﻿STRATA. 
  OF 
  THE 
  HAMPSHIRE 
  BASIN. 
  479 
  

  

  considerable 
  differences 
  between 
  these 
  two 
  sets 
  of 
  beds 
  and 
  the 
  

   faunas 
  which 
  they 
  contain. 
  

  

  The 
  officers 
  of 
  the 
  Geological 
  Survey, 
  it 
  is 
  true, 
  treat 
  these 
  two 
  sets 
  

   of 
  strata 
  as 
  being 
  upon 
  the 
  same 
  horizon 
  ; 
  but 
  they 
  at 
  the 
  same 
  time 
  

   maintain 
  the 
  identity 
  of 
  the 
  Headon-Hill 
  and 
  How-Ledge 
  limestones 
  ; 
  

   and 
  nothing 
  can 
  be 
  more 
  certain 
  than 
  that, 
  while 
  the 
  Colwell-Bay 
  

   brackish-water 
  beds 
  overlie 
  the 
  How-Ledge 
  limestone, 
  the 
  Headon- 
  

   Hill 
  brackish-water 
  beds 
  underlie 
  the 
  Headon-Hill 
  limestones. 
  

  

  The 
  great 
  difficulty 
  in 
  arriving 
  at 
  a 
  satisfactory 
  conclusion 
  con- 
  

   cerning 
  the 
  order 
  of 
  succession 
  of 
  the 
  strata 
  at 
  the 
  west 
  end 
  of 
  the 
  Isle 
  

   of 
  Wight 
  is 
  due 
  to 
  the 
  fact 
  that, 
  near 
  the 
  summit 
  of 
  the 
  anticlinal 
  

   in 
  Totland 
  Bay, 
  there 
  is 
  an 
  interruption 
  in 
  the 
  sequence, 
  owing 
  to 
  

   denudation, 
  to 
  the 
  beds 
  being 
  covered 
  up 
  by 
  later 
  deposits, 
  and 
  

   possibly 
  also 
  to 
  faulting. 
  While 
  a 
  substantial 
  agreement 
  exists 
  

   between 
  the 
  various 
  detailed 
  sections 
  which 
  have 
  been 
  published 
  of 
  

   the 
  strata 
  in 
  Colwell 
  Bay 
  and 
  Headon 
  Hill 
  respective^, 
  the 
  attempts 
  

   to 
  correlate 
  these 
  two 
  sections 
  have 
  given 
  rise 
  to 
  the 
  greatest 
  

   divergences 
  of 
  opinion. 
  

  

  Since 
  the 
  publication 
  of 
  my 
  own 
  attempt 
  to 
  explain 
  the 
  relations 
  

   of 
  these 
  sections, 
  several 
  other 
  memoirs 
  have 
  appeared 
  dealing 
  with 
  

   the 
  same 
  question. 
  Prof. 
  Blake*, 
  while 
  differing 
  from 
  me 
  on 
  many 
  

   points, 
  expresses 
  his 
  dissent 
  with 
  perfect 
  courtesy 
  and 
  fairness 
  . 
  Messrs. 
  

   Keeping 
  and 
  Tawney 
  have 
  also 
  published 
  their 
  interpretation 
  of 
  these 
  

   sections 
  f. 
  The 
  two 
  sections 
  recently 
  published, 
  though 
  measured 
  

   down 
  bed 
  by 
  bed, 
  differ 
  in 
  rnany 
  important 
  particulars 
  from 
  one 
  

   another, 
  from 
  the 
  sections 
  of 
  Mr. 
  Prestwich, 
  Dr. 
  Wright, 
  the 
  Geolo- 
  

   gical 
  Survey, 
  and 
  from 
  that 
  published 
  by 
  myself. 
  This 
  arises, 
  as 
  I 
  

   believe, 
  from 
  too 
  great 
  a 
  reliance 
  being 
  placed 
  upon 
  the 
  constancy 
  

   of 
  particular 
  bands 
  among 
  these 
  very 
  variable 
  estuarine 
  deposits. 
  

  

  In 
  dealing 
  with 
  the 
  stratigraphical 
  evidence, 
  Messrs. 
  Keeping 
  and 
  

   Tawney 
  state 
  that 
  I 
  have 
  altogether 
  misrepresented 
  the 
  position 
  of 
  

   the 
  "Marine 
  or 
  Middle 
  Headon.' 
  1 
  Any 
  one 
  who 
  will 
  refer 
  to 
  my 
  

   former 
  paper 
  will 
  at 
  once 
  see 
  that 
  the 
  position 
  which 
  I 
  assume 
  is 
  that 
  

   of 
  altogether 
  denying 
  the 
  existence 
  of 
  any 
  such 
  group 
  as 
  the 
  Middle 
  or 
  

   Marine 
  Headon. 
  Under 
  the 
  circumstances 
  I 
  may 
  perhaps 
  be 
  forgiven 
  

   for 
  quoting 
  what 
  I 
  actually 
  did 
  state 
  on 
  the 
  subject. 
  Speaking 
  of 
  

   the 
  Headon 
  group, 
  I 
  said 
  " 
  this 
  group 
  of 
  freshwater 
  and 
  estuarine 
  

   beds 
  is 
  more 
  than 
  400 
  feet 
  in 
  thickness, 
  and 
  exhibits 
  many 
  indica- 
  

   tions 
  of 
  the 
  prevalence 
  from 
  time 
  to 
  time 
  of 
  brackish-water 
  and 
  

   marine 
  conditions;" 
  and, 
  again, 
  " 
  in 
  all 
  the 
  lower 
  part 
  of 
  the 
  series 
  

   we 
  find 
  a 
  tendency 
  to 
  the 
  recurrence 
  of 
  brackish- 
  water 
  conditions 
  : 
  

   and 
  in 
  these 
  intercalated 
  nuvio-marine 
  bands 
  we 
  find 
  numerous 
  

   Cerithia, 
  Cyrence, 
  and 
  dwarfed 
  Ostrece." 
  

  

  Precisely 
  similar 
  conclusions 
  to 
  those 
  which 
  I 
  had 
  arrived 
  at 
  

   were 
  announced 
  by 
  Professor 
  Sedgwick 
  as 
  the 
  result 
  of 
  the 
  careful 
  

   study 
  of 
  the 
  Headon-Hill 
  strata, 
  which 
  he 
  made 
  with 
  the 
  assistance 
  

   of 
  Prof. 
  Henslow. 
  Professor 
  Sedgwick 
  states 
  that 
  " 
  in 
  Headon 
  Hill 
  

   the 
  middle 
  argillaceous 
  group 
  contains 
  innumerable 
  freshwater 
  shells, 
  

  

  * 
  Proc. 
  Geol. 
  Assoc, 
  vol. 
  vii. 
  p. 
  151. 
  

  

  t 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxvii. 
  (1881) 
  p. 
  85. 
  

  

  