﻿NEWTON" 
  : 
  GEOLOGICAL 
  ZONES 
  AND 
  THEIR 
  MOLLTJSCA. 
  293 
  

  

  into 
  about 
  nine 
  liemerte, 
  so 
  that 
  the 
  time-value 
  of 
  a 
  hemera, 
  on 
  

   this 
  evidence, 
  is 
  equal 
  to 
  the 
  time 
  taken 
  to 
  deposit 
  about 
  80 
  feet 
  of 
  

   strata 
  on 
  an 
  average." 
  

  

  Briefly 
  Mr. 
  Buckman's 
  scheme 
  is 
  as 
  follows 
  : 
  — 
  

  

  (A) 
  The 
  Arietidan 
  Epoch 
  represents 
  four 
  ages, 
  viz., 
  Asteroceratan, 
  

   Deroceratan, 
  Harpoceratan, 
  and 
  Ludwigian. 
  

  

  The 
  Asteroceratan 
  Age 
  includes 
  a 
  part 
  of 
  the 
  Lower 
  Lias, 
  beginning 
  

   with 
  the 
  zone 
  of 
  Ammonites 
  Bucklandi 
  and 
  ending 
  with 
  the 
  oxijnotus 
  

   zone. 
  This 
  age 
  is 
  composed 
  of 
  seven 
  hemerse 
  in 
  ascending 
  order: 
  

   rotiformis, 
  Gmuendensis, 
  Birchi, 
  Turneri, 
  obtusi, 
  stellaris, 
  and 
  oxynoti. 
  

  

  The 
  Deroceratan 
  Age 
  embraces 
  the 
  rest 
  of 
  the 
  Lower 
  Lias 
  and 
  

   nearly 
  all 
  the 
  Middle 
  Lias, 
  and 
  includes 
  seven 
  hemerse 
  : 
  raricostati, 
  

   armati, 
  Jamesoni, 
  Valdani, 
  striati, 
  margaritati, 
  and 
  spinati. 
  

  

  The 
  Harpoceratan 
  Age 
  includes 
  a 
  small 
  part 
  of 
  the 
  Middle 
  Lias 
  and 
  

   tlie 
  whole 
  of 
  the 
  Upper 
  Lias; 
  it 
  contains 
  ten 
  hemerae 
  : 
  acuti, 
  falciferi, 
  

   hifrontis, 
  lillice, 
  variabilis, 
  striaiuli, 
  Striiclcmanni, 
  dispansi, 
  Bumortierice, 
  

   Moorei. 
  

  

  The 
  Ludwigian 
  Age 
  includes 
  part 
  of 
  the 
  Yeovil 
  Sands 
  and 
  part 
  of 
  

   the 
  Inferior 
  Oolite 
  ; 
  it 
  comprises 
  six 
  hemerse 
  : 
  Aaletisis, 
  opalinrformis, 
  

   Scissi, 
  Miirchisonce, 
  Bradfordensis, 
  concavi. 
  

  

  (B) 
  The 
  Stepheoceratidan 
  Epoch 
  consists 
  of 
  two 
  ages— 
  Sonninian 
  or 
  

   oldest 
  and 
  Parkinsonian 
  or 
  latest. 
  These 
  are 
  again 
  subdivided 
  into 
  

   liemerae. 
  This 
  epoch 
  extends 
  from 
  the 
  lower 
  division 
  of 
  the 
  Inferior 
  

   Oolite 
  to 
  the 
  Cornbrash 
  of 
  the 
  Bathonian 
  Series. 
  

  

  The 
  Sonninian 
  Age 
  constitutes 
  five 
  hemera3 
  : 
  discitce, 
  Sonninice, 
  

   WitchellicB, 
  Sauzei, 
  Blagdeni. 
  

  

  In 
  the 
  Parkinsonian 
  Age 
  is 
  represented 
  the 
  following 
  hemerae 
  : 
  

   Niortensis, 
  garantiance, 
  Truelli, 
  zigzag, 
  fiisccB, 
  subcontracti, 
  (maxillata), 
  

   (coarctatoe), 
  disci. 
  

  

  Complicated 
  as 
  Mr. 
  Buckman's 
  sj'stem 
  appears, 
  there 
  is 
  no 
  doubt 
  as 
  

   to 
  its 
  uniqueness 
  of 
  detail 
  and 
  its 
  far-reaching 
  consequences, 
  both 
  to 
  

   the 
  geologist 
  and 
  the 
  palseoconchologist. 
  To 
  the 
  former 
  it 
  is 
  expected 
  

   to 
  serve 
  as 
  a 
  ' 
  geological 
  calendar', 
  so 
  that 
  collectors 
  may 
  be 
  able 
  to 
  

   date 
  the 
  species 
  they 
  find, 
  whilst 
  to 
  the 
  latter 
  it 
  is 
  intended 
  as 
  an 
  

   assistance 
  in 
  biological 
  research, 
  and 
  so 
  to 
  advance 
  the 
  study 
  of 
  

   evolution. 
  Its 
  methods 
  will, 
  doubtless, 
  have 
  to 
  be 
  considered 
  in 
  all 
  

   future 
  classifications 
  connected, 
  at 
  any 
  rate, 
  with 
  the 
  history 
  of 
  Jurassic 
  

   rocks. 
  The 
  ' 
  hemerse 
  ' 
  have 
  already 
  been 
  adopted, 
  and 
  especially 
  is 
  this 
  

   the 
  case 
  in 
  Mr. 
  L. 
  Richardson's 
  memoirs 
  ^ 
  on 
  the 
  " 
  Liassic 
  Dentaliidte 
  ", 
  

   "The 
  Inferior 
  Oolite, 
  etc., 
  of 
  the 
  Bath-Doulting 
  District",- 
  and 
  

   " 
  The 
  Inferior 
  Oolite, 
  etc., 
  between 
  Rissington 
  and 
  Burford".^ 
  

  

  We 
  will 
  now 
  consider 
  the 
  zones 
  of 
  the 
  Cretaceous 
  period, 
  in 
  which 
  

   molluscan 
  remains 
  have 
  played 
  an 
  important 
  part. 
  Taking 
  its 
  lower 
  

   portion 
  first, 
  we 
  have 
  to 
  recognize 
  the 
  analytical 
  researches 
  of 
  

   Professor 
  Judd, 
  C.B.,* 
  in 
  connection 
  with 
  his 
  memoir 
  of 
  1868 
  "On 
  

   the 
  Speeton 
  Clay", 
  the 
  term 
  ' 
  Speeton 
  Clay' 
  having 
  been 
  founded 
  

  

  1 
  Quart. 
  Journ. 
  Geol. 
  Soc, 
  vol. 
  Ixii, 
  pp. 
  573-96, 
  pi. 
  xlv, 
  1906. 
  

   - 
  Ibid., 
  vol. 
  Ixiii, 
  pp. 
  383-4,36, 
  1907. 
  

   ■' 
  Ibid., 
  vol. 
  Ixiii, 
  pp. 
  437-44, 
  1907. 
  

   ■* 
  Ibid., 
  vol. 
  xxiv, 
  p. 
  218, 
  1868. 
  

  

  