﻿404 
  the 
  mollesca 
  oe 
  the 
  chalk 
  bock, 
  [aug. 
  1 
  897, 
  

  

  Discussion. 
  

  

  Dr. 
  "W. 
  P. 
  Heme 
  congratulated 
  the 
  Author 
  on 
  the 
  completion 
  of 
  

   this 
  detailed 
  contribution 
  to 
  our 
  knowledge 
  of 
  the 
  Chalk 
  Eock 
  

   fauna, 
  and 
  referred 
  to 
  the 
  interest 
  of 
  the 
  records 
  of 
  Chlamys 
  and 
  

   Arctica 
  at 
  this 
  horizon. 
  That 
  the 
  nodular 
  condition 
  characteristic 
  

   of 
  this 
  lithological 
  feature 
  had 
  been 
  formed 
  at 
  some 
  depth 
  was 
  an 
  

   hypothesis 
  now 
  being 
  generally 
  accepted 
  ; 
  but 
  the 
  Author, 
  in 
  dis- 
  

   cussing 
  the 
  question 
  of 
  the 
  depth 
  at 
  which 
  the 
  deposit 
  had 
  been 
  

   formed, 
  scarcely 
  seemed 
  to 
  lay 
  sufficient 
  stress 
  on 
  the 
  action 
  of 
  

   currents, 
  which 
  to 
  the 
  speaker 
  appeared 
  of 
  essential 
  value 
  in 
  the 
  

   formation 
  of 
  the 
  nodular 
  rock. 
  Analyses 
  carried 
  out 
  recently 
  show 
  

   that 
  the 
  glauconitic 
  material 
  is 
  generally 
  present 
  only 
  in 
  small 
  

   quantity, 
  the 
  carbonate 
  of 
  lime 
  in 
  most 
  cases 
  exceeding 
  90 
  per 
  cent. 
  ; 
  

   so 
  that 
  the 
  higher 
  bathymetric 
  limit 
  assigned 
  by 
  the 
  Author 
  appears 
  

   to 
  be 
  the 
  more 
  probable. 
  The 
  repetition 
  of 
  a 
  lower 
  or 
  Cenomanian 
  

   fauna 
  in 
  the 
  Chalk 
  Rock, 
  to 
  which 
  the 
  Author 
  has 
  again 
  called 
  

   attention, 
  is 
  one 
  of 
  great 
  interest, 
  and 
  the 
  beds 
  containing 
  these 
  

   forms 
  should 
  be 
  considered 
  as 
  the 
  true 
  upper 
  limit 
  of 
  the 
  Middle 
  

   Chalk, 
  all 
  the 
  more 
  arbitrary 
  boundaries 
  adopted 
  having 
  completely 
  

   broken 
  down. 
  

  

  Mr. 
  W. 
  "Whitaker 
  also 
  spoke. 
  

  

  