly 
  filled 
  by 
  glacial 
  deposits 
  that 
  

   throughout 
  nearly 
  its 
  entire 
  length 
  the 
  stream 
  is 
  reestablished 
  in 
  the 
  old 
  course. 
  The 
  

   valley 
  of 
  the 
  lower 
  Illinois 
  ranges 
  in 
  width 
  from 
  2^ 
  to 
  fully 
  15 
  miles. 
  The 
  narrowest 
  

   portions 
  of 
  the 
  lower 
  valley 
  are 
  a 
  short 
  section 
  at 
  Peoria, 
  where 
  it 
  passes 
  through 
  the 
  

   Shelbyville 
  morainic 
  system, 
  and 
  a 
  section 
  embracing 
  the 
  lower 
  60 
  miles, 
  where 
  it 
  

   traverses 
  the 
  Eocarboniferous 
  and 
  Silurian 
  limestones.a 
  

  

  o 
  Leverett, 
  Frank-: 
  The 
  Illinais^glacial 
  lobe. 
  U. 
  S. 
  Geological 
  Survey, 
  mon. 
  xxxvin. 
  

  

  