﻿SUBDIVISIONS 
  OF 
  THE 
  SPEETON 
  CLAY. 
  581 
  

  

  our 
  actual 
  knowledge 
  of 
  the 
  Speeton 
  section 
  does 
  not 
  extend 
  to 
  any 
  

   great 
  depth 
  into 
  the 
  Jurassic 
  portion 
  of 
  the 
  series 
  *. 
  

  

  Supposed 
  Fault 
  in 
  Speeton 
  Gap. 
  

  

  It 
  has 
  been 
  suggested 
  that 
  a 
  fault 
  of 
  considerable 
  throw 
  may 
  exist 
  

   between 
  the 
  chalk 
  and 
  the 
  main 
  mass 
  of 
  the 
  clays 
  at 
  Speeton, 
  with 
  

   a 
  course 
  coinciding 
  nearly 
  with 
  the 
  ravine 
  of 
  the 
  Speeton 
  Beck. 
  

   But 
  I 
  think 
  the 
  supposed 
  indications 
  of 
  a 
  fault 
  may 
  be 
  better 
  ex- 
  

   plained 
  by 
  an 
  ancient 
  foundering 
  of 
  the 
  chalk 
  escarpment, 
  possibly 
  in 
  

   pre-glacial 
  times. 
  I 
  have 
  seen 
  the 
  beach 
  cleared 
  off 
  the 
  Gap 
  and 
  for 
  

   some 
  distance 
  both 
  northward 
  and 
  southward, 
  and 
  could 
  find 
  nothing 
  

   more 
  important 
  than 
  a 
  small 
  break 
  which 
  seems 
  to 
  cross 
  the 
  beach 
  

   slightly 
  north 
  of 
  the 
  Gap, 
  as 
  shown 
  in 
  fig. 
  1, 
  and 
  which 
  is 
  quite 
  of 
  

   minor 
  consequence. 
  

  

  The 
  Vertical 
  Section. 
  

  

  As 
  it 
  is 
  impossible 
  to 
  obtain 
  a 
  detailed 
  section 
  in 
  the 
  cliff, 
  I 
  have 
  

   measured 
  the 
  succession 
  of 
  the 
  beds 
  on 
  the 
  shore 
  as 
  opportunities 
  

   occurred 
  ; 
  and 
  though 
  the 
  difficulties 
  met 
  with 
  on 
  a 
  sloping 
  shore 
  

   preclude 
  the 
  possibility 
  of 
  absolute 
  accuracy, 
  I 
  am 
  confident 
  that 
  

   the 
  following 
  sections, 
  which 
  are 
  based 
  on 
  a 
  long 
  series 
  of 
  obser- 
  

   vations, 
  give, 
  where 
  completed, 
  the 
  true 
  sequence 
  of 
  the 
  beds 
  and 
  

   approximate 
  very 
  closely 
  to 
  their 
  true 
  thickness. 
  

  

  In 
  tabulating 
  these 
  sections 
  I 
  have 
  not 
  been 
  able 
  to 
  adopt 
  in 
  its 
  

   entirety 
  the 
  scheme 
  of 
  classification 
  propounded 
  by 
  Judd, 
  for 
  reasons 
  

   which 
  will 
  be 
  given 
  in 
  full 
  detail 
  ; 
  but 
  have 
  found 
  it 
  easier 
  to 
  apply 
  

   a 
  new 
  system 
  of 
  division 
  based 
  on 
  the 
  Belemnites. 
  The 
  lines 
  of 
  

   this 
  division 
  sometimes 
  coincide 
  with 
  those 
  already 
  in 
  use, 
  and 
  

   sometimes 
  do 
  not, 
  as 
  will 
  be 
  pointed 
  out 
  in 
  my 
  descriptions. 
  

  

  Belemnites 
  is 
  undoubtedly 
  the 
  most 
  plentiful 
  fossil 
  of 
  the 
  clays, 
  

   and 
  occurs 
  in 
  the 
  greatest 
  profusion 
  in 
  nearly 
  every 
  bed 
  above 
  the 
  

   Coprolite-bed. 
  And 
  though 
  I 
  am 
  aware 
  that 
  these 
  fossils 
  are 
  not 
  

   usually 
  considered 
  desirable 
  for 
  stratigraphical 
  purposes, 
  yet 
  in 
  this 
  

   case 
  they 
  are 
  so 
  palpably 
  the 
  natural 
  guide 
  to 
  the 
  section, 
  that 
  as 
  

   such 
  I 
  have 
  not 
  scrupled 
  to 
  use 
  them. 
  As 
  will 
  be 
  shown, 
  they 
  occur 
  

   in 
  well-defined 
  species 
  or 
  groups, 
  having 
  on 
  the 
  whole 
  well-defined 
  

   limits 
  corresponding 
  to 
  definite 
  horizons 
  in 
  the 
  clays 
  and 
  to 
  marked 
  

   changes 
  in 
  the 
  fauna. 
  

  

  I 
  propose 
  therefore 
  in 
  this 
  paper 
  to 
  divide 
  the 
  Speeton 
  section 
  in 
  

   the 
  following 
  manner 
  : 
  — 
  

  

  A. 
  Marls 
  with 
  Belemnites 
  minimus, 
  List., 
  and 
  allies. 
  

  

  B. 
  Zone 
  of 
  Belemnites 
  semicanaliculatus 
  ? 
  f 
  and 
  allies. 
  

  

  C. 
  Zone 
  of 
  Belemnites 
  jaculum, 
  Phil., 
  and 
  varieties. 
  

  

  D. 
  Zone 
  of 
  Belemnites 
  lateralis, 
  Phil., 
  and 
  varieties. 
  

  

  E. 
  Coprolitic 
  seam. 
  

  

  F. 
  Bituminous 
  shales 
  with 
  varieties 
  of 
  Belemnites 
  Owenii, 
  Pratt. 
  

  

  * 
  In 
  J. 
  Leckenby's 
  " 
  Notes 
  on 
  the 
  Speeton 
  Clay 
  " 
  (Geologist, 
  vol. 
  ii. 
  p. 
  9), 
  we 
  

   possess 
  a 
  valuable 
  record 
  of 
  beds 
  somewhat 
  lower 
  than 
  any 
  which 
  have 
  been 
  

   recently 
  exposed, 
  but 
  the 
  details 
  are 
  unfortunately 
  meagre 
  (see 
  diagram, 
  fig. 
  2, 
  

   facing 
  p. 
  618, 
  and 
  note 
  at 
  p. 
  584). 
  

  

  t 
  Adopting 
  this 
  specific 
  name 
  as 
  used 
  by 
  Judd, 
  for 
  discussion 
  of 
  which 
  see 
  

   Appendix 
  (p. 
  611). 
  

  

  