﻿JURASSIC 
  CLAYS 
  OF 
  LINCOLNSHIRE. 
  559 
  

  

  At 
  Ringstead 
  Bay 
  Waagen 
  mentions 
  * 
  the 
  occurrence 
  of 
  Ammo- 
  

   nites 
  alternans 
  in 
  the 
  clays 
  which 
  succeed 
  those 
  containing 
  Ostrea 
  

   deltoidea, 
  whilst 
  it 
  is 
  absent 
  in 
  his 
  so-called 
  Middle 
  Kimeridge, 
  

   which 
  contains 
  Exogyra 
  virgula, 
  and 
  is 
  what 
  is 
  generally 
  considered 
  

   as 
  the 
  upper 
  portion 
  of 
  the 
  Lower 
  Kimeridge. 
  In 
  this 
  area, 
  there- 
  

   fore, 
  the 
  fossil 
  zones 
  of 
  the 
  Lower 
  Kimeridge 
  agree 
  closely 
  with 
  

   those 
  of 
  Lincolnshire. 
  

  

  Exogyra 
  virgula 
  has 
  not 
  as 
  yet 
  been 
  obtained 
  from 
  the 
  Kimeridge 
  

   Clays 
  of 
  Lincolnshire. 
  In 
  Cambridgeshire 
  this 
  fossil 
  is 
  found 
  

   chiefly 
  in 
  the 
  uppermost 
  portion 
  of 
  the 
  Lower 
  Kimeridge, 
  and 
  is 
  

   occasionally 
  met 
  with 
  in 
  the 
  lower 
  zones. 
  Exogyra 
  virgula 
  should 
  

   occur 
  in 
  Lincolnshire 
  in 
  clays 
  a 
  little 
  higher 
  in 
  the 
  series 
  than 
  

   those 
  of 
  Horncastle 
  ; 
  but 
  at 
  present 
  there 
  appears 
  to 
  be 
  no 
  exposure 
  

   between 
  the 
  Horncastle 
  pits 
  and 
  the 
  Upper 
  Kimeridge 
  of 
  Fulletby. 
  

  

  The 
  paucity 
  of 
  sections 
  in 
  the 
  Upper 
  Jurassic 
  Clays 
  of 
  Lincoln- 
  

   shire 
  renders 
  the 
  mapping 
  of 
  the 
  various 
  divisions 
  rather 
  unsatis- 
  

   factory, 
  and 
  it 
  must 
  be 
  remembered 
  that 
  the 
  lines 
  drawn 
  on 
  the 
  

   accompanying 
  map 
  (fig. 
  1, 
  p. 
  456), 
  separating 
  the 
  various 
  clays, 
  have 
  

   been 
  set 
  down 
  in 
  accordance 
  with 
  our 
  present 
  somewhat 
  limited 
  

   knowledge 
  of 
  their 
  distribution. 
  Subsequent 
  discoveries 
  may 
  modify 
  

   them 
  considerably. 
  

  

  The 
  boundaries 
  of 
  the 
  Lower 
  and 
  Middle 
  Jurassic 
  and 
  the 
  Cre- 
  

   taceous 
  have 
  been 
  taken 
  in 
  great 
  measure 
  from 
  the 
  Geological 
  Survey 
  

   Map 
  (sheet 
  83). 
  

  

  4. 
  Summary. 
  

  

  The 
  facts 
  stated 
  in 
  the 
  foregoing 
  paper 
  indicate 
  that 
  the 
  Upper 
  

   Jurassic 
  Clays 
  of 
  Lincolnshire 
  may 
  be 
  divided 
  into 
  : 
  — 
  

  

  3. 
  Kimeridge 
  Clay 
  : 
  — 
  

  

  (b) 
  Upper 
  Kimeridge 
  : 
  thin 
  papery 
  shales, 
  with 
  Discina 
  

  

  latissima. 
  

   (a) 
  Lower 
  Kimeridge: 
  dark 
  clays, 
  with 
  septarian 
  nodules, 
  

   subdivided 
  into 
  : 
  — 
  

   (iii.) 
  Clays 
  with 
  Amm. 
  mutabilis, 
  Astarte 
  supracorallina, 
  

  

  &c. 
  

   (ii.) 
  Clays 
  with 
  Amm. 
  alternans. 
  

   (i.) 
  Clays 
  crowded 
  with 
  Ostrea 
  deltoidea. 
  

  

  2. 
  Corallian. 
  Black 
  selenitiferous 
  clays, 
  with 
  Amm. 
  plicatilis, 
  

   Amm. 
  caivtonensis, 
  Bel. 
  abbreviatus, 
  Gryphcea 
  dilatata, 
  Ostrea 
  

   deltoidea, 
  &c. 
  

  

  1. 
  Oxford 
  Clay, 
  subdivided 
  into 
  five 
  palseontological 
  zones, 
  with 
  

   the 
  Kellaways 
  Rock 
  at 
  its 
  base. 
  

  

  Discussion. 
  

  

  Prof. 
  Blake 
  was 
  fully 
  prepared 
  to 
  hear 
  of 
  the 
  separation 
  of 
  rocks 
  

   of 
  Corallian 
  age 
  in 
  Lincolnshire, 
  though 
  as 
  those 
  rocks 
  are 
  them- 
  

   selves 
  of 
  an 
  episodal 
  character, 
  the 
  features 
  which 
  specially 
  dis- 
  

   tinguish 
  them 
  are 
  not 
  likely 
  to 
  occur. 
  Yet 
  he 
  was 
  perfectly 
  aware 
  

   * 
  Op. 
  cit. 
  p. 
  5. 
  

  

  