﻿464 
  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [June 
  22, 
  

  

  reached 
  when 
  the 
  movement 
  there 
  would 
  cease, 
  and 
  the 
  glacier 
  

   would 
  be 
  discharged 
  over, 
  and 
  not 
  through, 
  the 
  ice 
  -filled 
  hollow. 
  In 
  

   the 
  Lago 
  Maggiore 
  the 
  ice, 
  according 
  to 
  Prof. 
  Ramsay's 
  theory, 
  

   would 
  have 
  at 
  its 
  exit 
  to 
  ascend 
  a 
  slope 
  of 
  five 
  degrees 
  from 
  its 
  

   deepest 
  part 
  ; 
  it 
  is 
  therefore 
  contended 
  that 
  in 
  such 
  a 
  case 
  the 
  de- 
  

   pression 
  would 
  be 
  simply 
  filled 
  up, 
  the 
  glacier 
  passing 
  over 
  it. 
  

  

  Sir 
  C. 
  Lyell* 
  considers 
  that 
  the 
  great 
  lake-basins 
  of 
  Switzerland 
  

   have 
  not 
  been 
  scooped 
  out, 
  but 
  that 
  they 
  are 
  all 
  due 
  to 
  unequal 
  

   movements 
  of 
  upheaval 
  and 
  subsidence 
  during 
  the 
  great 
  oscillations 
  

   of 
  level 
  since 
  the 
  commencement 
  of 
  the 
  glacial 
  epoch. 
  But 
  whether 
  

   or 
  not 
  this 
  theory 
  is 
  applicable 
  to 
  the 
  Swiss 
  and 
  Italian 
  lake-basins, 
  

   it 
  does 
  not 
  apply 
  to 
  those 
  of 
  British 
  North 
  America 
  and 
  of 
  Northern 
  

   Europe, 
  where 
  there 
  are 
  lakes 
  of 
  all 
  sizes, 
  increasing 
  in 
  number 
  

   northwards, 
  and 
  in 
  association 
  with, 
  and 
  evidently 
  forming 
  part 
  of, 
  

   the 
  evidences 
  of 
  glaciation. 
  Further, 
  it 
  does 
  not 
  explain 
  the 
  pal- 
  

   pable 
  connexion 
  of 
  rock-basins 
  with 
  glacial 
  action 
  ; 
  and 
  if 
  it 
  cannot 
  

   be 
  admitted 
  that 
  there 
  have 
  been 
  unequal 
  movements 
  of 
  upheaval 
  

   and 
  subsidence 
  for 
  the 
  innumerable 
  rock-basins 
  of 
  glaciated 
  coun- 
  

   tries, 
  no 
  other 
  solution 
  remains 
  than 
  that 
  they 
  have 
  been 
  eroded, 
  

   and 
  we 
  naturally 
  look 
  to 
  ice 
  as 
  the 
  agent 
  of 
  erosion. 
  

  

  The 
  author 
  accepts 
  Prof. 
  Ramsay's 
  theory 
  as 
  being 
  sufficient 
  to 
  

   solve 
  the 
  main 
  difficulty, 
  (1) 
  because 
  of 
  the 
  immense 
  depth 
  of 
  some 
  

   of 
  the 
  basins 
  ; 
  (2) 
  because 
  the 
  grinding 
  power 
  augments 
  by 
  increased 
  

   depth, 
  even 
  should 
  the 
  ice 
  be 
  dammed 
  up, 
  as 
  is 
  shown 
  by 
  the 
  issue 
  

   of 
  streams 
  of 
  water, 
  mud, 
  and 
  gravel 
  from 
  the 
  bottom 
  of 
  glaciers, 
  

   excepting 
  those 
  of 
  the 
  higher 
  parts 
  of 
  the 
  Alps, 
  which 
  result 
  from 
  

   the 
  melting 
  of 
  the 
  ice 
  at 
  the 
  upper 
  surface 
  of 
  the 
  glacier, 
  and 
  espe- 
  

   cially 
  a 
  not 
  inconsiderable 
  portion 
  from 
  that 
  of 
  the 
  lower 
  surface 
  

   next 
  the 
  earth, 
  in 
  consequence 
  of 
  abrasion. 
  

  

  He 
  applies 
  these 
  facts 
  to 
  the 
  consideration 
  of 
  the 
  question 
  of 
  a 
  

   depression 
  in 
  the 
  pathway 
  of 
  a 
  glacier 
  which 
  has 
  reached 
  such 
  a 
  

   depth 
  that 
  the 
  ice 
  is 
  not 
  bodily 
  discharged, 
  but 
  simply 
  fills 
  it. 
  The 
  

   ice 
  of 
  the 
  bottom 
  and 
  sides 
  of 
  the 
  hollow 
  would 
  be 
  slowly 
  melted 
  by 
  

   the 
  earth's 
  heat, 
  and 
  as 
  the 
  ice 
  at 
  the 
  lower 
  end 
  of 
  the 
  basin 
  melted, 
  

   the 
  whole 
  mass 
  would 
  be 
  pushed 
  along 
  by 
  the 
  thrust 
  of 
  the 
  moving 
  

   glacier 
  above 
  it. 
  The 
  water 
  coming 
  down 
  the 
  bottom 
  of 
  the 
  glacier 
  

   from 
  above 
  would 
  pour 
  into 
  the 
  crevices 
  at 
  the 
  upper 
  end 
  ; 
  it 
  would 
  

   pass 
  underneath 
  and 
  be 
  forced 
  out 
  at 
  the 
  lower 
  end, 
  carrying 
  with 
  

   it 
  the 
  mud 
  produced 
  by 
  the 
  crushing 
  of 
  the 
  rock, 
  through 
  the 
  grind- 
  

   ing 
  along 
  the 
  floor 
  of 
  the 
  glacier 
  by 
  the 
  ice 
  as 
  it 
  melted 
  at 
  the 
  lower 
  

   end 
  of 
  the 
  basin. 
  The 
  water 
  coming 
  from 
  above 
  would 
  assist 
  in 
  

   melting 
  the 
  ice, 
  especially 
  in 
  summer 
  ; 
  but 
  its 
  most 
  important 
  effect 
  

   would 
  be 
  the 
  scouring 
  out 
  of 
  the 
  bottom 
  of 
  the 
  basin, 
  so 
  that 
  an 
  ever 
  

   clean 
  face 
  of 
  rock 
  would 
  be 
  presented 
  to 
  the 
  huge 
  tool 
  operating 
  upon 
  

   it. 
  This 
  action 
  would 
  resemble 
  the 
  production 
  of 
  pot-holes 
  on 
  our 
  

   coasts, 
  and 
  in 
  the 
  hard 
  beds 
  of 
  many 
  rivers, 
  by 
  the 
  moving 
  water 
  

   turning 
  a 
  stone 
  in 
  a 
  hollow, 
  and 
  so 
  gradually 
  deepening 
  it. 
  A 
  lake- 
  

   basin 
  is 
  an 
  immense 
  pot-hole, 
  in 
  which 
  the 
  mass 
  of 
  ice 
  that 
  filled 
  it 
  

  

  * 
  Antiquity 
  of 
  Man, 
  p. 
  31G. 
  

  

  