﻿^°1- 
  53-] 
  0N 
  ROCKS 
  FROM 
  THE 
  BALUCHISIA^ 
  BORDER. 
  301 
  

  

  Basaltic 
  Rocks. 
  

  

  No. 
  1463. 
  Sp. 
  gr. 
  =2828. 
  From 
  Bharab 
  Chah. 
  

   „ 
  1422. 
  „ 
  2-888. 
  „ 
  Amir 
  Chah. 
  

  

  No. 
  1463 
  occurs 
  as 
  a 
  dyke 
  4| 
  feet 
  wide, 
  running 
  up 
  vertically 
  

   through 
  the 
  granite 
  of 
  which 
  a 
  hill 
  at 
  Bharab 
  Chah 
  is 
  composed. 
  It 
  

   is 
  a 
  compact, 
  dark 
  greenish-grey 
  basalt. 
  Under 
  the 
  microscope 
  it 
  

   is 
  seen 
  to 
  be 
  composed 
  of 
  crystals 
  of 
  augite, 
  felspar, 
  and 
  magnetite. 
  

   The 
  augites 
  are 
  sometimes 
  club-shaped, 
  but 
  are 
  mostly 
  in 
  very 
  

   irregular 
  forms. 
  They 
  are 
  much 
  cracked 
  and 
  penetrated 
  by 
  infil- 
  

   tration-canals. 
  The 
  pyroxene 
  exhibits 
  no 
  dichroism, 
  and 
  its 
  double 
  

   refraction 
  is 
  not 
  strong, 
  showing 
  generally 
  the 
  yellow, 
  and 
  occa- 
  

   sionally 
  the 
  red, 
  of 
  Newton's 
  first 
  order. 
  It 
  extinguishes 
  at 
  from 
  

   25° 
  to 
  30° 
  from 
  the 
  cleavage-lines, 
  when 
  only 
  one 
  set 
  is 
  seen. 
  

   Cross-cleavage 
  is 
  not 
  well 
  developed, 
  but 
  when 
  visible 
  a 
  single 
  bar 
  

   is 
  seen 
  in 
  converging 
  polarized 
  light. 
  

  

  The 
  felspar-prisms 
  are 
  mostly 
  lath-shaped, 
  and 
  generally 
  show 
  

   straight 
  extinction. 
  Multiple 
  twinning 
  is 
  not 
  to 
  be 
  seen, 
  but 
  a 
  

   few 
  show 
  traces 
  of 
  binary 
  macles. 
  The 
  refraction 
  of 
  the 
  felspar 
  is 
  

   higher 
  than 
  that 
  of 
  the 
  Canada 
  balsam, 
  which 
  shows 
  that 
  they 
  are 
  

   not 
  orthoclase. 
  The 
  binary 
  twinning 
  and 
  straight 
  extinction 
  seem 
  

   to 
  indicate 
  that 
  some 
  of 
  the 
  felspars, 
  at 
  any 
  rate, 
  are 
  oligoclase. 
  

   This 
  is 
  not 
  improbable, 
  as 
  this 
  rock 
  is 
  probably 
  allied 
  to 
  the 
  

   andesites 
  previously 
  described, 
  and 
  oligoclase 
  is 
  very 
  characteristic 
  

   of 
  them. 
  

  

  This 
  specimen 
  is 
  highly 
  altered. 
  None 
  of 
  the 
  minerals 
  are 
  at 
  all 
  

   fresh, 
  and 
  the 
  felspars 
  especially 
  have 
  become 
  very 
  opaque 
  from 
  

   the 
  formation 
  of 
  secondary 
  granular 
  mineral 
  matter 
  in 
  them. 
  A 
  

   chloritic-serpentinous 
  mineral, 
  varying 
  in 
  colour 
  from 
  pale 
  green 
  to 
  

   reddish 
  brown 
  in 
  some 
  cases 
  and 
  yellow-green 
  in 
  others, 
  is 
  very 
  

   abundant 
  : 
  it 
  is 
  distinctly 
  dichroic. 
  Whether 
  this 
  represents 
  in 
  

   places 
  a 
  glassy 
  base, 
  or 
  whether 
  it 
  is 
  wholly 
  altered 
  felsitic 
  matter, 
  

   is 
  difficult 
  to 
  say. 
  The 
  rock 
  would, 
  by 
  many, 
  be 
  called 
  a 
  melaphyre 
  

   or 
  diabase, 
  but 
  I 
  prefer 
  to 
  name 
  it 
  altered 
  basalt. 
  

  

  No. 
  1422 
  is 
  a 
  compact 
  rock 
  of 
  purple-black 
  colour, 
  which 
  is 
  said 
  

   to 
  be 
  very 
  abundant 
  at 
  Amir 
  Chah. 
  It 
  consists 
  of 
  iron 
  micro- 
  

   granules, 
  set 
  in 
  a 
  base 
  composed 
  of 
  aluminous 
  serpentine. 
  

  

  The 
  iron 
  is 
  in 
  part 
  magnetite 
  and 
  in 
  part 
  limonite. 
  It 
  varies 
  

   from 
  opaque 
  to 
  translucent, 
  and 
  in 
  colour 
  from 
  a 
  deep 
  brown 
  to 
  a 
  

   black-brown. 
  It 
  is 
  disseminated 
  through 
  the 
  slice 
  in 
  microgranules 
  

   and 
  in 
  irregularly-shaped 
  patches, 
  which 
  rarely 
  coalesce 
  into 
  uniform 
  

   and 
  unbroken 
  masses. 
  It 
  nowhere 
  presents 
  crystalline 
  outlines. 
  

  

  The 
  serpentinous 
  groundmass 
  remains 
  dark 
  when 
  revolved 
  be- 
  

   tween 
  crossed 
  nicols, 
  but 
  countless 
  fibres 
  and 
  dots 
  of 
  doubly- 
  

   refracting 
  material, 
  probably 
  chrysotile 
  or 
  kaolin, 
  shine 
  like 
  stars 
  in 
  

   the 
  Milky 
  Way. 
  In 
  this 
  groundmass, 
  pseudomorphs 
  of 
  felspars, 
  

   pyroxene, 
  and 
  olivine 
  can 
  be 
  made 
  out, 
  the 
  original 
  shapes 
  of 
  the 
  

   minerals 
  beiug 
  outlined 
  by 
  deposits 
  of 
  iron 
  oxide. 
  No 
  trace 
  of 
  

   twinning 
  can 
  be 
  discerned 
  in 
  the 
  felspars, 
  as 
  none 
  of 
  the 
  original 
  

  

  