﻿32 
  X. 
  MELLARD 
  EEADE 
  ON 
  THE 
  

  

  only 
  by 
  well-worn 
  fragments 
  of 
  the 
  columella. 
  Cyprina 
  islandica 
  

   is 
  invariably 
  found 
  in 
  fragments, 
  sometimes 
  angular 
  and 
  sometimes 
  

   worn, 
  while 
  the 
  hinge, 
  being 
  more 
  adapted 
  to 
  rolling, 
  is 
  usually 
  much 
  

   rounded 
  and 
  worn. 
  It 
  is 
  quite 
  exceptional 
  to 
  find 
  a 
  perfect 
  valve 
  of 
  

   a 
  bivalve, 
  and 
  it 
  is 
  confined, 
  as 
  far 
  as 
  my 
  experience 
  goes, 
  to 
  small 
  

   and 
  strong 
  valves. 
  I 
  had 
  the 
  good 
  fortune 
  to 
  find 
  a 
  perfect 
  valve 
  of 
  

   Leda 
  pernula 
  at 
  Edge 
  Hill*. 
  I 
  have 
  also 
  a 
  perfect 
  valve 
  of 
  Tellina 
  

   balthica, 
  retaining 
  part 
  of 
  the 
  colouring, 
  from 
  the 
  sewer 
  in 
  Thomas 
  

   Lane, 
  Broad 
  Green. 
  Some 
  few 
  other 
  species 
  occasionally 
  occur 
  more 
  

   or 
  less 
  perfect 
  ; 
  but 
  we 
  may 
  safely 
  say 
  that, 
  as 
  a 
  rule, 
  those 
  only 
  are 
  

   preserved 
  which, 
  by 
  the 
  peculiarity 
  of 
  their 
  form, 
  or 
  their 
  minuteness 
  

   combined 
  with 
  their 
  form, 
  are 
  fitted 
  to 
  resist 
  pressure 
  or 
  rolling 
  about. 
  

   Again, 
  the 
  association 
  of 
  the 
  various 
  species, 
  distributed 
  entirely 
  

   without 
  order 
  through 
  the 
  clays, 
  shows 
  that 
  they 
  could 
  not 
  possibly 
  

   have 
  lived 
  together 
  on 
  the 
  same 
  bottom, 
  some 
  being 
  peculiar 
  to 
  sand, 
  

   others 
  to 
  mud, 
  some 
  to 
  rock, 
  and 
  others 
  to 
  shingle, 
  some 
  requiring 
  

   deep 
  water, 
  and 
  others 
  shallow 
  ; 
  so 
  that 
  the 
  conclusion 
  is 
  irresistibly 
  

   forced 
  upon 
  us 
  that 
  they 
  must 
  have 
  been 
  to 
  a 
  large 
  extent 
  trans- 
  

   ported. 
  Had 
  the 
  confusion 
  been 
  due 
  to 
  the 
  ploughing 
  up 
  of 
  icebergs, 
  as 
  

   suggested 
  by 
  Forbes, 
  the 
  disturbance 
  at 
  each 
  stage 
  of 
  subsidence 
  would 
  

   not 
  have 
  reached 
  beyond 
  a 
  certain 
  depth 
  below 
  the 
  surface 
  of 
  the 
  sea, 
  

   and 
  all 
  below 
  that 
  depth 
  would 
  have 
  been 
  free. 
  It 
  is 
  in 
  fact 
  impossible 
  

   to 
  construct 
  a 
  satisfactory 
  explanation 
  which 
  does 
  not 
  allow 
  for 
  a 
  

   successively 
  varying 
  depth 
  of 
  sea-bottom 
  from 
  zero 
  up 
  to 
  1400, 
  and 
  

   perhaps 
  even 
  2000 
  feet. 
  We 
  have, 
  as 
  before 
  shown, 
  every 
  reason 
  

   to 
  infer 
  that 
  some 
  at 
  least 
  of 
  the 
  bottom 
  beds 
  of 
  the 
  drift, 
  of 
  which 
  

   I 
  purpose 
  giving 
  you 
  sections 
  and 
  more 
  fully 
  explaining 
  in 
  my 
  second 
  

   paper, 
  are 
  those 
  originally 
  formed 
  on 
  the 
  first 
  subsidence 
  of 
  the 
  land 
  

   after 
  the 
  retreat 
  of 
  the 
  ice-sheet 
  to 
  the 
  mountain-districts 
  of 
  the 
  

   northf. 
  In 
  several 
  examples 
  we 
  see 
  the 
  bottom-clay 
  reposing 
  upon 
  

   the 
  sand 
  ground-moraine 
  derived 
  from 
  the 
  Triassic 
  rocks, 
  with 
  the 
  

   line 
  of 
  division 
  as 
  sharply 
  defined 
  as 
  could 
  well 
  be 
  ; 
  and 
  resting 
  upon 
  

   the 
  sand 
  and 
  in 
  the 
  clay 
  are 
  boulders 
  and 
  pebbles, 
  evidently 
  transported 
  

   from 
  the 
  north, 
  and 
  having 
  their 
  surfaces 
  scratched, 
  indented, 
  and 
  

   polished^. 
  This 
  bottom-clay 
  is 
  largely 
  composed 
  of 
  the 
  red 
  sand 
  

   upon 
  which 
  it 
  rests, 
  and 
  out 
  of 
  which, 
  together 
  with 
  mud 
  from 
  more 
  

   distant 
  localities, 
  it 
  has 
  been 
  formed. 
  This 
  is 
  the 
  distinguishing 
  

   difference 
  between 
  the 
  inferior 
  and 
  the 
  overlying 
  clays, 
  and 
  varies 
  

   from 
  a 
  strongly 
  marked 
  distinction, 
  according 
  to 
  the 
  proportions 
  of 
  

   the 
  included 
  sand, 
  to 
  a 
  difference 
  of 
  appearance 
  only 
  minute. 
  If, 
  

   however, 
  we 
  examine 
  the 
  constitution 
  of 
  the 
  clay 
  itself, 
  we 
  find 
  no 
  

   real 
  or 
  appreciable 
  distinction 
  from 
  that 
  above 
  it 
  ; 
  for 
  in 
  both 
  the 
  same 
  

   distribution 
  of 
  shell-fragments 
  occurs, 
  and 
  the 
  included 
  boulders 
  are 
  

  

  * 
  Now 
  in 
  the 
  possession 
  of 
  Mr. 
  Darbishire. 
  

  

  t 
  The 
  existence 
  of 
  the 
  ice-sheet 
  and 
  the 
  proofs 
  of 
  the 
  statement 
  will 
  be 
  given 
  

   before 
  the 
  subject 
  is 
  completed. 
  (See 
  also 
  abstract 
  of 
  the 
  author's 
  paper 
  on 
  

   Glacial 
  Striae 
  at 
  Miller's 
  Bridge, 
  'Proceedings 
  of 
  the 
  Liverpool 
  Geological 
  

   Society,' 
  Session 
  1872-73.) 
  

  

  J 
  These 
  are 
  found 
  162 
  feet 
  below 
  the 
  surface 
  at 
  Widnes, 
  or 
  140 
  feet 
  below 
  

   the 
  ordnance 
  datum 
  in 
  the 
  ancient 
  bed 
  of 
  the 
  Mersey. 
  See 
  " 
  The 
  Buried 
  Valley 
  

   of 
  the 
  Mersey," 
  by 
  the 
  author, 
  in 
  the 
  same 
  volume. 
  

  

  