﻿NEWTON 
  : 
  GEOLOGICAL 
  ZONES 
  AND 
  THEIR 
  MOLLUSCA. 
  299 
  

  

  withdrawn 
  from 
  the 
  moUuscau 
  group 
  as 
  Avas 
  done 
  among 
  the 
  older 
  

   zones 
  of 
  the 
  Mesozoic 
  rocks, 
  from 
  the 
  fact 
  that 
  other 
  organisms, 
  and 
  

   chiefly 
  the 
  Echiuoids, 
  occur 
  much 
  more 
  abundantly 
  than 
  shells, 
  and, 
  

   moreover, 
  are 
  considered 
  to 
  possess 
  chai'acters 
  which, 
  better 
  adapt 
  

   them 
  for 
  the 
  subdividing 
  of 
  the 
  beds. 
  

  

  In 
  1870 
  Caleb 
  Evans 
  ^ 
  published 
  the 
  results 
  of 
  a 
  study 
  he 
  had 
  made 
  

   of 
  the 
  Chalk 
  sections 
  between 
  Croydon 
  and 
  Oxtead 
  in 
  Surrey. 
  He 
  

   found 
  that 
  the 
  Chalk 
  deposits 
  of 
  that 
  area 
  were 
  divisible 
  into 
  zones, 
  

   similar 
  to 
  those 
  which 
  had 
  been 
  recognized 
  in 
  Northern 
  France 
  by 
  

   Hehert,- 
  in 
  North-AVest 
  Germany 
  by 
  Von 
  Strombeck,^ 
  in 
  Saxonj- 
  and 
  

   lioliemia 
  by 
  Schloenbach,* 
  and 
  in 
  Western 
  France 
  by 
  Triger.^ 
  He 
  

   therefore 
  concluded 
  that 
  the 
  wliole 
  of 
  these 
  so-called 
  ' 
  Chalk 
  ' 
  beds 
  

   were 
  formed 
  in 
  one 
  hydrographical 
  area. 
  He 
  pointed 
  out 
  also 
  that 
  

   the 
  Pelecypod 
  shell 
  variously 
  quoted 
  as 
  Inoceramus 
  mytiloides, 
  lahiatus, 
  

   or 
  prohlematicus 
  was 
  an 
  abundant 
  organism 
  of 
  the 
  second 
  oldest 
  zone 
  

   of 
  his 
  scheme, 
  and 
  as 
  commonly 
  found 
  in 
  Continental 
  areas 
  as 
  in 
  this 
  

   country. 
  The 
  index-fossils 
  used 
  for 
  discriminating 
  the 
  zones 
  are 
  

   a 
  combination 
  of 
  forms 
  withdrawn 
  from 
  the 
  Mollusca 
  and 
  Echino- 
  

   dermata. 
  The 
  zones 
  were 
  as 
  follows: 
  — 
  

  

  Zone 
  with 
  Micraster 
  coranguinum 
  in 
  the 
  upper 
  part 
  and 
  Inoceramus 
  

   Cuvieri 
  below. 
  = 
  Chalk 
  with 
  bands 
  of 
  flints. 
  

  

  Zone 
  with 
  Micraster 
  coranguinum 
  in 
  the 
  upper 
  part 
  and 
  Ananchytes 
  

   ovafa 
  and 
  Spondylus 
  spinosiis 
  below. 
  = 
  Chalk 
  with, 
  bands 
  of 
  flints. 
  

  

  Zone 
  with 
  Uolaster 
  planus 
  and 
  Micraster 
  corhovis. 
  = 
  Lowest 
  beds 
  

   of 
  Chalk 
  with 
  bands 
  of 
  flint 
  nodules. 
  

  

  Zone 
  with 
  Inoceramus 
  Broyigniarti 
  and 
  Galerites 
  alhogalerus, 
  var. 
  

   stibrotundus. 
  =AVhite 
  Chalk 
  wdth 
  few 
  flints. 
  

  

  Zone 
  of 
  Ammojiites 
  peramphis 
  and 
  Inoceramus 
  mytiloides. 
  = 
  White 
  

   Chalk 
  without 
  flints. 
  

  

  Zone 
  of 
  Ammonites 
  varicms 
  and 
  Belemnitella 
  plena. 
  = 
  Chalk 
  Marl 
  

   and 
  Grey 
  Chalk. 
  

  

  Writing 
  on 
  the 
  " 
  ximmonite 
  Zones 
  in 
  the 
  Isle 
  of 
  Thanet 
  " 
  during 
  

   1874, 
  F. 
  A. 
  Bedwell 
  ^ 
  acknowledged 
  that 
  Ammonites 
  marked 
  definite 
  

   beds 
  or 
  "zones 
  of 
  life" 
  as 
  he 
  expressed 
  it. 
  He 
  regarded 
  it 
  as 
  

   necessary 
  for 
  accurate 
  palseontological 
  work 
  that 
  collectors 
  should 
  

   obtain 
  their 
  fossils 
  from 
  properly 
  detailed 
  sections 
  where 
  separate 
  

   deposits 
  could 
  be 
  searched 
  rather 
  than 
  from 
  indiscriminate 
  positions 
  

   in 
  the 
  cliffs. 
  The 
  total 
  thickness 
  of 
  the 
  Chalk 
  in 
  the 
  Isle 
  of 
  Thanet 
  

   was 
  given 
  as 
  180 
  feet, 
  and 
  in 
  this 
  the 
  author 
  marked 
  the 
  occurrence 
  

   of 
  eighty-nine 
  large 
  Ammonites 
  with 
  an 
  average 
  diameter 
  of 
  3 
  feet, 
  

  

  ^ 
  " 
  On 
  some 
  Sections 
  of 
  Chalk 
  between 
  Croydon 
  and 
  Oxtead 
  " 
  : 
  Geol. 
  Assoc., 
  

  

  1870, 
  pp. 
  1-40 
  (separately 
  published). 
  

   2 
  Bull. 
  Soc. 
  G6ol. 
  France, 
  ser. 
  ii, 
  vol. 
  xiv, 
  p. 
  731, 
  1857 
  ; 
  vol. 
  xvi, 
  p. 
  143, 
  1858 
  ; 
  

  

  vol. 
  XX, 
  p. 
  605, 
  1863, 
  etc. 
  

   ^ 
  Zeitsch. 
  deutsch. 
  geol. 
  Ges., 
  vol. 
  xv, 
  p. 
  97, 
  1863. 
  

   ■* 
  Palseontographica, 
  vol. 
  xiii, 
  p. 
  267, 
  1866. 
  

   ® 
  Echinoides 
  Dep. 
  Sarthe 
  (Cotteau 
  & 
  Triger), 
  1855-69 
  (Zoologique 
  et 
  strati- 
  

  

  graphique). 
  

   " 
  Proc. 
  Geol. 
  Assoc, 
  vol. 
  iii, 
  p. 
  217, 
  1874; 
  Geological 
  Magazine, 
  1874, 
  

  

  pp. 
  16, 
  94. 
  

  

  