﻿706 
  SEARLES 
  Y. 
  WOOD 
  ON 
  THE 
  NEWER 
  

  

  The 
  same 
  movement, 
  of 
  depression, 
  however, 
  carried 
  the 
  salt 
  water 
  

   on 
  the 
  French 
  side 
  np 
  the 
  Somme 
  valley 
  as 
  far 
  as 
  Abbeville, 
  and 
  gave 
  

   rise 
  to 
  the 
  sand 
  and 
  gravel 
  with 
  marine 
  shells 
  in 
  which 
  the 
  Cyrena 
  

   occurs 
  at 
  Menchecourt, 
  the 
  upper 
  part 
  of 
  which, 
  according 
  to 
  Prof. 
  

   Prestwich's 
  sections 
  in 
  the 
  ' 
  Philosophical 
  Transactions 
  ' 
  for 
  1864, 
  

   seems 
  to 
  be 
  about 
  85, 
  and 
  the 
  lower 
  about 
  35 
  feet 
  above 
  0. 
  D. 
  

  

  M. 
  Rutot 
  refers 
  this 
  sand 
  and 
  gravel 
  to 
  a 
  depression 
  of 
  the 
  

   Somme 
  valley 
  causing 
  a 
  reentry 
  of 
  the 
  sea 
  there 
  *, 
  and 
  states 
  that 
  

   it 
  is 
  overlain 
  by 
  clayey 
  bands 
  containing 
  in 
  their 
  midst 
  sand 
  with 
  

   freshwater 
  shells 
  only 
  (being 
  the 
  reverse 
  of 
  the 
  feature 
  disclosed 
  by 
  

   Clacton) 
  ; 
  and 
  he 
  attributes 
  this 
  to 
  the 
  reelevation 
  of 
  the 
  valley 
  ; 
  but 
  

   inasmuch 
  as 
  an 
  elevation 
  of 
  the 
  land 
  would 
  convert 
  the 
  central 
  or 
  

   deeper 
  part 
  of 
  a 
  saltwater 
  estuary, 
  rather 
  than 
  the 
  shallower 
  sides 
  

   of 
  it, 
  into 
  a 
  freshwater 
  river, 
  and 
  it 
  is 
  on 
  the 
  sloping 
  sides 
  of 
  the 
  

   Somme 
  valley 
  that 
  the 
  bed 
  thus 
  passing 
  up 
  from 
  a 
  salt 
  to 
  a 
  fresh- 
  

   water 
  condition 
  occurs, 
  it 
  seems 
  clear 
  to 
  me 
  that 
  it 
  could 
  only 
  have 
  

   arisen 
  from 
  that 
  augmentation 
  in 
  the 
  volume 
  of 
  the 
  fresh 
  water 
  

   which 
  I 
  have 
  traced 
  in 
  the 
  case 
  of 
  the 
  Cyrena-f 
  ovulation 
  in 
  the 
  

   Thames 
  valley. 
  It 
  is 
  the 
  gravel 
  occupying 
  the 
  centre 
  of 
  the 
  Somme 
  

   valley, 
  beneath 
  the 
  modern 
  peat, 
  to 
  which 
  the 
  reelevation 
  gave 
  rise, 
  

   that 
  corresponds, 
  in 
  my 
  view, 
  most 
  nearly 
  to 
  r/ 
  of 
  my 
  figures. 
  This 
  

   elevation 
  brought 
  the 
  sea-level 
  down 
  to 
  that 
  of 
  the 
  beaches 
  of 
  the 
  

   buried 
  cliffs 
  ; 
  but 
  the 
  gravel 
  beneath 
  the 
  peat 
  descends 
  below 
  this 
  

   level 
  at 
  Menchecourt, 
  because 
  it 
  occupies 
  the 
  centre 
  of 
  (he 
  old 
  

   river-bottom. 
  

  

  On 
  the 
  shore 
  at 
  Selsea 
  in 
  Sussex, 
  10 
  miles 
  south, 
  and 
  seaward 
  of 
  

   the 
  line 
  of 
  submergence 
  thus 
  indicated 
  by 
  the 
  Avisford 
  and 
  Bourne- 
  

   Oommon 
  sand 
  and 
  shingle, 
  and 
  midway 
  between 
  those 
  two 
  places, 
  

   but 
  at 
  full 
  120 
  feet 
  less 
  elevation 
  (for 
  it 
  is 
  washed 
  by 
  the 
  sea 
  at 
  high 
  

   water), 
  occurs 
  a 
  bed 
  of 
  mud 
  rich 
  in 
  marine 
  mollusca, 
  with 
  which 
  

   mammalian 
  remains 
  have 
  also 
  occurred. 
  This 
  bed 
  is 
  described 
  by 
  

   Mr. 
  Godwin- 
  Austen 
  t 
  as 
  overlain 
  by 
  the 
  clayey 
  gravel 
  with 
  great 
  

   blocks 
  of 
  hypersthene 
  rock 
  described 
  in 
  Stage 
  VII. 
  as 
  a 
  formation 
  of 
  

   the 
  minor 
  glaciation, 
  and 
  shown 
  in 
  fig. 
  XLII. 
  by 
  the 
  letter 
  G; 
  and 
  

   a 
  list 
  of 
  the 
  mollusca 
  from 
  it 
  have 
  been 
  given 
  by 
  him 
  and 
  by 
  Mr. 
  

   Dixon 
  t, 
  to 
  which 
  Mr. 
  Alfred 
  Bell 
  has 
  made 
  many 
  additions 
  §. 
  

   The 
  whole 
  form 
  a 
  remarkable 
  group, 
  showing 
  on 
  the 
  one 
  hand, 
  by 
  

  

  * 
  Bulletin 
  de 
  la 
  Societe 
  Royale 
  Malacologique 
  de 
  Belgique 
  for 
  1881. 
  Prof. 
  

   Prestwich 
  also, 
  in 
  his 
  memoir 
  in 
  the 
  Phil. 
  Trans, 
  for 
  1864 
  (p. 
  284), 
  shows 
  the 
  

   gravel 
  with 
  Cyrena 
  and 
  marine 
  shells 
  at 
  Menchecourt 
  as 
  underlain 
  by 
  sandy- 
  

   marl 
  containing 
  chiefly 
  land 
  and 
  freshwater 
  shells. 
  This 
  indicates 
  that 
  a 
  

   change 
  of 
  the 
  ancient 
  Somme 
  from 
  a 
  freshwater 
  to 
  a 
  marine 
  condition 
  took 
  

   place 
  by 
  the 
  depression 
  Avhich 
  I 
  have 
  traced, 
  just 
  as 
  Clacton 
  does 
  for 
  the 
  

   ancient 
  Thames 
  system. 
  

  

  t 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xiii. 
  p. 
  40. 
  

  

  \ 
  Geology 
  of 
  Sussex, 
  1st 
  edit. 
  p. 
  13. 
  

  

  § 
  These, 
  according 
  to 
  a 
  list 
  furnished 
  by 
  Mr. 
  Bell 
  to 
  my 
  late 
  father, 
  in 
  my 
  

   possession, 
  are 
  25 
  in 
  number, 
  making 
  with 
  the 
  species 
  mentioned 
  by 
  Dixon 
  and 
  

   G-odwin 
  -Austen, 
  and 
  one 
  by 
  S. 
  P. 
  Woodward 
  (in 
  MS.), 
  a 
  total 
  of 
  79, 
  after 
  

   deducting 
  six 
  repeated 
  synonymously, 
  there 
  being 
  some 
  obsolete 
  names 
  in 
  

   Dixon's 
  list. 
  The 
  whole 
  79 
  are 
  species 
  living 
  on 
  the 
  south 
  coast 
  of 
  England, 
  

   except 
  the 
  two 
  mentioned 
  in 
  the 
  text 
  as 
  confined 
  to 
  the 
  Lusitanian 
  coast. 
  

  

  