﻿MUSSELS 
  OF 
  CENTRAL 
  AND 
  NOETHERN 
  MINNESOTA. 
  7 
  

  

  that 
  of 
  the 
  Red 
  River 
  of 
  the 
  North, 
  a 
  large 
  lake, 
  called 
  Lake 
  Agassiz, 
  

   was 
  formed 
  along 
  the 
  edge 
  of 
  the 
  ice. 
  As 
  the 
  ice 
  withdrew, 
  this 
  lake 
  

   extended 
  northward 
  along 
  the 
  Red 
  River 
  Valley 
  as 
  far 
  as 
  what 
  is 
  

   now 
  Lake 
  Winnipeg. 
  Lake 
  Agassiz 
  was 
  700 
  miles 
  long 
  and 
  covered 
  

   110,000 
  square 
  miles, 
  and 
  its 
  duration 
  is 
  estimated 
  to 
  have 
  been 
  

   about 
  a 
  thousand 
  years. 
  Its 
  outlet, 
  known 
  as 
  the 
  glacial 
  river 
  

   Warren, 
  was 
  along 
  the 
  vaUey 
  now 
  occupied 
  by 
  Lakes 
  Traverse 
  and 
  

   Big 
  Stone 
  and 
  the 
  Minnesota 
  River, 
  into 
  the 
  Mississippi, 
  At 
  that 
  

   period, 
  therefore, 
  the 
  Mississippi 
  River 
  may 
  be 
  said 
  to 
  have 
  had 
  its 
  

   origin 
  in 
  Lake 
  Agassiz. 
  And 
  during 
  the 
  thousand 
  years 
  of 
  its 
  

   existence, 
  this 
  lake 
  had 
  abundant 
  opportunity 
  to 
  become 
  populated 
  

   with 
  fresh-water 
  mussels 
  ascending 
  from 
  the 
  Mississippi. 
  The 
  lake 
  

   disappeared, 
  however, 
  and 
  the 
  valley 
  of 
  the 
  Minnesota 
  River 
  sepa- 
  

   rated 
  from 
  that 
  of 
  the 
  Red 
  River. 
  But 
  the 
  mussel 
  faunas 
  of 
  the 
  two 
  

   rivers 
  were 
  derived 
  from 
  identically 
  the 
  same 
  source, 
  and 
  the 
  only 
  

   differences 
  would 
  be 
  the 
  few 
  minor 
  changes 
  that 
  have 
  crept 
  in 
  since 
  

   then. 
  

  

  Many 
  other 
  glacial 
  lakes 
  were 
  formed 
  during 
  the 
  melting 
  of 
  the 
  

   ice 
  sheet, 
  only 
  to 
  be 
  subsequently 
  obliterated. 
  But 
  while 
  they 
  

   existed 
  they 
  served 
  as 
  temporary 
  channels 
  for 
  the 
  migration 
  of 
  fish 
  

   and 
  mussels 
  from 
  the 
  south. 
  Two 
  of 
  these 
  are 
  of 
  especial 
  interest, 
  in 
  

   view 
  of 
  the 
  results 
  of 
  our 
  present 
  investigation. 
  Lake 
  L^pham 
  once 
  

   covered 
  the 
  region 
  south 
  of 
  the 
  Mesabi 
  Iron 
  Range, 
  and 
  drained 
  

   southeast 
  along 
  the 
  valley 
  now 
  occupied 
  by 
  the 
  St. 
  Louis 
  and 
  Cloquet 
  

   Rivers. 
  This 
  lake 
  was 
  very 
  shallow 
  and 
  temporary 
  and, 
  as 
  far 
  as 
  

   can 
  be 
  determined, 
  was 
  not 
  connected 
  with 
  the 
  Mississippi 
  River 
  in 
  

   any 
  way. 
  This 
  fact 
  accounts 
  for 
  the 
  paucity 
  of 
  mussels 
  in 
  that 
  

   portion 
  of 
  the 
  State, 
  as 
  well 
  as 
  in 
  all 
  the 
  Lake 
  Superior 
  drainage. 
  

  

  Lake 
  Nicollet 
  was 
  formed 
  around 
  the 
  headwaters 
  of 
  the 
  Mississippi 
  

   River 
  and 
  covered 
  an 
  area 
  of 
  1,500 
  square 
  miles. 
  It 
  drained 
  south- 
  

   west 
  into 
  the 
  valley 
  now 
  occupied 
  by 
  the 
  Crow 
  Wing 
  River 
  and 
  

   thence 
  into 
  the 
  Mississippi. 
  The 
  Crow 
  Wing 
  River 
  thus 
  becomes 
  the 
  

   modern 
  representative 
  of 
  the 
  old 
  headwaters 
  of 
  the 
  Mississippi, 
  and 
  

   is 
  older 
  than 
  that 
  portion 
  of 
  the 
  latter 
  river 
  which 
  now 
  extends 
  from 
  

   the 
  mouth 
  of 
  the 
  Crow 
  Wing 
  up 
  to 
  Lake 
  Itasca. 
  These 
  facts 
  explain 
  

   the 
  richness 
  of 
  the 
  mussel 
  fauna 
  in 
  the 
  Crow 
  Wing 
  and 
  its 
  tributaries. 
  

   At 
  two 
  places 
  in 
  the 
  area 
  covered 
  by 
  the 
  present 
  survey 
  the 
  bed 
  rocks 
  

   appear 
  above 
  the 
  drift 
  with 
  sufficient 
  prominence 
  to 
  materially 
  affect 
  

   the 
  mussel 
  distribution. 
  At 
  Carlton 
  the 
  St. 
  Louis 
  River 
  plunges 
  

   over 
  a 
  rocky 
  ledge 
  and 
  through 
  a 
  gorge, 
  which 
  prevents 
  the 
  passage 
  

   of 
  either 
  fish 
  or 
  mussels. 
  Consequently 
  that 
  portion 
  of 
  the 
  Lake 
  

   Superior 
  drainage 
  which 
  is 
  tributary 
  to 
  the 
  St. 
  Louis 
  River 
  above 
  

   Carlton 
  is 
  devoid 
  of 
  mussels. 
  

  

  