﻿58 
  ME. 
  T. 
  L. 
  WALKEK 
  ON 
  THE 
  [Feb. 
  1 
  897,, 
  

  

  forms. 
  The 
  same 
  mineral 
  is 
  a 
  very 
  frequent 
  accessory 
  in 
  the 
  

   Norwegian 
  zircon-syenites, 
  though 
  the 
  secondary 
  products 
  are 
  not 
  so 
  

   well 
  developed 
  there 
  as 
  in 
  the 
  Onaping 
  rocks. 
  This 
  mineral 
  has 
  

   been 
  identified 
  in 
  the 
  zircon-syenites 
  as 
  wohlerite, 
  and 
  it 
  is 
  possible 
  

   that 
  the 
  associates 
  of 
  wohlerite 
  may 
  be 
  found 
  in 
  the 
  Sudbury 
  nickel- 
  

   bearing 
  rocks. 
  A 
  mechanical 
  or 
  chemical 
  separation 
  of 
  this 
  mineral 
  

   was 
  impossible. 
  

  

  The 
  reddish 
  granite 
  at 
  Onaping 
  Station 
  is 
  composed 
  of 
  micro- 
  

   pegmatite, 
  orthoclase 
  with 
  a 
  little 
  free 
  quartz, 
  and 
  about 
  equal 
  

   quantities 
  of 
  wohlerite 
  and 
  secondary 
  hornblende, 
  which 
  was 
  pro- 
  

   bably 
  derived 
  from 
  the 
  former. 
  Orthoclase 
  has 
  replaced 
  plagioclase 
  

   in 
  the 
  micropegmatite, 
  which 
  constitutes 
  about 
  two-thirds 
  of 
  the 
  

   rock, 
  and 
  has 
  attained 
  a 
  high 
  degree 
  of 
  perfection. 
  "Wohlerite 
  is 
  

   present 
  as 
  grains, 
  which 
  at 
  times 
  deserve 
  the 
  name 
  of 
  crystals, 
  and 
  

   may 
  be 
  seen 
  to 
  be 
  optically 
  biaxial, 
  with 
  a 
  very 
  large 
  optic 
  angle. 
  

   The 
  secondary 
  hornblende 
  derived 
  from 
  it 
  contains 
  numerous 
  deli- 
  

   cate 
  feathery 
  crystals 
  of 
  biotite, 
  which 
  are 
  also 
  probably 
  of 
  secondary 
  

   nature. 
  

  

  South-eastward 
  from 
  Onaping, 
  near 
  the 
  contact, 
  the 
  granite 
  

   becomes 
  fine-grained 
  and 
  darker 
  in 
  colour, 
  while 
  the 
  microscope 
  

   shows 
  a 
  slight 
  increase 
  in 
  plagioclase 
  and 
  iron 
  ores, 
  and 
  a 
  decrease- 
  

   in 
  free 
  quartz. 
  

  

  In 
  this 
  eruptive, 
  as 
  in 
  the 
  one 
  previously 
  described, 
  micropeg- 
  

   matite 
  is 
  characteristic 
  for 
  the 
  granitic 
  rocks 
  connected 
  with 
  basic 
  

   noritic 
  borders. 
  Harker 
  has 
  observed 
  the 
  same 
  occurrence 
  in 
  his 
  

   studies 
  of 
  the 
  Carrock 
  Fell 
  gabbro 
  in 
  England. 
  Elsewhere 
  micro- 
  

   pegmatitic 
  rocks 
  are 
  generally 
  muscovite-bearing, 
  but 
  in 
  the 
  Sudbury 
  

   eruptives 
  muscovite 
  is 
  very 
  seldom 
  found. 
  A 
  wider 
  examination 
  

   might 
  show 
  that 
  micropegmatite 
  is 
  characteristic 
  for 
  all 
  rocks 
  which 
  

   are 
  midway 
  between 
  the 
  more 
  acid 
  and 
  the 
  more 
  basic 
  portion 
  of 
  

   differentiated 
  eruptives. 
  

  

  Some 
  of 
  the 
  most 
  important 
  deposits 
  of 
  nickeliferous 
  pyrrhotite 
  

   discovered 
  in 
  the 
  Sudbury 
  district 
  are 
  situated 
  along 
  the 
  north- 
  

   western 
  border 
  of 
  the 
  Windy 
  Lake 
  eruptive. 
  We 
  have 
  here 
  to 
  deal 
  

   with 
  an 
  eruptive 
  whose 
  length 
  is 
  unknown, 
  and 
  whose 
  width 
  is 
  nearly 
  

   4 
  miles. 
  The 
  gradual 
  transition, 
  from 
  typical 
  pyrrhotite-norite 
  on 
  

   the 
  one 
  hand 
  to 
  hornblende-granite 
  on 
  the 
  other, 
  shows 
  that 
  in 
  most 
  

   respects 
  it 
  is 
  identical 
  with 
  the 
  Whitson 
  Lake 
  eruptive. 
  These 
  

   eruptive 
  areas, 
  which 
  are 
  bordered 
  locally 
  with 
  norite 
  and 
  pyrrhotite- 
  

   norite, 
  cannot 
  properly 
  be 
  spoken 
  of 
  as 
  basic 
  eruptives, 
  since 
  the 
  

   average 
  acidity 
  for 
  the 
  whole 
  of 
  the 
  eruptives 
  is 
  at 
  least 
  62 
  per 
  cent, 
  

   of 
  silica. 
  In 
  this 
  respect 
  the 
  Sudbury 
  nickel-bearing 
  eruptives 
  differ 
  

   from 
  those 
  of 
  Norway 
  as 
  described 
  by 
  Yogt. 
  

  

  Bell's 
  map 
  shows 
  a 
  greenstone 
  area 
  extending 
  from 
  Lake 
  Sagi- 
  

   tchi-wai-a-ga-mog 
  south-westward 
  into 
  the 
  township 
  of 
  Morgan. 
  

   This 
  area 
  is 
  in 
  all 
  probability 
  only 
  a 
  basic 
  border 
  of 
  the 
  Windy 
  

   Lake 
  eruptive. 
  In 
  this 
  case 
  the 
  length 
  of 
  the 
  eruptive 
  is 
  at 
  least 
  

   25 
  miles, 
  while 
  further 
  investigation 
  may 
  show 
  that 
  it 
  is 
  even 
  

   longer. 
  

  

  