﻿THE 
  GLACIAL 
  PEEIOD 
  IN 
  NORTH 
  BRITAIN. 
  

  

  333 
  

  

  the 
  interior 
  of 
  continents, 
  where 
  we 
  have 
  reason 
  to 
  believe 
  no 
  sea 
  

   has 
  entered 
  since 
  the 
  glacial 
  period. 
  

  

  I 
  have 
  fancied 
  that 
  some 
  of 
  these 
  terraces 
  may 
  have 
  originated 
  

   in 
  the 
  following 
  manner. 
  Suppose 
  the 
  channel 
  of 
  one 
  of 
  our 
  

   Highland 
  rivers 
  to 
  be 
  occupied. 
  by 
  a 
  retreating 
  glacier 
  when 
  the 
  

   climate 
  was 
  gradually 
  growing 
  milder. 
  During 
  warm 
  seasons, 
  when 
  

   much 
  snow 
  was 
  melting, 
  gravel, 
  sand, 
  and 
  other 
  debris 
  would 
  be 
  

   washed 
  down 
  the 
  hill-sides 
  and 
  lodge 
  against 
  the 
  flank 
  of 
  the 
  glacier. 
  

   The 
  rivulets 
  and 
  streams 
  woidd 
  at 
  such 
  times 
  come 
  down 
  from 
  the 
  

   neighbouring 
  heights, 
  carrying 
  with 
  them 
  much 
  matter 
  of 
  this 
  sort. 
  

   At 
  present 
  it 
  all 
  finds 
  its 
  way 
  into 
  the 
  bed 
  of 
  the 
  river 
  ; 
  but 
  when 
  the 
  

   channel 
  was 
  occupied 
  by 
  a 
  glacier 
  this 
  debris 
  would 
  be 
  arrested 
  by 
  

   the 
  mass 
  of 
  ice 
  and 
  lodge 
  in 
  the 
  depression 
  between 
  the 
  glacier 
  and 
  

   the 
  hill 
  (fig. 
  3). 
  This 
  hollow 
  would 
  therefore 
  be 
  gradually 
  filled 
  up 
  

   and 
  might 
  be 
  traversed 
  at 
  times 
  by 
  streams 
  of 
  water. 
  When 
  the 
  

   glacier 
  melted, 
  the 
  mass 
  of 
  stuff 
  resting 
  against 
  it 
  would 
  lose 
  its 
  sup- 
  

   port 
  and 
  fall 
  down 
  in 
  a 
  steep 
  slope, 
  thus 
  giving 
  rise 
  to 
  the 
  terraced 
  

   banks 
  we 
  now 
  find 
  (fig. 
  4). 
  

  

  Fig. 
  3. 
  — 
  Section 
  of 
  valley 
  with 
  glacier 
  in 
  retreat. 
  

  

  m. 
  

  

  c. 
  Glacier. 
  a 
  & 
  b. 
  Gravelly 
  debris 
  lodging 
  between 
  the 
  glacier 
  and 
  the 
  

  

  sides 
  of 
  the 
  valley. 
  

  

  Fig. 
  4. 
  — 
  Section 
  of 
  valley 
  after 
  disappearance 
  of 
  glacier. 
  

  

  

  - 
  > 
  : 
  

  

  a, 
  b. 
  Gravel 
  terraces. 
  

  

  It 
  is 
  a 
  mistake, 
  therefore, 
  to 
  refer 
  all 
  these 
  gravel 
  terraces 
  and 
  

   platforms 
  of 
  stratified 
  material 
  to 
  the 
  action 
  of 
  the 
  sea, 
  as 
  geologists 
  

   have 
  sometimes 
  done, 
  forgetting 
  that 
  the 
  sea 
  is 
  by 
  no 
  means 
  essen- 
  

   tial 
  to 
  their 
  formation. 
  The 
  total 
  absence 
  of 
  marine 
  fossils 
  ought 
  

   to 
  caution 
  us 
  against 
  such 
  hasty 
  inferences. 
  Extensive 
  beds 
  of 
  stra- 
  

   tified 
  gravel, 
  sand, 
  and 
  silt 
  seem 
  to 
  have 
  been 
  formed 
  in 
  all 
  countries 
  

   that 
  were 
  formerly 
  occupied 
  by 
  glaciers. 
  

  

  I 
  conceive 
  that 
  in 
  many 
  of 
  the 
  valleys 
  the 
  bed 
  of 
  the 
  stream 
  

   might 
  be 
  wholly 
  occupied 
  by 
  ice, 
  the 
  rivers 
  being 
  frozen 
  nearly 
  from 
  

   top 
  & 
  to 
  bottom— 
  and 
  that, 
  on 
  the 
  approach 
  of 
  summer, 
  a 
  great 
  quantity 
  

  

  