﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  IO3 
  

  

  border 
  phase 
  is 
  considerably 
  metamorphosed 
  and 
  converted 
  into 
  

   a 
  thorough 
  gneiss, 
  with 
  the 
  augen 
  (the 
  uncrushed 
  remnants 
  of 
  

   original 
  large 
  feldspar 
  crystals) 
  alined 
  in 
  the 
  direction 
  of 
  the 
  

   foliation. 
  This 
  also 
  is 
  coincident 
  with 
  the 
  direction 
  of 
  foliation 
  

   in 
  the 
  Grenville 
  and 
  Laurentian 
  rocks. 
  While 
  it 
  is 
  true 
  that 
  the 
  

   metamorphism 
  exhibited 
  by 
  the 
  syenite 
  is 
  not 
  as 
  severe 
  in 
  degree 
  

   as 
  that 
  shown 
  by 
  the 
  other 
  two 
  groups, 
  it 
  is 
  clear 
  that 
  there 
  was 
  

   severe 
  compression 
  of 
  the 
  region 
  at, 
  or 
  after, 
  the 
  time 
  of 
  syenite 
  

   intrusion, 
  and 
  compression 
  under 
  quite 
  similar 
  conditions 
  as 
  

   regards 
  overlying 
  load. 
  

  

  The 
  Theresa 
  syenite 
  does 
  not 
  appear 
  so 
  foliated 
  as 
  does 
  the 
  

   Alexandria, 
  chiefly 
  because 
  of 
  difference 
  in 
  composition, 
  which 
  

   shows 
  itself 
  mineralogically 
  in 
  the 
  much 
  slighter 
  development 
  of 
  

   hornblende 
  and 
  mica, 
  the 
  rock 
  consisting 
  largely 
  of 
  feldspar. 
  It 
  

   also 
  lacks 
  the 
  coarsely 
  porphyritic 
  phase. 
  Foliation 
  is 
  therefore 
  

   much 
  less 
  prominent, 
  though 
  the 
  rock 
  shows 
  crushing 
  and 
  recrys- 
  

   tallization 
  in 
  degree 
  quite 
  comparable 
  with 
  the 
  other. 
  It 
  has 
  

   therefore 
  likely 
  experienced 
  compression 
  of 
  substantially 
  equiva- 
  

   lent 
  amount 
  and 
  duration, 
  but 
  its 
  composition 
  prohibits 
  good 
  

   foliation 
  development. 
  

  

  Picton 
  granite. 
  This, 
  the 
  latest 
  of 
  the 
  early 
  intrusives 
  of 
  

   the 
  district, 
  shows 
  little 
  or 
  no 
  foliation, 
  and 
  to 
  the 
  eye 
  gives 
  

   little 
  evidence 
  of 
  crushing, 
  as 
  if 
  the 
  intrusion 
  was 
  wholly 
  sub- 
  

   sequent 
  to 
  the 
  great 
  squeezing 
  of 
  the 
  region. 
  The 
  thin 
  sections 
  

   bear 
  out 
  this 
  impression. 
  

  

  This 
  evidence 
  would 
  seem 
  to 
  indicate 
  compressive 
  stresses 
  ap- 
  

   plied 
  at 
  intervals 
  through 
  a 
  considerable 
  length 
  of 
  time 
  during 
  

   the 
  region's 
  very 
  early 
  history, 
  with 
  gradual 
  cessation, 
  and 
  that 
  

   the 
  foliation 
  structure 
  in 
  the 
  Grenville 
  and 
  Laurentian 
  rocks 
  

   must 
  be 
  due 
  to 
  something 
  more 
  than 
  the 
  pressure 
  and 
  heat 
  fur- 
  

   nished 
  by 
  the 
  intrusion 
  of 
  the 
  Laurentian 
  granites. 
  

  

  Joints 
  

  

  The 
  clean-cut 
  divisional 
  planes, 
  usually 
  highly 
  inclined, 
  which 
  

   occur 
  in 
  most 
  rocks, 
  are 
  termed 
  joints. 
  While 
  generally 
  vertical, 
  

   or 
  nearly 
  so, 
  they 
  may 
  have 
  any 
  inclination. 
  In 
  a 
  " 
  joint 
  set 
  " 
  

   the 
  divisional 
  planes 
  show 
  a 
  close 
  approach 
  to 
  parallelism, 
  both 
  

   in 
  trend 
  and 
  in 
  inclination. 
  In 
  most 
  regions 
  more 
  than 
  one 
  set 
  

   is 
  present. 
  When 
  there 
  are 
  two, 
  the 
  usual 
  condition 
  is 
  that 
  they 
  

   are 
  approximately 
  at 
  right 
  angles 
  to 
  one 
  another. 
  Often 
  there 
  

   are 
  more 
  than 
  two 
  sets 
  as 
  is 
  the 
  case 
  in 
  our 
  region 
  here. 
  When 
  

   four 
  sets 
  are 
  present 
  it 
  is 
  usually 
  found 
  that 
  they 
  are 
  separable 
  

  

  