﻿Vol. 
  53.] 
  THE 
  CEETACEOTJS 
  STEATA 
  OF 
  COUNTY 
  ANTRIM. 
  587 
  

  

  two 
  formations 
  in 
  the 
  western 
  counties 
  of 
  England 
  has 
  convinced 
  

   the 
  majority 
  of 
  English 
  students 
  of 
  Cretaceous 
  geology 
  that 
  such 
  

   a 
  separation 
  is 
  not 
  justified 
  by 
  the 
  evidence, 
  which 
  tends 
  to 
  prove 
  

   that 
  they 
  are 
  different 
  lithological 
  conditions 
  of 
  the 
  same 
  division, 
  

   the 
  greensands 
  being 
  more 
  conspicuous 
  in 
  the 
  western 
  counties, 
  

   near 
  the 
  ancient 
  coast-line, 
  while 
  the 
  clays 
  of 
  the 
  Gault 
  predominate 
  

   to 
  the 
  east. 
  

  

  The 
  results 
  of 
  these 
  researches 
  have 
  also 
  convinced 
  these 
  observers 
  

   that 
  a 
  true 
  Cenomanian 
  base-line, 
  the 
  Chloritic 
  Marl, 
  exists 
  at 
  the 
  

   summit 
  of 
  the 
  greensands, 
  characterized 
  by 
  a 
  marked 
  change 
  in 
  the 
  

   fauna 
  and 
  lithological 
  conditions, 
  and 
  by 
  the 
  presence 
  of 
  fossils 
  

   derived 
  from 
  the 
  underlying 
  strata. 
  The 
  views 
  thus 
  briefly 
  

   summarized 
  have 
  been 
  clearly 
  set 
  forth 
  by 
  Messrs, 
  Jukes-Browne 
  & 
  

   Hill, 
  1 
  who* 
  have 
  also 
  argued 
  that 
  the 
  same 
  statements 
  are 
  applicable 
  

   to 
  the 
  Cretaceous 
  strata 
  in 
  the 
  North 
  of 
  France. 
  Believing 
  that 
  

   these 
  results 
  have 
  placed 
  the 
  classification 
  on 
  a 
  secure 
  basis, 
  I 
  am 
  

   of 
  opinion 
  that 
  the 
  Glauconitic 
  Sands 
  can 
  no 
  longer 
  be 
  retained 
  as 
  

   Cenomanian, 
  but 
  must 
  be 
  placed 
  in 
  the 
  combined 
  Upper 
  Greensand- 
  

   and-Gault 
  division, 
  for 
  which 
  sooner 
  or 
  later 
  a 
  convenient 
  reference- 
  

   name 
  will 
  be 
  required. 
  

  

  In 
  attempting 
  to 
  correlate 
  more 
  precisely 
  the 
  English 
  and 
  Irish 
  

   greensands, 
  the 
  somewhat 
  different 
  character 
  of 
  the 
  fauna 
  in 
  the 
  

   Central 
  and 
  Eastern 
  Divisions 
  must 
  be 
  kept 
  constantly 
  in 
  mind, 
  and 
  

   the 
  non-recognition 
  of 
  these 
  factors 
  appears 
  to 
  be 
  the 
  cause 
  of 
  the 
  

   differences 
  between 
  the 
  classifications 
  published 
  by 
  Tate 
  and 
  

   Barrois. 
  Eor 
  comparison, 
  the 
  subdivisions 
  of 
  the 
  Upper 
  Greensand 
  

   adopted 
  are 
  as 
  follows 
  : 
  — 
  

  

  Devon 
  and 
  Wiltshire. 
  Zones. 
  

  

  f 
  Warminster 
  Beds 
  Pecten 
  asper. 
  

  

  Upper 
  Greensand 
  \ 
  Devizes 
  Beds 
  f 
  Ammonites 
  [Sckloen- 
  

  

  [JBlackdown 
  Beds 
  (in 
  part) 
  ... 
  |_ 
  bachia] 
  inflatus. 
  

  

  Though 
  the 
  retention 
  of 
  Pecten 
  asper 
  as 
  the 
  title 
  of 
  a 
  zone 
  is 
  open 
  to 
  

   objection, 
  no 
  species 
  is 
  sufficiently 
  characteristic 
  of 
  this 
  horizon 
  to 
  take 
  its 
  

   place 
  satisfactorily. 
  

  

  The 
  main 
  features 
  in 
  the 
  Glauconitic 
  Sands 
  which 
  should 
  be 
  

   emphasized 
  are 
  : 
  — 
  

  

  1. 
  Exogyra 
  laevigata, 
  Pecten 
  [Janira] 
  quinquecostatus, 
  and 
  P. 
  

   \_Amussium] 
  orbicularis 
  are 
  ubiquitous. 
  

  

  2. 
  The 
  Central 
  Division 
  is 
  characterized 
  by 
  the 
  great 
  abundance 
  

   and 
  large 
  size 
  of 
  the 
  dimyarian 
  pelecypoda. 
  

  

  3. 
  The 
  Islandmagee 
  area 
  is, 
  on 
  the 
  contrary, 
  marked 
  by 
  an 
  

   absence 
  of 
  such 
  pelecypoda, 
  and 
  by 
  the 
  abundance 
  of 
  the 
  subgenus 
  

   Chlamys 
  and 
  small 
  brachiopoda. 
  

  

  Speaking 
  generally, 
  the 
  lithological 
  character 
  of 
  the 
  strata, 
  

   together 
  with 
  the 
  presence 
  and 
  large 
  size 
  of 
  Exogyra 
  laevigata 
  and 
  

   Pecten 
  orbicularis, 
  find 
  their 
  nearest 
  parallel 
  in 
  Bed 
  3 
  of 
  Meyer, 
  2 
  

   and 
  Bed 
  7 
  of 
  Downes, 
  3 
  that 
  is, 
  high 
  representatives 
  of 
  the 
  Black- 
  

   down 
  Series, 
  or 
  at 
  the 
  very 
  base 
  of 
  the 
  Upper 
  Greensand 
  ; 
  but 
  the 
  

  

  1 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  lii. 
  (1896) 
  pp. 
  99-178 
  ; 
  see 
  especially 
  

   pp. 
  170-177. 
  2 
  Ibid. 
  vol. 
  xxx. 
  (1874) 
  p. 
  373. 
  

  

  3 
  Ibid. 
  vol. 
  xxxviii. 
  (1882) 
  p. 
  75, 
  & 
  vol. 
  xli. 
  (1885) 
  p. 
  27. 
  

  

  