﻿50 
  ME. 
  T. 
  L. 
  WALKER 
  ON 
  THE 
  [Feb. 
  1897, 
  

  

  except 
  for 
  the 
  presence 
  of 
  hornblende-inclusions, 
  does 
  not 
  differ 
  from 
  

   that 
  of 
  the 
  type-rock. 
  

  

  Passing 
  eastward, 
  the 
  rock 
  becomes 
  slightly 
  finer-grained, 
  but 
  

   does 
  not 
  differ 
  materially 
  from 
  the 
  type-rock. 
  About 
  200 
  yards 
  

   from 
  the 
  smelting- 
  works 
  at 
  Murray 
  Mines, 
  the 
  rock 
  when 
  examined 
  

   microscopically 
  is 
  seen 
  to 
  differ 
  from 
  the 
  former 
  specimens 
  in 
  two 
  

   ways 
  : 
  there 
  are 
  differences 
  on 
  the 
  one 
  hand 
  which 
  are 
  due 
  to 
  

   metamorphism, 
  and 
  these 
  may 
  be 
  regarded 
  as 
  of 
  secondary 
  nature 
  ; 
  

   and 
  on 
  the 
  other 
  hand 
  there 
  are 
  differences 
  of 
  a 
  primary 
  nature, 
  

   and 
  these 
  are 
  to 
  be 
  explained 
  as 
  due 
  to 
  the 
  differentiation 
  of 
  the 
  

   original 
  rock-magma. 
  Neither 
  crystals 
  of 
  hypersthene 
  nor 
  even 
  pre- 
  

   served 
  remnants 
  of 
  the 
  mineral, 
  such 
  as 
  were 
  noticed 
  in 
  the 
  previous 
  

   rocks, 
  can 
  be 
  observed, 
  and 
  we 
  are 
  able 
  to 
  prove 
  its 
  presence 
  in 
  the 
  

   original 
  rock 
  only 
  by 
  reference 
  to 
  the 
  areas 
  of 
  bastite 
  and 
  secondary 
  

   hornblende. 
  The 
  more 
  or 
  less 
  regularly 
  rectangular 
  areas 
  have 
  

   been 
  derived 
  from 
  hypersthene, 
  while 
  quite 
  irregular 
  areas 
  have 
  

   been 
  probably 
  derived 
  from 
  augite. 
  Primary 
  hornblende 
  is 
  not 
  so 
  

   abundant 
  as 
  previously, 
  while 
  biotite, 
  which 
  appears 
  to 
  be 
  of 
  

   primary 
  nature, 
  is 
  more 
  abundant. 
  Plagioclase 
  is 
  characterized 
  by 
  

   brown 
  dust-like 
  inclusions, 
  and 
  by 
  small 
  colourless 
  crystals 
  which 
  

   are 
  probably 
  zoisite 
  or 
  epidote. 
  

  

  The 
  plagioclase-crystals 
  contain 
  numerous 
  particles 
  of 
  secondary 
  

   green 
  hornblende, 
  which 
  is 
  at 
  times 
  so 
  plentiful 
  as 
  to 
  somewhat 
  

   conceal 
  the 
  original 
  felspar-boundaries. 
  The 
  same 
  indistinctness 
  is 
  

   often 
  observed 
  in 
  connexion 
  with 
  the 
  secondary 
  products 
  resulting 
  

   from 
  hypersthene 
  and 
  augite. 
  Bastite-sub 
  stance 
  seems 
  to 
  have 
  

   been 
  transported 
  in 
  solution 
  from 
  the 
  original 
  hypersthene-areas, 
  

   and 
  to 
  have 
  produced 
  the 
  secondary 
  hornblende 
  in 
  the 
  plagioclase 
  

   by 
  reacting 
  upon 
  it. 
  Generally 
  the 
  solution 
  followed 
  cleavage- 
  

   planes 
  in 
  the 
  felspar, 
  but 
  frequently 
  the 
  cleavage-paths 
  cannot 
  be 
  

   traced. 
  This 
  process, 
  whereby 
  secondary 
  hornblende 
  is 
  formed 
  by 
  

   the 
  action 
  upon 
  plagioclase 
  of 
  solutions 
  carrying 
  bastite-substance, 
  

   and 
  the 
  deposition 
  of 
  the 
  hornblende 
  distant 
  from 
  the 
  bastite-areas, 
  

   may 
  be 
  referred 
  to 
  as 
  the 
  * 
  migration 
  of 
  hornblende/ 
  and 
  hornblende 
  

   so 
  formed 
  may 
  be 
  called 
  * 
  immigrated 
  hornblende.' 
  

  

  Between 
  the 
  smelting-works 
  and 
  the 
  Murray 
  Mines 
  ore-deposits 
  

   the 
  rock 
  is 
  finer-grained 
  and 
  more 
  altered. 
  The 
  microscope 
  shows 
  

   that 
  the 
  secondary 
  hornblende 
  is 
  nearly 
  all 
  of 
  the 
  bluish-green 
  type, 
  

   bastite 
  having 
  almost 
  disappeared. 
  The 
  migration 
  of 
  hornblende 
  

   has 
  become 
  much 
  more 
  general, 
  so 
  that 
  the 
  old 
  boundaries 
  of 
  the 
  

   bisilicates 
  are 
  very 
  imperfectly 
  preserved 
  in 
  the 
  areas 
  of 
  their 
  

   secondary 
  products. 
  It 
  is 
  also 
  worthy 
  of 
  note 
  that 
  a 
  few 
  of 
  the 
  

   areas 
  of 
  secondary 
  hornblende 
  seem 
  to 
  have 
  suffered 
  a 
  still 
  further 
  

   change, 
  and 
  to 
  have 
  given 
  rise 
  to 
  dark 
  brown, 
  fine, 
  scaly 
  biotite. 
  

   This 
  seems 
  to 
  be 
  the 
  final 
  product 
  of 
  the 
  alteration 
  which 
  changes 
  

   hypersthene 
  successively 
  to 
  bastite-magnetite 
  aggregate, 
  pleochroic 
  

   bluish-green 
  hornblende, 
  and 
  finally 
  scaly 
  biotite. 
  The 
  production 
  

   of 
  biotite 
  from 
  secondary 
  hornblende 
  seems 
  to 
  have 
  been 
  much 
  

   more 
  frequent 
  in 
  the 
  small 
  individuals 
  included 
  in 
  the 
  felspar. 
  The 
  

   plagioclase 
  swarms 
  with 
  epidote-crystals 
  and 
  shows 
  very 
  irregular 
  

  

  