﻿486 
  T. 
  <*• 
  BONUEY 
  OK 
  THE 
  GLACIER-EROSION 
  

  

  rock) 
  serves 
  as 
  a 
  foundation-stone 
  for 
  the 
  tower. 
  Here, 
  then, 
  in 
  the 
  

   very 
  path 
  of 
  the 
  glacier, 
  we 
  have 
  these 
  ridgy 
  hills, 
  which 
  the 
  ice 
  has 
  

   but 
  superficially 
  moulded. 
  How, 
  then, 
  could 
  it 
  excavate 
  the 
  lake- 
  

   basin 
  ? 
  The 
  contours 
  also 
  of 
  the 
  ground 
  all 
  round 
  the 
  head 
  of 
  the 
  

   lake 
  seemed 
  to 
  be 
  wholly 
  uninfluenced 
  by 
  any 
  great 
  ice-stream 
  

   acting 
  from 
  the 
  lake. 
  I 
  could 
  therefore 
  come 
  to 
  no 
  other 
  con- 
  

   clusion 
  than 
  that 
  the 
  glacier 
  in 
  its 
  passage 
  has 
  but 
  slightly 
  altered 
  the 
  

   physical 
  features 
  of 
  the 
  district, 
  which 
  all 
  spoke 
  of 
  the 
  usual 
  sub- 
  

   aerial 
  agencies. 
  

  

  I 
  must 
  now 
  call 
  attention 
  to 
  a 
  point 
  perhaps 
  of 
  some 
  importance. 
  

   From 
  the 
  former 
  head 
  of 
  the 
  lake, 
  near 
  Chiavenna, 
  to 
  its 
  end 
  at 
  Lecco, 
  

   is 
  about 
  thirty-four 
  miles. 
  The 
  fall 
  is 
  considerably 
  less 
  than 
  300 
  

   feet 
  ; 
  how 
  much, 
  it 
  is 
  difficult 
  to 
  say 
  exactly. 
  Suppose, 
  then, 
  that 
  

   all 
  which 
  is 
  at 
  the 
  present 
  time 
  under 
  water 
  is 
  the 
  result 
  of 
  glacial 
  

   excavation, 
  and 
  that 
  the 
  slopes 
  of 
  the 
  valley 
  above 
  lake-level 
  are 
  

   mainly 
  (as 
  I 
  think 
  all 
  who 
  know 
  the 
  district 
  will 
  admit) 
  the 
  result 
  

   of 
  river 
  and 
  subaerial 
  denudation 
  ; 
  it 
  follows 
  that 
  the 
  stream 
  had 
  a 
  

   fall 
  of 
  considerably 
  less 
  than 
  1 
  in 
  600. 
  I 
  doubt 
  whether 
  this 
  would 
  

   be 
  sufficient 
  for 
  eroding 
  a 
  valley 
  of 
  this 
  character 
  in 
  such 
  hard 
  rocks. 
  

  

  Again, 
  the 
  height 
  of 
  Chiavenna 
  is 
  1040 
  feet 
  above 
  the 
  sea 
  ; 
  the 
  

   deepest 
  soundings 
  in 
  the 
  lake 
  are 
  1341 
  feet, 
  or 
  642 
  below 
  the 
  sea 
  ; 
  

   and 
  the 
  height 
  of 
  the 
  hills 
  above 
  Como 
  is 
  about 
  900 
  feet. 
  To 
  what 
  

   are 
  we 
  to 
  attribute 
  an 
  excavating-power 
  so 
  enormous 
  ? 
  A 
  more 
  

   unfavourable 
  position 
  for 
  the 
  exercise 
  of 
  any 
  erosive 
  action 
  on 
  the 
  

   part 
  of 
  a 
  glacier 
  could 
  hardly 
  be 
  conceived. 
  On 
  the 
  other 
  hand, 
  

   supposing 
  this 
  enormous 
  basin 
  to 
  have 
  been 
  hollowed 
  out 
  by 
  ice, 
  

   ought 
  not 
  the 
  rocks 
  all 
  around 
  to 
  bear 
  the 
  most 
  marked 
  indications 
  

   of 
  the 
  passage 
  of 
  this 
  powerful 
  agent 
  ? 
  ought 
  not 
  those 
  ridges 
  of 
  

   hills 
  above 
  Como, 
  which 
  lie 
  right 
  in 
  its 
  path, 
  to 
  have 
  had 
  their 
  

   sharp 
  summits 
  planed 
  flat 
  '? 
  or 
  did 
  the 
  glacier, 
  when 
  it 
  had 
  crawled 
  

   up 
  their 
  steep 
  slopes, 
  tumble, 
  like 
  an 
  exhausted 
  caterpillar, 
  helpless 
  

   down 
  the 
  other 
  side? 
  

  

  I 
  pass 
  now 
  to 
  what 
  are 
  often 
  called 
  the 
  Italian 
  valleys 
  of 
  Monte 
  

   Eosa. 
  Here 
  my 
  first 
  care 
  was 
  to 
  examine 
  the 
  Lake 
  of 
  Orta, 
  which 
  

   resembles 
  the 
  Como 
  arm 
  in 
  being 
  separated 
  from 
  the 
  Italian 
  plain 
  

   by 
  a 
  low 
  ridge, 
  and 
  in 
  discharging 
  its 
  waters 
  from 
  its 
  northern 
  end. 
  

   These 
  hills 
  are 
  a 
  quartzose 
  felsite 
  ; 
  and 
  the 
  eastern 
  bank 
  of 
  the 
  lake 
  

   consists 
  chiefly 
  of 
  schists. 
  The 
  most 
  conspicuous 
  of 
  the 
  felsite 
  hills, 
  

   that 
  on 
  which 
  the 
  Torre 
  de 
  Baccione 
  stands, 
  has 
  a 
  little 
  valley 
  on 
  

   each 
  side, 
  of 
  which 
  the 
  eastern 
  has 
  formed 
  a 
  distinct 
  delta. 
  From 
  

   this 
  point 
  the 
  lake 
  is 
  enclosed 
  by 
  a 
  generally 
  steep 
  bank 
  or 
  terrace, 
  

   perhaps 
  100 
  feet 
  high, 
  above 
  which 
  rather 
  steep 
  slopes 
  rise 
  up 
  to 
  the 
  

   plateau 
  on 
  which 
  stands 
  the 
  village 
  of 
  Gozzano. 
  A 
  glacier 
  has 
  evi- 
  

   dently 
  passed 
  over 
  this 
  barrier, 
  as 
  moraine 
  heaps 
  of 
  great 
  perched 
  

   blocks 
  of 
  granite, 
  gneiss, 
  and 
  schists 
  are 
  strewn 
  about. 
  In 
  the 
  slope 
  

   above 
  the 
  lake, 
  stratified 
  drift 
  is 
  seen 
  ; 
  it 
  is 
  considerably 
  below 
  the 
  

   moraines 
  ; 
  and 
  perched 
  blocks 
  lie 
  on 
  the 
  surface 
  of 
  the 
  bank 
  all 
  

   about. 
  If 
  these 
  have 
  not 
  been 
  washed 
  out 
  of 
  some 
  upper 
  layer 
  of 
  

   soil 
  or 
  rolled 
  from 
  above, 
  the 
  glacier 
  must 
  have 
  passed 
  over 
  this 
  

   drift. 
  

  

  