﻿558 
  MR. 
  T. 
  ROBERTS 
  ON 
  THE 
  UPPER 
  

  

  On 
  the 
  south 
  coast, 
  Prof. 
  Blake 
  states 
  * 
  that 
  the 
  clays 
  near 
  the 
  

   base 
  of 
  the 
  Kimeridge 
  Clay 
  in 
  Ringstead 
  Bay 
  are 
  crowded 
  with 
  

   Ostrea 
  deltoidea, 
  and 
  that 
  west 
  of 
  Weymouth 
  this 
  same 
  fossil 
  is 
  

   chiefly 
  found 
  near 
  the 
  base, 
  but 
  is 
  not 
  limited 
  to 
  this 
  zone, 
  as 
  it 
  

   occurs 
  scattered 
  through 
  the 
  clay. 
  Waagen 
  similarly 
  mentions 
  the 
  

   occurrence 
  of 
  this 
  fossil 
  in 
  the 
  lower 
  portion 
  of 
  the 
  Kimeridge 
  Clay 
  

   at 
  Ringstead 
  Bay 
  f. 
  

  

  It 
  appears 
  therefore 
  that 
  the 
  basement-clays 
  of 
  the 
  Lower 
  

   Kimeridge 
  throughout 
  England 
  are, 
  in 
  almost 
  every 
  locality 
  where 
  

   they 
  have 
  been 
  observed, 
  characterized 
  by 
  the 
  abundance 
  of 
  Ostrea 
  

   deltoidea. 
  In 
  Lincolnshire 
  we 
  find 
  that 
  at 
  Woodhall 
  Spa, 
  West 
  

   Barkwith, 
  and 
  apparently 
  at 
  North 
  Kelsey, 
  there 
  are 
  similar 
  clays 
  

   which 
  should 
  be 
  placed 
  on 
  the 
  same 
  horizon. 
  Prof. 
  Judd 
  is 
  of 
  

   opinion 
  that 
  the 
  clays 
  of 
  Woodhall 
  Spa 
  belong 
  to 
  the 
  lower 
  portion 
  

   of 
  the 
  Kimeridge 
  Clay. 
  He 
  states 
  that 
  the 
  Lower 
  Kimeridge 
  of 
  

   Lincolnshire 
  is 
  divisible 
  into 
  two 
  well-marked 
  zones 
  : 
  in 
  the 
  upper, 
  

   he 
  adds, 
  " 
  Ostrea 
  deltoidea 
  never, 
  I 
  believe, 
  occurs 
  ; 
  while 
  in 
  the 
  

   lower, 
  which 
  is 
  well 
  seen 
  in 
  a 
  pit 
  at 
  Woodhall 
  Spa, 
  that 
  fossil 
  

   occurs 
  in 
  prodigious 
  numbers 
  " 
  J. 
  Prof. 
  Blake 
  also 
  places 
  these 
  

   clays 
  low 
  down 
  in 
  the 
  Kimeridge 
  Clay. 
  

  

  Should 
  these 
  deltoidea-cl&ys 
  of 
  Lincolnshire 
  prove 
  to 
  be 
  the 
  

   basement 
  beds 
  of 
  the 
  Lower 
  Kimeridge, 
  and 
  there 
  is 
  every 
  reason 
  

   for 
  regarding 
  them 
  as 
  such, 
  there 
  would 
  be 
  additional 
  evidence 
  for 
  

   placing 
  the 
  underlying 
  selenitiferous 
  clays 
  in 
  the 
  Corallian. 
  

  

  The 
  clays 
  of 
  the 
  succeeding 
  zone 
  have 
  for 
  their 
  characteristic 
  

   fossil 
  Ammonites 
  alternans, 
  whilst 
  this 
  fossil 
  is 
  absent 
  from 
  the 
  

   clays 
  of 
  the 
  overlying 
  zone. 
  

  

  In 
  Cambridgeshire 
  the 
  following 
  zones 
  have 
  been 
  made 
  out 
  in 
  

   the 
  Lower 
  Kimeridge 
  : 
  — 
  

  

  1. 
  Clays 
  with 
  Exogyra 
  virgula. 
  

  

  2. 
  „ 
  Ammonites 
  alternans. 
  

  

  3. 
  „ 
  Astarte 
  supracorallina. 
  

  

  4. 
  „ 
  Ostrea 
  deltoidea. 
  

  

  This 
  arrangement 
  differs 
  somewhat 
  from 
  that 
  of 
  Lincolnshire. 
  

   Amm. 
  alternans 
  is 
  chiefly 
  found 
  in 
  the 
  upper 
  portion 
  of 
  the 
  Lower 
  

   Kimeridge 
  of 
  Cambridgeshire, 
  whereas 
  in 
  Lincolnshire 
  it 
  is 
  charac- 
  

   teristic 
  of 
  a 
  lower 
  zone. 
  Astarte 
  supracorallina 
  occurs 
  throughout 
  

   the 
  Lower 
  Kimeridge 
  of 
  Lincolnshire 
  ; 
  it 
  has 
  not 
  as 
  yet 
  been 
  observed 
  

   in 
  the 
  upper 
  zones 
  in 
  Cambridgeshire. 
  

  

  The 
  fossil 
  zones 
  of 
  the 
  Kimeridge 
  Clay 
  are 
  in 
  some 
  instances 
  only 
  

   of 
  little 
  value 
  and 
  are 
  only 
  applicable 
  to 
  a 
  limited 
  area. 
  Prof. 
  

   Blake 
  states 
  § 
  that 
  " 
  in 
  the 
  Kimeridge 
  Clay 
  .... 
  many 
  fossils 
  

   which 
  in 
  one 
  locality 
  are 
  highly 
  characteristic 
  of 
  a 
  particular 
  por- 
  

   tion, 
  are 
  absent 
  in 
  that 
  portion 
  in 
  another 
  locality 
  and 
  charac- 
  

   terize 
  instead 
  a 
  lower 
  or 
  higher 
  horizon." 
  This 
  statement 
  fully 
  

   bears 
  out 
  the 
  observation 
  mentioned 
  above. 
  

  

  * 
  Op. 
  tit. 
  p. 
  212. 
  

  

  t 
  ' 
  Versuch 
  einer 
  allg. 
  Classif. 
  der 
  Schichten 
  des 
  oberen 
  Jura,' 
  p. 
  5. 
  

  

  | 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  toI. 
  xxiv. 
  p. 
  240. 
  § 
  Op. 
  tit. 
  p. 
  197. 
  

  

  