﻿"Vol. 
  53.] 
  THE 
  CKETACE0T7S 
  STKATA 
  OF 
  COUNTY 
  ANTKIM. 
  571 
  

  

  no 
  pleochroism, 
  but, 
  like 
  the 
  muscovite, 
  are 
  easily 
  recognized 
  by 
  

   their 
  glitter, 
  especially 
  when 
  the 
  residue 
  is 
  being 
  washed 
  in 
  

   water. 
  

  

  Tourmaline 
  is 
  very 
  rare, 
  and 
  when 
  it 
  occurs 
  is 
  in 
  the 
  pris- 
  

   matic 
  forms 
  with 
  which 
  we 
  shall 
  have 
  to 
  deal 
  more 
  fully 
  in 
  the 
  

   higher 
  zones. 
  

  

  The 
  principal 
  points 
  of 
  note 
  in 
  the 
  above 
  zone 
  are 
  : 
  — 
  

  

  1. 
  The 
  abundance 
  and 
  large 
  size 
  of 
  the 
  glauconite-grains. 
  

  

  2. 
  Their 
  derivation 
  in 
  all 
  cases 
  as 
  casts 
  of 
  the 
  internal 
  chambers 
  

   of 
  foraminifera, 
  etc. 
  

  

  3. 
  The 
  extreme 
  rounding 
  of 
  the 
  grains 
  of 
  quartz. 
  

  

  4. 
  The 
  presence 
  of 
  muscovite 
  and 
  biotite, 
  rutile, 
  and 
  zircon 
  

   (the 
  latter 
  more 
  usually 
  rounded), 
  and 
  the 
  rarity 
  of 
  tourmaline. 
  

  

  Glauconitic 
  Marls. 
  

   Woodburn 
  Glen. 
  (No. 
  6 
  in 
  Table 
  II.) 
  

  

  The 
  rock 
  is 
  a 
  blue-grey 
  marl, 
  dotted 
  with 
  glauconitic 
  grains. 
  

  

  The 
  original 
  weight, 
  after 
  drying, 
  = 
  80-63 
  grammes, 
  After 
  

   solution 
  in 
  20°/ 
  hydrochloric 
  acid, 
  there 
  remained 
  29*18 
  grammes 
  

   of 
  residue 
  =36-19°/ 
  . 
  Total 
  composition: 
  — 
  

  

  Carbonate 
  of 
  lime, 
  etc 
  63 
  - 
  91 
  % 
  

  

  Sandy 
  clay 
  = 
  18"30grs. 
  = 
  22-70% 
  

  

  Heavy 
  residue 
  = 
  10-88 
  „ 
  = 
  13-39% 
  

  

  100 
  

   The 
  main 
  residue 
  consisted 
  essentially 
  of 
  a 
  dark 
  blue 
  siliceous 
  

   clay, 
  containing 
  minute 
  flakes 
  of 
  mica 
  and 
  spheres 
  of 
  iron 
  pyrites. 
  

  

  The 
  heavy 
  residue 
  chiefly 
  contained 
  grains 
  of 
  glauconite, 
  many 
  

   of 
  which 
  show 
  clear 
  traces 
  of 
  their 
  origin 
  as 
  organic 
  casts. 
  Most 
  

   of 
  these 
  are 
  Globigerinoid 
  or 
  Rotaline 
  in 
  form, 
  one-, 
  three-, 
  or 
  five- 
  

   chambered 
  aggregates 
  being 
  frequently 
  noticed. 
  The 
  remainder 
  is 
  

   mainly 
  composed 
  of 
  quartz-grains, 
  the 
  larger 
  ones 
  perfectly 
  rounded 
  

   and 
  colourless, 
  or 
  else 
  subangular 
  and 
  even 
  highly 
  angular 
  ; 
  while 
  

   the 
  finer 
  residue 
  consists 
  almost 
  entirely 
  of 
  quartzose 
  angular 
  

   particles 
  and 
  flakes 
  of 
  silvery 
  muscovite. 
  

  

  By 
  means 
  of 
  heavy 
  liquid 
  the 
  following 
  minerals 
  were 
  obtained 
  : 
  — 
  

   Tourmaline. 
  Crystals 
  of 
  this 
  mineral 
  are 
  abundant, 
  the 
  

   hexagonal 
  prism 
  and 
  rhombohedral 
  terminations 
  being 
  well 
  

   developed. 
  The 
  length 
  varies 
  from 
  -048 
  to 
  *161 
  mm., 
  and 
  the 
  

   breadth 
  from 
  '029 
  to 
  -068 
  mm. 
  The 
  colour 
  is 
  usually 
  yellow- 
  

   brown 
  to 
  purple-brown, 
  minute 
  dark 
  enclosures 
  also 
  being 
  very 
  

   abundant. 
  The 
  absorption 
  is, 
  as 
  usual, 
  very 
  strong, 
  with 
  O 
  >E, 
  

   and 
  in 
  the 
  smaller 
  examples 
  the 
  polarization-colours 
  are 
  high, 
  of 
  

   delicate 
  pink 
  and 
  blue 
  tints. 
  A 
  few 
  fragments 
  are 
  also 
  present. 
  

  

  Rutile 
  occurs 
  in 
  red 
  and 
  deep 
  yellow-brown 
  rods 
  (maximum 
  

   length 
  -165 
  mm., 
  breadth 
  -03 
  mm.) 
  and 
  light 
  yellow 
  irregular 
  frag- 
  

   ments. 
  One 
  of 
  the 
  crystals 
  is 
  beautifully 
  zoned 
  and 
  twinned, 
  giving 
  

   rise 
  to 
  the 
  familiar 
  knee-shaped 
  combination. 
  In 
  one 
  of 
  the 
  larger 
  

   yellow 
  masses 
  numerous 
  enclosures 
  of 
  ellipsoid, 
  rod-like, 
  and 
  

   irregular 
  character 
  are 
  visible. 
  

  

  