﻿THE 
  GLACIER-EROSION 
  THEORY 
  OP 
  LAKE-BASINS. 
  479 
  

  

  36. 
  Notes 
  on 
  the 
  Upper 
  Engadine 
  and 
  the 
  Italian 
  Valleys 
  of 
  

   Monte 
  Rosa, 
  and 
  their 
  Relation 
  to 
  the 
  Glacier-erosion 
  Theory 
  

   o/Lake-basins. 
  By 
  the 
  Rev. 
  T. 
  G. 
  Bonney, 
  M.A., 
  F.G.S., 
  Fellow 
  

   and 
  Tutor 
  of 
  St. 
  John's 
  College, 
  Cambridge. 
  (Read 
  May27, 
  1874.) 
  

  

  This 
  paper 
  may 
  be 
  regarded 
  as 
  a 
  continuation 
  of 
  two 
  which 
  I 
  have 
  

   already 
  had 
  the 
  honour 
  to 
  communicate 
  to 
  the 
  Geological 
  Society 
  * 
  ; 
  

   and 
  with 
  a 
  view 
  of 
  preventing 
  misapprehension, 
  I 
  think 
  it 
  will 
  be 
  

   well 
  to 
  state 
  clearly 
  what 
  I 
  am 
  seeking 
  to 
  demonstrate, 
  and 
  the 
  

   mode 
  in 
  which 
  I 
  am 
  endeavouring 
  to 
  effect 
  my 
  purpose. 
  

  

  As 
  I 
  have 
  already 
  stated, 
  I 
  am 
  unable 
  to 
  accept 
  the 
  theory 
  which 
  

   was 
  put 
  forward 
  by 
  Professor 
  Ramsay 
  in 
  a 
  paper 
  communicated 
  to 
  

   this 
  Society 
  f, 
  a 
  theory 
  which 
  attributes 
  the 
  existence 
  of 
  the 
  various 
  

   Alpine 
  lake-basins 
  mainly 
  to 
  the 
  erosive 
  action 
  of 
  the 
  glaciers 
  by 
  

   which 
  they 
  were 
  once 
  occupied. 
  I 
  do 
  not 
  deny 
  the 
  possibility 
  of 
  

   some 
  lake-basins 
  being 
  the 
  result 
  of 
  glacial 
  erosion, 
  or 
  of 
  others 
  

   being 
  considerably 
  modified 
  by 
  it 
  ; 
  the 
  position 
  which 
  I 
  am 
  en- 
  

   deavouring 
  to 
  maintain 
  is 
  that 
  none 
  of 
  the 
  greater 
  Alpine 
  lake- 
  

   basins 
  has 
  been 
  primarily 
  so 
  formed, 
  or 
  indeed 
  has 
  undergone 
  

   any 
  important 
  secondary 
  modification. 
  I 
  will 
  add 
  that 
  all 
  the 
  op- 
  

   portunities 
  which 
  I 
  have 
  had 
  of 
  examination 
  of 
  lake-basins 
  in 
  this 
  

   and 
  other 
  countries 
  have 
  suggested 
  to 
  me 
  serious 
  doubts 
  as 
  to 
  the 
  

   excavating 
  power 
  of 
  glaciers 
  ; 
  and, 
  notwithstanding 
  the 
  weighty 
  

   arguments 
  wbich 
  have 
  been 
  advanced 
  in 
  favour 
  of 
  this 
  theory 
  in 
  

   more 
  northern 
  regions 
  J, 
  I 
  am 
  still 
  disposed 
  to 
  believe, 
  from 
  what 
  I 
  

   have 
  seen, 
  that 
  it 
  is 
  only 
  under 
  very 
  exceptional 
  circumstances 
  that 
  

   they 
  can 
  in 
  any 
  proper 
  sense 
  of 
  the 
  word 
  excavate 
  a 
  rock-basin. 
  

  

  The 
  principle 
  which 
  has 
  directed 
  my 
  mode 
  of 
  operation 
  has 
  been 
  

   the 
  following 
  : 
  — 
  If 
  a 
  key 
  is 
  to 
  be 
  a 
  master-key 
  to 
  a 
  number 
  of 
  locks, 
  

   it 
  must 
  open 
  them 
  all 
  ; 
  so 
  if 
  a 
  theory 
  is 
  to 
  be 
  accepted 
  as 
  a 
  general 
  

   one, 
  we 
  must 
  apply 
  it 
  to 
  as 
  many 
  instances 
  as 
  possible. 
  

  

  In 
  order 
  then 
  to 
  test 
  this 
  theory 
  of 
  glacier 
  erosion, 
  I 
  have, 
  year 
  

   by 
  year, 
  travelled 
  over 
  different 
  portions 
  of 
  the 
  Alps 
  (as 
  well 
  as 
  

   other 
  mountain-regions) 
  constantly 
  endeavouring 
  to 
  apply 
  this 
  and 
  

   other 
  theories 
  to 
  the 
  physiography 
  of 
  the 
  country, 
  and 
  to 
  ascertain 
  

   which 
  appears 
  to 
  satisfy 
  best 
  the 
  difficulties 
  of 
  each 
  problem. 
  

  

  It 
  seemed 
  to 
  me 
  that, 
  viewing 
  the 
  nature 
  of 
  the 
  theory, 
  it 
  could 
  

   be 
  better 
  tested 
  in 
  this 
  way 
  than 
  by 
  any 
  minute 
  examination 
  of 
  a 
  

   single 
  district. 
  When 
  any 
  advantage 
  appeared 
  likely 
  to 
  accrue 
  I 
  

   have 
  done 
  this 
  ; 
  but, 
  as 
  the 
  fact 
  of 
  the 
  passage 
  and 
  the 
  general 
  

   direction 
  of 
  the 
  flow 
  of 
  the 
  glaciers 
  over 
  certain 
  regions 
  are 
  not 
  dis- 
  

   pixted, 
  I 
  have 
  not 
  thought 
  it 
  worth 
  while 
  to 
  burden 
  either 
  this 
  com- 
  

   munication 
  or 
  my 
  note-book 
  with 
  the 
  results 
  of 
  minor 
  observations, 
  

   especially 
  when 
  they 
  led 
  to 
  no 
  important 
  conclusions. 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxvii. 
  p. 
  312, 
  and 
  vol. 
  xxix. 
  p. 
  382. 
  

  

  t 
  Ibid. 
  vol. 
  xviii. 
  p. 
  185. 
  

  

  I 
  See 
  especially 
  Mr. 
  J. 
  G-eikie's 
  new 
  work, 
  ' 
  The 
  Great 
  Ice 
  Age.' 
  

  

  