﻿THE 
  GIACIAL 
  PERIOD 
  IN 
  NORTH 
  BRITAIN. 
  331 
  

  

  comparatively 
  sheltered 
  places. 
  The 
  material 
  of 
  which 
  these 
  ridges 
  

   are 
  usually 
  composed 
  is 
  of 
  a 
  loose 
  incoherent 
  nature 
  ; 
  and 
  the 
  present 
  

   slope 
  of 
  their 
  sides 
  is 
  often 
  as 
  steep 
  as 
  what 
  the 
  sand 
  and 
  pebbles 
  can 
  

   He 
  at. 
  Now 
  the 
  angle 
  of 
  repose 
  of 
  such 
  stuff 
  in 
  strongly 
  agitated 
  

   water 
  is 
  much 
  less 
  than 
  it 
  is 
  in 
  air. 
  Long 
  narrow 
  mounds 
  sloping 
  

   steeply 
  on 
  both 
  sides 
  could 
  not 
  have 
  preserved 
  this 
  form 
  when 
  lashed 
  

   by 
  the 
  waves 
  and 
  breakers 
  ; 
  and 
  I 
  therefore 
  maintain 
  that 
  when 
  the 
  

   movement 
  of 
  emergence 
  brought 
  them 
  near 
  the 
  surface 
  of 
  the 
  water 
  

   they 
  would 
  have 
  been 
  levelled 
  to 
  the 
  angle 
  of 
  repose 
  which 
  gravel 
  

   beaches 
  usually 
  exhibit. 
  

  

  A 
  large 
  iceberg 
  running 
  aground 
  amongst 
  gravel 
  might 
  cause 
  

   mounds 
  like 
  the 
  Kaims, 
  but 
  this 
  could 
  take 
  place 
  only 
  in 
  water 
  of 
  

   considerable 
  depth. 
  Heavy 
  packs 
  of 
  ice 
  driven 
  forcibly 
  ashore 
  might 
  

   perhaps 
  also 
  give 
  rise 
  to 
  similar 
  ridges, 
  although 
  scarcely, 
  I 
  should 
  

   think, 
  of 
  such 
  great 
  dimensions. 
  But 
  unless 
  the 
  mounds 
  were 
  formed 
  

   high 
  up 
  on 
  the 
  beach 
  beyond 
  the 
  extreme 
  limit 
  of 
  the 
  tide 
  they 
  would 
  

   be 
  levelled 
  again 
  by 
  the 
  return 
  of 
  the 
  waves. 
  If 
  formed 
  in 
  this 
  way 
  

   they 
  should 
  also 
  contain 
  some 
  littoral 
  shells, 
  and 
  their 
  curves 
  ought, 
  

   as 
  a 
  rule, 
  to 
  present 
  the 
  convex 
  side 
  to 
  the 
  land, 
  and 
  not 
  to 
  the 
  sea. 
  

   The 
  sea 
  cutting 
  into 
  the 
  face 
  of 
  a 
  bank 
  may 
  no 
  doubt 
  cause 
  a 
  steep 
  

   slope 
  on 
  one 
  side, 
  but 
  not 
  a 
  narrow 
  crooked 
  ridge, 
  steep 
  on 
  both 
  sides 
  

   like 
  a 
  railway 
  embankment. 
  

  

  The 
  Swedish 
  Osar* 
  and 
  the 
  American 
  Horsebacks 
  seem 
  to 
  resemble 
  

   the 
  Kaims 
  and 
  Eskers 
  in 
  their 
  linear 
  character, 
  gravelly 
  composition, 
  

   steep 
  sides, 
  and 
  want 
  of 
  fossils. 
  Sir 
  Charles 
  Lyell, 
  in 
  his 
  account 
  

   of 
  the 
  Swedish 
  Osar, 
  says 
  he 
  met 
  with 
  only 
  one 
  instance 
  of 
  shells 
  

   occurring 
  in 
  them, 
  viz. 
  in 
  the 
  top 
  of 
  a 
  ridge 
  near 
  the 
  Castle 
  of 
  

   Upsala 
  ; 
  but 
  as 
  the 
  species 
  he 
  mentions 
  consist 
  of 
  edible 
  mollusca 
  

   (mussels, 
  cockles, 
  and 
  periwinkles), 
  there 
  may 
  be 
  a 
  doubt 
  as 
  to 
  

   whether 
  their 
  presence 
  in 
  this 
  very 
  exceptional 
  instance 
  has 
  not 
  been 
  

   due 
  to 
  some 
  accidental 
  cause. 
  Agassiz, 
  in 
  his 
  description 
  of 
  the 
  

   glacial 
  phenomena 
  of 
  Maine, 
  says 
  the 
  horsebacks 
  " 
  are 
  unquestionably 
  

   of 
  a 
  moraine 
  nature, 
  and 
  yet 
  they 
  are 
  not 
  moraines 
  in 
  the 
  ordinary 
  

   sense 
  of 
  the 
  term." 
  Some 
  of 
  these 
  horsebacks 
  run 
  from 
  north 
  to 
  

   south 
  ; 
  but 
  occasionally 
  they 
  trend 
  from 
  east 
  to 
  west. 
  " 
  This," 
  he 
  

   says, 
  " 
  is 
  the 
  case 
  where 
  a 
  morainic 
  accumulation 
  of 
  loose 
  materials 
  

   may 
  have 
  been 
  pushed 
  forward 
  along 
  the 
  margin, 
  in 
  front 
  of 
  an 
  ex- 
  

   tensive 
  sheet 
  of 
  ice 
  moving 
  southward, 
  and 
  then 
  left 
  unchanged 
  by 
  

   the 
  subsequent 
  retreat 
  northward 
  of 
  the 
  whole 
  mass. 
  I 
  conceive 
  

   that 
  such 
  horsebacks 
  running 
  east 
  and 
  west 
  may 
  be 
  compared 
  to 
  

   terminal 
  moraines, 
  which, 
  as 
  is 
  is 
  well 
  known, 
  owe 
  their 
  origin 
  to 
  

   oscillations 
  of 
  the 
  front 
  end 
  of 
  a 
  glacier 
  pushing 
  forward 
  a 
  mass 
  of 
  

   loose 
  materials, 
  thus 
  throwing 
  it 
  up 
  into 
  a 
  transverse 
  ridge, 
  and 
  then 
  

   melting 
  away 
  to 
  some 
  point 
  further 
  back." 
  (Agassiz 
  in 
  the 
  Atlantic 
  

   Monthly, 
  Feb. 
  & 
  March, 
  1867). 
  He 
  makes 
  no 
  mention 
  of 
  any 
  

   marine 
  fossils 
  occurring 
  in 
  these 
  horseback 
  ridges, 
  and 
  does 
  not 
  seem 
  

   to 
  think 
  that 
  the 
  sea 
  was 
  concerned 
  in 
  their 
  formation. 
  I 
  may 
  also 
  

   mention 
  that 
  some 
  of 
  these 
  American 
  ridges 
  occur 
  in 
  the 
  region 
  of 
  

  

  * 
  Under 
  the 
  name 
  of 
  Osar 
  it, 
  would 
  seem 
  that 
  deposits 
  of 
  more 
  than 
  one 
  kind 
  

   have 
  been 
  described, 
  perhaps 
  of 
  different 
  ages 
  and 
  various 
  modes 
  of 
  formation. 
  

  

  