﻿MARINE 
  DRIFTS 
  IN 
  NORTH 
  WALES. 
  191 
  

  

  contained 
  no 
  marine 
  fossils), 
  because 
  freshwater 
  would 
  tend 
  to 
  flow 
  

   from, 
  and 
  not 
  to, 
  the 
  rising 
  ground 
  on 
  which 
  they 
  are 
  situated 
  *. 
  

  

  V. 
  Drietless 
  Areas 
  is 
  North 
  Wales. 
  

  

  The 
  term 
  " 
  driftless 
  " 
  (which 
  I 
  have 
  used 
  for 
  the 
  sake 
  of 
  brevity) 
  

   is 
  here 
  intended 
  to 
  apply 
  to 
  those 
  districts 
  in 
  which 
  I 
  have 
  not 
  yet 
  

   seen 
  any 
  decided 
  instances 
  of 
  rounded 
  gravel 
  and 
  stratified 
  sand 
  at 
  

   levels 
  higher 
  than 
  the 
  1000 
  feet 
  contour-line. 
  

  

  1. 
  South 
  and 
  North 
  of 
  Pont 
  Fadog. 
  — 
  The 
  discovery 
  of 
  high-level 
  

   marine 
  drifts 
  on 
  the 
  eastern 
  borders 
  of 
  the 
  Welsh 
  mountains 
  N. 
  of 
  

   Llangollen 
  Vale 
  naturally 
  excited 
  an 
  expectation 
  that 
  similar 
  drifts 
  

   might 
  be 
  found 
  S. 
  of 
  the 
  Yale 
  (an 
  expectation, 
  however, 
  which 
  was 
  

   not 
  realized). 
  On 
  ascending 
  from 
  Pont 
  Padog 
  (about 
  3| 
  miles 
  W. 
  

   of 
  Chirk 
  railway-station), 
  and 
  walking 
  in 
  a 
  southerly 
  direction 
  over 
  

   the 
  plateau 
  between 
  the 
  lime-kilns 
  and 
  Gwernydd-gymal 
  f 
  , 
  though 
  

   the 
  ground 
  in 
  many 
  places 
  was 
  covered 
  with 
  numerous 
  fragments 
  

   of 
  Silurian 
  and 
  Carboniferous 
  grit 
  and 
  limestone, 
  I 
  could 
  not 
  find 
  a 
  

   single 
  instance 
  of 
  even 
  an 
  approximately 
  rounded 
  stone 
  or 
  of 
  stra- 
  

   tified 
  sand. 
  Several 
  so-called 
  gravel-pits 
  (two 
  of 
  them 
  west 
  of 
  Plas- 
  

   crogen) 
  are 
  marked 
  on 
  the 
  6-inch 
  Ordnance 
  map 
  ; 
  but 
  they 
  all 
  con- 
  

   sist 
  of 
  perfectly 
  angular 
  stones, 
  and 
  sand 
  arising 
  from 
  the 
  mere 
  

   disintegration 
  of 
  the 
  sandstone 
  rock 
  in 
  situ. 
  Prom 
  what 
  I 
  saw 
  on 
  

   former 
  occasions 
  of 
  the 
  westerly 
  continuation 
  of 
  this 
  plateau 
  as 
  far 
  as 
  

   the 
  New 
  Inn 
  (at 
  the 
  great 
  bend 
  of 
  the 
  river 
  Ceiriog), 
  I 
  have 
  reason 
  

   to 
  believe 
  that 
  the 
  whole 
  of 
  it, 
  or 
  almost 
  the 
  whole 
  of 
  it, 
  is 
  free 
  

   from 
  marine 
  drift. 
  Neither 
  have 
  I 
  seen 
  high-level 
  marine 
  drift 
  

   further 
  south. 
  On 
  ascending 
  the 
  northern 
  slope 
  of 
  the 
  Ceiriog 
  valley, 
  

   the 
  rounded 
  stones 
  seen 
  at 
  or 
  near 
  to 
  the 
  bottom 
  of 
  the 
  valley 
  

   speedily 
  disappeared, 
  and 
  none 
  but 
  strikingly 
  angular 
  stones 
  could 
  

   be 
  found 
  the 
  whole 
  way 
  up 
  to 
  the 
  summit 
  of 
  the 
  ridge, 
  and 
  down 
  

   the 
  north 
  side, 
  in 
  the 
  direction 
  of 
  Llangollen, 
  until 
  a 
  level 
  of 
  about 
  

   400 
  feet 
  above 
  the 
  sea 
  was 
  reached. 
  Even 
  at 
  that 
  comparatively 
  

   low 
  level 
  the 
  drift 
  presented 
  a 
  more 
  or 
  less 
  " 
  pell-mell" 
  appearance, 
  

   though 
  in 
  other 
  parts 
  of 
  the 
  Dee 
  valley, 
  up 
  to 
  a 
  considerable 
  height, 
  

   well-rounded 
  shingle 
  and 
  stratified 
  sand 
  may 
  be 
  seen 
  J. 
  

  

  * 
  It 
  ought 
  likewise 
  to 
  be 
  stated 
  that 
  while 
  the 
  general 
  form 
  of 
  the 
  ground 
  is 
  

   undoubtedly 
  preglacial, 
  the 
  shape 
  of 
  the 
  drift-knolls 
  presents 
  little 
  or 
  no 
  ap- 
  

   pearance 
  of 
  having 
  been 
  modified 
  by 
  subaerial 
  agency 
  since 
  the 
  time 
  they 
  were 
  

   left 
  by 
  the 
  sea. 
  This 
  might 
  be 
  expected, 
  not 
  only 
  from 
  their 
  proximity 
  to 
  the 
  

   summit 
  of 
  the 
  mountain-ridge, 
  but 
  (in 
  the 
  northern 
  part 
  of 
  the 
  area) 
  from 
  their 
  

   being 
  on 
  the 
  border 
  of 
  an 
  extensive 
  covering 
  of 
  peat, 
  which 
  absorbs 
  most 
  of 
  the 
  

   rainfall, 
  the 
  remainder 
  supplying 
  a 
  few 
  small 
  streams 
  which 
  have 
  made 
  chan- 
  

   nels 
  showing 
  sections 
  of 
  the 
  clay 
  and 
  gravel 
  from 
  1 
  to 
  2 
  feet 
  in 
  depth. 
  There 
  

   is 
  reason 
  for 
  believing 
  that 
  in 
  the 
  greater 
  part 
  of 
  the 
  area 
  the 
  denudation 
  is 
  

   chiefly 
  subterranean, 
  the 
  rain-water 
  finding 
  its 
  way 
  down 
  to 
  the 
  underlying 
  

   Carboniferous 
  limestone. 
  It 
  is 
  not 
  generally 
  known 
  that 
  under 
  Minera 
  Moun- 
  

   tain 
  there 
  is 
  one 
  of 
  the 
  largest 
  (if 
  not 
  the 
  largest) 
  of 
  the 
  subterranean 
  rivers 
  in 
  

   Britain. 
  

  

  t 
  The 
  average 
  level 
  of 
  the 
  part 
  of 
  the 
  plateau 
  I 
  went 
  over 
  may 
  be 
  about 
  

   1150 
  feet 
  above 
  the 
  sea. 
  

  

  \ 
  It 
  ought 
  to 
  be 
  stated 
  that 
  large 
  boulders 
  which 
  have 
  been 
  drifted 
  from 
  the 
  

   Arenig 
  Mountains 
  in 
  an 
  easterly 
  direction 
  are 
  common 
  on 
  the 
  high 
  ground 
  

  

  