﻿574 
  DR. 
  W. 
  ITvASER 
  HUME 
  ON 
  [Dec. 
  1 
  897, 
  

  

  The 
  original 
  weight 
  after 
  drying 
  = 
  41-39 
  grammes. 
  After 
  soution 
  

   in 
  20% 
  hydrochloric 
  acid 
  there 
  remained 
  24*6 
  grammes 
  = 
  59*4/ 
  , 
  or 
  

   total 
  percentage 
  composition 
  : 
  — 
  

  

  Carbonate 
  of 
  lime 
  40*6 
  % 
  

  

  Eesidue 
  59-4% 
  

  

  100 
  

  

  The 
  residue 
  consists 
  mainly 
  of 
  sand-grains, 
  very 
  minute 
  glauconitic 
  

   casts, 
  fragments 
  of 
  opal 
  showing 
  traces 
  of 
  organic 
  structure, 
  and 
  

   abundant 
  thin 
  flakes 
  of 
  muscovite 
  exhibiting 
  iridescent 
  tints. 
  In 
  

   addition 
  the 
  following 
  minerals 
  were 
  observed 
  : 
  rutile, 
  no 
  definite 
  

   crystals, 
  but 
  red 
  and 
  orange-yellow 
  fragments; 
  zircon, 
  both 
  in 
  

   well-terminated 
  crystals 
  and 
  rounded 
  grains, 
  *085 
  mm. 
  in 
  diameter 
  ; 
  

   tourmaline, 
  generally 
  showing 
  perfect 
  prismatic 
  outline 
  and 
  good 
  

   rhombohedral 
  terminations 
  ; 
  biotite 
  in 
  thin 
  brown 
  cleavage-flakes. 
  

  

  A 
  green 
  mineral 
  showing 
  strong 
  cleavage 
  parallel 
  to 
  the 
  vertical 
  

   axes 
  with 
  occasional 
  cross 
  cleavages 
  at 
  90°, 
  having 
  straight 
  

   extinction, 
  fair 
  polarization-colours, 
  and 
  no 
  apparent 
  pleochroism, 
  

   most 
  resembles 
  enstatite 
  in 
  its 
  appearance 
  and 
  characters. 
  

  

  A 
  dull 
  black 
  mineral 
  occurring 
  in 
  rounded 
  botryoidal 
  fragments 
  

   is 
  also 
  present, 
  often 
  displaying 
  a 
  bluish 
  tint. 
  When 
  tested 
  in 
  

   borax 
  and 
  sodium-carbonate 
  beads 
  in 
  the 
  reducing 
  flame, 
  no 
  

   evidence 
  of 
  manganese 
  or 
  iron 
  was 
  obtained. 
  At 
  present, 
  therefore, 
  

   its 
  true 
  nature 
  must 
  remain 
  uncertain, 
  although 
  both 
  limonite 
  

   and 
  psilomelane 
  have 
  suggested 
  themselves. 
  

  

  Yellowish 
  brittle 
  masses 
  are 
  also 
  present, 
  of 
  less 
  hardness 
  than 
  

   glass, 
  but 
  not 
  as 
  yet 
  further 
  recognized. 
  

  

  Yellow 
  Sandstone. 
  

  

  Colin 
  Glen. 
  (No. 
  5 
  in 
  Table 
  II.) 
  

  

  Forty 
  grammes 
  of 
  the 
  rock 
  yielded 
  25-3 
  grammes 
  of 
  residue 
  

   = 
  63-25%, 
  that 
  is:— 
  

  

  Carbonate 
  of 
  lime 
  36'75% 
  

  

  Eesidue 
  63-25°/ 
  

  

  100 
  

   The 
  residue 
  consists 
  mainly 
  of 
  small 
  quartz-grains 
  less 
  than 
  

   •25 
  mm, 
  in 
  diameter, 
  thin 
  flakes 
  of 
  muscovite, 
  tourmaline 
  in 
  

   beautifully-preserved 
  crystals 
  (showing 
  hexagonal 
  prisms 
  terminated 
  

   by 
  rhombohedral 
  faces), 
  rutile 
  in 
  deep 
  red, 
  more 
  or 
  less 
  rounded 
  

   grains, 
  and 
  rounded 
  examples 
  of 
  zircon. 
  

  

  The 
  rock 
  differs 
  from 
  that 
  previously 
  described 
  in 
  not 
  con- 
  

   taining 
  any 
  glauconitic 
  casts, 
  and 
  both 
  the 
  Yellow 
  Sandstones 
  are 
  

   lacking 
  in 
  iron 
  pyrites, 
  therein 
  differing 
  from 
  the 
  Grey 
  Marls 
  of 
  

   Woodburn. 
  

  

  Enclosure 
  in 
  Grey 
  Marls. 
  

   Woodburn 
  Glen. 
  (No. 
  4 
  in 
  Table 
  II.) 
  

  

  Of 
  the 
  enclosed 
  calcareous 
  sandstone 
  79 
  '97 
  grammes 
  was 
  dis- 
  

   solved 
  in 
  20% 
  hydrochloric 
  acid, 
  yielding 
  49*84 
  grammes 
  of 
  residue, 
  

   almost 
  the 
  whole 
  of 
  which 
  can 
  be 
  classed 
  as 
  heavy. 
  

  

  