﻿lvi 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Oolite, 
  the 
  prevalence 
  of 
  sands, 
  Land-plants, 
  and 
  beds 
  of 
  coal, 
  occur 
  

   in 
  such 
  a 
  manner 
  as 
  to 
  leave 
  no 
  doubt 
  of 
  the 
  presence 
  of 
  terrestrial 
  

   surfaces 
  on 
  which 
  the 
  Plants 
  grew, 
  and 
  all 
  these 
  phenomena 
  lead 
  to 
  

   the 
  conclusion 
  that 
  various 
  considerable 
  oscillations 
  of 
  level 
  took 
  place 
  

   in 
  the 
  British 
  area 
  during 
  the 
  deposition 
  of 
  the 
  strata 
  both 
  of 
  the 
  

   Inferior 
  Oolite 
  and 
  of 
  the 
  formations 
  that 
  immediately 
  succeed 
  it. 
  

  

  Again, 
  near 
  Kempston, 
  in 
  Bedfordshire, 
  the 
  Cornbrash 
  and 
  Kel- 
  

   loway 
  rock 
  are 
  both 
  absent, 
  and 
  the 
  Oxford 
  clay 
  was 
  pointed 
  out 
  to 
  

   me 
  by 
  Mr. 
  Howell, 
  resting 
  directly 
  and 
  apparently 
  quite 
  conformably 
  

   on 
  the 
  Great 
  Oolite. 
  The 
  fragmentary 
  character 
  of 
  the 
  Portland 
  

   rocks 
  is 
  confessed 
  by 
  all. 
  

  

  It 
  is 
  probable 
  that 
  the 
  oscillations 
  of 
  level 
  that 
  these 
  phenomena 
  

   indicate 
  may 
  be 
  intimately 
  connected 
  with 
  the 
  loss 
  of 
  old 
  and 
  the 
  

   appearance 
  of 
  new 
  species 
  in 
  our 
  area 
  ; 
  for 
  it 
  is 
  certain 
  that 
  apparent 
  

   conformity, 
  as 
  in 
  the 
  case 
  of 
  the 
  Great 
  Oolite 
  lying 
  on 
  the 
  Upper 
  Lias, 
  

   is 
  often 
  deceptive, 
  and 
  is 
  in 
  itself 
  no 
  positive 
  proof 
  of 
  direct 
  sequence 
  ; 
  

   and 
  it 
  is 
  not 
  unlikely 
  that 
  during 
  gaps 
  in 
  the 
  regular 
  sequence 
  of 
  

   formations, 
  of 
  some 
  of 
  which 
  we 
  may 
  have 
  no 
  traces 
  remaining, 
  many 
  

   old 
  forms 
  died 
  out 
  or 
  changed, 
  and 
  new 
  ones, 
  at 
  intervals, 
  migrated 
  

   hither. 
  At 
  the 
  same 
  time, 
  it 
  is 
  clear 
  that 
  the 
  breaks 
  in 
  succession 
  

   in 
  these 
  mesozoic 
  strata 
  are 
  very 
  different 
  in 
  magnitude 
  from 
  those 
  of 
  

   the 
  palaeozoic 
  epoch 
  that 
  were 
  accompanied 
  by 
  total 
  unconformity 
  *. 
  

  

  Purbeck 
  and 
  Wealden 
  Strata. 
  — 
  We 
  now 
  come 
  to 
  a 
  period 
  in 
  the 
  geo- 
  

   logical 
  history 
  of 
  the 
  British 
  marine 
  mesozoic 
  rocks 
  in 
  which, 
  though 
  

   not 
  accompanied 
  by 
  much 
  apparent 
  physical 
  disturbance, 
  the 
  break 
  

   in 
  the 
  succession 
  of 
  species 
  is 
  as 
  great 
  as 
  in 
  any 
  part 
  of 
  the 
  palaeo- 
  

   zoic 
  series. 
  I 
  allude 
  to 
  the 
  total 
  change 
  of 
  species 
  that 
  marks 
  the 
  

   introduction 
  of 
  the 
  marine 
  Cretaceous 
  formations. 
  

  

  That 
  this 
  break 
  in 
  palaeontological 
  succession 
  was 
  accompanied 
  

   by 
  an 
  enormous 
  lapse 
  of 
  time 
  is 
  proved 
  by 
  the 
  presence 
  of 
  the 
  Pur- 
  

   beck 
  and 
  Wealden 
  strata 
  lying 
  between 
  the 
  Oolitic 
  and 
  Cretaceous 
  

   series 
  ; 
  and, 
  but 
  for 
  them, 
  when 
  the 
  two 
  series 
  come 
  in 
  contact, 
  so 
  

   conformable, 
  apparently, 
  are 
  the 
  Cretaceous 
  to 
  the 
  Oolitic 
  rocks, 
  that, 
  

   unlike 
  some 
  of 
  the 
  cases 
  cited 
  with 
  regard 
  to 
  the 
  palaeozoic 
  forma- 
  

   tions, 
  we 
  have, 
  by 
  disturbance 
  and 
  denudation 
  of 
  the 
  Oolite 
  strata 
  

   previous 
  to 
  the 
  Cretaceous 
  epoch, 
  no 
  very 
  obvious 
  hint 
  of 
  the 
  enor- 
  

   mous 
  lapse 
  of 
  time 
  that 
  lay 
  between 
  the 
  two 
  great 
  marine 
  periods. 
  

  

  It 
  is 
  needless 
  for 
  my 
  argument 
  specially 
  to 
  analyze 
  the 
  contents 
  

   of 
  the 
  Purbeck 
  and 
  "Wealden 
  strata. 
  Of 
  the 
  4 
  species 
  of 
  Plants, 
  

   90 
  Insects, 
  several 
  Mammalia, 
  10 
  Cyprides, 
  1 
  Echinus, 
  17 
  Lamelli- 
  

   branchiate 
  Mollusks, 
  14 
  Gasteropoda, 
  18 
  Fish, 
  and 
  11 
  Reptiles 
  now 
  

   known 
  in 
  the 
  Purbeck 
  rocks, 
  a 
  considerable 
  proportion 
  of 
  the 
  forms 
  

   are 
  common 
  to 
  the 
  three 
  subdivisions 
  of 
  the 
  formation, 
  and 
  none 
  of 
  

   them, 
  unless 
  doubtfully 
  Paludina 
  elongata, 
  pass 
  up 
  into 
  the 
  Wealden 
  

   beds. 
  In 
  the 
  latter 
  there 
  are 
  known 
  19 
  species 
  of 
  Plants, 
  11 
  

   Cyprides, 
  25 
  Lamellibranchiate 
  Mollusks, 
  8 
  Gasteropoda, 
  12 
  Fish, 
  

   and 
  18 
  Reptiles 
  ; 
  and 
  all 
  of 
  these, 
  with 
  one 
  doubtful 
  exception, 
  are 
  

  

  * 
  They 
  are, 
  however, 
  somewhat 
  comparable 
  to 
  the 
  relations 
  of 
  the 
  Lower 
  and 
  

   Upper 
  Llandovery 
  rocks 
  to 
  each 
  other, 
  or 
  to 
  the 
  variations 
  in 
  the 
  subdivisions 
  of 
  

   the 
  Magnesian 
  Limestone, 
  which 
  were 
  formed 
  during 
  minor 
  oscillations 
  of 
  level. 
  

  

  