﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  39 
  

  

  dack 
  syenite. 
  In 
  the 
  most 
  basic 
  variety 
  seen, 
  these 
  dark 
  minerals 
  

   constitute 
  no 
  more 
  than 
  i^fc 
  of 
  the 
  rock, 
  the 
  remainder 
  being 
  

   feldspar 
  with 
  a 
  little 
  quartz. 
  

  

  Granting 
  the 
  equivalence 
  of 
  the 
  rock 
  with 
  the 
  general 
  augite 
  

   syenite, 
  its 
  age 
  is 
  rather 
  definitely 
  fixed 
  as 
  one 
  of 
  the 
  great 
  

   intrusives' 
  of 
  the 
  region, 
  younger 
  than 
  the 
  Grenville 
  and 
  the 
  

   Laurentian 
  granite, 
  and 
  also 
  younger 
  than 
  the 
  anorthosite 
  intru- 
  

   sion. 
  Since 
  this 
  latter 
  rock 
  is 
  not 
  represented 
  in 
  the 
  district, 
  and 
  

   the 
  only 
  direct 
  evidence 
  of 
  age 
  seen 
  in 
  connection 
  with 
  the 
  

   Theresa 
  syenite 
  is 
  that 
  it 
  cuts 
  the 
  Grenville, 
  this 
  additional 
  evi- 
  

   dence 
  is 
  welcome. 
  

  

  Alexandria 
  syenite. 
  The 
  intrusive 
  mass 
  of 
  S3^enite 
  called 
  for 
  

   convenience 
  by 
  the 
  above 
  name, 
  since 
  nearly 
  the 
  entire 
  mass 
  is 
  

   in 
  Alexandria 
  township, 
  lies 
  west 
  and 
  north 
  of 
  Redwood, 
  with 
  

   a 
  major 
  axis 
  of 
  nearly 
  6 
  miles, 
  and 
  with 
  a 
  greatest 
  breadth 
  of 
  

   nearly 
  2 
  miles 
  ; 
  this 
  on 
  the 
  supposition 
  that 
  but 
  a 
  single 
  intrusion 
  

   is 
  here 
  represented, 
  as 
  is 
  believed 
  to 
  be 
  the 
  case. 
  It 
  is 
  possible 
  

   that 
  two 
  intrusions 
  are 
  here 
  in 
  which 
  case 
  the 
  southern 
  one 
  

   fourth 
  must 
  be 
  separated 
  from 
  the 
  rest. 
  

  

  Much 
  of 
  the 
  rock 
  is 
  considerably 
  crushed, 
  granulated 
  and 
  

   recrystallized, 
  converting 
  it 
  into 
  an 
  augen 
  gneiss. 
  The 
  size 
  of 
  

   the 
  augen, 
  many 
  of 
  which 
  "are 
  a 
  half 
  inch 
  long, 
  bespeaks 
  either 
  

   a 
  very 
  coarse 
  grained 
  rock 
  originally, 
  or 
  a 
  porphyry, 
  the 
  latter 
  

   being 
  regarded 
  as 
  most 
  probable. 
  These 
  coarse 
  augen 
  gneisses 
  

   are 
  chiefly 
  peripheral, 
  and 
  mostly 
  at 
  the 
  south 
  end 
  of 
  the 
  mass. 
  

   Centrally, 
  considerable 
  cores 
  of 
  much 
  less 
  mashed 
  rock 
  remain 
  

   which, 
  while 
  of 
  medium 
  coarseness 
  of 
  grain, 
  do 
  not 
  approach 
  the 
  

   coarseness 
  of 
  the 
  augen. 
  The 
  bulk 
  of 
  the 
  rock 
  is 
  an 
  augen 
  

   gneiss 
  with 
  small 
  augen, 
  and 
  it 
  may 
  be 
  that 
  the 
  coarse 
  augen 
  

   gneiss 
  at 
  the 
  south 
  should 
  be 
  separated 
  from 
  the 
  remainder 
  ; 
  the 
  

   two 
  seem, 
  however, 
  to 
  grade 
  into 
  one 
  another, 
  and 
  no 
  evidence 
  

   that 
  one 
  cut 
  the 
  other 
  was 
  found, 
  except 
  that 
  in 
  a 
  few 
  localities 
  

   the 
  coarse 
  augen 
  gneiss 
  is 
  cut 
  by 
  dikes 
  of 
  fine 
  grained 
  red 
  granite. 
  

   These 
  seem 
  rather 
  acid 
  for 
  dikes 
  from 
  the 
  syenite. 
  It 
  is 
  possible 
  

   that 
  they 
  are 
  stray 
  dikes 
  of 
  Picton 
  granite. 
  

  

  The 
  least 
  mashed 
  cores 
  show 
  a 
  rock 
  of 
  granitic 
  texture 
  and 
  

   medium 
  grain, 
  composed 
  chiefly 
  of 
  a 
  reddish 
  feldspar 
  and 
  black 
  

   hornblende, 
  the 
  latter 
  in 
  suflicient 
  quantity 
  to 
  give 
  some 
  of 
  the 
  

   rock 
  a 
  strong 
  resemlblance 
  to 
  a 
  diorite. 
  These 
  least 
  gneissoid 
  por-' 
  

   tions 
  always 
  show 
  much 
  mashing, 
  when 
  seen 
  in 
  thin 
  section, 
  the 
  

   feldspars 
  being 
  granulated 
  at 
  their 
  margins, 
  and 
  the 
  hornblendes 
  

   fraying 
  out 
  into 
  biotite 
  scales. 
  This 
  change 
  increases 
  until 
  

  

  