﻿STEATA 
  OE 
  THE 
  HAMPSHIRE 
  "BASIN. 
  469 
  

  

  is 
  much 
  more 
  in 
  harmony 
  with 
  the 
  conclusions 
  of 
  Mr. 
  Prestwich 
  as 
  

   given 
  in 
  the 
  paragraph 
  cited 
  above. 
  Like 
  the 
  latter 
  author, 
  

   Mr. 
  Gardner 
  restricts 
  the 
  name 
  of 
  Lower 
  Bagshot 
  to 
  the 
  oldest 
  part 
  

   of 
  the 
  Middle 
  Eocene, 
  which 
  immediately 
  overlies 
  the 
  London 
  Clay, 
  

   and 
  he 
  finds 
  a 
  probable 
  representative 
  of 
  the 
  Middle 
  Bag-shot 
  in 
  his 
  

   " 
  Bournemouth 
  Marine," 
  and 
  of 
  the 
  Upper 
  Bagshot 
  in 
  his 
  Boscombe 
  

   Sand 
  with 
  its 
  remarkable 
  pebble-beds*. 
  

  

  In 
  his 
  memoir 
  on 
  the 
  London 
  basin, 
  Mr. 
  Whitaker 
  admits 
  that 
  

   the 
  grounds 
  on 
  which 
  the 
  classification 
  of 
  the 
  Geological 
  Survey 
  is 
  

   based 
  are 
  far 
  from 
  being 
  satisfactory. 
  As 
  an 
  explanation 
  of 
  the 
  

   difficulties 
  he 
  feels, 
  he 
  suggests 
  that 
  the 
  Barton 
  Clay 
  may 
  be 
  absent, 
  

   and 
  in 
  this 
  way 
  the 
  representative 
  of 
  a 
  higher 
  series 
  of 
  beds 
  may 
  

   come 
  to 
  rest 
  on 
  the 
  strata 
  of 
  Lower-Bracklesham 
  age 
  f. 
  But 
  of 
  the 
  

   existence 
  of 
  any 
  lacuna 
  between 
  the 
  Upper 
  and 
  Middle 
  Bagshots 
  no 
  

   evidence 
  has 
  ever 
  been 
  produced 
  ; 
  and 
  the 
  difficulty 
  experienced 
  by 
  

   Mr. 
  Prestwich 
  and 
  the 
  officers 
  of 
  the 
  Geological 
  Survey 
  in 
  fixing 
  

   upon 
  a 
  clear 
  line 
  of 
  demarcation 
  between 
  them 
  seems 
  to 
  point 
  to 
  

   the 
  conclusion 
  that 
  the 
  one 
  series 
  graduates 
  insensibly 
  into 
  the 
  

   other. 
  

  

  Still 
  more 
  recently 
  Mr. 
  Herries 
  has 
  brought 
  forward 
  the 
  evidence 
  

   of 
  some 
  additional 
  species 
  of 
  Mollusca, 
  which 
  he 
  has 
  found 
  in 
  the 
  

   Upper 
  Bagshot 
  beds 
  of 
  the 
  London 
  basin, 
  as 
  throwing 
  fresh 
  light 
  on 
  

   the 
  vexed 
  question 
  of 
  their 
  geological 
  age 
  ±. 
  These 
  fossils 
  are 
  un- 
  

   fortunately 
  all 
  casts 
  in 
  ironstone, 
  and 
  it 
  is 
  admitted 
  that 
  their 
  

   identification 
  is 
  in 
  most 
  cases 
  very 
  doubtful 
  ; 
  nevertheless 
  it 
  is 
  

   argued 
  that 
  the 
  balance 
  of 
  evidence 
  is 
  in 
  favour 
  of 
  associating 
  the 
  

   Upper 
  Bagshot 
  with 
  the 
  Barton 
  rather 
  than 
  with 
  the 
  Bracklesham 
  

   series. 
  As 
  there 
  are, 
  however, 
  only 
  three 
  species 
  said 
  to 
  be 
  certainly 
  

   recognizable, 
  which 
  are 
  peculiar 
  Barton 
  forms 
  (though 
  one 
  at 
  least 
  

   of 
  these 
  has 
  certainly 
  been 
  found 
  in 
  the 
  Bracklesham 
  series), 
  it 
  must 
  

   be 
  admitted 
  that 
  the 
  additional 
  evidence 
  is 
  not 
  of 
  any 
  very 
  great 
  

   weight. 
  Mr. 
  Herries, 
  however, 
  concludes 
  from 
  his 
  study 
  of 
  this 
  

   fauna 
  that 
  while 
  the 
  Upper 
  Bagshot 
  is 
  the 
  equivalent 
  of 
  the 
  Barton 
  

   Clay, 
  " 
  that 
  part 
  at 
  least 
  of 
  the 
  Hampshire-basin 
  Upper 
  Bagshot 
  which 
  

   at 
  its 
  summit, 
  immediately 
  under 
  the 
  freshwater 
  Lower 
  Headon 
  at 
  

   Hordwell, 
  contains 
  Olivet 
  Branderi 
  and 
  C. 
  ( 
  Vicarya) 
  concavum, 
  is 
  a 
  

   distinct 
  and 
  probably 
  higher 
  horizon 
  "§. 
  A 
  still 
  later 
  paper 
  on 
  the 
  

   subject 
  by 
  Mr. 
  Tawney 
  makes 
  the 
  same 
  admission 
  as 
  to 
  the 
  imper- 
  

   fection 
  of 
  the 
  evidence 
  on 
  which 
  the 
  "Upper 
  Bagshot" 
  of 
  the 
  

   London 
  and 
  Hampshire 
  basins 
  are 
  placed 
  on 
  the 
  same 
  horizon. 
  The 
  

   author, 
  however, 
  argues 
  in 
  favour 
  of 
  the 
  continued 
  use 
  of 
  the 
  term 
  

   for 
  the 
  strata 
  of 
  the 
  Hampshire 
  basin, 
  or, 
  in 
  other 
  words, 
  of 
  applying 
  

   the 
  same 
  name 
  to 
  two 
  sets 
  of 
  strata 
  of 
  admittedly 
  different 
  age. 
  

  

  It 
  will 
  be 
  seen 
  from 
  this 
  review 
  of 
  opinion 
  upon 
  the 
  subject 
  that, 
  

   while 
  the 
  general 
  correlation 
  of 
  the 
  beds 
  of 
  the 
  Hampshire 
  and 
  Paris 
  

   basins 
  is 
  undisputed, 
  the 
  exact 
  age 
  of 
  the 
  Bagshots 
  of 
  the 
  London 
  

  

  * 
  Quart. 
  Journ. 
  Geo!. 
  Soc. 
  vol. 
  xxxv. 
  (1879) 
  pp. 
  210, 
  227. 
  

   t 
  Mem. 
  Geol. 
  Surv. 
  Gt. 
  Britain, 
  vol. 
  iv. 
  pt. 
  i. 
  p. 
  333. 
  

   } 
  Geol. 
  Mag. 
  new 
  ser. 
  dec. 
  ii. 
  vol. 
  viii. 
  p. 
  171. 
  

   § 
  Loc. 
  cit. 
  p. 
  173. 
  

  

  