﻿JURASSIC 
  CLAYS 
  OF 
  LINCOLNSHIRE. 
  555 
  

  

  near 
  Brigg 
  (1), 
  and 
  since 
  the 
  line 
  of 
  strike 
  of 
  these 
  clays 
  appears 
  to 
  

   be 
  approximately 
  north 
  and 
  south, 
  the 
  clays 
  in 
  the 
  first-named 
  cutting 
  

   must 
  be 
  on 
  a 
  higher 
  horizon 
  than 
  those 
  of 
  the 
  latter. 
  The 
  fossils 
  

   obtained 
  by 
  myself 
  from 
  the 
  Brigg 
  cutting 
  did 
  not 
  include 
  a 
  single 
  

   Lower- 
  Kimeridge 
  species, 
  but 
  all 
  occur 
  in 
  the 
  selenitiferous 
  clays 
  

   further 
  south, 
  and 
  the 
  lithological 
  character 
  of 
  the 
  clays 
  is 
  identical, 
  

   and 
  they 
  also 
  lie 
  on 
  the 
  same 
  line 
  of 
  strike. 
  

  

  Prof*. 
  Blake's 
  sketch 
  map 
  * 
  is 
  not 
  quite 
  correctly 
  drawn 
  in 
  the 
  

   neighbourhood 
  of 
  Brigg, 
  Wrawby, 
  and 
  Barnetby 
  Junction, 
  and 
  this 
  

   gives 
  an 
  erroneous 
  position 
  to 
  the 
  sections 
  in 
  that 
  district. 
  

  

  The 
  Upper 
  Kimeridge 
  Clays 
  of 
  Lincolnshire 
  have 
  been 
  described 
  

   by 
  Prof. 
  Blake. 
  They 
  are 
  well 
  seen 
  in 
  the 
  brickyard 
  west 
  of 
  Ful- 
  

   letby, 
  and 
  are 
  composed 
  of 
  thin 
  papery 
  shales 
  in 
  which 
  Discina 
  

   latissima 
  occurs 
  in 
  some 
  abundance. 
  This 
  was 
  the 
  only 
  section 
  

   visited 
  in 
  the 
  clays 
  of 
  this 
  horizon. 
  

  

  (b) 
  Correlation. 
  

   It 
  has 
  already 
  been 
  shown 
  that 
  the 
  zone 
  of 
  black 
  selenitiferous 
  

   clays 
  overlies 
  the 
  Oxford 
  Clays 
  containing 
  cordati 
  Ammonites, 
  i. 
  e. 
  

   the 
  uppermost 
  portion 
  of 
  that 
  formation. 
  They 
  are 
  not 
  of 
  Oxford- 
  

   Clay 
  age 
  because 
  : 
  — 
  

  

  1. 
  They 
  do 
  not 
  contain 
  a 
  single 
  species 
  peculiar 
  to 
  the 
  Oxford 
  

  

  Clay. 
  m 
  

  

  2. 
  The 
  fossils 
  are 
  not 
  pyritized 
  ; 
  

  

  3. 
  Some 
  of 
  the 
  fossils 
  are 
  characteristic 
  of 
  the 
  Corallian. 
  

  

  The 
  question 
  now 
  arises, 
  are 
  they 
  of 
  Corallian 
  age 
  ? 
  If 
  these 
  

   black 
  clays 
  are 
  compared 
  with 
  the 
  Ampthill 
  Clay 
  of 
  Cambridge- 
  

   shire 
  it 
  will 
  be 
  seen 
  that 
  they 
  agree 
  in 
  the 
  following 
  particulars 
  : 
  — 
  

  

  1. 
  Lithologically 
  they 
  are 
  identical, 
  both 
  being 
  dark 
  clays 
  often 
  

  

  highly 
  charged 
  with 
  selenite 
  crystals 
  ; 
  

  

  2. 
  The 
  fossils 
  Ostrea 
  deltoidea 
  and 
  Gryphcea 
  dilatata 
  occur 
  in 
  

  

  both 
  ; 
  

  

  3. 
  Prom 
  the 
  accompanying 
  table 
  it 
  will 
  be 
  seen 
  that 
  out 
  of 
  

  

  23 
  species 
  determined, 
  16 
  are 
  common 
  to 
  the 
  Ampthill 
  

   Clay 
  of 
  Cambridgeshire. 
  

  

  That 
  these 
  selenitiferous 
  clays 
  are 
  Corallian 
  is 
  clearly 
  shown 
  by 
  

   the 
  following 
  facts 
  : 
  — 
  

  

  1 
  . 
  They 
  apparently 
  overlie 
  conformably 
  the 
  uppermost 
  zone 
  of 
  

  

  Oxford 
  Clay 
  characterized 
  by 
  the 
  presence 
  of 
  cordati 
  

   Ammonites 
  and 
  Amm. 
  perarmatus. 
  

  

  2. 
  All 
  the 
  determined 
  species 
  which 
  the 
  writer 
  has 
  seen 
  from 
  

  

  these 
  clays 
  also 
  occur 
  in 
  the 
  Corallian 
  of 
  other 
  areas, 
  and, 
  

   further, 
  they 
  contain 
  several 
  species 
  which 
  are 
  peculiar 
  to 
  

   that 
  formation, 
  e. 
  g. 
  Amm. 
  cawtonensis, 
  Pholadomya 
  con- 
  

   centrica, 
  Avicula 
  pteropernoides, 
  &c. 
  

  

  3. 
  The 
  accompanying 
  list 
  of 
  fossils 
  does 
  not 
  include 
  a 
  single 
  

  

  species 
  peculiar 
  to 
  either 
  the 
  Oxford 
  or 
  Kimeridge 
  Clays. 
  

  

  * 
  Op. 
  cit 
  p. 
  202. 
  

  

  