﻿482 
  PKOF. 
  J. 
  W. 
  JTJJDD 
  ON 
  THE 
  EOCENE 
  AND 
  OLIGOCEXE 
  

  

  points 
  are 
  not 
  only 
  in 
  perfect 
  agreement 
  as 
  to 
  thickness 
  and 
  general 
  

   characters, 
  but 
  that 
  the 
  numerous 
  minor 
  subdivisions 
  at 
  the 
  one 
  

   place 
  are 
  found 
  exactly 
  repeated 
  at 
  the 
  other. 
  

  

  Let 
  us 
  examine 
  these 
  statements 
  and 
  the 
  supposed 
  proofs 
  of 
  them 
  

   a 
  little 
  more 
  closely. 
  The 
  distance 
  between 
  the 
  point 
  where 
  the 
  

   Colwell-Bay 
  beds 
  rise 
  from 
  the 
  shore 
  and 
  that 
  where 
  their 
  supposed 
  

   representatives 
  are 
  seen 
  at 
  Headon 
  Hill 
  is 
  1 
  J 
  mile 
  or 
  2640 
  yards. 
  

   For 
  a 
  distance 
  of 
  about 
  1200 
  yards 
  from 
  Headon 
  Hill 
  to 
  the 
  Tot 
  land 
  

   brickyard 
  we 
  have 
  no 
  trace 
  of 
  these 
  brackish-water 
  beds 
  ; 
  but 
  for 
  

   the 
  remaining 
  1440 
  yards 
  they 
  can 
  be 
  traced 
  with 
  occasional 
  inter- 
  

   ruptions. 
  

  

  Near 
  Bramble 
  Chine, 
  where 
  the 
  beds 
  are 
  exposed 
  on 
  the 
  shore 
  at 
  

   low 
  water, 
  the 
  Colwell-Bay 
  brackish-water 
  series 
  is 
  divisible 
  into 
  a 
  

   number 
  of 
  local 
  bands, 
  which 
  were 
  well 
  described 
  by 
  Dr. 
  Wright, 
  

   and 
  may 
  be 
  distinguished 
  by 
  the 
  names 
  of 
  the 
  Cerithiam-'bed 
  *, 
  the 
  

   Oyster-bed, 
  the 
  Venus-bed, 
  the 
  Psammobia-bed, 
  and 
  the 
  Neri- 
  

   tina-hed, 
  the 
  total 
  thickness 
  of 
  these 
  brackish-water 
  beds 
  being 
  

   about 
  30 
  feet. 
  These 
  local 
  divisions 
  can 
  be 
  traced 
  in 
  the 
  cliff 
  for 
  a 
  

   short 
  distance 
  ; 
  but 
  less 
  than 
  300 
  yards 
  away 
  from 
  the 
  point 
  where 
  

   the 
  beds 
  rise 
  on 
  the 
  shore, 
  their 
  characters 
  are 
  seen 
  to 
  undergo 
  a 
  

   total 
  change 
  ; 
  instead 
  of 
  the 
  several 
  distinct 
  bands 
  wc 
  have 
  noticed, 
  

   we 
  find 
  the 
  brackish- 
  water 
  beds 
  represented 
  by 
  a 
  mass 
  of 
  dwarfed 
  

   oysters 
  between 
  20 
  and 
  30 
  feet 
  thick. 
  Tracing 
  the 
  beds 
  in 
  the 
  

   cliff 
  for 
  a 
  distance 
  of 
  another 
  350 
  yards, 
  we 
  find 
  the 
  characters 
  of 
  

   this 
  so-called 
  Marine 
  or 
  Middle 
  Headon 
  series 
  undergoing 
  another 
  

   complete 
  change 
  : 
  masses 
  of 
  light-brown 
  and 
  ferruginous 
  sands 
  

   come 
  down 
  to 
  within 
  8 
  or 
  10 
  feet 
  of 
  the 
  How-Ledge 
  limestone 
  ; 
  

   the 
  brackish-water 
  beds 
  are 
  reduced 
  to 
  a 
  thickness 
  of 
  5 
  or 
  6 
  feet 
  

   only, 
  and 
  their 
  fauna 
  exhibits 
  a 
  much 
  smaller 
  admixture 
  of 
  marine 
  

   forms 
  : 
  Cerithia 
  and 
  a 
  few 
  dwarfed 
  Ostrece 
  occur, 
  with 
  great 
  num- 
  

   bers 
  of 
  Gyrence 
  ; 
  but 
  many 
  of 
  the 
  marine 
  genera 
  found 
  in 
  the 
  

   exposures 
  to 
  the 
  eastward 
  appear 
  to 
  be 
  here 
  quite 
  unrepresented. 
  

   At 
  Warden 
  Point 
  the 
  brackish-water 
  beds 
  are 
  now 
  concealed 
  ; 
  but 
  

   in 
  the 
  tumbled 
  cliffs 
  on 
  the 
  other 
  side 
  of 
  the 
  point 
  we 
  again 
  

   find 
  their 
  representatives 
  f 
  . 
  A 
  careful 
  study 
  of 
  this 
  part 
  of 
  the 
  

   cliff 
  shows 
  that 
  the 
  marine 
  and 
  brackish-water 
  shells 
  are 
  confined 
  

   to 
  several 
  thin 
  and 
  inconstant 
  bands. 
  At 
  a 
  distance 
  of 
  less 
  than 
  500 
  

   yards 
  from 
  the 
  point 
  where 
  the 
  brackish-water 
  beds 
  are 
  lost 
  in 
  the 
  

   cliffs, 
  through 
  denudation, 
  we 
  are 
  able 
  to 
  trace 
  their 
  representatives 
  in 
  

   the 
  Totland-Bay 
  brickyard. 
  This 
  brickyard 
  has 
  been 
  opened 
  for 
  a 
  

  

  * 
  Messrs. 
  Keeping 
  and 
  Tawney 
  differ 
  from 
  previous 
  observers 
  in 
  calling 
  one 
  

   of 
  the 
  forms 
  of 
  Cerithiwm 
  which 
  occur 
  here 
  C 
  ventricosum. 
  The 
  species 
  is 
  quite 
  

   distinct 
  from 
  the 
  shell 
  known 
  by 
  that 
  name 
  in 
  the 
  zone 
  of 
  C. 
  concavum. 
  

  

  t 
  My 
  original 
  section, 
  drawn 
  on 
  the 
  true 
  scale, 
  both 
  horizontal 
  and 
  vertical, 
  

   when 
  reduced 
  to 
  the 
  size 
  of 
  a 
  plate 
  in 
  the 
  Quarterly 
  Journal 
  of 
  the 
  Society, 
  was 
  

   too 
  small 
  to 
  allow 
  of 
  some 
  of 
  the 
  relations 
  of 
  the 
  beds 
  being 
  clearly 
  shown. 
  I 
  

   therefore, 
  for 
  the 
  sake 
  of 
  clearness, 
  added 
  a 
  second 
  section, 
  in 
  which 
  the 
  vertical 
  

   scale 
  was 
  exaggerated. 
  In 
  this 
  latter 
  section 
  the 
  position 
  of 
  the 
  Colwell 
  Bay 
  

   marine 
  bed 
  at 
  Warden 
  Point 
  is 
  clearly 
  shown, 
  as 
  my 
  critics 
  admit 
  ; 
  they 
  never- 
  

   theless 
  refuse 
  to 
  accept 
  this 
  section 
  as 
  illustrating 
  my 
  views, 
  but 
  severely 
  cri- 
  

   ticise 
  the 
  other 
  section 
  for 
  its 
  want 
  of 
  clearness. 
  In 
  the 
  same 
  way 
  they 
  dwell 
  

   at 
  great 
  length 
  on 
  some 
  obvious 
  printer's 
  errors 
  in 
  the 
  lists 
  of 
  fossils. 
  

  

  