﻿1864.] 
  

  

  HIND 
  GLACIAL 
  DRIFT, 
  

  

  129 
  

  

  § 
  6. 
  Parallelism 
  of 
  Escarpments 
  in 
  America. 
  

  

  In 
  1860* 
  I 
  described 
  the 
  remarkable 
  paral- 
  

   lelism 
  which 
  exists 
  between 
  great 
  escarpments 
  

   in 
  America 
  north 
  of 
  the 
  40th 
  parallel 
  of 
  latitude. 
  

  

  1st. 
  The 
  Niagara 
  escarpment. 
  

  

  2nd. 
  The 
  Riding, 
  Duck, 
  and 
  Porcupine 
  Hill 
  

   escarpment, 
  west 
  of 
  Lake 
  Winnipeg. 
  

  

  3rd. 
  The 
  escarpment 
  of 
  the 
  Grand 
  Coteau 
  

   de 
  Missouri. 
  

  

  These 
  are 
  all 
  roughly 
  parallel 
  to 
  one 
  another, 
  

   and 
  are 
  many 
  hundred 
  miles 
  in 
  length. 
  The 
  

   lowest, 
  the 
  Niagara, 
  varies 
  from 
  600 
  feet 
  to 
  

   1300 
  feet 
  above 
  the 
  sea 
  ; 
  the 
  second, 
  west 
  of 
  

   Lake 
  Winnipeg, 
  from 
  1600 
  feet 
  to 
  2000 
  ; 
  the 
  

   third, 
  the 
  Grand 
  Coteau 
  de 
  Missouri, 
  from 
  2000 
  

   to 
  3000 
  feet 
  and 
  more 
  above 
  the 
  ocean 
  (see 
  

   fig. 
  3). 
  They 
  have 
  all 
  easterly, 
  north-easterly, 
  

   or 
  northerly 
  aspects, 
  in 
  relatively 
  different 
  parts 
  

   of 
  their 
  lengths 
  f 
  , 
  and 
  appear 
  to 
  have 
  a 
  com- 
  

   mon 
  origin. 
  If 
  it 
  can 
  be 
  shown 
  conclusively, 
  

   as 
  Mr. 
  Whitney 
  believes, 
  that 
  the 
  driftless 
  

   area 
  in 
  Wisconsin 
  has 
  never 
  been 
  overflowed, 
  

   these 
  escarpments, 
  as 
  well 
  as 
  those 
  of 
  their 
  

   great 
  outliers 
  in 
  the 
  " 
  far 
  West," 
  can 
  only 
  be 
  

   due 
  to 
  the 
  same 
  agent 
  which 
  excavated 
  the 
  

   basins 
  of 
  the 
  great 
  American 
  lakes. 
  

  

  The 
  symmetrical 
  escarpments 
  of 
  the 
  Grand 
  

   Coteau 
  de 
  Missouri, 
  the 
  Riding 
  Mountain 
  and 
  

   its 
  prolongations, 
  and 
  portions 
  of 
  the 
  Niagara 
  

   escarpments, 
  are 
  probably 
  the 
  result, 
  to 
  a 
  large 
  

   extent, 
  of 
  the 
  action 
  of 
  glacial 
  rivers 
  under- 
  

   mining 
  and 
  washing 
  away 
  the 
  soft 
  strata 
  of 
  

   the 
  sedimentary 
  rocks, 
  and 
  excavating 
  in 
  ad- 
  

   vance 
  of 
  the 
  glacial 
  mass 
  itself; 
  and 
  they 
  re- 
  

   present 
  different 
  and 
  closely 
  succeeding 
  gla- 
  

   cial 
  periods 
  (the 
  Missouri 
  escarpment 
  being 
  

   older 
  than 
  that 
  of 
  the 
  Riding 
  Mountain), 
  with, 
  

   however, 
  a 
  distinct 
  geological 
  interval 
  between 
  

   them. 
  The 
  close 
  proximity 
  of 
  the 
  isothermal 
  

   curves 
  in 
  these 
  latitudes 
  to 
  the 
  general 
  direc- 
  

   tion 
  of 
  the 
  escarpments 
  of 
  the 
  Grand 
  Coteau 
  

   and 
  Riding 
  Mountain 
  is 
  a 
  very 
  interesting 
  

   and 
  important 
  feature 
  in 
  connexion 
  with 
  the 
  

   cause 
  which 
  produced 
  them. 
  

  

  * 
  See 
  my 
  ' 
  Narrative 
  of 
  the 
  Canadian 
  Exploring 
  

   Expeditions 
  of 
  1857 
  and 
  1858,' 
  vol. 
  ii. 
  p. 
  266, 
  for 
  a 
  

   notice 
  of 
  these 
  escarpments. 
  

  

  t 
  The 
  western 
  exception 
  at 
  Cypres 
  Hills 
  has 
  been 
  

   already 
  noticed. 
  Here 
  the 
  flanks 
  of 
  the 
  Rocky 
  Moun- 
  

   tains 
  are 
  approached. 
  

  

  VOL. 
  XX. 
  PART 
  I. 
  

  

  T*H 
  

  

  *£ 
  

  

  ^J 
  

  

  ■oo 
  -^ 
  

  

  !2 
  ^ 
  

  

  