﻿STBATA 
  OF 
  THE 
  HAMPSHIRE 
  BASIN. 
  483 
  

  

  number 
  of 
  years 
  ; 
  and 
  I 
  have 
  had 
  frequent 
  opportunities 
  of 
  tracing 
  the 
  

   succession 
  of 
  beds 
  exposed 
  in 
  it, 
  which 
  the 
  Rev. 
  0. 
  Fisher 
  and 
  Mr. 
  

   A. 
  H. 
  S. 
  Lucas* 
  rightly 
  place 
  on 
  the 
  horizon 
  of 
  the 
  brackish-water 
  

   beds 
  of 
  Colwell 
  Bay 
  and 
  Warden 
  Cliff. 
  The 
  strata 
  exposed 
  here 
  are 
  

   as 
  follows 
  :— 
  At 
  the 
  top 
  we 
  find 
  a 
  mass 
  of 
  clays 
  containing 
  a 
  few 
  

   freshwater 
  shells. 
  These 
  clays 
  are 
  more 
  than 
  6 
  feet 
  in 
  thickness 
  : 
  

   and 
  at 
  their 
  base 
  is 
  found 
  a 
  band 
  containing 
  dwarfed 
  oysters 
  and 
  

   other 
  brackish-water 
  shells. 
  Gytlierea 
  incrassata 
  I 
  have 
  not 
  found 
  

   in 
  this 
  band, 
  though 
  it 
  very 
  probably 
  may 
  occur 
  there. 
  The 
  

   brackish-water 
  band, 
  however, 
  which 
  is 
  never 
  more 
  than 
  18 
  inches 
  

   thick, 
  is 
  so 
  inconstant 
  that 
  in 
  parts 
  of 
  the 
  pit 
  which 
  I 
  have 
  seen 
  ex- 
  

   cavated 
  it 
  is 
  found 
  to 
  thin 
  out 
  and 
  disappear 
  altogether; 
  it 
  is 
  

   underlain 
  by 
  10 
  or 
  12 
  feet 
  of 
  finely 
  laminated 
  white 
  sands 
  passing 
  

   into 
  sandy 
  clays. 
  In 
  the 
  foundation 
  of 
  a 
  kiln 
  these 
  clays 
  were 
  

   seen 
  to 
  pass 
  down 
  into 
  others 
  crowded 
  with 
  Potamomya 
  and 
  other 
  

   freshwater 
  shells. 
  

  

  JSTow 
  in 
  Headon 
  Hill, 
  where 
  these 
  beds 
  are 
  next 
  supposed 
  to 
  be 
  

   seen, 
  it 
  is 
  argued 
  that 
  we 
  find 
  the 
  " 
  Middle 
  Marine 
  " 
  of 
  Colwell 
  

   Bay 
  not 
  only 
  having 
  the 
  thickness, 
  but 
  exhibiting 
  all 
  the 
  minor 
  

   subdivisions 
  exposed 
  at 
  the 
  point 
  where 
  it 
  rises 
  from 
  the 
  shore, 
  each 
  

   little 
  band 
  with 
  precisely 
  the 
  same 
  series 
  of 
  fossils 
  in 
  it. 
  

  

  Between 
  the 
  two 
  points 
  compared, 
  there 
  is 
  a 
  distance 
  of 
  a 
  mile 
  

   and 
  a 
  half; 
  for 
  more 
  than 
  half 
  this 
  distance 
  we 
  can 
  trace 
  the 
  series 
  

   of 
  beds 
  at 
  frequent 
  intervals, 
  and 
  we 
  find 
  it 
  undergoing 
  four 
  com- 
  

   plete 
  changes 
  ; 
  and 
  at 
  the 
  last 
  place 
  where 
  it 
  is 
  seen 
  it 
  appears 
  to 
  

   be 
  on 
  the 
  point 
  of 
  thinning 
  out 
  and 
  disappearing 
  altogether. 
  Yet, 
  

   in 
  the 
  next 
  three 
  quarters 
  of 
  a 
  mile 
  it 
  is 
  supposed 
  to 
  recover 
  all 
  its 
  

   old 
  characters, 
  its 
  original 
  thickness, 
  and 
  even 
  every 
  minute 
  sub- 
  

   division 
  is 
  supposed 
  to 
  be 
  recognizable 
  in 
  it 
  ! 
  

  

  The 
  strata 
  seen 
  at 
  Headon 
  Hill, 
  however, 
  have 
  in 
  fact 
  very 
  little 
  

   in 
  common 
  with 
  those 
  of 
  Colwell 
  Bay. 
  In 
  order 
  to 
  make 
  a 
  

   " 
  Middle 
  Marine 
  series," 
  a 
  number 
  of 
  brackish-water 
  beds 
  have 
  

   been 
  grouped 
  with 
  a 
  number 
  of 
  purely 
  freshwater 
  strata, 
  including 
  

   limestones 
  crowded 
  with 
  Limnaia, 
  Planorbis, 
  and 
  Paluclina, 
  and 
  beds 
  

   of 
  lignite. 
  In 
  the 
  one 
  set 
  of 
  beds 
  Oeriihium 
  concavum 
  occurs 
  in 
  

   prodigious 
  abundance, 
  in 
  the 
  other 
  it 
  is 
  exceedingly 
  rare. 
  The 
  

   difference 
  between 
  the 
  two 
  series 
  of 
  beds 
  compared 
  was 
  long 
  ago 
  

   pointed 
  out 
  by 
  Mr. 
  Gf. 
  B. 
  Sowerby, 
  and 
  has 
  been 
  admitted 
  by 
  

   Sedgwick, 
  Forbes, 
  and 
  the 
  officers 
  of 
  the 
  Geological 
  Survey. 
  The 
  

   one 
  point 
  which 
  they 
  have 
  in 
  common 
  is 
  an 
  abundance 
  of 
  the 
  

   conspicuous 
  and 
  showy 
  Cytlierea 
  incrassata 
  ; 
  and 
  hence 
  the 
  local 
  

   fossil-collectors 
  call 
  each 
  of 
  them 
  a 
  " 
  Venus-bed." 
  

  

  My 
  critics 
  have 
  collected 
  about 
  50 
  species 
  of 
  fossils 
  from 
  both 
  

   these 
  beds, 
  and 
  state 
  that 
  they 
  find 
  them 
  to 
  be 
  identical. 
  But 
  it 
  is 
  

   clear, 
  from 
  what 
  is 
  stated 
  about 
  certain 
  species, 
  that 
  they 
  differ, 
  not 
  

   only 
  from 
  myself, 
  but 
  from 
  other 
  English 
  and 
  continental 
  palaeon- 
  

   tologists 
  as 
  to 
  the 
  identification 
  of 
  many 
  forms 
  of 
  Mollusca. 
  They 
  

   have 
  collected, 
  too, 
  only 
  the 
  shells 
  of 
  the 
  highest 
  brackish-water 
  

   bands 
  at 
  Headon 
  for 
  comparison 
  with 
  those 
  of 
  the 
  Colwell-Bay 
  bed, 
  

   * 
  Geol. 
  Mag. 
  dec. 
  ii. 
  vol. 
  ix. 
  (1882) 
  pp. 
  102, 
  138. 
  

  

  