﻿1 
  86 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  been 
  known 
  of 
  the 
  Great 
  Oolite, 
  the 
  assemblage 
  obtained 
  from 
  that 
  

   locality 
  exceeding 
  all 
  others 
  united 
  in 
  number 
  of 
  species*. 
  

  

  Cephalopoda. 
  — 
  Ammonites. 
  — 
  Only 
  42 
  species 
  occur 
  in 
  the 
  Inferior 
  

   Oolite; 
  yet 
  the 
  Lias 
  holds 
  293 
  species, 
  only 
  three 
  of 
  which 
  pass 
  to 
  this 
  

   horizon 
  — 
  Harpoceras 
  concavum, 
  and 
  Harpoceras 
  radians 
  and 
  insigne 
  ; 
  

   and 
  only 
  one 
  species 
  of 
  the 
  42 
  (Am. 
  fuscus) 
  passes 
  to 
  higher 
  beds. 
  

   The 
  restriction 
  is 
  remarkable 
  and, 
  on 
  stratigraphical 
  grounds, 
  im- 
  

   portant. 
  These 
  42 
  species 
  occupy 
  the 
  three 
  zones 
  of 
  Murchisoni, 
  

   Hu.mpliriesianus, 
  and 
  Parhinsoni, 
  these 
  three 
  types 
  definitely 
  holding 
  

   their 
  position 
  or 
  horizons 
  in 
  the 
  Inferior 
  Oolite 
  : 
  and 
  whether 
  the 
  

   beds 
  are 
  largely 
  developed 
  or 
  not, 
  their 
  succession 
  is 
  everywhere 
  the 
  

   same 
  through 
  Britain 
  and 
  on 
  the 
  continent. 
  No 
  group 
  of 
  the 
  

   Mollusca 
  is 
  so 
  constant 
  in 
  distribution 
  or 
  so 
  valuable 
  to 
  the 
  strati- 
  

   graphical 
  geologist 
  ; 
  but 
  side 
  by 
  side 
  with 
  the 
  Ammonites 
  we 
  may 
  

   place 
  the 
  Echinoidea 
  as 
  equivalent 
  in 
  value, 
  and 
  equally 
  reliable 
  in 
  

   stratigraphical 
  geology. 
  Besides 
  the 
  true 
  Ammonites, 
  one 
  species 
  of 
  

   Ancyloceras 
  occurs 
  in 
  the 
  Inferior 
  Oolite 
  t. 
  

  

  The 
  Cottcswold 
  range 
  is 
  classical 
  ground 
  for 
  the 
  clear 
  and 
  definite 
  

   exposition 
  of 
  the 
  history 
  of 
  the 
  Inferior- 
  and 
  Great-Oolite 
  horizons 
  ; 
  

   it 
  may 
  be 
  said, 
  with 
  the 
  Jura, 
  to 
  elucidate 
  the 
  entire 
  physical 
  and 
  

   zoological 
  history 
  of 
  the 
  Lower-Oolitic 
  period. 
  

  

  Trigonellites. 
  — 
  These 
  opercula 
  to 
  the 
  shells 
  of 
  the 
  Ammonites 
  have 
  

   yet 
  to 
  receive 
  much 
  attention 
  ; 
  they 
  are 
  now 
  recognized 
  as 
  an 
  im- 
  

   portant 
  factor 
  in 
  the 
  study 
  of 
  the 
  Ammonitidae. 
  Waagen, 
  Suess, 
  

   Neumayr, 
  and 
  others 
  recognize 
  their 
  importance 
  : 
  and 
  when 
  sought 
  

   for 
  through 
  sections 
  made 
  in 
  the 
  chambers 
  they 
  are 
  much 
  commoner 
  

   than 
  we 
  once 
  believed. 
  Pine 
  examples 
  have 
  occurred 
  in 
  the 
  Oxford 
  

   Clay 
  (T. 
  lameUosus 
  and 
  T. 
  politus), 
  T. 
  antiquatus 
  in 
  the 
  Corallian 
  

   beds, 
  and 
  T. 
  latus 
  in 
  the 
  Kimmeridge. 
  

  

  Nautili. 
  — 
  The 
  six 
  species 
  of 
  Nautilus 
  that 
  occur 
  in 
  the 
  Inferior 
  

   Oolite 
  are 
  all 
  confined 
  to 
  it. 
  21 
  species 
  are 
  known 
  in 
  the 
  Jurassic 
  

   rocks 
  ; 
  and, 
  with 
  the 
  exception 
  of 
  N. 
  liexagonus 
  (which 
  occurs 
  in 
  the 
  

   Cornbrash, 
  Kellaways 
  Hock, 
  and 
  Corallian 
  beds), 
  all 
  the 
  species 
  are 
  

   representative 
  and 
  restricted, 
  as 
  much 
  so 
  as 
  the 
  N. 
  pompilius 
  of 
  the 
  

   present 
  day 
  ; 
  in 
  other 
  words, 
  omitting 
  the 
  Lias 
  species 
  (included 
  in 
  

   the 
  21), 
  the 
  13 
  Oolitic 
  species 
  occupy 
  each 
  only 
  one 
  horizon 
  — 
  six 
  

   species 
  in 
  the 
  Inferior 
  Oolite, 
  three 
  in 
  the 
  Great 
  Oolite, 
  one 
  in 
  the 
  

   Cornbrash, 
  two 
  in 
  the 
  Kellaways, 
  and 
  one 
  in 
  the 
  Kimmeridge 
  Clay. 
  

  

  Belemnites. 
  — 
  I 
  have 
  stated 
  that 
  115 
  species 
  are 
  known 
  in 
  the 
  

   British 
  Jurassic 
  rocks, 
  but 
  only 
  16 
  species 
  occur 
  in 
  the 
  Inferior 
  

   Oolite 
  ; 
  two 
  horizons 
  above 
  this, 
  the 
  Fuller's 
  Earth 
  and 
  Great 
  Oolite, 
  

   yield 
  only 
  three 
  species 
  each 
  ; 
  none 
  arc 
  known 
  in 
  the 
  Forest 
  Marble 
  

   and 
  Cornbrash 
  ; 
  3 
  occur 
  in 
  the 
  Kellaways 
  Rock, 
  13 
  in 
  the 
  Oxford 
  

   Clay, 
  4 
  in 
  the 
  Corallian, 
  and 
  8 
  in 
  the 
  Kimmeridge 
  Clay 
  ; 
  so 
  that 
  

   the 
  115 
  known 
  species 
  are 
  spread 
  through 
  all 
  the 
  horizons 
  but 
  

  

  * 
  The 
  "Walton 
  Collection, 
  now 
  in 
  the 
  Woodwardian 
  Museum, 
  Cambridge, 
  

   doubtless 
  contains 
  a 
  large 
  number 
  of 
  undescribed 
  species. 
  

  

  t 
  Ancyloceras 
  anmdatum 
  is 
  the 
  only 
  species 
  in 
  the 
  Inferior 
  Oolite 
  ; 
  and 
  the 
  

   Kellaways 
  and 
  Oxford-Clay 
  species, 
  A. 
  calloviense. 
  completes 
  our 
  knowledge 
  of 
  

   the 
  non-involute 
  forms 
  of 
  the 
  Jurassic 
  Ammonitidae. 
  

  

  