﻿190 
  D. 
  MACKINTOSH 
  ON 
  HIGH-LEVEL 
  

  

  3. 
  forced 
  up 
  by 
  the 
  grounding 
  of 
  floating 
  Ice 
  ? 
  — 
  It 
  is 
  obvious 
  that 
  

   floating 
  ice, 
  either 
  local 
  or 
  from 
  a 
  distance, 
  on 
  being 
  intercepted 
  by 
  

   rising 
  ground, 
  might 
  have 
  forced 
  up 
  previously 
  deposited 
  gravel 
  and 
  

   sand, 
  and 
  at 
  the 
  same 
  time 
  contributed 
  its 
  load 
  of 
  stones, 
  so 
  as 
  to 
  

   leave 
  a 
  knoll-shaped 
  elevation 
  *. 
  

  

  4. 
  Accumulated 
  by 
  currents 
  ? 
  — 
  It 
  is 
  the 
  general 
  belief 
  of 
  geologists 
  

   that 
  the 
  Irish 
  eskers 
  were 
  piled 
  up 
  by 
  currents 
  in 
  a 
  shallow 
  sea 
  ; 
  and 
  

   the 
  same 
  agency, 
  in 
  all 
  probability, 
  accumulated 
  the 
  mounds 
  of 
  gravel 
  

   and 
  sand 
  often 
  seen 
  at 
  low 
  levels 
  in 
  the 
  N.W. 
  of 
  England 
  and 
  E. 
  of 
  

   Wales 
  f 
  . 
  As 
  an 
  example 
  of 
  conditions 
  which 
  may 
  have 
  been 
  favour- 
  

   able 
  to 
  accumulation 
  by 
  currents 
  in 
  the 
  area 
  under 
  consideration, 
  

   it 
  may 
  be 
  stated 
  that 
  when 
  the 
  sea, 
  through 
  the 
  sinking 
  of 
  the 
  land, 
  

   reached 
  a 
  height 
  of 
  what 
  is 
  now 
  1250 
  feet 
  above 
  its 
  present 
  surface- 
  

   level, 
  its 
  depth 
  must 
  have 
  been 
  about 
  100 
  feet 
  at 
  what 
  is 
  now 
  the 
  

   level 
  of 
  the 
  Erondeg 
  shelly 
  gravel 
  knoll, 
  so 
  as 
  to 
  leave 
  a 
  vertical 
  

   range 
  of 
  100 
  feet 
  for 
  the 
  play 
  of 
  currents 
  along 
  shore 
  or 
  in 
  other 
  

   directions 
  J. 
  In 
  many 
  of 
  the 
  knolls 
  there 
  are 
  clear 
  traces 
  of 
  

   current-bedding, 
  while 
  the 
  paucity 
  of 
  well-striated 
  stones 
  and 
  of 
  

   contorted 
  laminae 
  would 
  seem 
  to 
  militate 
  against 
  the 
  idea 
  of 
  the 
  

   knolls 
  having 
  been 
  accumulated 
  by 
  the 
  stranding 
  of 
  floating 
  ice. 
  

   It 
  ought 
  likewise 
  to 
  be 
  remembered 
  that 
  many 
  of 
  the 
  larger 
  knolls 
  

   (N.W. 
  of 
  Erwy 
  and 
  Mountain 
  Lodge, 
  for 
  instance) 
  are 
  situated 
  in 
  

   depressions 
  with 
  rising 
  ground 
  on 
  the 
  N. 
  side, 
  or 
  on 
  the 
  side 
  from 
  

   which 
  the 
  erratic 
  -laden 
  ice 
  must 
  have 
  floated 
  ; 
  in 
  other 
  words, 
  they 
  

   occur 
  in 
  positions 
  in 
  which 
  they 
  might 
  have 
  been 
  left 
  by 
  currents 
  

   but 
  not 
  by 
  stranding 
  ice. 
  

  

  5. 
  Reasons 
  why 
  they 
  often 
  occupy 
  Per 
  cited 
  Positions. 
  — 
  Among 
  

   these 
  reasons 
  may 
  be 
  mentioned 
  the 
  possible 
  tendency 
  of 
  the 
  rising 
  

   ground 
  on 
  which 
  they 
  now 
  stand 
  (when 
  it 
  was 
  under 
  the 
  sea) 
  to 
  

   intercept 
  currents 
  and 
  floating 
  ice 
  so 
  as 
  to 
  cause 
  an 
  accumulation 
  of 
  

   gravel 
  and 
  sand. 
  The 
  perched, 
  or 
  comparatively 
  perched, 
  knolls 
  

   are 
  chiefly 
  to 
  be 
  found 
  in 
  the 
  Frondeg 
  district 
  towards 
  the 
  north 
  end 
  

   of 
  Minera 
  Mountain, 
  where 
  it 
  is 
  possible, 
  if 
  not 
  probable, 
  that 
  the 
  

   large 
  knolls 
  situated 
  W. 
  and 
  NVW. 
  of 
  Cae-newydd 
  (or 
  Cae-mynydd) 
  

   were 
  accumulated 
  round 
  rocky 
  nuclei. 
  The 
  great 
  Hafod 
  knoll 
  

   towards 
  the 
  south 
  end 
  of 
  the 
  drift-area 
  may 
  be 
  said 
  to 
  occupy 
  a 
  semi- 
  

   perched 
  position, 
  the 
  ground 
  only 
  rising 
  from 
  it 
  in 
  a 
  northerly 
  

   direction 
  §. 
  In 
  concluding 
  this 
  part 
  of 
  the 
  subject 
  it 
  may 
  be 
  re- 
  

   marked 
  that 
  the 
  occurrence 
  of 
  drift-knolls 
  in 
  perched 
  positions 
  is 
  

   incompatible 
  with 
  the 
  idea 
  of 
  their 
  freshwater 
  origin 
  (even 
  if 
  they 
  

  

  * 
  In 
  the 
  Arctic 
  regions 
  the 
  stranding 
  of 
  floating 
  ice 
  on 
  sea-beaches 
  forces 
  up 
  

   the 
  shingle 
  into 
  ridges 
  and 
  hummocks. 
  

  

  t 
  Notably 
  around 
  Ellesmere, 
  Shropshire. 
  

  

  % 
  It 
  may 
  likewise 
  be 
  remarked 
  that 
  the 
  sea-bed 
  in 
  an 
  easterly 
  direction 
  must 
  

   then 
  have 
  deepened 
  much 
  more 
  suddenly, 
  and 
  to 
  a 
  much 
  greater 
  extent, 
  than 
  

   is 
  now 
  the 
  case 
  around 
  the 
  shores 
  of 
  England 
  and 
  Wales. 
  When 
  the 
  sea-level 
  

   coincided 
  with 
  what 
  is 
  now 
  the 
  1260 
  feet 
  contour-line, 
  its 
  depth 
  over 
  the 
  site 
  

   of 
  the 
  railway 
  between 
  Wrexham 
  and 
  Euabon 
  must 
  have 
  been 
  nearly 
  1000 
  

   feet. 
  

  

  § 
  As 
  this 
  knoll 
  is 
  situated 
  on 
  a 
  slope 
  facing 
  the 
  south, 
  it 
  cannot 
  be 
  explained 
  

   by 
  the 
  stranding 
  of 
  ice. 
  

  

  