﻿^°* 
  53'] 
  SUDBTJEY 
  NICKEL 
  DISTEICT 
  (CANADA.). 
  57 
  

  

  abundant 
  white 
  mineral 
  forming 
  the 
  groundmass 
  for 
  the 
  dark 
  

   mineral. 
  Though 
  a 
  norite, 
  this 
  rock 
  differs 
  in 
  appearance 
  from 
  the 
  

   Whitson 
  Lake 
  eruptive 
  in 
  being 
  coarser-grained 
  and 
  of 
  a 
  much 
  

   lighter 
  colour. 
  

  

  The 
  microscope 
  shows 
  that 
  here 
  the 
  hypersthene, 
  though 
  often 
  

   quite 
  fresh, 
  is 
  more 
  frequently 
  changed 
  partly 
  or 
  even 
  entirely 
  to 
  

   bastite 
  or 
  secondary 
  hornblende. 
  The 
  plagioclase-crystals 
  are 
  quite 
  

   free 
  from 
  the 
  dusty-brown 
  inclusions 
  observed 
  in 
  the 
  plagioclase 
  of 
  the 
  

   Whitson 
  Lake 
  norite. 
  This 
  difference 
  is 
  largely 
  responsible 
  for 
  the 
  

   comparatively 
  light 
  colour 
  of 
  the 
  Windy 
  Lake 
  norite 
  as 
  contrasted 
  

   with 
  the 
  dark 
  colour 
  of 
  the 
  Whitson 
  Lake 
  norite. 
  

  

  A 
  specimen 
  collected 
  \ 
  mile 
  east 
  differs 
  from 
  the 
  last 
  in 
  being 
  

   slightly 
  more 
  altered 
  and 
  of 
  somewhat 
  more 
  acid 
  character. 
  Some 
  

   crystals 
  of 
  plagioclase 
  exhibit 
  in 
  an 
  unusual 
  degree 
  zonal 
  structure 
  

   and 
  wandering 
  extinction. 
  In 
  some 
  cases 
  there 
  is 
  a 
  difference 
  of 
  

   38° 
  between 
  the 
  extinction 
  of 
  the 
  central 
  and 
  marginal 
  portions 
  of 
  

   the 
  same 
  individual. 
  Such 
  plagioclase-crystals 
  generally 
  border 
  on 
  

   small 
  areas 
  of 
  quartz 
  and 
  micropegmatite, 
  and 
  appear 
  to 
  have 
  con- 
  

   tinued 
  their 
  growth 
  till 
  all 
  the 
  constituents 
  except 
  the 
  quartz 
  and 
  

   micropegmatite 
  had 
  crystallized. 
  The 
  central 
  portion 
  is 
  therefore 
  

   •composed 
  of 
  one 
  of 
  the 
  most 
  basic 
  plagioclases, 
  while 
  the 
  marginal 
  

   portion 
  represents 
  one 
  of 
  the 
  most 
  acid 
  of 
  the 
  series. 
  

  

  Eastward 
  the 
  rock 
  becomes 
  coarser 
  in 
  grain, 
  and 
  the 
  greyish 
  

   norite 
  gives 
  place 
  to 
  what 
  might 
  be 
  taken 
  macroscopically 
  for 
  a 
  

   hornblende-syenite. 
  A 
  specimen 
  collected 
  2^ 
  miles 
  west 
  of 
  Onaping 
  

   Station, 
  when 
  examined 
  microscopically, 
  shows 
  that 
  secondary 
  horn- 
  

   blende 
  is 
  the 
  only 
  bisilicate 
  present. 
  Micropegmatite 
  and 
  quartz 
  

   are 
  more 
  abundant 
  : 
  the 
  felspar 
  of 
  the 
  micropegmatite 
  is 
  well- 
  

   twinned 
  plagioclase. 
  There 
  are 
  a 
  few 
  grains 
  of 
  a 
  yellowish 
  pleochroic 
  

   mineral, 
  which 
  has 
  strong 
  polarization-colours 
  and 
  a 
  high 
  index 
  of 
  

   refraction. 
  As 
  this 
  mineral 
  becomes 
  much 
  more 
  abundant 
  near 
  

   Onaping 
  Station, 
  it 
  will 
  be 
  more 
  fully 
  dealt 
  with 
  later 
  : 
  it 
  seems 
  to 
  

   alter 
  to 
  radiating 
  aggregates 
  of 
  pale 
  lemon-yellow 
  hornblende. 
  

  

  Towards 
  Onaping 
  Station 
  there 
  is 
  a 
  marked 
  increase 
  in 
  the 
  

   quantity 
  of 
  micropegmatite, 
  which 
  forms 
  about 
  half 
  the 
  rock. 
  Well- 
  

   defined 
  felspar- 
  crystals 
  form 
  the 
  centres 
  for 
  radiating 
  micropeg- 
  

   matite 
  areas. 
  Taking 
  into 
  consideration 
  the 
  prominent 
  part 
  played 
  

   by 
  micropegmatite 
  and 
  the 
  porphyritic 
  nature 
  of 
  the 
  rock, 
  it 
  may 
  be 
  

   called 
  a 
  ' 
  hornblende-porphyry 
  with 
  a 
  micropegmatitic 
  groundmass.' 
  

  

  There 
  is, 
  moreover, 
  another 
  important 
  constituent. 
  This 
  occurs 
  

   commonly 
  in 
  groups 
  of 
  irregular 
  grains, 
  and 
  is 
  distinctly 
  pleochroic 
  — 
  

   lemon, 
  yellowish-green, 
  and 
  colourless. 
  The 
  index 
  of 
  refraction 
  

   is 
  high, 
  and 
  the 
  surface 
  appears 
  to 
  be 
  quite 
  rough 
  when 
  seen 
  

   under 
  the 
  microscope. 
  The 
  double 
  refraction 
  is 
  high, 
  so 
  that 
  it 
  

   polarizes 
  in 
  orange-green 
  and 
  red 
  tints 
  when 
  quartz 
  of 
  the 
  same 
  

   thickness 
  polarizes 
  in 
  grey. 
  It 
  is 
  always 
  associated 
  with 
  the 
  

   radiating 
  aggregates 
  of 
  seconda 
  y 
  hornblende 
  above 
  mentioned. 
  

   "This 
  mineral 
  appears 
  to 
  have 
  occupied 
  a 
  prominent 
  place 
  in 
  the 
  

   •original 
  rock, 
  where 
  it 
  largely 
  replaced 
  the 
  bisilicates. 
  Having 
  

   .crystallized 
  later 
  than 
  the 
  quartz, 
  it 
  presents 
  very 
  seldom 
  idiomorphic 
  

  

  