﻿468 
  PKOF. 
  J. 
  W. 
  JUDD 
  ON 
  THE 
  EOCENE 
  AND 
  OLIGOCENE 
  

  

  London 
  Clay 
  were 
  regarded 
  by 
  Mr. 
  Prestwich 
  as 
  probably 
  repre- 
  

   senting 
  the 
  Lower 
  Bagshot 
  of 
  the 
  London 
  basin, 
  and 
  as 
  being, 
  like 
  it, 
  

   of 
  freshwater 
  origin*. 
  The 
  pipe-clays 
  with 
  abundant 
  vegetable 
  

   remains 
  at 
  Corfe, 
  Branksea, 
  Studland, 
  and 
  Alum 
  Bay, 
  all 
  appear 
  to 
  

   be 
  in 
  this 
  part 
  of 
  the 
  Middle 
  Eocene 
  series. 
  It 
  is 
  worthy 
  of 
  note 
  

   that 
  Mr. 
  Prestwich 
  confined 
  the 
  term 
  Lower 
  Bagshot 
  beds 
  to 
  his 
  

   stratum 
  5 
  of 
  Whitecliff 
  Bay, 
  which 
  he 
  had 
  previously 
  called 
  the 
  

   " 
  Lower 
  Bracklesham 
  Sands 
  " 
  f. 
  

  

  The 
  Middle 
  Bagshot 
  of 
  the 
  London 
  basin 
  is 
  only 
  from 
  40 
  to 
  (50 
  

   feet 
  in 
  thickness 
  ; 
  it 
  is 
  of 
  somewhat 
  argillaceous 
  composition, 
  and 
  

   of 
  undoubted 
  marine 
  origin. 
  So 
  inconstant 
  are 
  its 
  characters, 
  

   however, 
  in 
  different 
  parts 
  of 
  the 
  London 
  basin, 
  that 
  the 
  line 
  of 
  

   demarcation 
  between 
  this 
  and 
  the 
  other 
  divisions 
  of 
  the 
  Bagshot 
  

   beds 
  which 
  was 
  adopted 
  by 
  Mr. 
  Prestwich, 
  has 
  evidently 
  not 
  been 
  

   followed 
  by 
  the 
  officers 
  of 
  the 
  Geological 
  Survey. 
  

  

  The 
  Middle 
  Bagshots 
  contain 
  only 
  a 
  few 
  marine 
  fossils 
  : 
  but 
  these 
  

   are 
  sufficient 
  to 
  enable 
  us 
  to 
  correlate 
  them, 
  without 
  doubt, 
  with 
  the 
  

   lower 
  part 
  of 
  the 
  Bracklesham 
  series 
  in 
  the 
  Hampshire 
  basin. 
  The 
  

   Upper 
  Bagshot 
  of 
  the 
  London 
  basin 
  has 
  a 
  thickness 
  varying 
  from 
  

   100 
  to 
  L50 
  feet, 
  and 
  only 
  differs 
  from 
  the 
  Middle 
  Bagshot 
  in 
  its 
  

   more 
  purely 
  arenaceous 
  character, 
  a 
  distinction 
  which 
  is 
  far 
  from 
  

   being 
  constant. 
  The 
  Dpper, 
  like 
  the 
  Middle 
  Bagshots, 
  are 
  of 
  marine 
  

   origin 
  ; 
  but 
  the 
  fossils 
  are 
  exceedingly 
  rare 
  and 
  very 
  badly 
  preserved. 
  

  

  With 
  regard 
  to 
  the 
  portions 
  of 
  the 
  Hampshire 
  Eocenes 
  with 
  which 
  

   the 
  Upper 
  Bagshot 
  of 
  the 
  London 
  basin 
  ought 
  to 
  be 
  correlated, 
  the 
  

   greatest 
  difference 
  of 
  opinion 
  has 
  prevailed. 
  Mr. 
  Prestwich's 
  views 
  

   are 
  clearly 
  stated 
  in 
  the 
  following 
  passage 
  : 
  — 
  

  

  "How 
  far 
  the 
  Upper 
  Bagshot 
  Sands 
  are 
  related 
  to 
  the 
  Brackles- 
  

   ham 
  series 
  it 
  is 
  difficult 
  to 
  say. 
  The 
  few 
  fossils 
  I 
  have 
  found 
  in 
  

   those 
  sands 
  arc 
  not 
  sufficiently 
  distinctive 
  to 
  enable 
  me 
  to 
  pronounce 
  

   a 
  decided 
  opinion. 
  As. 
  however, 
  the 
  fossiliferous 
  Middle 
  Bagshot 
  

   Sands 
  are 
  very 
  thin, 
  and 
  represent 
  apparently 
  only 
  the 
  lower 
  or 
  

   middle 
  part 
  of 
  the 
  Bracklesham 
  series, 
  I 
  think 
  it 
  probable 
  that 
  it 
  is 
  

   the 
  upper 
  beds 
  of 
  sand 
  and 
  clay 
  of 
  the 
  latter 
  which 
  pass 
  north- 
  

   wards 
  into 
  the 
  thick 
  sands 
  of 
  the 
  Upper 
  Bagshot 
  Sands. 
  Still 
  it 
  

   is 
  possible 
  that 
  part 
  of 
  them 
  may 
  represent 
  the 
  Barton 
  series 
  ; 
  for 
  

   we 
  see 
  at 
  Barton 
  how 
  shifting 
  the 
  upper 
  part 
  of 
  that 
  series 
  is 
  — 
  how 
  

   clay 
  predominates 
  at 
  one 
  place 
  and 
  sands 
  at 
  another 
  " 
  J. 
  

  

  In 
  the 
  various 
  publications 
  of 
  the 
  Geological 
  Survey, 
  however, 
  

   the 
  thin 
  division 
  of 
  the 
  Middle 
  Bagshot 
  is 
  correlated 
  without 
  any 
  

   expression 
  of 
  doubt 
  with 
  the 
  whole 
  of 
  the 
  Bracklesham 
  and 
  Barton 
  

   series, 
  a 
  mass 
  of 
  strata 
  which 
  at 
  Whitecliff 
  Bay 
  exceeds 
  700 
  feet 
  

   in 
  thickness, 
  while 
  a 
  series 
  of 
  sands 
  overlying 
  the 
  Barton 
  Clay 
  is 
  

   regarded 
  as 
  the 
  representative 
  of 
  the 
  Upper 
  Bagshot. 
  

  

  Mr. 
  Gardner's 
  studies 
  of 
  the 
  beds 
  in 
  the 
  Bournemouth 
  area 
  have 
  

   led 
  him 
  to 
  another, 
  and 
  much 
  more 
  probable, 
  correlation 
  of 
  the 
  

   Middle 
  Eocenes 
  of 
  the 
  Hampshire 
  and 
  London 
  basins, 
  a 
  view 
  which 
  

  

  * 
  Quart, 
  Jouru. 
  Geol. 
  Soc. 
  vol. 
  iii. 
  (1847) 
  p. 
  395. 
  

   t 
  Ibid. 
  vol. 
  xiii. 
  (1857) 
  p. 
  90, 
  note. 
  

   | 
  Ibid. 
  vol. 
  xiii. 
  p. 
  132. 
  

  

  