﻿484 
  T. 
  G. 
  BON-NET 
  OS 
  THE 
  GLACIER-EKOSION 
  

  

  down 
  its 
  western 
  shore, 
  bears 
  the 
  marks 
  of 
  a 
  glacier 
  that 
  has 
  de- 
  

   scended 
  it 
  ; 
  and, 
  in 
  a 
  word, 
  looking 
  down 
  the 
  lake, 
  the 
  rocks 
  are 
  

   rounded 
  by 
  the 
  glaciers 
  which 
  once 
  descended 
  from 
  the 
  several 
  

   mountain-sides 
  ; 
  but 
  there 
  is 
  nothing 
  to 
  suggest 
  any 
  scooping 
  action, 
  

   no 
  great 
  modification 
  of 
  the 
  outline 
  of 
  the 
  lake 
  corresponding 
  to 
  

   the 
  entrance 
  of 
  a 
  glacier 
  valley, 
  while 
  the 
  existence 
  of 
  one 
  or 
  

   two 
  promontories 
  is 
  difficult 
  to 
  explain 
  on 
  any 
  theory 
  of 
  glacial 
  

   erosion. 
  

  

  I 
  think, 
  therefore, 
  we 
  are 
  justified 
  in 
  concluding 
  : 
  — 
  

  

  That 
  this 
  lake-basin 
  has 
  no 
  immediate 
  connexion 
  with 
  any 
  of 
  the 
  

   lateral 
  valleys. 
  

  

  That 
  it 
  once 
  extended 
  to 
  within 
  a 
  few 
  dozen 
  yards 
  of 
  the 
  summit 
  

   of 
  the 
  pass, 
  and 
  that 
  some 
  of 
  its 
  drainage 
  was 
  discharged 
  into 
  the 
  

   Yal 
  Bregaglia. 
  

  

  That 
  the 
  lake-basin 
  (and 
  the 
  above-named 
  gorge) 
  is 
  anterior 
  to 
  a 
  

   period 
  when 
  the 
  Forno 
  glacier 
  was 
  of 
  enormous 
  thickness. 
  

  

  That, 
  considering 
  the 
  slight 
  descent 
  of 
  this 
  uppermost 
  trough 
  of 
  

   the 
  Inn 
  valley, 
  no 
  glacier 
  formed 
  on 
  the 
  north 
  side 
  of 
  the 
  Maloya 
  Pass 
  

   could 
  have 
  excavated 
  the 
  Silser 
  See. 
  

  

  Hence 
  that 
  the 
  basin 
  and 
  all 
  the 
  other 
  physical 
  features 
  of 
  the 
  

   head 
  of 
  the 
  Inn 
  valley 
  are 
  anterior 
  to 
  the 
  glacial 
  epoch, 
  and 
  have 
  not 
  

   been 
  much 
  altered 
  during 
  it 
  or 
  since. 
  

  

  The 
  first 
  thousand 
  feet 
  of 
  descent 
  from 
  the 
  Maloya 
  Pass 
  into 
  the 
  

   Val 
  Bregaglia 
  is 
  very 
  steep, 
  its 
  head 
  almost 
  meriting 
  the 
  title 
  of 
  a 
  

   cirque. 
  The 
  descent 
  after 
  that 
  is 
  generally 
  gradual, 
  with 
  the 
  excep- 
  

   tion 
  of 
  a 
  sudden 
  fall 
  between 
  Casaccia 
  and 
  Vico 
  Soprano, 
  corre- 
  

   sponding 
  with 
  the 
  entrance 
  of 
  the 
  Albigna 
  torrent. 
  The 
  usual 
  signs 
  

   of 
  glacial 
  action, 
  perched 
  blocks, 
  roches 
  moutonnees, 
  and 
  large 
  

   moraines, 
  may 
  be 
  detected 
  at 
  intervals 
  all 
  the 
  way 
  down 
  to 
  Chia- 
  

   venna. 
  Among 
  the 
  blocks 
  porphyritic 
  granite 
  and 
  coarse 
  gneiss 
  are 
  

   conspicuous, 
  evidently 
  brought 
  down 
  by 
  the 
  tributary 
  glaciers 
  from 
  

   the 
  left 
  bank 
  ; 
  the 
  rock 
  in 
  the 
  bed 
  of 
  the 
  valley 
  consists 
  of 
  mica- 
  schist 
  

   (in 
  one 
  place 
  so 
  fissile 
  as 
  to 
  be 
  quarried 
  for 
  roofing-slates) 
  and 
  

   hornblendic 
  schists. 
  The 
  valley 
  is 
  generally 
  narrow, 
  and 
  Y-shaped 
  ; 
  

   and 
  the 
  ice-marks 
  may 
  be 
  seen 
  sometimes 
  only 
  a 
  short 
  distance 
  above 
  

   the 
  torrent. 
  They 
  are 
  very 
  conspicuous 
  after 
  passing 
  Piuro, 
  near 
  

   the 
  opening 
  of 
  the 
  valley, 
  just 
  above 
  Chiavenna, 
  where 
  the 
  roches 
  

   moutonnees 
  are 
  magnificent, 
  and 
  the 
  characteristic 
  ice-marks 
  may 
  be 
  

   traced 
  within 
  some 
  twenty 
  feet 
  above 
  the 
  river. 
  One 
  example, 
  on 
  

   the 
  left 
  bank, 
  about 
  a 
  mile 
  from 
  Chiavenna, 
  is 
  very 
  interesting. 
  A 
  

   steep 
  knoll 
  of 
  rock, 
  some 
  40' 
  high, 
  is 
  divided 
  by 
  a 
  narrow 
  gap 
  from 
  

   a 
  cliff 
  some 
  50' 
  high, 
  which 
  forms 
  part 
  of 
  the 
  range 
  rising 
  on 
  the 
  

   left 
  bank 
  of 
  the 
  valley. 
  The 
  lowest 
  part 
  of 
  this 
  gap 
  is 
  perhaps 
  30 
  

   yards 
  above 
  the 
  (Mera) 
  torrent. 
  The 
  rock 
  is 
  a 
  dark 
  (serpentinous 
  ?) 
  

   schist 
  ; 
  the 
  whole 
  of 
  the 
  knoll 
  and 
  cliff 
  are 
  magnificently 
  glaciated, 
  

   the 
  striae 
  on 
  the 
  latter 
  being 
  very 
  conspicuous. 
  This 
  place, 
  there- 
  

   fore, 
  shows 
  (1) 
  that 
  the 
  base 
  of 
  the 
  old 
  Bregaglia 
  glacier 
  was 
  here 
  

   at 
  no 
  great 
  height 
  above 
  the 
  present 
  stream 
  ; 
  (2) 
  that 
  this 
  gap 
  was 
  

   either 
  excavated 
  by 
  it 
  or 
  anterior 
  to 
  it. 
  As 
  I 
  cannot 
  conceive 
  the 
  

   possibility 
  of 
  a 
  glacier 
  cutting 
  out 
  such 
  a 
  gap, 
  I 
  am 
  forced 
  to 
  con- 
  

  

  