﻿PLIOCENE 
  PERIOD 
  IN 
  ENGLAND. 
  707 
  

  

  the 
  presence 
  of 
  two 
  species, 
  Lutraria 
  rugosa 
  and 
  Pecten 
  poly- 
  

   morphvs 
  (which 
  are 
  Lusitanian 
  species 
  not 
  now 
  ranging 
  into 
  

   British 
  seas), 
  and 
  by 
  the 
  general 
  character 
  of 
  the 
  shells, 
  a 
  somewhat 
  

   warmer 
  sea 
  than 
  now 
  washes 
  the 
  Sussex 
  coast 
  ; 
  and 
  on 
  the 
  other, 
  

   by 
  the 
  absence 
  of 
  any 
  species 
  not 
  known 
  as 
  living 
  in 
  the 
  British 
  or 
  

   Lusitanian 
  seas, 
  a 
  much 
  more 
  modern 
  origin 
  than 
  the 
  Upper 
  Crag, 
  

   or 
  even 
  the 
  lower 
  part 
  of 
  the 
  sand 
  o 
  i, 
  or 
  the 
  Bridlington 
  or 
  Dim- 
  

   lington 
  beds 
  ; 
  all 
  of 
  which 
  do 
  contain 
  Crag 
  species 
  not 
  known 
  as 
  

   living 
  ; 
  while 
  the 
  absence 
  of 
  such 
  species 
  as 
  Astarte 
  borealis 
  (arctica) 
  

   found 
  in 
  the 
  gravel 
  h 
  \ 
  and 
  other 
  Arctic 
  species 
  found 
  in 
  the 
  clay 
  

   of 
  the 
  great 
  glaciation, 
  where 
  that 
  was 
  of 
  submarine 
  extrusion, 
  

   equally 
  remove 
  the 
  bed 
  from 
  any 
  connexion 
  with 
  the 
  period 
  of 
  the 
  

   major 
  glaciation. 
  It 
  appears 
  to 
  me 
  that 
  this 
  bed 
  coincides 
  nearly 
  

   with 
  the 
  base 
  of 
  the 
  Cty/'gjia-formation 
  in 
  the 
  Thames 
  valley, 
  and 
  was 
  

   formed 
  at 
  the 
  beginning 
  of 
  the 
  redepression 
  under 
  which 
  that 
  

   formation 
  took 
  place, 
  having 
  accumulated 
  before 
  the 
  invading 
  sea 
  

   reached 
  the 
  Avisford 
  and 
  Bourne-Common 
  level 
  ; 
  the 
  Lusitanian 
  

   character 
  of 
  the 
  mollusca, 
  which 
  distinguishes 
  it 
  from 
  what 
  I 
  regard 
  

   as 
  the 
  nearly 
  synchronous 
  gravel 
  of 
  the 
  Wash 
  country 
  (the 
  mollusca 
  

   of 
  which, 
  though 
  all 
  living 
  on 
  this 
  side 
  of 
  the 
  Atlantic, 
  comprise 
  four 
  

   species 
  confined 
  to 
  the 
  sea 
  north 
  of 
  the 
  British 
  Isles 
  *), 
  being 
  due 
  

   to 
  the 
  intervention 
  of 
  the 
  isthmus 
  between 
  Kent 
  and 
  France, 
  

   which 
  was 
  then 
  in 
  existence. 
  

  

  Upon 
  the 
  effect 
  which 
  such 
  an 
  isthmus 
  would 
  produce 
  in 
  this 
  way, 
  

   I 
  need 
  not 
  enlarge, 
  as 
  it 
  is 
  obvious 
  to 
  geologists, 
  and 
  its 
  existence 
  

   subsequently 
  to 
  the 
  great 
  glaciation 
  is 
  generally 
  conceded 
  ; 
  but 
  the 
  

   few 
  shells 
  and 
  other 
  organisms 
  found 
  by 
  Mr. 
  Prestwich 
  in 
  the 
  sands 
  

   at 
  100 
  feet 
  elevation 
  at 
  Avisford, 
  furnish 
  no 
  indication 
  of 
  that 
  

   warmer 
  sea 
  which 
  the 
  Selsea 
  shells 
  do 
  ; 
  and 
  they, 
  in 
  my 
  view, 
  

   accumulated 
  at 
  the 
  culmination 
  of 
  the 
  depression 
  that 
  preceded 
  the 
  

   minor 
  glaciation, 
  and 
  when 
  the 
  Selsea 
  bed 
  had 
  twenty 
  fathoms 
  

   water 
  over 
  it, 
  the 
  deposit 
  corresponding 
  to 
  the 
  sand 
  of 
  Avisford 
  

   which 
  accumulated 
  there 
  having 
  been 
  removed 
  by 
  the 
  waves 
  during 
  

   emergence. 
  The 
  approach 
  of 
  the 
  minor 
  glaciation 
  was 
  then 
  re- 
  

   frigerating 
  both 
  sea 
  and 
  land; 
  but 
  whether 
  the 
  disappearance 
  of 
  the 
  

   southern 
  shells 
  from 
  the 
  Sussex 
  coast 
  was 
  due 
  to 
  this 
  refrigeration 
  

   alone, 
  or 
  to 
  its 
  being 
  accompanied 
  by 
  the 
  letting 
  in 
  of 
  the 
  North 
  

   Sea 
  by 
  the 
  submergence 
  of 
  the 
  isthmus, 
  may 
  be 
  left 
  to 
  conjecture, 
  

   though 
  the 
  character 
  of 
  the 
  existing 
  English 
  fauna, 
  especially 
  the 
  

  

  * 
  The 
  gravel 
  of 
  Kelsea 
  Hill 
  has 
  yielded 
  only 
  two 
  of 
  these 
  shells, 
  that 
  of 
  

   March 
  all 
  four, 
  and 
  the 
  Nar 
  brickeartli 
  only 
  one. 
  The 
  rest 
  of 
  the 
  shells 
  from 
  

   all 
  the 
  marine 
  beds 
  in 
  Norfolk, 
  Cambridgeshire, 
  and 
  Yorkshire, 
  which 
  I 
  refer 
  

   to 
  the 
  Cyrefttf-formation, 
  still 
  live 
  in 
  British 
  seas. 
  Three 
  of 
  these 
  four, 
  viz. 
  

   Pleurotoma 
  pyramidally, 
  Astarte 
  borealis, 
  and 
  Tellina 
  lata 
  (calcarca), 
  are 
  given 
  

   in 
  Mr. 
  Shone's 
  list, 
  p. 
  394 
  of 
  vol. 
  xxiv. 
  of 
  the 
  Quart. 
  Journ., 
  as 
  occurring 
  in 
  the 
  

   upper 
  boulder-clay 
  of 
  the 
  north-west 
  ; 
  the 
  rest 
  of 
  these 
  shells 
  in 
  tbat 
  clay, 
  ex- 
  

   cept 
  the 
  Arctic 
  species 
  Natica 
  affinis 
  (clama), 
  still 
  living 
  in 
  British 
  seas. 
  The 
  

   fourth, 
  Trophon 
  scalariformis, 
  he 
  gives 
  with 
  Astarte 
  borealis 
  from 
  the 
  Middle 
  

   sands 
  of 
  the 
  north-west 
  (the 
  CV/rcwa-formation), 
  in 
  association 
  with 
  species 
  

   all 
  still 
  living 
  in 
  British 
  seas. 
  Space 
  does 
  not 
  allow 
  me 
  to 
  give 
  lists 
  of 
  the 
  

   mollusca 
  from 
  the 
  various 
  beds 
  examined 
  in 
  this 
  memoir. 
  

  

  