﻿^ 
  r 
  °^ 
  53*] 
  SUDBURY 
  NICKEL 
  DISTRICT 
  (CANADA). 
  55 
  

  

  twinning, 
  in 
  that 
  there 
  is 
  complete 
  interpenetration 
  of 
  the 
  horn- 
  

   blende-individuals, 
  which 
  in 
  the 
  ordinary 
  twinning 
  are 
  separated 
  by- 
  

   straight 
  lines, 
  as 
  is 
  the 
  case 
  with 
  plagioclase 
  when 
  twinned 
  poly- 
  

   synthetically. 
  It 
  has 
  been 
  long 
  remarked 
  that 
  areas 
  of 
  secondary 
  

   hornblende 
  extinguish 
  in 
  two 
  portions, 
  but 
  the 
  exact 
  orientation 
  of 
  

   the 
  one 
  portion 
  with 
  reference 
  to 
  the 
  other 
  has 
  not 
  been 
  previously 
  

   determined. 
  

  

  Specimens 
  from 
  an 
  island 
  near 
  the 
  narrows 
  of 
  Whitson 
  Lake 
  

   show 
  distinct 
  parallelism, 
  and 
  appear 
  to 
  be 
  gneissoid 
  granite. 
  The 
  

   scaly 
  biotite 
  which 
  occurred 
  sparingly 
  in 
  the 
  previous 
  specimens 
  is 
  

   here 
  a 
  prominent 
  constituent, 
  and 
  forms 
  continuous 
  films 
  of 
  small 
  

   individuals, 
  which 
  give 
  to 
  the 
  rock 
  its 
  parallel 
  structure. 
  Ortho- 
  

   clase 
  is 
  much 
  more 
  prominent 
  than 
  plagioclase, 
  while 
  micropeg- 
  

   matite 
  constitutes 
  nearly 
  half 
  the 
  rock. 
  It 
  is 
  interesting 
  to 
  note 
  

   that 
  the 
  felspar 
  present 
  in 
  the 
  micropegmatite 
  is 
  well-twinned 
  

   plagioclase. 
  

  

  Farther 
  north 
  the 
  islands 
  and 
  shores 
  present 
  the 
  same 
  rock 
  as 
  

   that 
  just 
  described, 
  except 
  that 
  scaly 
  biotite, 
  quartz, 
  and 
  orthoclase 
  

   are 
  almost 
  the 
  sole 
  constituents. 
  Micropegmatite 
  nearly 
  disappears 
  

   in 
  the 
  northernmost 
  specimens. 
  Sometimes 
  the 
  rock 
  contains 
  

   numerous 
  grains 
  of 
  calcite, 
  which 
  is 
  well 
  twinned 
  and 
  water-clear. 
  

   This 
  mineral 
  is 
  certainly 
  not 
  a 
  decomposition-product 
  of 
  the 
  granite, 
  

   which 
  is 
  quite 
  fresh. 
  It 
  may 
  be 
  a 
  primary 
  constituent, 
  or 
  more 
  

   probably 
  an 
  infiltration 
  into 
  the 
  small 
  cavities 
  of 
  the 
  originally 
  

   somewhat 
  porous 
  rock. 
  Similar 
  calcite-granites 
  have 
  been 
  reported 
  

   by 
  Hawes 
  from 
  New 
  Hampshire, 
  and 
  by 
  Tornebohm 
  from 
  Guomalo 
  

   in 
  Sweden. 
  

  

  The 
  north-western 
  contact 
  occurs 
  at 
  the 
  extreme 
  north 
  of 
  the 
  

   lake, 
  near 
  the 
  mouth 
  of 
  a 
  small 
  creek. 
  The 
  rock 
  to 
  the 
  north-west 
  

   is 
  the 
  silicified 
  breccia 
  previously 
  described. 
  

  

  This 
  cross-section 
  of 
  the 
  Whitson 
  Lake 
  eruptive 
  shows 
  that 
  it 
  

   extends 
  from 
  a 
  short 
  distance 
  south 
  of 
  Blezard 
  Mine 
  to 
  the 
  northern 
  

   end 
  of 
  the 
  lake, 
  a 
  distance 
  of 
  3| 
  miles, 
  and 
  that 
  there 
  is 
  a 
  gradual 
  

   increase 
  in 
  acidity 
  towards 
  the 
  north. 
  

  

  y. 
  Exposures 
  along 
  the 
  line 
  between 
  Lots 
  8 
  and 
  9 
  in 
  the 
  

   Township 
  of 
  Snider. 
  

  

  A 
  two 
  days' 
  trip 
  was 
  made 
  through 
  the 
  woods 
  along 
  the 
  line 
  

   between 
  lots 
  8 
  and 
  9 
  in 
  the 
  township 
  of 
  Snider, 
  in 
  order 
  to 
  study 
  

   further 
  and 
  map 
  the 
  Whitson 
  Lake 
  eruptive. 
  It 
  was 
  found 
  that 
  on 
  

   the 
  southern 
  shore 
  of 
  the 
  lake 
  the 
  rocks 
  exposed 
  were 
  gneissoid 
  

   granites 
  similar 
  to 
  those 
  seen 
  near 
  the 
  narrows 
  of 
  Whitson 
  Lake. 
  

   The 
  contact 
  occurs 
  about 
  \ 
  mile 
  north 
  of 
  the 
  lake. 
  Passing 
  south- 
  

   ward 
  towards 
  Meat 
  Bird 
  Lake, 
  the 
  granite 
  gradually 
  gave 
  place 
  to 
  

   the 
  normal 
  greenstone. 
  The 
  southern 
  contact 
  was 
  found 
  to 
  be 
  near 
  

   the 
  boundary-line 
  between 
  concessions 
  II. 
  and 
  III. 
  Its 
  width 
  is 
  

   therefore 
  about 
  4 
  miles. 
  

  

  Thus 
  it 
  is 
  seen 
  that 
  this 
  section 
  of 
  the 
  Whitson 
  Lake 
  eruptive 
  is 
  

   quite 
  similar 
  to 
  the 
  two 
  sections 
  already 
  described. 
  

  

  