﻿178 
  D. 
  MACKINTOSH 
  ON 
  GLACIAL 
  TRACES 
  IX 
  

  

  has 
  been 
  carefully 
  searched 
  for 
  ice-marks 
  further 
  west 
  and 
  east 
  (but 
  

   especially 
  further 
  east) 
  than 
  the 
  area 
  treated 
  of 
  in 
  this 
  paper, 
  it 
  

   might 
  be 
  going 
  too 
  far 
  to 
  invoke 
  an 
  ice-flow 
  assailing 
  the 
  Lake 
  

   District 
  from 
  without, 
  and 
  overriding 
  an 
  area 
  extending 
  west 
  and 
  

   east 
  from 
  the 
  Duddon 
  valley 
  to 
  Kentmere, 
  if 
  not 
  to 
  the 
  "West 
  Biding 
  

   of 
  Yorkshire, 
  and 
  as 
  far 
  south 
  at 
  least 
  as 
  Morecambe 
  Bay. 
  

  

  Traces 
  of 
  an 
  Ice-sheet 
  in 
  North 
  Wales. 
  — 
  The 
  state 
  of 
  the 
  basin 
  of 
  

   the 
  Irish 
  Sea 
  between 
  the 
  Lake 
  District 
  and 
  North 
  Wales, 
  at 
  the 
  

   time 
  of 
  the 
  greatest 
  development 
  of 
  the 
  ice, 
  cannot 
  be 
  well 
  ascer- 
  

   tained 
  without 
  a 
  wider 
  induction 
  of 
  facts 
  than 
  we 
  at 
  present 
  possess. 
  

   The 
  north-western 
  side 
  of 
  Snowdonia 
  has 
  been 
  principally 
  glaciated 
  

   from 
  the 
  S.E. 
  and 
  S. 
  or 
  in 
  the 
  direction 
  of 
  the 
  lower 
  valleys. 
  In 
  

   the 
  high-level 
  valleys, 
  as 
  long 
  ago 
  shown 
  by 
  Brofessor 
  Bamsay, 
  there 
  

   are 
  strise 
  which 
  indicate 
  a 
  thickness 
  of 
  ice 
  sufficient 
  to 
  have 
  enabled 
  

   it 
  to 
  cross 
  minor 
  ridges 
  and 
  hollows, 
  and 
  to 
  move 
  along 
  the 
  sides 
  of 
  

   hills 
  at 
  great 
  altitudes. 
  During 
  recent 
  visits 
  to 
  North 
  Wales 
  I 
  saw 
  

   many 
  glaciated 
  surfaces 
  between 
  the 
  Vale 
  of 
  Conway 
  and 
  Capel 
  

   Curig, 
  the 
  striae 
  varying 
  from 
  between 
  S.W. 
  and 
  W.S.W., 
  and 
  indi- 
  

   cating 
  an 
  ice-flow 
  capable 
  of 
  ignoring 
  hills 
  and 
  valleys. 
  In 
  the 
  

   great 
  Ogwen 
  Bass, 
  near 
  a 
  farm-house 
  called 
  Wern-go-ischaf, 
  I 
  found 
  

   an 
  extensive 
  rock-surface 
  striated 
  at 
  right 
  angles 
  to 
  the 
  pass 
  (or 
  

   nearly 
  N. 
  and 
  S.) 
  which 
  a 
  small 
  glacier 
  coming 
  down 
  from 
  above 
  

   did 
  not 
  seem 
  capable 
  of 
  explaining, 
  especially 
  as 
  the 
  lines 
  did 
  not 
  

   coincide 
  in 
  direction 
  with 
  the 
  small 
  lateral 
  valleys 
  on 
  the 
  right 
  and 
  

   left. 
  To 
  the 
  south 
  of 
  the 
  Snowdonian 
  range 
  of 
  mountains 
  I 
  

   happened 
  to 
  alight 
  on 
  a 
  number 
  of 
  phenomena 
  which 
  clearly 
  indi- 
  

   cated 
  the 
  southerly 
  movement 
  of 
  a 
  great 
  ice-sheet 
  capable 
  of 
  

   ignoring 
  or 
  crossing 
  deep 
  valleys, 
  and 
  which 
  probably 
  had 
  its 
  

   source 
  in 
  an 
  ice-dome 
  covering 
  the 
  peak 
  of 
  Snowdon 
  and 
  the 
  sur- 
  

   rounding 
  heights, 
  and 
  levelling 
  the 
  area 
  between 
  Snowdon 
  and 
  

   Moel-wyn. 
  The 
  group 
  of 
  mountains 
  of 
  which 
  Moel-wyn 
  is 
  the 
  

   principal, 
  furnishes 
  evidences 
  of 
  the 
  former 
  existence 
  of 
  such 
  an 
  

   ice-sheet. 
  On 
  the 
  southern 
  side 
  of 
  Bwlch-cwm-orthin 
  (which 
  

   separates 
  the 
  head 
  of 
  Cwm 
  Croesor 
  from 
  Cwm 
  Orthin) 
  away 
  from 
  

   any 
  valley, 
  and 
  at 
  a 
  height 
  of 
  more 
  than 
  1800 
  feet 
  above 
  the 
  sea, 
  

   I 
  found 
  a 
  number 
  of 
  rock-surfaces, 
  smoothed, 
  mammillated, 
  and 
  

   striated 
  from 
  about 
  W. 
  30° 
  N. 
  There 
  is 
  a 
  possibility 
  of 
  these 
  

   surfaces 
  having 
  been 
  glaciated 
  by 
  floating 
  ice 
  ; 
  but 
  when 
  viewed 
  in 
  

   connexion 
  with 
  roches 
  moutonnees 
  at 
  a 
  lower 
  level, 
  soon 
  to 
  be 
  noticed, 
  

   I 
  think 
  it 
  is 
  more 
  probable 
  that 
  the 
  agent 
  was 
  land-ice 
  of 
  a 
  thick- 
  

   ness 
  sufficient 
  to 
  fill 
  up 
  and 
  override 
  the 
  upper 
  part 
  of 
  Cwm 
  

   Croesor 
  before 
  it 
  found 
  its 
  way 
  to 
  the 
  irregular 
  plateau 
  on 
  which 
  

   the 
  glaciated 
  rocks 
  occur. 
  Between 
  Cwm 
  Croesor 
  and 
  Beddgellert 
  

   mammillated 
  rocks 
  may 
  be 
  almost 
  everywhere 
  observed; 
  but 
  the 
  

   greatest 
  display 
  occurs 
  immediately 
  to 
  the 
  south 
  of 
  the 
  bare 
  and 
  

   craggy 
  felstone 
  ridge 
  called 
  Yr 
  Arddu 
  ; 
  I 
  believe 
  they 
  are 
  unequalled 
  

   in 
  any 
  part 
  of 
  Wales 
  or, 
  perhaps, 
  in 
  the 
  Lake 
  District. 
  Their 
  regularly 
  

   rounded 
  and 
  approximately 
  dome-shaped 
  forms, 
  not 
  exceptionally, 
  

   but 
  as 
  a 
  general 
  rule, 
  furnish 
  an 
  unquestionable 
  evidence 
  of 
  a 
  great 
  

   flow 
  of 
  land-ice, 
  as 
  icebergs 
  would 
  have 
  tended 
  to 
  flatten 
  and 
  plane 
  

  

  