﻿292 
  PROCICKDINGS 
  OF 
  TIIK 
  MALACOLOGICAI, 
  SOCIETY. 
  

  

  Pelecypoda. 
  — 
  Lima 
  Etheridgei 
  ; 
  Peden 
  harhatus 
  ; 
  Ostrea 
  flahelloides, 
  

   sulcifera, 
  pijxiformis. 
  

  

  (3) 
  Zone 
  of 
  Ammonites 
  IIurcliisoncB 
  : 
  developed 
  at 
  Leckhamptoii 
  

   Hill, 
  Crickley 
  Hill, 
  Beacon 
  Hill, 
  Frocester 
  Hill, 
  Woottou-under-Edge, 
  

   and 
  the 
  Peak 
  at 
  llobin 
  Hood's 
  Baj- 
  (Yorkshire). 
  

  

  This 
  zone 
  exhibited 
  the 
  following 
  leading 
  Mollusca 
  in 
  its 
  various 
  

   beds 
  : 
  — 
  

  

  Cephalopoda. 
  — 
  Ammonites 
  MurchisoncG. 
  

  

  Gastropoda. 
  — 
  Chemnit%ia, 
  Nerincea. 
  

  

  Beneath 
  the 
  Ammonites 
  Murchisonce 
  zone 
  occurs 
  the 
  zone 
  of 
  

   A. 
  Jurensis, 
  containing 
  at 
  the 
  top 
  the 
  so-called 
  ' 
  Cephalopoda 
  Bed', 
  

   with 
  some 
  remaining 
  deposits 
  below, 
  the 
  whole 
  forming 
  the 
  ' 
  Sands 
  ' 
  ^ 
  

   (= 
  Cotteswold 
  Sands, 
  Midford 
  Sands, 
  etc.) 
  which 
  Wright 
  grouped 
  

   with 
  the 
  Uppermost 
  Lias. 
  

  

  The 
  chief 
  shells 
  of 
  this 
  zone 
  were 
  given 
  as 
  — 
  

  

  Cephalopoda. 
  — 
  Ammonites 
  02)alinus, 
  Jurensis, 
  radians, 
  insignis, 
  

   variabilis. 
  

  

  Pelecypoda. 
  — 
  Trigonia 
  Ramsay 
  i. 
  

  

  Since 
  AVright's 
  time 
  much 
  zonal 
  work 
  has 
  been 
  accomplished 
  on 
  the 
  

   British 
  Jurassic 
  rocks 
  by 
  various 
  investigators, 
  although 
  it 
  is 
  only 
  

   intended 
  in 
  the 
  present 
  observations 
  to 
  notice 
  the 
  leading 
  schemes 
  

   dealing 
  with 
  this 
  subject. 
  There 
  is, 
  however, 
  an 
  important 
  memoir 
  

   by 
  Mr. 
  S. 
  S. 
  Buckman- 
  which 
  should 
  be 
  referred 
  to, 
  because 
  it 
  

   illustrates 
  an 
  entirely 
  new 
  feature 
  in 
  the 
  subdivisions 
  of 
  the 
  Jurassic 
  

   Series. 
  Mr. 
  Buckman 
  divided 
  Jurassic 
  time 
  according 
  to 
  the 
  

   zoological 
  phenomena 
  of 
  the 
  Ammonite 
  fauna. 
  He 
  recognized 
  two 
  

   epochs, 
  the 
  Arietidan 
  or 
  earliest, 
  which 
  included 
  the 
  Ammonite 
  

   families 
  of 
  the 
  Arietidse 
  and 
  Hildoceratidse 
  ; 
  the 
  later 
  epoch 
  he 
  called 
  

   Stepheoceratidan, 
  characterized 
  by 
  the 
  families 
  Stepheoceratidse 
  and 
  

   Oppelidte. 
  These 
  two 
  epochs 
  are 
  further 
  subdivided 
  into 
  'ages', 
  

   which 
  latter 
  are 
  classified 
  into 
  ' 
  hemerse 
  ', 
  a 
  hemera 
  representing 
  

   a 
  chronological 
  unit, 
  or 
  in 
  other 
  words 
  indicating 
  the 
  time 
  during 
  

   which 
  the 
  beds 
  of 
  a 
  zone 
  were 
  deposited.^ 
  In 
  further 
  explanation 
  

   of 
  this 
  term 
  it 
  may 
  be 
  interesting 
  to 
  quote 
  a 
  paragraph 
  from 
  

   Mr. 
  Buckman's* 
  memoir 
  "On 
  the 
  Toarcian 
  of 
  Bredon 
  Hill 
  ", 
  which 
  

   shows 
  very 
  definitely 
  the 
  author's 
  own 
  intention 
  as 
  to 
  the 
  meaning 
  

   and 
  scope 
  of 
  'liemera'. 
  Speaking 
  of 
  the 
  approximate 
  depths 
  of 
  the 
  

   Toarcian 
  deposits 
  and 
  their 
  Ammonite 
  hemerse 
  he 
  remarks 
  — 
  " 
  Taking, 
  

   therefore, 
  the 
  various 
  maxima 
  of 
  deposits 
  in 
  the 
  South-West 
  of 
  

   England, 
  it 
  is 
  seen 
  that 
  the 
  work 
  accomplished 
  during 
  the 
  time 
  

   of 
  the 
  Toarcian 
  stage 
  is 
  represented 
  by 
  a 
  deposition 
  of 
  some 
  700 
  feet 
  

   of 
  strata. 
  The 
  time 
  during 
  which 
  this 
  work 
  Avas 
  performed 
  is 
  divided 
  

  

  ^ 
  See 
  Dr. 
  Wright's 
  paper 
  "On 
  the 
  Palffiontological 
  and 
  Stratigraphical 
  

   Eelations 
  of 
  the 
  so-called 
  ' 
  Sands 
  ' 
  of 
  the 
  Inferior 
  Oolite 
  " 
  : 
  Quart. 
  Journ. 
  

   Geol. 
  Soc, 
  vol. 
  xii, 
  p. 
  292, 
  1856. 
  

  

  - 
  " 
  On 
  the 
  Grouping 
  of 
  some 
  Divisions 
  of 
  so-called 
  ' 
  .Jurassic 
  ' 
  Time 
  " 
  : 
  Quart. 
  

   Journ. 
  Geol. 
  Soc, 
  vol. 
  liv, 
  pp. 
  442-69, 
  1898. 
  

  

  " 
  S. 
  S. 
  Buckman, 
  Geological 
  Magazine, 
  1902, 
  p. 
  556. 
  

  

  ■* 
  Quart. 
  .Journ. 
  Geol. 
  Soc, 
  vol. 
  lix, 
  p. 
  456, 
  1903. 
  

  

  