﻿Vol. 
  53.] 
  THE 
  CRETACEOUS 
  STRATA 
  OF 
  COUNTY 
  ANTRIM. 
  581 
  

  

  arrangements, 
  like 
  the 
  pillars 
  in 
  an 
  ancient 
  temple. 
  Chalcedonifica- 
  

   tion 
  has 
  proceeded 
  on 
  an 
  extensive 
  scale, 
  so 
  that 
  each 
  pillar 
  now 
  

   consists 
  of 
  colloid 
  silica, 
  which 
  has 
  assumed 
  a 
  beaded 
  form, 
  dne 
  to 
  the 
  

   formation 
  of 
  minute 
  stalactitic 
  outgrowths 
  of 
  chalcedony. 
  Prom 
  

   the 
  results 
  obtained 
  at 
  Woodburn, 
  we 
  are 
  led 
  to 
  the 
  conclusion 
  that 
  

   this 
  is 
  but 
  a 
  further 
  stage 
  in 
  the 
  iuterprismatic 
  silicification 
  of 
  the 
  

   shells 
  of 
  Inoceramus. 
  

  

  (b) 
  One 
  mm. 
  in 
  diameter 
  and 
  above 
  = 
  -28 
  gramme. 
  This 
  includes 
  

   a 
  pebble 
  of 
  quartz 
  with 
  chlorite 
  in 
  the 
  interspaces, 
  5 
  mm. 
  in 
  diameter. 
  

   Host 
  of 
  the 
  quartz-pebbles, 
  which 
  are 
  numerous, 
  are 
  subangular, 
  

   only 
  the 
  smaller 
  grains 
  being 
  truly 
  round. 
  Glauconitic 
  masses 
  are 
  

   numerous, 
  but 
  generally 
  display 
  no 
  organic 
  structure. 
  In 
  one 
  case, 
  

   however, 
  it 
  is 
  clear 
  that 
  the 
  whole 
  consists 
  of 
  a 
  delicate 
  sponge- 
  

   mesh 
  of 
  spicular 
  casts 
  still 
  bound 
  together, 
  and 
  further 
  enclosed 
  in 
  

   a 
  matrix 
  of 
  glauconitic 
  material. 
  Fragments 
  of 
  biotite, 
  by 
  their 
  

   arrangement 
  evidently 
  relics 
  of 
  biotite-mica-schists, 
  also 
  occur. 
  

  

  (c) 
  Residue 
  over 
  -5 
  mm. 
  in 
  diameter 
  = 
  *347 
  gramme. 
  This 
  consists 
  

   almost 
  exclusively 
  of 
  colourless, 
  angular, 
  subangular, 
  and 
  rounded 
  

   quartz-grains, 
  dark-green 
  and 
  yellow-green 
  glauconitic 
  casts 
  (in 
  

   general 
  having 
  no 
  recognizable 
  form, 
  though 
  one 
  distinct 
  spicular 
  

   rod 
  was 
  observed), 
  and 
  fragments 
  of 
  silicified 
  Inoceramus-iprisms. 
  

  

  (d) 
  Residue 
  over 
  '25 
  mm. 
  in 
  diameter. 
  Practically 
  the 
  same 
  as 
  c, 
  

   except 
  that 
  the 
  quartz-grains 
  are 
  far 
  more 
  angular. 
  

  

  (e) 
  Minute 
  residue, 
  about 
  '22 
  gramme. 
  The 
  organic 
  casts 
  are 
  more 
  

   prominent 
  than 
  in 
  the 
  previous 
  cases, 
  the 
  dark-green 
  casts 
  of 
  the 
  

   sponge-spicules 
  often 
  showing 
  expanded 
  knobs. 
  Beautiful 
  yellow 
  

   casts 
  of 
  foraminifera, 
  mostly 
  in 
  individual 
  rounded 
  cells, 
  but 
  some- 
  

   times 
  exhibiting 
  the 
  whole 
  structure 
  in 
  detail, 
  are 
  also 
  preserved. 
  

   Mr. 
  Chapman, 
  having 
  examined 
  these 
  together 
  with 
  those 
  of 
  the 
  

   Chloritic 
  Chalk 
  of 
  Woodburn, 
  has 
  kindly 
  supplied 
  me 
  with 
  the 
  

   following 
  report 
  : 
  — 
  

  

  ' 
  The 
  glauconite-grains 
  from 
  the 
  Chalk 
  of 
  the 
  above 
  localities 
  are 
  

   characterized 
  by 
  a 
  'quasi- 
  translucent 
  appearance, 
  which 
  is 
  in 
  distinct 
  

   contrast 
  to 
  that 
  of 
  the 
  glauconitic 
  grains 
  from 
  some 
  other 
  sedimen- 
  

   tary 
  deposits, 
  such 
  as 
  the 
  Nummulina-zonQ 
  of 
  the 
  Barton 
  Series 
  in 
  

   the 
  Isle 
  of 
  Wight, 
  or 
  the 
  glauconitic 
  clay 
  of 
  the 
  Gault 
  of 
  Copt 
  

   Point, 
  near 
  Folkestone. 
  

  

  ' 
  Two 
  kinds 
  of 
  casts 
  are 
  here 
  present 
  : 
  — 
  

  

  ' 
  Firstly, 
  those 
  which 
  have 
  been 
  moulded 
  within 
  the 
  chambers 
  of 
  

   the 
  foraminifera. 
  They 
  reproduce 
  most 
  delicately 
  all 
  the 
  minute 
  

   spaces 
  within 
  the 
  shell, 
  even 
  to 
  the 
  stolon-passages. 
  The 
  colour 
  of 
  

   these 
  internal 
  casts 
  is 
  usually 
  found 
  ranging 
  from 
  a 
  dull 
  yellow 
  to 
  

   an 
  apple-green. 
  

  

  ' 
  Secondly, 
  there 
  are 
  grains 
  in 
  which 
  the 
  external 
  form 
  of 
  the 
  

   foraminiferal 
  test 
  is 
  reproduced, 
  and 
  these 
  usually 
  have 
  a 
  less 
  

   definitely 
  finished 
  surface, 
  although 
  many 
  are 
  exactly 
  comparable 
  in 
  

   form 
  with 
  the 
  original 
  test. 
  In 
  point 
  of 
  fact, 
  the 
  casts 
  selected 
  

   exhibit 
  so 
  admirably 
  all 
  the 
  superficial 
  characters 
  of 
  the 
  original 
  

   shells 
  that 
  there 
  can 
  be 
  no 
  hesitation 
  in 
  assigning 
  to 
  the 
  majority 
  

   of 
  the 
  specimens 
  their 
  generic, 
  and 
  even 
  specific, 
  names. 
  

  

  