﻿458 
  MR. 
  S. 
  S. 
  BTJCKMAN 
  ON 
  THE 
  

  

  the 
  greater 
  part 
  of 
  the 
  Murehisonce-zone 
  consists 
  of 
  " 
  Sandstein 
  ; 
  '' 
  

   while, 
  apparently, 
  the 
  Clays 
  and 
  Shales, 
  — 
  considered 
  in 
  England 
  so 
  

   distinctive 
  of 
  the 
  Lias 
  — 
  continued 
  to 
  a 
  much 
  later 
  period 
  ; 
  because 
  

   the 
  zone 
  of 
  Trigonia 
  navis 
  is 
  described 
  as 
  consisting 
  of 
  " 
  Dunkle 
  

   gegeu 
  oben 
  glimmerreiche 
  Thone 
  " 
  *. 
  

  

  Returning 
  to 
  the 
  North 
  Cotteswolds, 
  we 
  find 
  yellow 
  sands 
  at 
  the 
  

   top 
  of 
  the 
  MurcJiisonce-zone 
  ; 
  while, 
  in 
  the 
  Banbury 
  district, 
  North- 
  

   ampton 
  Sand 
  continues 
  without 
  intermission 
  from 
  the 
  Opalinum- 
  

   zone 
  until 
  the 
  lower 
  part 
  of 
  the 
  Great 
  Oolite 
  inclusive 
  f 
  . 
  

  

  The 
  foregoing 
  remarks 
  will 
  show 
  that, 
  putting 
  different 
  localities 
  

   together, 
  there 
  exist, 
  with 
  but 
  very 
  few 
  breaks 
  — 
  which 
  breaks 
  

   continental 
  strata 
  would 
  perhaps 
  bridge 
  over 
  — 
  deposits 
  of 
  sands, 
  

   sand} 
  T 
  marls, 
  or 
  sandstone 
  from 
  the 
  time 
  of 
  the 
  Jamesoni-zone 
  to 
  

   the 
  lower 
  part 
  of 
  the 
  Great 
  Oolite 
  inclusive. 
  Thus 
  the 
  obvious 
  

   inference 
  is 
  that 
  the 
  presence 
  of 
  sandy 
  lithological 
  conditions 
  is 
  no 
  

   guide 
  to 
  the 
  age 
  of 
  the 
  deposits 
  : 
  consequently 
  we 
  ought 
  not 
  to 
  be 
  

   surprised 
  at 
  finding 
  the 
  Cotteswold, 
  Hidford, 
  and 
  Yeovil 
  Sands 
  upon 
  

   three 
  different 
  horizons 
  ; 
  the 
  surprise 
  would 
  be 
  to 
  find 
  them 
  on 
  the 
  

   same 
  horizon. 
  

  

  If 
  we 
  abolish 
  the 
  general 
  name 
  " 
  Midford 
  Sands," 
  and 
  retain 
  

   the 
  names 
  Cotteswold, 
  Midford, 
  and 
  Yeovil 
  Sands 
  as 
  local 
  names 
  

   for 
  deposits 
  on 
  three 
  different 
  horizons, 
  what 
  are 
  we 
  to 
  do 
  as 
  regards 
  

   the 
  dividing 
  line 
  between 
  Lias 
  and 
  Oolite, 
  which 
  has 
  always 
  been 
  

   such 
  a 
  bone 
  of 
  contention 
  ? 
  If 
  we 
  follow 
  the 
  method 
  of 
  Quenstedt, 
  

   Oppel, 
  and 
  others, 
  and 
  draw 
  the 
  line 
  of 
  division 
  between 
  Oolite 
  and 
  

   Lias 
  at 
  the 
  top 
  of 
  the 
  Jurense-zcme, 
  we 
  must 
  draw 
  a 
  very 
  arbitrary 
  

   line 
  through 
  the 
  middle 
  of 
  the 
  Cephalopoda-bed 
  in 
  Gloucestershire, 
  

   and 
  through 
  the 
  middle 
  of 
  the 
  Yeovil 
  Sands 
  in 
  the 
  district 
  south 
  of 
  

   the 
  Mendips. 
  If 
  we 
  follow 
  H. 
  B. 
  Woodward, 
  and 
  place 
  the 
  whole 
  

   of 
  the 
  sands 
  — 
  and 
  their 
  horizontal 
  equivalents, 
  I 
  suppose 
  — 
  in 
  the 
  

   Inferior-Oolite 
  series, 
  we 
  must 
  dive 
  down 
  into 
  what 
  is 
  known 
  as 
  

   Upper 
  Lias 
  Clay 
  in 
  Somerset, 
  to 
  draw 
  a 
  very 
  arbitrary 
  line, 
  and 
  a 
  line, 
  

   too, 
  totally 
  unacceptable 
  to 
  continental 
  geologists. 
  If 
  we 
  follow 
  

   Dr. 
  "Wright, 
  and 
  draw 
  the 
  line 
  of 
  demarcation 
  above 
  the 
  Opalinum- 
  

   zone, 
  we 
  find 
  that 
  it 
  results 
  in 
  parting 
  a 
  series 
  of 
  thoroughly 
  oolitic 
  

   limestones 
  from 
  the 
  Inferior 
  Oolite, 
  and 
  it 
  thus 
  becomes 
  an 
  arbi- 
  

   trary 
  line. 
  

  

  All 
  these 
  remarks 
  will 
  only 
  show 
  (1) 
  that 
  between 
  the 
  Lias 
  and 
  

   the 
  Oolite 
  there 
  practically 
  exists 
  no 
  constant 
  lithological 
  break 
  any- 
  

   where 
  in 
  the 
  region 
  where 
  it 
  has 
  usually 
  been 
  sought 
  ; 
  (2) 
  that 
  the 
  

   old 
  idea, 
  that 
  the 
  sands 
  necessarily 
  marked 
  a 
  transition 
  period 
  

   between 
  the 
  Lias 
  and 
  the 
  Oolite, 
  cannot 
  be 
  held. 
  Such 
  being 
  the 
  

   case, 
  shall 
  we 
  adopt 
  a 
  perfectly 
  arbitrary 
  line 
  of 
  division 
  irrespective 
  

   of 
  where 
  it 
  falls 
  ? 
  Or 
  is 
  it 
  possible 
  to 
  do 
  without 
  this 
  ? 
  

  

  Dr. 
  Vacek 
  % 
  has 
  proposed 
  to 
  extend 
  the 
  Lias 
  up 
  to 
  the 
  top 
  of 
  the 
  

   Murchisonaz-zone 
  ; 
  and, 
  in 
  the 
  correspondence 
  that 
  we 
  have 
  had 
  

   upon 
  the 
  subject, 
  he 
  would 
  extend 
  it 
  to 
  the 
  top 
  of 
  our 
  Concavum- 
  

  

  * 
  Oppel, 
  ' 
  Juraformation,' 
  p. 
  321. 
  t 
  Woodward, 
  op. 
  cit. 
  p. 
  310. 
  

  

  X 
  " 
  Die 
  Fauna 
  der 
  Oolithe 
  von 
  Cap 
  San 
  Yigilio," 
  Abh. 
  der 
  k.-k. 
  geologischen 
  

   Reichsanstalt, 
  Bd. 
  xii. 
  no. 
  3. 
  

  

  