﻿Q2 
  MR. 
  T. 
  L. 
  WALKER 
  ON 
  THE 
  [Feb. 
  1 
  897, 
  

  

  VIE. 
  Oli 
  vine-Diabase 
  Dykes. 
  

  

  These 
  dykes 
  are 
  the 
  youngest 
  of 
  the 
  Sudbury 
  rocks, 
  and 
  are 
  

   characterized 
  by 
  north-westerly 
  direction 
  with 
  only 
  very 
  slight 
  

   variations. 
  All 
  the 
  other 
  rocks 
  of 
  the 
  district 
  are 
  intersected 
  by 
  

   them. 
  The 
  extensive 
  area 
  over 
  which 
  these 
  dykes 
  occur, 
  taken 
  in 
  

   connexion 
  with 
  their 
  general 
  parallelism, 
  points 
  to 
  a 
  period 
  of 
  great 
  

   dynamical 
  action. 
  The 
  force 
  that 
  produced 
  the 
  cracks 
  through 
  

   which 
  the 
  diabase-magma 
  ascended 
  had 
  doubtless 
  a 
  part 
  in 
  the 
  

   production 
  of 
  amphibolites 
  and 
  flaser-gabbros 
  from 
  massive 
  pyroxene- 
  

   rocks, 
  in 
  the 
  metamorphism 
  of 
  the 
  norites, 
  and 
  in 
  the 
  crushing 
  of 
  

   the 
  Younger 
  Granites 
  and 
  granitic 
  borders 
  of 
  the 
  nickel- 
  bearing 
  

   areas. 
  As 
  the 
  dykes 
  intersect 
  all 
  the 
  other 
  rocks, 
  we 
  may 
  conclude 
  

   their 
  post-Huronian 
  age, 
  though 
  it 
  is 
  impossible 
  to 
  say 
  whether 
  they 
  

   were 
  formed 
  in 
  early 
  Palaeozoic 
  or 
  in 
  comparatively 
  recent 
  times. 
  

  

  One 
  of 
  the 
  best 
  representatives 
  of 
  this 
  dyke-system 
  is 
  well 
  exposed 
  

   quite 
  near 
  the 
  town 
  of 
  Sudbury, 
  and 
  can 
  be 
  followed 
  for 
  7 
  miles. 
  

   The 
  easternmost 
  exposure 
  is 
  on 
  the 
  southern 
  shore 
  of 
  Eamsay 
  Lake, 
  

   near 
  the 
  north-western 
  point 
  of 
  the 
  peninsula 
  which 
  nearly 
  divides 
  

   the 
  lake. 
  It 
  appears 
  again 
  on 
  the 
  north-western 
  shore 
  near 
  the 
  

   landing, 
  and 
  the 
  dyke 
  may 
  be 
  followed 
  by 
  frequent 
  exposures 
  past 
  

   the 
  town 
  of 
  Sudbury. 
  All 
  the 
  exposures 
  of 
  diabase 
  along 
  the 
  

   railway 
  between 
  Sudbury 
  and 
  Rayside 
  Stations 
  are 
  portions 
  of 
  the 
  

   same 
  dyke. 
  

  

  Another 
  dyke 
  of 
  this 
  system 
  crosses 
  the 
  railway 
  1 
  mile 
  east 
  of 
  

   Worthington 
  Station, 
  and 
  a 
  third 
  about 
  | 
  mile 
  east 
  of 
  the 
  station. 
  

   A 
  very 
  large 
  dyke 
  is 
  well 
  exposed 
  on 
  the 
  railway 
  near 
  Nairn 
  Station. 
  

   Many 
  others 
  might 
  be 
  mentioned, 
  some 
  of 
  which 
  are 
  said 
  to 
  have 
  

   other 
  directions, 
  but 
  all 
  those 
  examined 
  by 
  the 
  writer 
  have 
  a 
  general 
  

   north-westerly 
  direction. 
  In 
  width 
  they 
  vary 
  from 
  a 
  few 
  feet 
  to 
  

   50 
  yards. 
  

  

  Plagioclase 
  is 
  the 
  chief 
  constituent. 
  It 
  is 
  generally 
  quite 
  fresh, 
  

   but 
  is 
  occasionally 
  somewhat 
  clouded. 
  Idiomorphic 
  much-twinned 
  

   crystals 
  are 
  characteristic. 
  From 
  measurements 
  of 
  the 
  angles 
  of 
  

   extinction 
  the 
  felspar 
  seems 
  to 
  be 
  labradorite. 
  The 
  twinning 
  is 
  

   commonly 
  of 
  the 
  albite 
  law, 
  but 
  a 
  combination 
  of 
  the 
  albite 
  and 
  

   pericline 
  laws 
  is 
  frequent. 
  In 
  a 
  section 
  from 
  the 
  large 
  dyke 
  near 
  

   Murray 
  Mines 
  twinning 
  was 
  observed 
  combining 
  the 
  albite, 
  pericline, 
  

   and 
  Baveno 
  laws. 
  Twinning 
  of 
  plagioclase 
  according 
  to 
  the 
  Baveno 
  

   law 
  was 
  first 
  mentioned 
  by 
  Weiss, 
  and 
  more 
  fully 
  described 
  by 
  

   Brezina. 
  The 
  combination 
  of 
  this 
  rare 
  twinning 
  law 
  with 
  the 
  albite 
  

   and 
  pericline 
  laws 
  as 
  exhibited 
  in 
  the 
  diabase 
  from 
  near 
  Murray 
  

   Mines 
  is 
  very 
  interesting, 
  and 
  probably 
  has 
  never 
  been 
  previously 
  

   observed. 
  Plagioclase 
  being 
  by 
  far 
  the 
  earliest 
  to 
  crystallize, 
  the 
  

   ophitic 
  structure 
  is 
  beautifully 
  developed. 
  

  

  The 
  quantity 
  of 
  monoclinic 
  pyroxene 
  varies. 
  In 
  the 
  exposure 
  

   near 
  Murray 
  Mines 
  it 
  forms 
  about 
  a 
  quarter 
  of 
  the 
  rock, 
  while 
  at 
  

   other 
  points 
  on 
  this 
  dyke, 
  as 
  also 
  in 
  the 
  dykes 
  near 
  Worthington 
  

   Station, 
  it 
  does 
  not 
  constitute 
  more 
  than 
  an 
  eighth 
  of 
  the 
  rock. 
  

   Where 
  there 
  is 
  most 
  pyroxene 
  there 
  is 
  least 
  olivine, 
  and 
  vice 
  versa, 
  

  

  