﻿JURASSIC 
  CLAYS 
  OE 
  LINCOLNSHIRE. 
  557 
  

  

  4. 
  Gryplicea 
  dilatata 
  and 
  Ostrea 
  deltoidea 
  are 
  found 
  associated 
  

   together 
  in 
  these 
  selenitiferous 
  clays, 
  and 
  also 
  in 
  the 
  Coral- 
  

   lian, 
  but 
  not 
  in 
  the 
  Oxford 
  or 
  Kimeridge 
  Clays. 
  Gry- 
  

   phcea 
  dilatata 
  is 
  recorded 
  * 
  from 
  the 
  Kimeridge 
  Clay 
  of 
  

   Clophill, 
  in 
  Bedfordshire, 
  and 
  doubtfully 
  from 
  the 
  same 
  

   beds 
  at 
  Wolvercot, 
  Bucks. 
  Clophill 
  is 
  mapped 
  as 
  standing 
  

   on 
  Lower 
  Greensand, 
  and 
  the 
  clays 
  which 
  occur 
  below 
  it 
  

   are 
  probably 
  Corallian. 
  Ampthill, 
  the 
  typical 
  locality 
  for 
  

   the 
  Corallian 
  clays, 
  lies 
  a 
  little 
  to 
  the 
  east 
  of 
  Clophill. 
  

   Ostrea 
  deltoidea 
  is 
  stated 
  f 
  to 
  occur 
  in 
  the 
  Oxford 
  Clay 
  of 
  

   "Wiltshire 
  ; 
  but 
  the 
  writer 
  is 
  not 
  aware 
  of 
  any 
  other 
  locality 
  

   where 
  this 
  fossil 
  occurs 
  so 
  low 
  down 
  in 
  the 
  series. 
  With 
  

   these 
  two 
  doubtful 
  exceptions, 
  the 
  occurrence 
  of 
  Gryphaza 
  

   dilatata 
  associated 
  with 
  Ostrea 
  deltoidea 
  is 
  strictly 
  limited 
  

   to 
  the 
  Corallian 
  rocks, 
  the 
  former 
  being 
  found 
  in 
  the 
  Lower 
  

   Calcareous 
  Grit 
  and 
  Coralline 
  Oolite, 
  and 
  the 
  latter 
  in 
  the 
  

   Coralline 
  Oolite 
  and 
  supra-Coralline 
  Beds. 
  In 
  Lincoln- 
  

   shire 
  Gryphcea 
  dilatata 
  is 
  most 
  common 
  in 
  the 
  lower 
  part 
  

   of 
  the 
  selenitiferous 
  clays, 
  whilst 
  0. 
  deltoidea 
  is 
  more 
  fre- 
  

   quently 
  met 
  with 
  in 
  the 
  upper 
  part 
  of 
  these 
  clays. 
  

  

  From 
  these 
  considerations, 
  therefore, 
  it 
  seems 
  highly 
  probable 
  

   that 
  the 
  black 
  selenitiferous 
  clays 
  of 
  Lincolnshire 
  are 
  partly 
  repre- 
  

   sented 
  by 
  the 
  Ampthill 
  Clays 
  further 
  south, 
  and 
  that 
  they 
  are 
  of 
  

   Corallian 
  age. 
  Their 
  fauna 
  certainly 
  links 
  them 
  more 
  closely 
  with 
  

   the 
  Corallian 
  than 
  with 
  the 
  Oxford 
  or 
  Kimeridge 
  Clays. 
  jN"o 
  lime- 
  

   stone 
  corresponding 
  in 
  age 
  to 
  the 
  Elsworth 
  rock, 
  and 
  separating 
  the 
  

   Oxford 
  and 
  Corallian 
  Clays, 
  has 
  as 
  yet 
  been 
  met 
  with 
  in 
  Lincoln- 
  

   shire. 
  

  

  It 
  should 
  be 
  mentioned 
  that 
  the 
  occurrence 
  of 
  selenite 
  crystals 
  in 
  

   these 
  clays 
  is 
  of 
  little 
  classificatory 
  value 
  when 
  taken 
  alone, 
  because 
  

   such 
  crystals 
  are 
  commonly 
  met 
  with 
  in 
  the 
  Kimeridge 
  Clay 
  £, 
  and 
  

   to 
  some 
  extent 
  in 
  the 
  Oxford 
  Clay 
  §. 
  

  

  The 
  next 
  zone 
  of 
  clay 
  to 
  be 
  considered 
  is 
  that 
  in 
  which 
  Ostrea 
  

   deltoidea 
  occurs 
  in 
  considerable 
  abundance. 
  Prof. 
  Phillips, 
  in 
  

   describing 
  the 
  Kimeridge 
  Clay 
  near 
  Oxford, 
  states 
  that 
  near 
  its 
  base 
  

   is 
  a 
  bed 
  of 
  Ostrea 
  deltoidea, 
  which 
  has 
  been 
  recognized 
  as 
  far 
  north 
  as 
  

   Yorkshire 
  ||. 
  It 
  has 
  already 
  been 
  mentioned 
  that 
  at 
  the 
  base 
  of 
  the 
  

   Kimeridge 
  Clays 
  of 
  Cambridgeshire 
  is 
  a 
  layer 
  of 
  phosphatic 
  nodules. 
  

   The 
  clays 
  immediately 
  above 
  are 
  crowded 
  with 
  Ostrea 
  deltoidea. 
  

   Precisely 
  the 
  same 
  thing 
  occurs 
  in 
  Oxfordshire 
  %. 
  In 
  Wiltshire 
  

   Ostrea 
  deltoidea 
  is 
  common 
  in 
  all 
  the 
  beds 
  of 
  the 
  Kimeridge 
  clay 
  **. 
  

  

  * 
  Fitton, 
  Geol. 
  Trans. 
  2nd 
  ser. 
  iv. 
  p. 
  302. 
  

  

  t 
  Eamsay, 
  " 
  Geol. 
  of 
  parts 
  of 
  Wilts 
  and 
  Gloucester" 
  (Surv. 
  Mem.), 
  p. 
  20. 
  

  

  { 
  "Geol. 
  of 
  Banbury" 
  (Surv. 
  Mem.), 
  p. 
  46. 
  "Geol. 
  of 
  Oxford 
  and 
  Berk- 
  

   shire" 
  (Surv. 
  Mem.), 
  p. 
  9. 
  Phillips's 
  'Geology 
  of 
  Oxford,' 
  p. 
  325. 
  Hudle- 
  

   ston, 
  " 
  Yorkshire 
  Oolites 
  " 
  (Proc. 
  Geol. 
  Assoc, 
  vol. 
  iv. 
  p. 
  360), 
  &c. 
  

  

  § 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xlii. 
  p. 
  544. 
  

  

  || 
  " 
  Geol. 
  of 
  Oxford," 
  p. 
  325. 
  

  

  ^[ 
  Q.uart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xix. 
  p. 
  236. 
  Geol. 
  Trans. 
  2nd 
  ser. 
  iv. 
  p. 
  278. 
  

  

  ** 
  "Geology 
  of 
  parts 
  of 
  Wilts 
  and 
  Gloucester," 
  p. 
  23. 
  

  

  