﻿382 
  C. 
  J. 
  A. 
  METER 
  ON 
  THE 
  CRETACEOUS 
  ROCKS 
  OF 
  

  

  argillaceous 
  portion 
  of 
  the 
  Devon 
  Cretaceous 
  strata, 
  has 
  been 
  at 
  

   various 
  times 
  very 
  variously 
  estimated. 
  

  

  Sir 
  Henry 
  de 
  la 
  Beche 
  in 
  1826 
  * 
  and 
  again 
  in 
  1839 
  t 
  appears 
  to 
  

   have 
  classified 
  these 
  strata 
  "with 
  the 
  Upper 
  Greensand. 
  

  

  Dr. 
  Pitton 
  in 
  1836 
  J 
  makes 
  them 
  Lower 
  Greensand. 
  

  

  Mr. 
  Godwin- 
  Austen 
  in 
  1842 
  § 
  described 
  them 
  as 
  possibly 
  " 
  a 
  

   sandy 
  condition 
  of 
  the 
  Gault." 
  

  

  In 
  1863 
  ||, 
  and 
  again 
  in 
  1866% 
  I 
  attempted 
  to 
  show, 
  partly 
  on 
  

   pakeontological, 
  partly 
  on 
  stratigraphical 
  evidence, 
  that 
  these 
  strata 
  

   belonged 
  to 
  the 
  top 
  of 
  the 
  Lower 
  Greensand 
  rather 
  than 
  to 
  the 
  

   Gault 
  or 
  Upper 
  Greenland. 
  It 
  is 
  fair 
  to 
  say, 
  however, 
  that 
  the 
  

   palseontological 
  evidence 
  then 
  chiefly 
  relied 
  on 
  has 
  proved 
  far 
  from 
  

   trustworthy. 
  

  

  Mr. 
  Etheridge, 
  to 
  whose 
  opinion 
  as 
  a 
  palasontologist 
  every 
  one 
  

   may 
  well 
  bow 
  submissively, 
  places 
  these 
  beds 
  on 
  the 
  horizon 
  of 
  the 
  

   Gault, 
  mainly, 
  I 
  believe, 
  on 
  the 
  evidence 
  of 
  the 
  Black- 
  Ven 
  section. 
  

   At 
  the 
  present 
  moment 
  I 
  am 
  almost 
  prepared 
  to 
  agree 
  to 
  his 
  opinion. 
  

   The 
  sandy-argillaceous 
  strata 
  near 
  the 
  base 
  of 
  the 
  Black-Yen 
  section 
  

   contain 
  unquestionably 
  a 
  large 
  number 
  of 
  Gault 
  fossils 
  ; 
  and 
  there 
  

   is 
  full 
  evidence 
  of 
  the 
  continuance 
  of 
  similar 
  strata 
  to 
  the 
  west- 
  

   ward 
  ; 
  but, 
  still, 
  are 
  these 
  strata 
  entirely 
  Gault 
  ? 
  

  

  True 
  Gault, 
  such 
  as 
  one 
  knows 
  so 
  well 
  in 
  the 
  Isle 
  of 
  Wight, 
  is 
  to 
  

   be 
  seen 
  near 
  Punfield, 
  in 
  Swanage 
  Bay, 
  where 
  it 
  is 
  underlain 
  by 
  a 
  

   considerable 
  thickness 
  of 
  the 
  Lower 
  Greensand. 
  It 
  is 
  traceable 
  as 
  

   Gault 
  along 
  the 
  coast-line 
  as 
  far 
  westward 
  as 
  Mewps 
  Bay. 
  At 
  

   Lulworth 
  Cove 
  it 
  is 
  to 
  be 
  seen 
  no 
  longer 
  as 
  Gault, 
  which, 
  in 
  its 
  

   argillaceous 
  condition, 
  has 
  either 
  thinned 
  out 
  or 
  given 
  place 
  to 
  

   dark 
  greenish 
  sandy 
  strata 
  with 
  zones 
  of 
  large 
  concretionary 
  

   nodules. 
  

  

  These 
  beds 
  contain 
  Gault 
  fossils 
  in 
  abundance, 
  and 
  (what 
  is 
  well 
  

   worthy 
  of 
  notice) 
  pass 
  upwards 
  insensibly 
  into 
  Upper 
  Greensand, 
  

   and 
  downwards 
  into 
  ferruginous 
  sands 
  of 
  the 
  Lower 
  Greensand. 
  

  

  In 
  the 
  altered 
  condition 
  of 
  the 
  Gault 
  as 
  present 
  at 
  Lulworth, 
  

   one 
  finds, 
  therefore, 
  an 
  approach 
  already 
  to 
  the 
  condition 
  of 
  the 
  so- 
  

   called 
  Gault 
  as 
  seen 
  at 
  Black 
  Ven. 
  And 
  there 
  is 
  no 
  doubt 
  what- 
  

   ever 
  that 
  Gault 
  in 
  such 
  condition 
  is 
  present 
  both 
  at 
  Black 
  Yen 
  and 
  

   in 
  the 
  sections 
  to 
  the 
  westward. 
  But 
  is 
  this 
  all 
  ? 
  I 
  think 
  it 
  possible 
  

   that 
  Lower 
  Greensand, 
  which, 
  as 
  we 
  have 
  seen 
  at 
  Lulworth, 
  actually 
  

   accompanies 
  the 
  Gault 
  to 
  its 
  extinction 
  as 
  a 
  clay-bed, 
  may 
  form 
  

   a 
  part 
  also 
  of 
  the 
  still 
  doubtful 
  strata 
  to 
  the 
  westward. 
  As 
  to 
  the 
  

   correctness 
  of 
  this 
  supposition, 
  it 
  is 
  only 
  fair 
  to 
  say 
  I 
  have 
  no 
  evi- 
  

   dence 
  whatever. 
  

  

  The 
  Upper 
  Greensand 
  proper 
  of 
  the 
  Beer-Head 
  district 
  (beds 
  4 
  to 
  

   9 
  in 
  Table 
  II.) 
  exhibits 
  to 
  some 
  extent 
  a 
  purely 
  local 
  development. 
  

   The 
  zones 
  of 
  sandstone 
  pebbles 
  or 
  " 
  shingle-beds 
  " 
  described 
  by 
  Mr. 
  

   Godwin- 
  Austen 
  in 
  1842**, 
  for 
  instance, 
  and 
  which 
  form 
  so 
  marked 
  

  

  * 
  Trans. 
  Geol. 
  Soc. 
  ser. 
  2, 
  vol. 
  ii. 
  t 
  Ord. 
  Surv. 
  Beport, 
  p. 
  237. 
  

  

  % 
  Trans. 
  Geol. 
  Soc. 
  ser. 
  2, 
  vol. 
  iv. 
  p. 
  233. 
  § 
  Ibid. 
  vol. 
  vi. 
  p. 
  449. 
  

  

  || 
  Geologist, 
  vol. 
  vi. 
  p. 
  50. 
  *§ 
  Geol. 
  Mag. 
  vol. 
  iii. 
  p. 
  13, 
  

   ** 
  Trans. 
  Geol. 
  Soc. 
  ser. 
  2, 
  vol. 
  vi. 
  p. 
  449. 
  

  

  