﻿V°l' 
  53-] 
  THE 
  CRETACEOUS 
  STRATA 
  OF 
  COUNTY 
  ANTRIM. 
  573 
  

  

  The 
  heavy 
  residue 
  was 
  divided 
  by 
  sifting 
  into 
  four 
  parts 
  : 
  — 
  

  

  A. 
  Exceeding 
  1 
  mm. 
  in 
  diameter 
  = 
  # 
  33 
  gramme; 
  this 
  is 
  composed 
  

   almost 
  entirely 
  of 
  water-clear 
  rounded 
  grains 
  of 
  quartz. 
  But 
  some 
  

   which 
  are 
  green-tinted, 
  due 
  to 
  thin 
  films 
  of 
  chlorite, 
  are 
  more 
  

   angular 
  in 
  character. 
  

  

  B. 
  -345 
  gramme 
  is 
  formed 
  of 
  quartz- 
  and 
  glauconite-grains 
  in 
  

   about 
  equal 
  proportions, 
  these 
  having 
  an 
  average 
  diameter 
  of 
  *5 
  mm. 
  

   The 
  quartz 
  is, 
  in 
  the 
  main, 
  rounded 
  and 
  transparent. 
  A 
  few 
  

   silicified 
  Inoceramus-ipTisms 
  are 
  also 
  present, 
  together 
  with 
  red 
  and 
  

   black 
  fragments 
  whose 
  nature 
  has 
  not 
  been 
  determined. 
  The 
  

   glauconitic 
  grains 
  show 
  distinct 
  evidence 
  of 
  alteration 
  to 
  a 
  lighter 
  

   yellow-green 
  product, 
  only 
  the 
  darker 
  green 
  forms 
  retaining 
  their 
  

   organic 
  outline. 
  

  

  C. 
  The 
  finest 
  portion 
  of 
  the 
  residue 
  (8*18 
  grammes) 
  consists 
  of 
  

   minute 
  angular 
  grains 
  of 
  quartz, 
  some 
  of 
  them 
  almost 
  rod-like 
  in 
  

   character, 
  flakes 
  of 
  mica, 
  well- 
  crystallized 
  blocks 
  of 
  iron 
  pyrites, 
  

   and 
  green 
  glauconite-grains. 
  

  

  D. 
  The 
  heaviest 
  residue, 
  obtained 
  by 
  the 
  use 
  of 
  heavy 
  liquids, 
  

   though 
  not 
  abundant, 
  was 
  interesting. 
  The 
  minerals, 
  in 
  order 
  of 
  

   note, 
  are 
  as 
  follows 
  : 
  — 
  

  

  Iron 
  Pyrites 
  orMarcasite. 
  It 
  is 
  practically 
  impossible 
  to 
  

   distinguish 
  between 
  these 
  two 
  forms 
  of 
  iron 
  sulphide, 
  though 
  the 
  

   silvery 
  white 
  aggregations 
  more 
  probably 
  contain 
  a 
  larger 
  proportion 
  

   of 
  the 
  latter, 
  and 
  the 
  brass-yellow 
  cubic 
  crystals 
  may 
  be 
  safely 
  

   referred 
  to 
  the 
  former. 
  

  

  Tourmaline. 
  Crystals 
  of 
  this 
  mineral 
  are 
  fairly 
  abundant, 
  

   the 
  rhombohedral 
  faces 
  being 
  well-marked 
  at 
  one 
  extremity, 
  while 
  

   the 
  other 
  end 
  is 
  irregularly 
  outlined 
  or 
  flat, 
  having 
  apparently 
  

   suffered 
  fracture. 
  

  

  Zircon. 
  Fragments 
  of 
  this 
  mineral 
  are 
  numerous, 
  but 
  distinct 
  

   crystals 
  are 
  few 
  and 
  these 
  also 
  rarely 
  show 
  zoning. 
  

  

  Eutile 
  occurs 
  in 
  orange-yellow 
  irregularly-shaped 
  grains, 
  no 
  

   crystals 
  being 
  noted. 
  

  

  Anatase. 
  This 
  is, 
  so 
  far 
  as 
  I 
  am 
  aware, 
  the 
  first 
  record 
  of 
  this 
  

   mineral 
  in 
  the 
  Cretaceous 
  of 
  these 
  islands. 
  The 
  crystal 
  is 
  of 
  a 
  blue 
  

   colour, 
  changing 
  to 
  pale 
  golden 
  yellow. 
  The 
  pyramidal 
  form 
  is 
  

   clearly 
  shown 
  at 
  one 
  extremity, 
  but 
  the 
  other 
  end 
  has 
  been 
  cleaved 
  

   parallel 
  to 
  the 
  basal 
  plane. 
  The 
  lustre 
  is 
  adamantine, 
  and 
  the 
  length 
  

   = 
  •046 
  mm. 
  

  

  Chlorite 
  is 
  present 
  in 
  thin 
  micaceous 
  films. 
  

  

  This 
  zone 
  differs 
  from 
  the 
  preceding 
  by 
  : 
  — 
  

  

  1. 
  The 
  greater 
  abundance 
  of 
  detrital 
  materials. 
  

  

  2. 
  The 
  reduction 
  in 
  amount 
  of 
  glauconite. 
  

  

  3. 
  The 
  presence 
  of 
  anatase. 
  

  

  Yellow 
  Sandstone. 
  (Zone 
  of 
  Ostrea 
  carinata.) 
  

  

  Hillsport, 
  Islandmagee. 
  (No. 
  5 
  a 
  in 
  Table 
  II.) 
  

  

  The 
  specimens 
  obtained 
  were 
  of 
  a 
  light 
  yellow 
  colour, 
  and 
  

   apparently 
  consisted 
  of 
  quartz-grains 
  with 
  a 
  slight 
  admixture 
  of 
  

   glauconite. 
  

  

  