﻿Laurentian 
  Highlands 
  of 
  Canada. 
  121 
  

  

  follows 
  that 
  if 
  the 
  mountain 
  deformation 
  continued 
  until 
  the 
  

   axial 
  complex 
  began 
  to 
  consolidate, 
  it 
  would 
  also 
  be 
  deformed. 
  

   The 
  action 
  of 
  the 
  mountain-building 
  stresses 
  on 
  the 
  magmatic 
  

   central 
  mountain 
  mass 
  thus 
  affords 
  a 
  complete 
  explanation 
  of 
  

   the 
  cause 
  which 
  brought 
  about 
  not 
  only 
  the 
  folding, 
  foliation 
  

   and 
  granulation 
  in 
  the 
  banded 
  gneisses 
  but 
  also 
  explains 
  how 
  

   the 
  differentiation 
  of 
  the 
  magma 
  was 
  brought 
  about 
  so 
  that 
  a 
  

   banded 
  structure 
  was 
  made 
  possible. 
  During 
  the 
  final 
  stages 
  

   of 
  deformation, 
  the 
  gneissic 
  complex 
  had 
  evidently 
  passed, 
  for 
  

   the 
  most 
  part, 
  from 
  the 
  zone 
  of 
  flowage 
  to 
  the 
  zone 
  of 
  fracture 
  ; 
  

   for 
  slickensiding 
  between 
  the 
  bands, 
  granulation 
  and 
  fracture 
  

   became 
  the 
  dominant 
  deformational 
  processes. 
  

  

  Summary. 
  

  

  In 
  the 
  foregoing 
  pages, 
  the 
  geological 
  relations, 
  lithological 
  

   character, 
  and 
  structural 
  features 
  of 
  the 
  banded 
  gneisses 
  of 
  the 
  

   Laurentian 
  highland 
  of 
  Canada 
  have 
  been 
  briefly 
  described, 
  

   and 
  from 
  these 
  data 
  it 
  has 
  been 
  concluded 
  that 
  the 
  gneisses 
  com- 
  

   plex 
  was 
  originally 
  the 
  magmatic 
  center 
  of 
  a 
  Pre-Cambrian 
  

   mountain 
  chain 
  and 
  that 
  mountain-building 
  stresses 
  acted 
  upon 
  

   this 
  axial 
  magmatic 
  mass 
  during 
  its 
  consolidation 
  with 
  the 
  re- 
  

   sult 
  that 
  it 
  (1) 
  underwent 
  differentiation 
  aided 
  by 
  deformation 
  

   during 
  consolidation 
  and 
  (2) 
  by 
  further 
  deformation, 
  the 
  differen- 
  

   tiated 
  portions 
  became 
  flattened 
  out 
  into 
  bands 
  which 
  w 
  T 
  ere 
  then 
  

   crumpled 
  into 
  their 
  present 
  folded 
  structure. 
  This 
  hypothesis 
  

   is 
  supported 
  not 
  only 
  by 
  observations 
  in 
  the 
  field 
  where 
  the 
  

   various 
  stages 
  in 
  the 
  process 
  may 
  be 
  seen, 
  but 
  also 
  by 
  the 
  fact 
  

   that 
  it 
  affords 
  a 
  complete 
  explanation 
  of 
  the 
  heterogeneity, 
  

   banding, 
  foliation, 
  folding 
  and 
  other 
  characteristic 
  features 
  of 
  

   the 
  gneissic 
  complex. 
  Moreover, 
  it 
  postulates 
  only 
  such 
  con- 
  

   ditions 
  as 
  are 
  generally 
  accepted 
  by 
  geologists 
  the 
  world 
  over, 
  

   and 
  assumes 
  only 
  such 
  effects 
  as 
  must 
  necessarily 
  result 
  wher- 
  

   ever 
  such 
  conditions 
  arise 
  in 
  the 
  earth's 
  crust. 
  

  

  Stated 
  more 
  fully, 
  the 
  conclusions 
  with 
  regard 
  to 
  the 
  rela- 
  

   tions, 
  character, 
  and 
  origin 
  of 
  the 
  banded 
  gneisses 
  occurring 
  in 
  

   the 
  southern 
  part 
  of 
  the 
  great 
  Pre-Cambrian 
  Canadian 
  oldland 
  

   are 
  as 
  follows 
  : 
  

  

  (1) 
  The 
  Pre-Cambrian 
  basement 
  complex 
  occurring 
  through- 
  

   out 
  northeastern 
  Ontario 
  and 
  western 
  Quebec 
  may 
  be 
  divided 
  

   into 
  three 
  divisions, 
  a 
  northern 
  geosynclinal 
  belt 
  consisting 
  of 
  

   highly 
  folded 
  sediments 
  and 
  volcanic 
  flows 
  (Abitibi 
  group), 
  a 
  

   southern 
  geosynclinal 
  belt 
  chiefly 
  composed 
  of 
  crystalline 
  lime- 
  

   stone 
  (Grenville 
  series), 
  and 
  an 
  intermediate 
  geanticlinal 
  zone 
  

   of 
  Laurentian 
  banded 
  gneisses. 
  

  

  (2) 
  The 
  banded 
  gneisses 
  are 
  largely 
  igneous 
  in 
  origin. 
  

  

  (3) 
  From 
  the 
  geographical 
  and 
  structural 
  relationship 
  of 
  the 
  

   gneissic 
  complex 
  to 
  the 
  rocks 
  of 
  the 
  Abitibi 
  group 
  and 
  Gren- 
  

  

  