﻿116 
  M. 
  E. 
  Wilson 
  — 
  Banded 
  Gneisses 
  of 
  the 
  

  

  folds 
  are 
  generally 
  pitching 
  and 
  since 
  the 
  strike 
  of 
  the 
  bands 
  

   is 
  dominantly 
  in 
  a 
  northeasterly-southwesterly 
  direction, 
  it 
  is 
  

   inferred 
  that 
  the 
  banded 
  gneiss 
  has 
  been 
  folded 
  into 
  pitching 
  

   anticlines 
  and 
  synclines 
  having 
  a 
  northeasterly-southwesterly 
  

   trend. 
  In 
  some 
  places 
  the 
  biotite 
  has 
  been 
  smeared 
  out 
  along 
  

   the 
  contacts 
  of 
  the 
  bands, 
  giving 
  a 
  slickensided 
  appearance 
  

   which 
  has 
  evidently 
  resulted 
  from 
  differential 
  movements, 
  

   accompanying 
  the 
  folding. 
  

  

  In 
  describing 
  the 
  structure 
  of' 
  the 
  Laurentian 
  gneisses* 
  

   occurring 
  in 
  eastern 
  Ontario, 
  Adams 
  and 
  Barlow 
  note 
  that 
  the 
  

   foliation 
  of 
  the 
  gneiss 
  near 
  the 
  border 
  of 
  the 
  batholith 
  corre- 
  

   sponds 
  to 
  the 
  strike 
  of 
  the 
  surrounding 
  sedimentary 
  rocks 
  and 
  

   conclude 
  that 
  the 
  batholiths 
  are 
  anticlinal 
  in 
  their 
  relationship 
  

   to 
  the 
  Grenville 
  series, 
  the 
  anticlinal 
  axes 
  trending 
  N. 
  30° 
  £. 
  

   They 
  also 
  point 
  out 
  that 
  the 
  trend 
  of 
  the 
  foliation 
  and 
  band- 
  

   ing 
  in 
  the 
  batholiths 
  is 
  commonly 
  oval 
  or 
  elliptical 
  in 
  form, 
  

   and 
  while 
  no 
  further 
  statement 
  is 
  made 
  by 
  the 
  authors 
  as 
  to 
  

   structure 
  of 
  the 
  gneiss, 
  it 
  seems 
  apparent, 
  from 
  the 
  trend 
  of 
  

   the 
  foliation 
  indicated 
  on 
  their 
  maps, 
  that 
  the 
  gneiss 
  in 
  that 
  

   locality 
  also 
  has 
  a 
  folded 
  structure 
  similar 
  to 
  that 
  of 
  the 
  central 
  

   belt 
  of 
  gneisses 
  of 
  the 
  Laurentian 
  complex. 
  

  

  On 
  the 
  whole, 
  faulting 
  has 
  been 
  subordinate 
  to 
  folding 
  in 
  

   the 
  Laurentian 
  banded 
  gneisses, 
  but 
  faults 
  of 
  both 
  the 
  over- 
  

   thrust 
  and 
  normal 
  types 
  are 
  present. 
  The 
  pegmatite 
  and 
  

   aplite 
  dikes 
  which 
  are 
  transverse 
  to 
  the 
  banding 
  of 
  the 
  gneiss 
  

   have 
  been 
  very 
  commonly 
  intruded 
  along 
  fault 
  planes, 
  for 
  the 
  

   bands 
  on 
  opposite 
  sides 
  of 
  many 
  of 
  the 
  dikes 
  have 
  been 
  rela- 
  

   tively 
  displaced. 
  

  

  Origin. 
  

  

  A 
  discussion 
  of 
  the 
  possible 
  modes 
  of 
  origin 
  of 
  the 
  Lauren- 
  

   tian 
  gneissic 
  complex 
  resolves 
  itself 
  into 
  two 
  problems 
  : 
  (1) 
  Are 
  

   the 
  banded 
  gneisses 
  sedimentary 
  or 
  igneous 
  in 
  origin, 
  and 
  (2) 
  

   in 
  what 
  manner 
  did 
  the 
  rocks 
  become 
  banded, 
  folded 
  and 
  foli- 
  

   ated 
  into 
  their 
  present 
  condition. 
  

  

  Sedimentary 
  or 
  Igneous 
  Origin. 
  — 
  The 
  early 
  Canadian 
  geol- 
  

   ogists, 
  in 
  common 
  with 
  geologists 
  working 
  in 
  other 
  parts 
  of 
  

   the 
  world, 
  generally 
  assumed 
  that 
  banded 
  gneisses 
  owed 
  their 
  

   bedded-like 
  structure 
  to 
  subaqueous 
  deposition. 
  f 
  In 
  the 
  case 
  

   of 
  the 
  Laurentian 
  banded 
  gneisses, 
  this 
  seemed 
  particularly 
  

   obvious, 
  for 
  they 
  were 
  bedded 
  and 
  folded 
  like 
  stratified 
  sedi- 
  

   ments, 
  and 
  were 
  intimately 
  associated 
  with 
  limestone 
  and 
  other 
  

   rocks 
  which 
  were 
  undoubtedly 
  sedimentary 
  in 
  their 
  origin. 
  

   But 
  with 
  the 
  application 
  of 
  petrographical 
  and 
  chemical 
  inves- 
  

  

  * 
  Memoir 
  No. 
  6, 
  Geol. 
  Surv., 
  Dept. 
  of 
  Mines, 
  Can., 
  1910. 
  

   f 
  Geology 
  of 
  Canada, 
  p. 
  29, 
  1863. 
  Sterry 
  Hunt, 
  Royal 
  Society 
  of 
  Canada, 
  

   vol. 
  ii, 
  1884. 
  

  

  