﻿THE 
  GLACIAL 
  PERIOD 
  IN 
  NORTH 
  BRITAIN. 
  329 
  

  

  the 
  ice, 
  and 
  pouring 
  off 
  its 
  surface, 
  when 
  the 
  winter 
  covering 
  of 
  snow 
  

   thawed 
  rapidly. 
  And 
  when 
  the 
  glaciers 
  of 
  the 
  Clyde 
  valley 
  were 
  

   retreating 
  to 
  the 
  high 
  grounds 
  of 
  Lanarkshire, 
  what 
  sort 
  of 
  deposits 
  

   might 
  be 
  expected 
  to 
  form 
  in 
  front 
  of 
  them 
  at 
  the 
  time 
  they 
  were 
  

   pausing 
  near 
  Carnwath 
  or 
  Carstairs 
  ? 
  Would 
  they 
  not 
  be 
  something 
  

   like 
  the 
  Kaims 
  which 
  Mr. 
  Geikie 
  has 
  described 
  as 
  occurring 
  there 
  ? 
  

  

  It 
  is 
  not 
  to 
  be 
  supposed 
  that 
  all 
  the 
  ice 
  which 
  gathered 
  over 
  the 
  

   central 
  plain 
  of 
  Ireland 
  and 
  other 
  low 
  regions 
  of 
  a 
  like 
  nature 
  pro- 
  

   ceeded 
  from 
  the 
  hills, 
  although 
  glaciers 
  descending 
  from 
  the 
  moun- 
  

   tains 
  would, 
  of 
  course, 
  contribute 
  their 
  proportion. 
  For 
  if 
  a 
  great 
  

   thickness 
  of 
  snow 
  fell, 
  year 
  after 
  year, 
  over 
  the 
  whole 
  surface 
  of 
  the 
  

   country, 
  and 
  lay 
  there 
  without 
  melting, 
  the 
  bottom 
  layers 
  would 
  be 
  

   gradually 
  converted 
  into 
  ice, 
  the 
  thickness 
  of 
  which 
  would 
  depend 
  

   upon 
  the 
  depth 
  of 
  the 
  superincumbent 
  snow. 
  In 
  course 
  of 
  time, 
  as 
  

   the 
  weight 
  of 
  the 
  mass 
  increased, 
  motion 
  would 
  commence 
  by 
  the 
  

   ice 
  yielding 
  in 
  the 
  direction 
  of 
  least 
  resistance. 
  The 
  pressure 
  in 
  

   certain 
  places 
  being 
  unequal, 
  the 
  ice 
  would 
  move 
  (very 
  slowly, 
  no 
  

   doubt) 
  towards 
  the 
  quarter 
  where 
  the 
  pressure 
  was 
  weakest. 
  This, 
  

   it 
  is 
  likely, 
  would 
  in 
  most 
  cases 
  be 
  the 
  seaward 
  opening 
  of 
  the 
  chief 
  

   valleys 
  ; 
  and 
  motion 
  having 
  once 
  begun 
  there, 
  would 
  be 
  gradually 
  

   propagated 
  into 
  the 
  interior 
  of 
  the 
  country. 
  

  

  I 
  have 
  remarked 
  that 
  these 
  Kaims 
  often 
  lie 
  across 
  valleys 
  in 
  long 
  

   sinuous 
  lines, 
  forming 
  curves 
  or 
  segments 
  of 
  a 
  circle, 
  the 
  concavity 
  

   of 
  which 
  is 
  presented 
  to 
  the 
  head 
  of 
  the 
  valley, 
  and 
  their 
  convexity 
  

   towards 
  the 
  sea 
  or 
  downward 
  end, 
  as 
  in 
  terminal 
  moraines. 
  Such 
  

   would 
  seem 
  to 
  be 
  the 
  case 
  with 
  some 
  of 
  those 
  in 
  the 
  south 
  of 
  Scot- 
  

   land. 
  For 
  example, 
  in 
  the 
  statistical 
  account 
  of 
  the 
  parish 
  of 
  

   Greenlaw, 
  in 
  Berwickshire, 
  the 
  writer 
  makes 
  mention 
  of 
  certain 
  

   gravel 
  ridges 
  or 
  Kaims, 
  which 
  he 
  says 
  are 
  " 
  disposed 
  Wee 
  a 
  horse- 
  

   shoe, 
  iviih 
  the 
  hollow 
  towards 
  the 
  hills." 
  Some 
  of 
  the 
  most 
  notable 
  

   Irish 
  Eskers 
  lie 
  in 
  lines 
  across 
  the 
  vale 
  of 
  the 
  Shannon, 
  as, 
  for 
  

   example, 
  those 
  between 
  Athlone 
  and 
  Parsonstown. 
  Another 
  sweeps 
  

   round 
  the 
  northern 
  extremity 
  of 
  the 
  Slieve 
  Bloom 
  mountains 
  ; 
  and 
  

   Sir 
  Bichard 
  Griffiths 
  tells 
  us 
  of 
  a 
  large 
  one 
  called 
  the 
  Horseshoe, 
  from 
  

   its 
  peculiar 
  shape. 
  These 
  linear 
  ridges 
  of 
  gravel 
  seem 
  to 
  be 
  most 
  

   developed 
  in 
  low 
  districts 
  away 
  from 
  the 
  mountains. 
  In 
  such 
  loca- 
  

   lities 
  the 
  ice, 
  being 
  unconfmed 
  by 
  hills, 
  would 
  spread 
  out 
  into 
  a 
  wide 
  

   cake 
  or 
  sheet. 
  The 
  time 
  of 
  their 
  formation 
  appears 
  to 
  have 
  been 
  at 
  

   the 
  close 
  of 
  the 
  glacial 
  period, 
  not 
  during 
  the 
  submergence, 
  but 
  after 
  

   it, 
  when 
  the 
  icy 
  masses 
  had 
  begun 
  their 
  final 
  retreat. 
  The 
  material 
  

   they 
  consist 
  of 
  and 
  its 
  mode 
  of 
  arrangement 
  point 
  to 
  streams 
  of 
  

   water 
  flowing 
  over 
  the 
  surface 
  of 
  the 
  glaciers, 
  and 
  washing 
  the 
  gra- 
  

   velly 
  debris 
  into 
  heaps 
  along 
  their 
  margins. 
  A 
  mass 
  of 
  gravel 
  

   reposing 
  against 
  the 
  side 
  or 
  end 
  of 
  a 
  glacier 
  would 
  lose 
  its 
  support 
  

   when 
  the 
  ice 
  melted 
  away, 
  and, 
  falling 
  down 
  in 
  a 
  slope, 
  would 
  assume 
  

   the 
  form 
  of 
  a 
  steep-sided 
  mound. 
  Glaciers 
  are 
  subject 
  to 
  oscillations, 
  

   sometimes 
  advancing, 
  sometimes 
  receding, 
  according 
  to 
  the 
  varying 
  

   nature 
  of 
  the 
  seasons. 
  Suppose 
  the 
  end 
  of 
  a 
  glacier 
  to 
  push 
  forward 
  

   into 
  a 
  sheet 
  of 
  gravel 
  lying 
  in 
  front, 
  the 
  result 
  would 
  be 
  to 
  force 
  it 
  

   up 
  into 
  a 
  mound 
  all 
  along 
  the 
  edge 
  of 
  the 
  ice 
  (see 
  figs. 
  1 
  <fc 
  2). 
  

  

  