﻿128 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Jail, 
  20, 
  

  

  south 
  or 
  south-west. 
  This 
  feature 
  is 
  also 
  observed 
  in 
  all 
  the 
  outliers 
  

   in 
  the 
  great 
  prairies 
  and 
  plains 
  of 
  the 
  basin 
  of 
  Lake 
  Winnipeg. 
  The 
  

   terraces 
  of 
  Lake 
  Superior 
  and 
  the 
  escarpments, 
  with 
  their 
  correspond- 
  

   ing 
  terraces 
  in 
  the 
  Lake 
  Winnipeg 
  basin, 
  considered 
  in 
  relation 
  to 
  

   the 
  driftless 
  area 
  in 
  Wisconsin, 
  point 
  to 
  the 
  former 
  existence 
  of 
  great 
  

   glacial 
  lakes, 
  as 
  suggested 
  by 
  Mr. 
  Jamieson 
  to 
  explain 
  the 
  origin 
  of 
  

   the 
  Parallel 
  Roads 
  of 
  Glen 
  Roy. 
  The 
  clean-swept 
  floor 
  of 
  the 
  level 
  

   country 
  at 
  the 
  foot 
  of 
  the 
  great 
  escarpment 
  of 
  the 
  Riding, 
  Duck, 
  and 
  

   Porcupine 
  Mountains, 
  in 
  which 
  Lake 
  Winnipeg 
  and 
  its 
  associated 
  

   lakes 
  lie, 
  indicates 
  the 
  boundary 
  of 
  a 
  vast 
  glacier, 
  which 
  excavated 
  

   their 
  basins 
  and 
  left 
  its 
  dirt-beds 
  on 
  the 
  prairie 
  country 
  even 
  as 
  far 
  

   as 
  the 
  south 
  branch 
  of 
  the 
  Saskatchewan, 
  where 
  I 
  observed 
  the 
  

   forced 
  arrangement 
  of 
  slabs 
  in 
  unstratified 
  clay 
  in 
  1858. 
  

  

  § 
  5. 
  Anchor-ice 
  — 
  Excavation 
  of 
  Lake-basins. 
  

  

  It 
  has 
  been 
  frequently 
  stated 
  that 
  a 
  difficulty 
  arises 
  as 
  to 
  the 
  modus 
  

   operandi 
  by 
  which 
  a 
  moving 
  glacier 
  can 
  excavate 
  lake-basins. 
  May 
  

   not 
  the 
  manner 
  in 
  which 
  stratified 
  rocks, 
  at 
  least, 
  over 
  which 
  a 
  

   glacier 
  may 
  be 
  moving, 
  can 
  be 
  involved 
  in 
  its 
  mass 
  in 
  the 
  form 
  of 
  

   slabs 
  or 
  mud, 
  constituting 
  dirt-beds, 
  be 
  partially 
  explained 
  by 
  the 
  

   phenomena 
  attending 
  the 
  formation 
  of 
  ' 
  anchor-ice 
  ' 
  ? 
  It 
  is 
  no 
  

   uncommon 
  occurrence 
  for 
  the 
  anchors 
  of 
  the 
  nets 
  of 
  a 
  " 
  seal-fishery 
  " 
  

   on 
  the 
  north 
  shore 
  of 
  the 
  Gulf 
  of 
  St. 
  Lawrence 
  to 
  be 
  frozen 
  to 
  the 
  

   bottom 
  at 
  the 
  depth 
  of 
  from 
  30 
  to 
  60 
  feet 
  ; 
  and 
  when 
  anchors 
  are 
  

   then 
  raised, 
  they 
  bring 
  with 
  them 
  frozen 
  masses 
  of 
  sand. 
  But 
  it 
  is 
  

   in 
  rapid 
  rivers 
  that 
  the 
  formation 
  of 
  anchor-ice 
  is 
  most 
  remarkable, 
  

   and 
  most 
  effective 
  in 
  excavating 
  these 
  beds. 
  It 
  forms 
  on 
  the 
  beds 
  

   of 
  rivers 
  above 
  the 
  head 
  of 
  a 
  rapid, 
  and 
  frequently 
  bursts 
  up 
  with 
  a 
  

   load 
  of 
  frozen 
  mud 
  or 
  shingle, 
  or 
  slabs 
  of 
  rock, 
  which 
  it 
  has 
  torn 
  

   from 
  the 
  bottom. 
  This 
  phenomenon 
  is 
  witnessed 
  every 
  winter 
  in 
  the 
  

   valley 
  of 
  the 
  St. 
  Lawrence, 
  but 
  it 
  is 
  best 
  observed 
  after 
  a 
  prolonged 
  

   term 
  of 
  cold, 
  when 
  the 
  thermometer 
  indicates 
  a 
  temperature 
  con- 
  

   siderably 
  below 
  zero. 
  Anchor-ice 
  has 
  only 
  been 
  observed, 
  as 
  far 
  as 
  

   my 
  knowledge 
  of 
  the 
  subject 
  goes, 
  in 
  rapid 
  currents 
  in 
  open 
  water 
  ; 
  

   and 
  the 
  sudden 
  and 
  apparently 
  inexplicable 
  rise 
  of 
  the 
  St. 
  Lawrence 
  

   during 
  extreme 
  cold 
  is 
  most 
  probably 
  due 
  to 
  this 
  cause*. 
  It 
  is 
  not 
  

   difficult 
  to 
  see 
  how 
  the 
  rivers 
  issuing 
  from 
  beneath 
  the 
  precipitous 
  

   walls 
  of 
  glaciers, 
  as 
  described 
  by 
  Dr. 
  Rink, 
  may 
  rapidly 
  excavate 
  

   deep 
  channels 
  by 
  means 
  of 
  anchor-ice, 
  to 
  be 
  widened 
  by 
  the 
  sub- 
  

   sequent 
  operations 
  of 
  the 
  glacier 
  itself. 
  Nor 
  is 
  it 
  improbable 
  that 
  

   by 
  this 
  means 
  a 
  glacier 
  in 
  very 
  cold 
  climates 
  may 
  increase 
  from 
  the 
  

   bottom 
  upwards 
  with 
  a 
  load 
  of 
  frozen 
  mud 
  and 
  fragments 
  of 
  rock, 
  

   particularly 
  near 
  its 
  base, 
  when 
  that 
  does 
  not 
  meet 
  the 
  open 
  sea. 
  

   The 
  great 
  lakes 
  of 
  North 
  America, 
  including 
  Lake 
  Winnipeg, 
  are 
  

   excavated 
  on 
  the 
  edges 
  of 
  the 
  fossiliferous 
  rock-basins 
  ; 
  and 
  these 
  

   lakes 
  may 
  represent 
  the 
  boundary 
  of 
  a 
  glacial 
  mass 
  similar 
  to 
  that 
  

   which 
  now 
  covers 
  Greenland. 
  

  

  * 
  See 
  "Notes 
  on 
  Anchor-ice," 
  by 
  C. 
  T. 
  Keefer, 
  C.E.. 
  Canadian 
  Journal, 
  New 
  

   Series, 
  vol. 
  vii. 
  p. 
  173 
  (1862). 
  

  

  