﻿^°1- 
  53-] 
  StJDBURY 
  NICKEL 
  DISTRICT 
  ( 
  CANADA). 
  43 
  

  

  and 
  sphene. 
  Specimens 
  collected 
  farther 
  south-west 
  on 
  the 
  same 
  

   gneiss-terrane 
  contain 
  almost 
  equal 
  quantities 
  of 
  biotite 
  and 
  mus- 
  

   covite, 
  both 
  of 
  which 
  are 
  well 
  preserved. 
  

  

  III. 
  The 
  HrntoNiAN" 
  Rocks. 
  

  

  These 
  are 
  chiefly 
  confined 
  to 
  the 
  Huronian 
  belt, 
  which 
  in 
  the 
  

   neighbourhood 
  of 
  Sudbury 
  is 
  about 
  25 
  miles 
  wide. 
  Inliers 
  of 
  

   different 
  kinds 
  are 
  numerous, 
  but 
  these 
  will 
  be 
  described 
  in 
  a 
  later 
  

   section. 
  Quartzite, 
  grauwaeke, 
  mica-schist, 
  phyllite, 
  and 
  altered 
  

   volcanic 
  breccia 
  are 
  the 
  chief 
  constituents 
  of 
  the 
  Huronian 
  complex. 
  

   They 
  have 
  all 
  suffered 
  extensive 
  metamorphism, 
  so 
  that 
  it 
  is 
  

   generally 
  difficult 
  to 
  speak 
  definitely 
  as 
  to 
  their 
  origin. 
  Those 
  

   which 
  have 
  been 
  derived 
  by 
  the 
  disintegration 
  of 
  still 
  older 
  rocks 
  

   are 
  to 
  be 
  regarded 
  as 
  among 
  the 
  oldest-known 
  sediments. 
  It 
  is 
  

   possible 
  that 
  some 
  of 
  the 
  above 
  rocks 
  have 
  been 
  derived 
  from 
  acid 
  

   tuff's, 
  which 
  in 
  some 
  cases 
  may 
  have 
  been 
  deposited 
  in 
  the 
  primeval 
  

   sea, 
  as 
  suggested 
  by 
  the 
  frequently 
  perfect 
  stratification. 
  Some 
  may 
  

   have 
  been 
  derived 
  by 
  the 
  devitrification 
  of 
  flows 
  of 
  glassy, 
  occa- 
  

   sionally 
  porphyritic 
  eruptives. 
  Metamorphism 
  has 
  advanced 
  so 
  far 
  

   that 
  the 
  early 
  history 
  of 
  these 
  rocks 
  is 
  only 
  very 
  imperfectly 
  

   revealed. 
  All 
  of 
  the 
  above-mentioned 
  sources 
  have 
  doubtless 
  con- 
  

   tributed 
  to 
  the 
  formation 
  of 
  the 
  Huronian 
  strata 
  of 
  the 
  Sudbury 
  

   district. 
  

  

  (i) 
  Quartzites. 
  

  

  In 
  the 
  immediate 
  vicinity 
  of 
  Sudbury, 
  numerous 
  exposures 
  of 
  

   these 
  rocks 
  are 
  observed. 
  In 
  general 
  the 
  texture 
  is 
  very 
  fine, 
  the 
  

   stratification 
  obscure, 
  and 
  the 
  colour 
  ashen-grey. 
  The 
  microscope 
  

   shows 
  that 
  the 
  quartz-grains 
  interlock 
  as 
  if 
  much 
  secondary 
  

   enlargement 
  had 
  taken 
  place, 
  although 
  no 
  outline 
  of 
  original 
  grains 
  

   could 
  be 
  detected. 
  Grains 
  of 
  perthitic 
  felspar 
  and 
  scales 
  of 
  mus- 
  

   covite 
  are 
  mingled 
  sparingly 
  with 
  the 
  grains 
  of 
  quartz. 
  Small 
  

   clusters 
  of 
  brown 
  mica 
  and 
  rounded 
  spots 
  of 
  chlorite 
  are 
  often 
  seen 
  

   in 
  thin 
  sections. 
  The 
  general 
  strike 
  is 
  ~N. 
  30° 
  E. 
  A 
  short 
  distance 
  

   north 
  of 
  Sudbury, 
  on 
  the 
  way 
  to 
  Blezard 
  Mine, 
  an 
  evenly-stratified 
  

   quartzitic 
  rock 
  occurs. 
  Narrow 
  bands 
  of 
  a 
  few 
  millimetres 
  in 
  width 
  

   may 
  be 
  often 
  followed 
  for 
  some 
  score 
  yards. 
  A 
  microscopic 
  exami- 
  

   nation 
  shows 
  the 
  presence 
  of 
  much 
  muscovite 
  and 
  numerous 
  small 
  

   colonies 
  of 
  chlorite. 
  This 
  rock 
  is 
  also 
  well 
  exposed 
  along 
  the 
  road 
  

   to 
  Copper 
  Cliff 
  Mine, 
  about 
  a 
  mile 
  from 
  Sudbury. 
  West 
  of 
  Sudbury, 
  

   along 
  the 
  Canadian 
  Pacific 
  Railway, 
  the 
  quartzites 
  are, 
  as 
  a 
  rule, 
  

   very 
  thickly 
  bedded, 
  while 
  in 
  some 
  cases 
  bedding 
  is 
  scarcely 
  dis- 
  

   cernible. 
  

  

  South-east 
  of 
  Sudbury, 
  along 
  the 
  rocky 
  shores 
  of 
  Ramsay 
  Lake, 
  

   conglomeratic 
  phases 
  of 
  the 
  above 
  quartzites 
  occur. 
  The 
  pebbles 
  

   are 
  in 
  the 
  main 
  of 
  reddish 
  granite 
  and 
  vary 
  much 
  in 
  size. 
  As 
  a 
  

   rule, 
  the 
  south-eastern 
  side 
  of 
  the 
  Huronian 
  belt 
  is 
  composed 
  of 
  

   the 
  quartzitic 
  rocks 
  just 
  described. 
  The 
  conglomeratic 
  portions 
  

   are 
  undoubtedly 
  derived 
  from 
  still 
  older 
  Archaean 
  rocks, 
  while 
  the 
  

  

  