﻿JURASSIC 
  CLAYS 
  OP 
  LINCOLNSHIRE. 
  547 
  

  

  In 
  1862, 
  Professor 
  Seeley 
  * 
  divided 
  the 
  " 
  Fen-Clay 
  " 
  of 
  Cam- 
  

   bridgeshire 
  into 
  : 
  — 
  

  

  1. 
  Kimeridge 
  Clay. 
  

  

  2. 
  Ampthill 
  Clay 
  f, 
  which 
  he 
  regarded 
  as 
  Corallian. 
  

  

  3. 
  Oxford 
  Clay.* 
  

  

  The 
  Ampthill 
  Clay 
  rests 
  on 
  the 
  Elsworth 
  Rock, 
  which 
  was 
  con- 
  

   sidered 
  by 
  Seeley 
  to 
  be 
  " 
  the 
  uppermost 
  zone 
  of 
  the 
  Oxford 
  Clay." 
  

   He 
  states 
  that 
  " 
  the 
  upper 
  boundary 
  of 
  the 
  Tetworth 
  [Ampthill] 
  Clay 
  

   cannot 
  be 
  given 
  with 
  any 
  certainty 
  " 
  £. 
  

  

  In 
  the 
  Sedgwick 
  Essay 
  for 
  1885, 
  it 
  is 
  shown 
  that 
  (1) 
  the 
  Els- 
  

   worth 
  Rock 
  is 
  of 
  Lower-Calcareous-Grit 
  age, 
  (2) 
  the 
  basement-bed 
  

   of 
  the 
  Kimeridge 
  Clay 
  contains 
  numerous 
  phosphatic 
  nodules, 
  which 
  

   give 
  a 
  well-defined 
  upper 
  boundary 
  to 
  the 
  Ampthill 
  Clay. 
  The 
  

   succession 
  in 
  the 
  Upper 
  Jurassic 
  Clays 
  of 
  Cambridgeshire 
  is, 
  there- 
  

   fore, 
  as 
  follows 
  : 
  — 
  

  

  1. 
  Kimeridge 
  Clay 
  with 
  a 
  phosphatic-nodule 
  bed 
  at 
  its 
  base. 
  

  

  2. 
  Ampthill 
  Clay, 
  together 
  with 
  the 
  Elsworth 
  Rock, 
  represent- 
  

  

  ing 
  the 
  Corallian. 
  

  

  3. 
  Oxford 
  Clay. 
  

  

  During 
  the 
  past 
  summer 
  the 
  various 
  clay-pits 
  and 
  sections 
  marked 
  

   on 
  the 
  accompanying 
  map 
  (fig. 
  1) 
  were 
  visited 
  with, 
  a 
  view 
  of 
  

   ascertaining 
  whether 
  any 
  clays 
  corresponding 
  to 
  the 
  Ampthill 
  Clay 
  

   occur 
  in 
  Lincolnshire 
  between 
  the 
  Oxford 
  and 
  Kimeridge. 
  Parti- 
  

   cular 
  attention 
  was 
  given 
  to 
  those 
  exposures 
  which 
  are 
  situated 
  in 
  

   the 
  upper 
  part 
  of 
  the 
  Oxford 
  Clays, 
  and 
  the 
  lower 
  portion 
  of 
  the 
  

   Kimeridge 
  Clays 
  shown 
  in 
  the 
  Survey 
  Map 
  (sheet 
  83) 
  and 
  Blake's 
  

   sketch 
  map 
  (op. 
  cit. 
  p. 
  202). 
  It 
  is 
  proposed 
  in 
  this 
  paper 
  to 
  give 
  

   the 
  results 
  obtained 
  during 
  that 
  visit. 
  

  

  The 
  portion 
  of 
  Lincolnshire 
  occupied 
  by 
  these 
  Jurassic 
  Clays 
  is 
  

   more 
  or 
  less 
  completely 
  covered 
  by 
  drift, 
  and 
  the 
  only 
  places 
  where 
  

   sections 
  can 
  be 
  seen 
  in 
  the 
  clays 
  are 
  the 
  various 
  clay-pits, 
  and 
  occa- 
  

   sionally 
  in 
  the 
  railway- 
  cuttings. 
  Further, 
  some 
  of 
  the 
  drifts 
  are 
  

   largely 
  made 
  up 
  of 
  Jurassic 
  Clays, 
  which 
  are 
  not 
  in 
  place, 
  because 
  

   they 
  contain 
  fragments 
  of 
  chalk 
  and 
  other 
  rocks. 
  Sometimes 
  these 
  

   glacial 
  clays 
  are 
  fossiliferous, 
  and 
  great 
  care 
  has 
  to 
  be 
  taken 
  that 
  the 
  

   fossils 
  obtained 
  in 
  any 
  locality 
  come 
  from 
  the 
  undisturbed 
  clay, 
  and 
  

   not 
  from 
  the 
  drift. 
  

  

  2. 
  The 
  Oxford 
  Clay. 
  

  

  The 
  general 
  character 
  of 
  the 
  Oxford 
  Clay 
  of 
  Lincolnshire 
  is 
  that 
  

   of 
  a 
  dark 
  blue 
  clay, 
  with 
  pyritized 
  fossils 
  and 
  nodules 
  of 
  iron 
  

   pyrites 
  §. 
  Morris 
  |j 
  describes 
  the 
  basement 
  beds 
  in 
  the 
  Casewick 
  

   Cutting, 
  where 
  he 
  recognizes 
  the 
  Kellaways 
  Rock 
  : 
  a 
  more 
  complete 
  

   account 
  of 
  this 
  subdivision 
  is 
  also 
  given 
  in 
  the 
  Survey 
  Memoir 
  ^[. 
  

  

  * 
  Ann. 
  Mag. 
  Nat. 
  Hist. 
  3rd 
  ser. 
  vol. 
  x. 
  p. 
  101. 
  

  

  t 
  This 
  clay 
  has 
  also 
  been 
  called 
  the 
  Bluntisham, 
  Tetworth, 
  and 
  Gamlingay 
  

   Clays. 
  

  

  | 
  Geologist, 
  vol. 
  iv. 
  p. 
  553. 
  § 
  Mem. 
  Geol. 
  Surv. 
  sheet 
  83, 
  p. 
  76. 
  

  

  i| 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  ix. 
  p. 
  333. 
  % 
  Sheet 
  83, 
  p. 
  73. 
  

  

  2a2 
  

  

  