﻿114 
  M. 
  E\ 
  Wilson 
  — 
  Banded 
  Gneisses 
  of 
  the 
  

  

  but 
  muscovite, 
  biotite, 
  garnet, 
  epidote, 
  and 
  titanite 
  are 
  also 
  

   commonly 
  present. 
  Other 
  minerals 
  less 
  commonly 
  present 
  are 
  

   cyanite, 
  molybdenite, 
  graphite, 
  and 
  allanite. 
  Like 
  the 
  other 
  

   rocks 
  of 
  the 
  complex, 
  the 
  pegmatite 
  and 
  aplite 
  have 
  undergone 
  

   some 
  mineralogical 
  and 
  mechanical 
  alteration, 
  the 
  evidences 
  of 
  

   deformation 
  being 
  particularly 
  apparent. 
  

  

  Pyroxenite, 
  amphibolite, 
  and 
  amphibolite- 
  gneiss. 
  — 
  The 
  

   rocks 
  in 
  this 
  subdivision 
  of 
  the 
  Laurentian 
  have 
  been 
  grouped 
  

   together 
  because 
  they 
  are 
  largely 
  composed 
  of 
  lime 
  silicates, 
  

   and 
  hence 
  are 
  similar 
  in 
  chemical 
  composition, 
  although 
  miner- 
  

   alogically 
  somewhat 
  different. 
  They 
  occur 
  chiefly 
  as 
  small 
  

   lenticular 
  masses 
  in 
  the 
  banded 
  gneiss, 
  and 
  are 
  largely 
  limited 
  

   to 
  a 
  few 
  localities 
  near 
  the 
  south 
  side 
  of 
  the 
  central 
  belt 
  of 
  

   gneisses. 
  The 
  pyroxenite 
  consists 
  chiefly 
  of 
  diopside, 
  while 
  the 
  

   amphibolite 
  is 
  largely 
  composed 
  of 
  either 
  hornblende 
  or 
  trem- 
  

   olite. 
  Other 
  minerals 
  observed 
  in 
  these 
  rocks 
  were 
  biotite, 
  

   scapolite, 
  garnet, 
  a 
  carbonate, 
  and 
  serpentine, 
  the 
  latter 
  occur- 
  

   ring 
  as 
  an 
  alteration 
  product 
  from 
  the 
  cliopside. 
  

  

  Garnetiferons 
  mica-schist. 
  — 
  Within 
  the 
  central 
  belt 
  of 
  

   banded 
  gneisses, 
  particularly 
  near 
  their 
  northern 
  border, 
  there 
  

   are 
  areas 
  of 
  fine-grained 
  garnetiferous 
  mica 
  schist 
  very 
  similar 
  

   in 
  appearance 
  to 
  some 
  of 
  the 
  mica 
  schist 
  of 
  sedimentary 
  origin 
  

   occurring 
  in 
  the 
  Abitibi 
  group 
  farther 
  to 
  the 
  northward. 
  This 
  

   mica-schist 
  consists 
  of 
  biotite 
  quartz, 
  orthoclase, 
  albite, 
  and 
  

   either 
  pink 
  or 
  red 
  garnet 
  and 
  possesses 
  a 
  mosaic-like 
  texture 
  

   very 
  similar 
  to 
  the 
  crystalloblastic 
  texture 
  of 
  the 
  paragneisses. 
  

  

  Structural 
  Features. 
  

  

  Foliation. 
  — 
  By 
  far 
  the 
  larger 
  part 
  of 
  the 
  rocks 
  comprising 
  

   the 
  Laurentian 
  complex 
  are 
  foliated 
  and 
  for 
  this 
  reason 
  are 
  

   largely 
  classed 
  as 
  gneisses. 
  This 
  foliation 
  has 
  been 
  brought 
  

   about, 
  for 
  the 
  most 
  part, 
  by 
  the 
  parallel 
  orientation 
  of 
  biotite 
  

   plates 
  and 
  hornblende 
  prisms 
  but 
  also, 
  in 
  some 
  cases, 
  by 
  the 
  

   flattening 
  of 
  the 
  feldspar 
  and 
  quartz 
  in 
  the 
  same 
  plane. 
  Very 
  

   commonly 
  the 
  biotite 
  of 
  the 
  biotite 
  gneiss 
  is 
  seen 
  to 
  " 
  eye 
  " 
  

   around 
  small 
  lense-shaped 
  fragments 
  of 
  feldspar, 
  giving 
  rise 
  to 
  

   the 
  characteristic 
  augen 
  structure, 
  which 
  results 
  from 
  deforma- 
  

   tion. 
  The 
  trend 
  of 
  the 
  foliation, 
  like 
  that 
  of 
  the 
  banding, 
  

   indicates 
  that 
  it 
  has 
  the 
  form 
  of 
  anticlines 
  and 
  synclines 
  simu- 
  

   lating 
  the 
  structure 
  of 
  folded 
  sedimentary 
  rocks 
  in 
  every 
  

   respect. 
  

  

  Banding. 
  — 
  The 
  most 
  striking 
  and 
  the 
  most 
  characteristic 
  

   structural 
  feature 
  of 
  the 
  central 
  belt 
  of 
  Laurentian 
  gneisses 
  is 
  

   the 
  banding 
  which 
  is 
  everywhere 
  developed. 
  The 
  extreme 
  

   complexity 
  of 
  the 
  structures 
  exhibited 
  by 
  these 
  bands 
  and 
  the 
  

   heterogeneity 
  of 
  the 
  rocks 
  which 
  they 
  contain 
  even 
  in 
  a 
  single 
  

  

  