﻿Laurentian 
  Highlands 
  of 
  Canada. 
  119 
  

  

  the 
  time 
  at 
  which 
  the 
  deformation 
  occurred, 
  that 
  is, 
  according 
  

   to 
  whether 
  it 
  took 
  place 
  at 
  the 
  time 
  of 
  intrusion 
  or 
  long 
  after 
  

   consolidation. 
  

  

  Wherever 
  the 
  Laurentian 
  gneiss 
  and 
  granite 
  have 
  been 
  

   observed 
  in 
  contact 
  with 
  rocks 
  of 
  the 
  Abitibi 
  group 
  and 
  the 
  

   Grenville 
  series, 
  they 
  are 
  always 
  intrusive 
  into 
  the 
  latter, 
  yet 
  

   the 
  presence 
  of 
  conglomerate 
  containing 
  granite 
  pebbles 
  in 
  the 
  

   Abitibi 
  group 
  and 
  the 
  occurrence 
  of 
  siliceous 
  sediments 
  in 
  the 
  

   Grenville 
  series 
  indicate 
  that 
  older 
  granitic 
  rocks 
  were 
  at 
  one 
  

   time 
  widely 
  present 
  in 
  the 
  region 
  and 
  it 
  might 
  be 
  possible 
  that 
  

   this 
  ancient 
  granite 
  comprises 
  a 
  considerable 
  part 
  of 
  the 
  Lau- 
  

   rentian 
  gneissic 
  complex. 
  However, 
  no 
  evidence 
  was 
  observed 
  

   anywhere 
  throughout 
  the 
  gneissic 
  complex 
  of 
  the 
  presence 
  of 
  

   granite 
  or 
  gneiss 
  of 
  two 
  distinct 
  periods 
  of 
  intrusion, 
  and 
  if 
  

   such 
  occurred, 
  the 
  evidence 
  of 
  their 
  presence 
  has 
  been 
  entirely 
  

   obliterated 
  by 
  deformation. 
  On 
  the 
  other 
  hand, 
  — 
  if 
  it 
  be 
  

   assumed 
  that 
  the 
  banding 
  of 
  the 
  banded 
  gneisses 
  originated 
  as 
  

   a 
  result 
  of 
  deformation, 
  — 
  it 
  is 
  apparent 
  that 
  the 
  larger 
  part 
  of 
  

   the 
  simplex 
  was 
  undergoing 
  consolidation 
  at 
  the 
  time 
  the 
  band- 
  

   ing 
  was 
  being 
  developed 
  ; 
  for 
  pegmatite 
  and 
  aplite 
  were 
  being 
  

   given 
  off 
  from 
  the 
  magma 
  during 
  stages 
  in 
  the 
  development 
  

   of 
  the 
  bands, 
  as 
  shown 
  by 
  the 
  occurrence 
  of 
  dikes 
  of 
  these 
  

   rocks 
  transverse 
  to 
  the 
  banding 
  and 
  in 
  all 
  stages 
  of 
  deforma- 
  

   tion, 
  some 
  being 
  exceedingly 
  crumpled 
  and 
  others 
  undisturbed. 
  

  

  In 
  a 
  paper 
  published 
  in 
  1887 
  *' 
  On 
  the 
  Origin 
  of 
  Certain 
  

   Banded 
  Gneisses," 
  J. 
  J. 
  Teall* 
  concluded 
  that 
  banded 
  gneisses 
  

   might 
  originate 
  by 
  the 
  deformation 
  of 
  a 
  heterogeneous 
  plutonic 
  

   mass, 
  the 
  evidence 
  for 
  this 
  conclusion 
  being 
  (1) 
  that 
  plutonic 
  

   rocks 
  are 
  commonly 
  heterogeneous 
  and 
  (2) 
  that 
  a 
  plutonic 
  

   igneous 
  mass 
  may 
  undergo 
  deformation 
  during 
  intrusion 
  or 
  

   later 
  as 
  a 
  result 
  of 
  mountain-building 
  stresses. 
  It 
  is 
  proposed 
  

   in 
  this 
  paper 
  to 
  suggest 
  that 
  the 
  Laurentian 
  banded 
  gneisses, 
  in 
  

   the 
  particular 
  locality 
  studied 
  by 
  the 
  writer, 
  not 
  only 
  originated 
  

   by 
  the 
  deformation 
  of 
  a 
  heterogeneous 
  plutonic 
  mass 
  but 
  that 
  

   the 
  heterogeneity 
  was 
  itself 
  developed, 
  to 
  a 
  large 
  extent, 
  as 
  a 
  

   result 
  of 
  the 
  deformation 
  and 
  that 
  the 
  deformation 
  was 
  related 
  

   to 
  mountain-building 
  stresses 
  which 
  acted 
  upon 
  the 
  magma 
  

   during 
  and 
  following 
  its 
  consolidation. 
  

  

  Plutonic 
  masses 
  of 
  rock 
  when 
  examined 
  over 
  areas 
  of 
  con- 
  

   siderable 
  extent, 
  are 
  generally 
  found 
  to 
  be 
  heterogeneous. 
  

   This 
  heterogeneity 
  must 
  obviously 
  be 
  due 
  to 
  either 
  assimilation 
  

   of 
  foreign 
  rock, 
  or 
  to 
  differentiation 
  within 
  the 
  magma 
  itself. 
  

   That 
  assimilation 
  occurred 
  in 
  the 
  case 
  of 
  the 
  Laurentian 
  com- 
  

   plex 
  is 
  evident 
  from 
  the 
  occurrence 
  of 
  partially 
  assimilated 
  

   fragments 
  of 
  both 
  the 
  Abitibi 
  group 
  and 
  the 
  Grenville 
  series 
  

   along 
  the 
  batholithic 
  border, 
  but 
  whether 
  this 
  process 
  was 
  of 
  

   *Geol. 
  Mag., 
  vol. 
  iv, 
  pp. 
  484-492, 
  1887. 
  

  

  