﻿406 
  N. 
  STORY-MASKELYNE 
  AND 
  W. 
  FLIGHT 
  ON 
  THE 
  CHARACTER 
  

  

  32. 
  On 
  the 
  Character 
  of 
  the 
  Diamantiferotts 
  Rock 
  of 
  Sooth 
  Africa. 
  

   By 
  Prof. 
  N. 
  Story-Maskelyne, 
  F.R.S., 
  Keeper, 
  and 
  Dr. 
  W. 
  Flight, 
  

   Assistant, 
  of 
  the 
  Mineral 
  Department, 
  British 
  Museum. 
  (Bead 
  

   June 
  10, 
  1874.) 
  

  

  Introductory 
  Note. 
  

  

  The 
  character 
  of 
  the 
  rock 
  in 
  which 
  the 
  diamonds 
  are 
  found 
  in 
  

   South 
  Africa, 
  in 
  the 
  various 
  diggings 
  of 
  Du 
  Toit's 
  Pan, 
  Bultfontein, 
  

   (the 
  Old) 
  De 
  Beer's, 
  and 
  the 
  Colesberg 
  Kopje 
  or 
  New 
  Bush, 
  is 
  

   essentially 
  the 
  same. 
  

  

  In 
  some 
  observations 
  I 
  made 
  to 
  the 
  Society 
  on 
  the 
  occasion 
  of 
  a 
  

   notice 
  of 
  Mr. 
  Dunn's 
  on 
  the 
  subject 
  of 
  the 
  rocks 
  of 
  the 
  Diamond- 
  

   fields, 
  I 
  gave 
  a 
  brief 
  account 
  of 
  the 
  minerals 
  of 
  which 
  the 
  particular 
  

   rock 
  in 
  question 
  appeared 
  to 
  be 
  composed. 
  I 
  had 
  at 
  that 
  time 
  only 
  

   optical, 
  crystallographic, 
  and 
  pyrognostic 
  features 
  to 
  go 
  upon. 
  

   Since 
  then 
  these 
  minerals 
  have 
  been 
  carefully 
  selected 
  and 
  sepa- 
  

   rated, 
  and 
  have 
  been 
  analyzed 
  in 
  the 
  Laboratory 
  of 
  the 
  Mineral 
  

   Department 
  by 
  the 
  careful 
  and 
  accurate 
  hand 
  of 
  my 
  colleague 
  

   Dr. 
  Flight 
  ; 
  and 
  the 
  results 
  that 
  gentleman 
  has 
  obtained 
  confirm 
  in 
  

   almost 
  every 
  particular 
  the 
  forecast 
  I 
  gave 
  to 
  the 
  Society 
  regarding 
  

   these 
  minerals. 
  

  

  The 
  specimens 
  of 
  rock 
  examined 
  by 
  us 
  came 
  from 
  various 
  depths 
  — 
  

   from 
  near 
  the 
  surface 
  down 
  to 
  180 
  feet 
  (in 
  the 
  case 
  of 
  one 
  mass 
  

   from 
  the 
  Colesberg 
  Kopje). 
  

  

  Their 
  general 
  character 
  is 
  that 
  of 
  a 
  soft 
  and 
  somewhat 
  pulverulent 
  

   ground-mass, 
  composed 
  of 
  a 
  mineral 
  soapy 
  to 
  the 
  touch 
  and 
  of 
  a 
  

   light 
  yellowish 
  colour 
  in 
  the 
  upper, 
  and 
  of 
  an 
  olive-green 
  to 
  bluish- 
  

   grey 
  colour 
  in 
  the 
  lower 
  regions 
  of 
  the 
  excavations. 
  In 
  this 
  

   ground-mass 
  are 
  seen 
  interspersed 
  fragments 
  of 
  shale 
  more 
  or 
  less 
  

   altered 
  and 
  a 
  micaceous-looking 
  mineral 
  which 
  sometimes 
  rises 
  into 
  

   an 
  important 
  constituent 
  of 
  the 
  rock. 
  It 
  is 
  a 
  mineral 
  of 
  the 
  

   vermiculite 
  group. 
  Crystals 
  of 
  a 
  fine 
  bright 
  green 
  colour 
  of 
  a 
  

   ferriferous 
  enstatite 
  (bronzite) 
  are 
  not 
  infrequent; 
  and 
  a 
  hornblendic 
  

   mineral 
  is 
  occasionally 
  met 
  with, 
  apparently 
  rather 
  as 
  an 
  accidental 
  

   than 
  as 
  a 
  constituent 
  ingredient 
  : 
  it 
  closely 
  resembles 
  the 
  mineral 
  

   known 
  as 
  smaragdite. 
  Garnet 
  is 
  also 
  frequently 
  but 
  sparsely 
  met 
  

   with. 
  Ilmenite 
  also 
  is 
  present, 
  generally 
  in 
  rather 
  greater 
  abun- 
  

   dance 
  than 
  the 
  garnet. 
  A 
  more 
  important 
  mineral, 
  however, 
  than 
  

   these 
  as 
  a 
  constituent 
  of 
  the 
  rock, 
  since 
  it 
  occurs 
  in 
  much 
  larger 
  and 
  

   more 
  generally 
  diffused 
  fragments, 
  is 
  a 
  kind 
  of 
  bronzite 
  of 
  a 
  paler 
  

   buff 
  tint, 
  and 
  in 
  this 
  respect, 
  as 
  in 
  the 
  size 
  of 
  its 
  crystals, 
  differing 
  

   from 
  the 
  former 
  bronzite, 
  which 
  owes 
  its 
  brilliant 
  green 
  to 
  a 
  small 
  

   amount 
  of 
  nickel, 
  and 
  exists 
  uniformly 
  in 
  small 
  prismatic 
  crystals 
  

   not 
  larger 
  than 
  a 
  canary 
  seed. 
  A 
  diallage 
  much 
  altered, 
  but 
  

   recognizable 
  by 
  its 
  optical 
  as 
  well 
  as 
  by 
  its 
  mineral 
  characters, 
  is 
  

   present 
  to 
  some 
  amount 
  in 
  the 
  rock 
  of 
  Du 
  Toit's 
  Pan. 
  

  

  Opaline 
  silica, 
  occasionally 
  in 
  the 
  form 
  of 
  hyalite 
  and 
  sometimes 
  

   resembling 
  hornstone, 
  is 
  disseminated 
  through 
  the 
  greater 
  part 
  of 
  

  

  