﻿408 
  N. 
  STORY-MASKELYNE 
  AND 
  W. 
  FLIGHT 
  ON 
  THE 
  CHARACTER 
  

  

  many 
  of 
  these 
  stones, 
  while 
  at 
  the 
  same 
  time 
  they 
  offer 
  no 
  evidence 
  

   of 
  attrition 
  — 
  the 
  eroded 
  lines 
  carried 
  on 
  their 
  octahedral 
  faces 
  by 
  so 
  

   many 
  of 
  the 
  diamonds, 
  indicating 
  (as 
  shown 
  by 
  Gustav 
  Eose) 
  the 
  

   probability 
  of 
  their 
  having 
  been 
  exposed 
  to 
  an 
  incipient 
  combustion, 
  — 
  

   these 
  facts, 
  added 
  to 
  the 
  brecciated 
  character 
  of 
  many 
  of 
  the 
  rocky 
  

   masses 
  containing 
  fragments 
  of 
  carbonaceous 
  shale, 
  all 
  seem 
  to 
  

   point 
  to 
  a 
  great 
  disturbance 
  of 
  the 
  original 
  enstatite 
  rock. 
  This 
  

   rock, 
  probably 
  at 
  some 
  depth 
  below 
  the 
  present 
  surface, 
  and 
  possibly 
  

   at 
  the 
  places 
  of 
  its 
  contact 
  with 
  carbonaceous 
  shales, 
  was 
  probably 
  

   the 
  original 
  home 
  of 
  the 
  diamond 
  — 
  the 
  alterations 
  that 
  have 
  ensued 
  

   from 
  its 
  shattering, 
  at 
  a 
  period 
  subsequent 
  to 
  its 
  becoming 
  solidified, 
  

   having 
  aided 
  in 
  effecting 
  the 
  hydration 
  that 
  has 
  so 
  largely 
  changed 
  

   it 
  from 
  an 
  enstatite 
  rock 
  into 
  a 
  mixture 
  of 
  enstatite 
  with 
  a 
  

   hydrated 
  enstatite, 
  a 
  combination 
  which, 
  both 
  in 
  its 
  composition 
  

   and 
  structure, 
  recalls 
  vividly 
  to 
  the 
  mind 
  the 
  similar 
  mixture 
  of 
  the 
  

   former 
  mineral 
  with 
  the 
  so-called 
  pseudophite 
  in 
  which 
  it 
  occurs 
  at 
  

   Zdar 
  in 
  Moravia. 
  — 
  N. 
  S. 
  M. 
  

  

  I. 
  Rock 
  of 
  Bttltfontein. 
  

  

  The 
  ground-mass 
  of 
  this 
  rock 
  is 
  formed 
  of 
  a 
  drab-coloured 
  mineral, 
  

   which 
  appears 
  to 
  be 
  quite 
  broken 
  into 
  fragments 
  that 
  are 
  cemented 
  

   by 
  calcite 
  in 
  bar-like 
  forms, 
  much 
  resembling 
  crystals 
  of 
  felspar. 
  

   This 
  contains 
  a 
  good 
  deal 
  of 
  the 
  bright 
  green 
  bronzite 
  which 
  will 
  be 
  

   hereafter 
  noticed, 
  while 
  garnet, 
  always 
  surrounded 
  by 
  crystals 
  of 
  a 
  

   kind 
  of 
  vermiculite, 
  is 
  more 
  abundant 
  than 
  in 
  the 
  varieties 
  of 
  these 
  

   rocks 
  from 
  other 
  localities. 
  There 
  is 
  also 
  a 
  paler-coloured 
  bronzite 
  

   (see 
  No. 
  4) 
  ; 
  and 
  the 
  whole 
  rock 
  appears 
  to 
  have 
  undergone 
  more 
  ' 
  

   than 
  ordinary 
  change. 
  

  

  This 
  rock 
  has 
  the 
  following 
  composition 
  : 
  — 
  

  

  Oxygen 
  Eatios. 
  

  

  Lime 
  carbonate 
  59*625 
  

  

  Magnesia 
  carbonate 
  4-972 
  

  

  Iron 
  carbonate 
  3*016 
  

  

  Silicic 
  acid 
  20*700 
  11*04 
  

  

  Alumina 
  0*553 
  

  

  Iron 
  protoxide 
  4*296 
  0*95 
  1 
  q 
  9 
  - 
  

  

  Magnesia 
  5*799 
  2*32 
  J 
  6 
  '^' 
  

  

  Lime 
  0*524 
  

  

  "Water 
  undetermined 
  

  

  99*485 
  

  

  Treatment 
  with 
  potash 
  removed 
  only 
  a 
  small 
  portion 
  (2*996 
  per 
  

   cent.), 
  which 
  consisted 
  chiefly 
  of 
  silicic 
  acid; 
  some 
  portion 
  of 
  this 
  

   constituent 
  was 
  most 
  probably 
  protected 
  by 
  the 
  carbonates 
  from 
  the 
  

   action 
  of 
  the 
  alkali. 
  The 
  rock 
  consists, 
  it 
  will 
  be 
  seen, 
  of 
  nearly 
  

   68 
  per 
  cent, 
  of 
  carbonate 
  and 
  a 
  few 
  per 
  cent, 
  of 
  opaline 
  silica, 
  the 
  

   remaining 
  constituent 
  being 
  a 
  hydrated 
  ferro-magnesian 
  silicate, 
  

   very 
  similar 
  to 
  that 
  which 
  will 
  be 
  described 
  as 
  occurring 
  in 
  the 
  drab- 
  

   coloured 
  rock 
  from 
  New 
  Rush. 
  

  

  