﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  lOI 
  

  

  of 
  all 
  the 
  types 
  of 
  Grenville 
  rocks 
  of 
  the 
  district 
  does 
  not 
  give 
  

   the 
  impression 
  of 
  a 
  group 
  of 
  extra 
  well 
  foliated 
  rocks. 
  This 
  is 
  

   largely 
  due 
  to 
  the 
  comparative 
  scarcity 
  of 
  micas, 
  and 
  of 
  amphi- 
  

   boles 
  of 
  slender 
  habit, 
  in 
  the 
  series 
  and 
  the 
  abundance 
  of 
  

   pyroxenes 
  and 
  of 
  stout 
  amphiboles. 
  This 
  again 
  is 
  a 
  result 
  of 
  

   the 
  prominently 
  anamorphic 
  character 
  of 
  the 
  metamorphism. 
  

  

  The 
  foliation 
  of 
  the 
  Grenville 
  rocks 
  is 
  parallel 
  to 
  the 
  bedding. 
  

   In 
  the 
  schist 
  series 
  rapid 
  alternations 
  of 
  materials 
  of 
  somewhat 
  

   varying 
  composition 
  is 
  a 
  feature, 
  producing 
  a 
  very 
  well 
  banded 
  

   structure, 
  sometimes 
  so 
  fine 
  as 
  to 
  somewhat 
  mimic 
  a 
  coarse 
  

   foliation. 
  

  

  Foliation 
  of 
  the 
  granite 
  gneiss. 
  It 
  has 
  been 
  shown 
  that 
  the 
  

   Laurentian 
  granite 
  is 
  characterized 
  by 
  frequent 
  inclusions 
  of 
  

   older 
  rocks, 
  chiefly 
  of 
  amphibolitic 
  types, 
  and 
  that 
  there 
  is 
  also 
  

   present 
  much 
  intermediate 
  material, 
  resulting 
  from 
  the 
  soaking 
  

   of 
  the 
  amphibolite 
  with 
  granitic 
  substance, 
  or 
  from 
  its 
  actual 
  

   digestion 
  by 
  the 
  granite. 
  The 
  rock 
  itself 
  contains 
  normally 
  

   some 
  mica 
  or 
  hornblende, 
  and 
  hence, 
  through 
  the 
  greater 
  por- 
  

   tion 
  of 
  the 
  mass 
  these 
  minerals 
  are 
  present 
  in 
  varying 
  quantity, 
  

   and 
  the 
  rock 
  is 
  susceptible 
  of 
  foliation 
  development 
  under 
  the 
  

   proper 
  conditions. 
  That 
  such 
  conditions 
  have 
  obtained 
  is 
  clearly 
  

   shown, 
  a 
  foliation 
  cleavage 
  of 
  varying 
  prominence 
  appearing 
  

   nearly 
  everywhere, 
  though 
  it 
  becomes 
  very 
  obscure 
  in 
  those 
  

   relatively 
  small 
  portions 
  of 
  the 
  mass 
  which 
  consist 
  solely 
  of 
  

   quartz 
  and 
  feldspar. 
  The 
  general 
  rock 
  is 
  thus 
  foliated 
  but 
  with 
  

   foliation 
  of 
  the 
  crude 
  type 
  which 
  proclaims 
  the 
  rock 
  a 
  gneiss, 
  

   rather 
  than 
  a 
  schist. 
  

  

  The 
  foliation 
  structure 
  of 
  the 
  granite 
  gneiss 
  conforms 
  everywhere 
  

   in 
  dip 
  and 
  strike 
  to 
  that 
  of 
  the 
  adjacent 
  Grenville 
  rocks. 
  While 
  

   this 
  by 
  no 
  means 
  excludes 
  the 
  possibility 
  that 
  the 
  Grenville 
  rocks 
  

   may 
  have 
  been 
  compressed 
  and 
  foliated 
  prior 
  to 
  the 
  intrusion 
  of 
  

   the 
  granite, 
  it 
  does 
  demonstrate 
  that 
  both 
  sets 
  of 
  rocks 
  have 
  

   undergone 
  compression 
  in 
  common, 
  subsequent 
  to 
  this 
  intrusion. 
  

   It 
  is 
  quite 
  possible 
  that 
  much 
  of 
  this 
  compression 
  was 
  a 
  result 
  

   of 
  the 
  actual 
  intrusion, 
  and 
  that 
  the 
  granite 
  gneiss 
  actually 
  

   solidified 
  with 
  a 
  foliated 
  structure. 
  This 
  is 
  not 
  at 
  all 
  uncommon 
  

   in 
  great 
  bathylithic 
  intrusions, 
  which, 
  in 
  order 
  to 
  make 
  a 
  place 
  

   for 
  themselves, 
  must 
  endeavor 
  to 
  shoulder 
  aside 
  the 
  rocks 
  previ- 
  

   ously 
  occupying 
  the 
  space. 
  This 
  shouldering 
  pressure 
  exerted 
  

   on 
  the 
  adjacent 
  rocks 
  under 
  bathylithic, 
  or 
  deep 
  seated, 
  condi- 
  

   tions, 
  that 
  is 
  with 
  a 
  thick 
  cover 
  of 
  overlying 
  rocks, 
  tends 
  to 
  

   give 
  the 
  rocks 
  thus 
  compressed 
  a 
  foliation 
  which 
  parallels 
  the 
  

  

  