﻿Yol. 
  53.] 
  THE 
  CRETACEOUS 
  STRATA 
  OF 
  COTINTY 
  ANTRIM. 
  575 
  

  

  Total 
  percentage 
  composition 
  : 
  — 
  

  

  Carbonate 
  of 
  lime 
  37-68% 
  

  

  Clay, 
  etc 
  1*86 
  °/ 
  

  

  Heavy 
  residue 
  6046 
  °/ 
  

  

  100 
  

  

  The 
  largest 
  fragment 
  is 
  a 
  block 
  of 
  quartz, 
  coloured 
  green 
  by 
  thin 
  

   chloritic 
  films, 
  4 
  mm. 
  in 
  length 
  and 
  3*5 
  mm. 
  in 
  breadth. 
  There 
  are 
  

   also 
  yellow 
  grains 
  of 
  the 
  same 
  mineral 
  (2 
  mm. 
  in 
  greatest 
  diameter), 
  

   most 
  of 
  the 
  water-clear 
  type 
  having 
  an 
  average 
  size 
  of 
  1*5 
  mm. 
  

   While 
  the 
  majority 
  are 
  extremely 
  rounded, 
  it 
  should 
  be 
  noted 
  that 
  

   those 
  having 
  a 
  green 
  tint 
  are 
  in 
  almost 
  all 
  cases 
  distinctly 
  sub- 
  

   angular. 
  Glauconite 
  is 
  also 
  present, 
  showing 
  traces 
  of 
  organic 
  

   structure. 
  A 
  few 
  cleavage-flakes 
  of 
  red 
  orthoclase 
  also 
  occur. 
  The 
  

   greater 
  part 
  of 
  the 
  residue 
  consists, 
  therefore, 
  of 
  beautifully 
  rounded 
  

   quartz- 
  and 
  glauconite-grains. 
  

  

  In 
  a 
  heavy 
  liquid 
  having 
  a 
  specific 
  gravity 
  of 
  over 
  3*34, 
  a 
  large 
  

   crop 
  of 
  minerals 
  was 
  obtained, 
  including 
  — 
  

  

  1. 
  Rounded 
  transparent 
  dark-bordered 
  zircons. 
  

  

  2. 
  Deep 
  red 
  and 
  light 
  yellow 
  grains 
  of 
  r 
  utile. 
  

  

  3. 
  Beautifully 
  perfect 
  crystals 
  (rhombic 
  dodecahedra) 
  of 
  garnet 
  

   of 
  a 
  pink 
  to 
  red 
  colour, 
  remaining 
  entirely 
  isotropic 
  under 
  crossed 
  

   nicols. 
  

  

  4. 
  Crystallized 
  iron 
  pyrites. 
  

  

  5. 
  Kyanite 
  is 
  also 
  present 
  in 
  some 
  quantity, 
  having 
  the 
  same 
  

   characters 
  as 
  the 
  mineral 
  described 
  under 
  the 
  Glauconitic 
  Marls 
  

   (p. 
  572). 
  

  

  In 
  the 
  lighter 
  residue 
  occur 
  large 
  crystals 
  of 
  tourmaline 
  and 
  

   green 
  flakes 
  of 
  chlorite. 
  

  

  It 
  will 
  thus 
  be 
  seen 
  that 
  these 
  enclosed 
  fragments 
  are 
  particularly 
  

   distinguished 
  by 
  the 
  abundance 
  of 
  their 
  detrital 
  residue, 
  the 
  

   minerals 
  noticed 
  being 
  quartz, 
  orthoclase, 
  zircon, 
  rutile, 
  tourmaline, 
  

   garnet, 
  kyanite, 
  iron 
  pyrites, 
  glauconite, 
  and 
  chlorite. 
  In 
  the 
  

   presence 
  of 
  garnet 
  and 
  kyanite 
  this 
  grit 
  resembles 
  the 
  Glauco- 
  

   nitic 
  Marls 
  rather 
  than 
  the 
  Yellow 
  Marls 
  in 
  which 
  it 
  is 
  enclosed. 
  

  

  Inoceramus-band. 
  (Zone 
  of 
  Inoceramus 
  Crispi, 
  Tate.) 
  

   Woodburn 
  Glen. 
  (No. 
  3 
  in 
  Table 
  II.) 
  

  

  After 
  solution 
  81*42 
  grammes 
  yielded 
  27*34 
  grammes 
  of 
  insoluble 
  

   material, 
  25*97 
  of 
  which 
  may 
  be 
  called 
  heavy 
  residue. 
  

   Jl 
  Total 
  composition 
  : 
  — 
  

  

  Carbonate 
  of 
  lime 
  66*42% 
  

  

  Clay 
  = 
  1-37 
  grs. 
  = 
  1-68% 
  

  

  Heavy 
  residue 
  = 
  25*97 
  „ 
  = 
  31*90 
  °/ 
  

  

  100 
  

  

  The 
  residue, 
  above 
  1 
  mm. 
  in 
  diameter, 
  consists 
  in 
  the 
  main 
  of 
  

   angular 
  and 
  rounded 
  fragments 
  of 
  quartz- 
  and 
  glauconite-grains. 
  

   These 
  occasionally 
  show 
  their 
  origin 
  as 
  organic 
  casts, 
  and 
  have 
  a 
  

  

  