﻿350 
  F. 
  G. 
  H. 
  PKICE 
  ON 
  THE 
  GAULT 
  OF 
  FOLKESTONE. 
  

  

  tities, 
  from 
  which 
  circumstance 
  it 
  may 
  he 
  well 
  to 
  describe 
  this 
  as 
  the 
  

   zone 
  of 
  Ammonites 
  auritus. 
  

  

  The 
  genus 
  Cerithium 
  is 
  well 
  represented 
  in 
  the 
  Lower 
  Division, 
  

   in 
  which 
  (ranging 
  from 
  bed 
  No. 
  II. 
  up 
  to 
  this 
  bed) 
  as 
  many 
  

   as 
  16 
  different 
  species 
  have 
  been 
  met 
  with. 
  Of 
  these 
  10 
  appear 
  

   not 
  to 
  have 
  been 
  described. 
  I 
  have 
  only 
  enumerated 
  10 
  species 
  

   in 
  my 
  table 
  ; 
  of 
  the 
  remaining 
  six 
  I 
  have 
  only 
  found 
  single 
  specimens, 
  

   and 
  have 
  therefore 
  deferred 
  noting 
  them 
  until 
  more 
  data 
  shall 
  have 
  

   been 
  obtained. 
  This 
  group 
  will 
  form 
  an 
  excellent 
  subject 
  for 
  a 
  mono- 
  

   graph 
  at 
  a 
  future 
  time. 
  

  

  Bed 
  VIII. 
  

  

  This 
  constitutes 
  the 
  junction-bed 
  or 
  " 
  passage 
  " 
  between 
  the 
  Upper 
  

   and 
  Lower 
  Gault, 
  and 
  is 
  measured 
  from 
  the 
  first 
  line 
  of 
  nodules 
  

   before 
  cited 
  as 
  forming 
  the 
  top 
  of 
  bed 
  VII. 
  to 
  a 
  second 
  line 
  of 
  

   nodules. 
  It 
  has 
  a 
  total 
  thickness 
  of 
  10 
  inches, 
  and 
  is 
  well 
  known 
  

   by 
  the 
  name 
  of 
  the 
  " 
  nodule 
  bed." 
  

  

  This 
  passage-bed, 
  for 
  such 
  it 
  really 
  is, 
  contains 
  many 
  species 
  

   belonging 
  to 
  both 
  the 
  Upper 
  and 
  Lower 
  Gault, 
  and 
  marks 
  the 
  total 
  

   extinction 
  of 
  many 
  Lower-Gault 
  forms, 
  no 
  less 
  than 
  the 
  introduc- 
  

   tion 
  of 
  others 
  which 
  took 
  their 
  place. 
  

  

  Few 
  species 
  of 
  Gasteropoda, 
  which 
  are 
  so 
  plentiful 
  in 
  the 
  top 
  beds 
  

   of 
  the 
  lower 
  division, 
  pass 
  into 
  this 
  junction-bed 
  ; 
  they 
  are 
  here 
  

   generally 
  found 
  in 
  the 
  form 
  of 
  casts 
  or 
  much 
  enveloped 
  in 
  phos- 
  

   phate. 
  Several 
  Ammonites 
  belonging 
  to 
  the 
  various 
  groups 
  are 
  

   found 
  here. 
  The 
  characteristic 
  species 
  is 
  Ammonites 
  Beudanti, 
  which 
  

   is 
  not 
  found 
  in 
  any 
  other 
  part 
  of 
  the 
  Gault. 
  It 
  may 
  be 
  well 
  to 
  

   mention 
  that 
  this 
  well-marked 
  form 
  obtains 
  largely 
  in 
  the 
  zone 
  of 
  

   Ammonites 
  mammillatus 
  in 
  the 
  Upper 
  Neocomian 
  or 
  Folkestone-beds 
  

   of 
  the 
  Lower 
  Greensand. 
  

  

  The 
  nodules 
  of 
  this 
  zone, 
  like 
  the 
  nodules 
  at 
  the 
  base 
  of 
  the 
  

   Gault 
  in 
  bed 
  I., 
  contain 
  for 
  the 
  most 
  part 
  a 
  remanie 
  group 
  of 
  fossils. 
  

  

  The 
  Lower 
  Gault 
  appears 
  to 
  have 
  been 
  especially 
  favourable 
  to 
  

   the 
  life 
  and 
  development 
  of 
  the 
  Gasteropoda 
  ; 
  for 
  as 
  many 
  as 
  46 
  

   species 
  have 
  been 
  obtained 
  (as 
  may 
  be 
  observed 
  in 
  the 
  accompanying 
  

   table) 
  from 
  those 
  beds 
  ; 
  and 
  they 
  reached 
  their 
  maximum 
  of 
  develop- 
  

   ment 
  in 
  bed 
  VII. 
  Nine 
  of 
  these 
  species 
  extend 
  into 
  the 
  nodule- 
  

   bed 
  No. 
  VIII. 
  , 
  there 
  being 
  but 
  two 
  species 
  peculiar 
  to 
  it. 
  

  

  Out 
  of 
  the 
  11 
  species 
  of 
  Gasteropoda 
  found 
  in 
  the 
  Upper 
  Gault, 
  

   6 
  appear 
  to 
  have 
  survived 
  from 
  the 
  Lower, 
  and 
  5 
  are 
  peculiar 
  to 
  the 
  

   Upper, 
  thus 
  showing 
  that 
  the 
  conditions 
  of 
  the 
  Upper-Gault 
  sea 
  

   were 
  unfavourable 
  to 
  the 
  continuance 
  of 
  the 
  more 
  delicate 
  forms 
  of 
  

   life, 
  or, 
  if 
  they 
  were 
  continued, 
  that 
  the 
  chemical 
  constituents 
  of 
  the 
  

   sediments 
  deposited 
  during 
  the 
  formation 
  of 
  these 
  marls 
  were 
  

   unfavourable 
  to 
  the 
  preservation 
  of 
  specimens. 
  

  

  Out 
  of 
  73 
  species 
  of 
  Lamellibranchiata 
  that 
  I 
  have 
  met 
  with 
  in 
  

   the 
  whole 
  deposit, 
  39 
  become 
  extinct 
  in 
  the 
  lower 
  division, 
  or 
  in 
  

   bed 
  VIII. 
  ; 
  4 
  are 
  peculiar 
  to 
  that 
  bed, 
  and 
  16 
  to 
  the 
  Upper 
  Gault 
  ; 
  

   whereas 
  only 
  14 
  species 
  are 
  continued 
  from 
  the 
  lower 
  beds. 
  

  

  Taking 
  the 
  whole 
  of 
  the 
  fauna 
  of 
  the 
  Gault, 
  of 
  which 
  I 
  have 
  

  

  