﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  XI 
  

  

  What 
  relation 
  the 
  two 
  bear 
  to 
  one 
  another 
  could 
  not 
  be 
  definitely 
  

   ascertained. 
  Either 
  the 
  augen 
  gneiss 
  is 
  a 
  crushed 
  border 
  phase 
  of 
  

   the 
  other, 
  that 
  representing 
  an 
  uncrushed 
  core, 
  or 
  else 
  it 
  is 
  a 
  

   separate 
  and 
  older 
  rock. 
  It 
  is 
  a 
  fairly 
  basic 
  rock, 
  varying 
  much 
  in 
  

   this 
  respect, 
  seems 
  at 
  times 
  to 
  owe 
  its 
  character 
  to 
  partial 
  as- 
  

   similation 
  of 
  amphibolite, 
  and 
  so 
  far 
  as 
  seen, 
  its 
  exposed 
  contacts 
  

   are 
  all 
  with 
  Grenville 
  rocks, 
  which 
  it 
  cuts. 
  If 
  the 
  two 
  intrusives 
  

   belong 
  together 
  the 
  mass 
  reaches 
  considerable 
  size 
  and 
  is 
  to 
  be 
  

   classed 
  as 
  a 
  small 
  bathylith. 
  If 
  the 
  augen 
  gneiss 
  is 
  distinct 
  from 
  

   the 
  other 
  the 
  latter 
  is 
  only 
  a 
  stock. 
  

  

  In 
  case 
  the 
  augen 
  gneiss 
  is 
  distinct 
  the 
  question 
  naturally 
  arises 
  

   whether 
  it 
  may 
  not 
  be 
  merely 
  a 
  porphyritic 
  phase 
  of 
  the 
  Lauren- 
  

   tian 
  granite 
  gneiss. 
  A 
  decisive 
  answer 
  to 
  this 
  question 
  can 
  not 
  be 
  

   given 
  owing 
  to 
  lack 
  of 
  contacts 
  between 
  the 
  two 
  classes 
  of 
  rock. 
  

   But 
  such 
  evidence 
  as 
  there 
  is 
  seems 
  decidedly 
  against 
  such 
  a 
  cor- 
  

   relation. 
  The 
  rock 
  is 
  a 
  more 
  basic 
  one 
  than 
  the 
  general 
  run 
  of 
  the 
  

   granite 
  gneiss, 
  and 
  is 
  not 
  so 
  severely 
  crushed, 
  or 
  granulated. 
  The 
  

   weight 
  of 
  the 
  evidence 
  is 
  decidedly 
  in 
  favor 
  of 
  the 
  view 
  that 
  it 
  

   is 
  a 
  gneissoid, 
  border 
  phase 
  of 
  the 
  syenite. 
  

  

  Syenite 
  southwest 
  of 
  Theresa. 
  Up 
  the 
  creek 
  valley 
  above 
  

   Theresa 
  are 
  exposures 
  aggregating 
  about 
  a 
  square 
  mile 
  in 
  extent 
  of 
  

   a 
  gray 
  to 
  gray 
  green 
  rock 
  which 
  is 
  a 
  syenite. 
  It 
  may 
  have 
  con- 
  

   siderably 
  greater 
  extent 
  underneath 
  the 
  sandstone 
  which 
  adjoins 
  

   it 
  on 
  each 
  side. 
  It 
  is 
  by 
  no 
  means 
  so 
  mashed 
  as 
  the 
  granite 
  gneiss 
  

   and 
  seems 
  clearly 
  a 
  younger 
  rock, 
  but 
  since 
  it 
  is 
  not 
  found 
  in 
  as- 
  

   sociation 
  with 
  any 
  of 
  the 
  other 
  younger 
  igneous 
  rocks 
  its 
  age 
  rela- 
  

   tions 
  to 
  them 
  are 
  not 
  ascertainable. 
  

  

  There 
  is 
  a 
  single 
  outcrop 
  of 
  a 
  coarse, 
  unmashed 
  eruptive 
  which 
  

   is 
  to 
  be 
  classed 
  as 
  a 
  gabbro, 
  close 
  to 
  the 
  upper 
  bridge 
  at 
  Theresa 
  

   on 
  the 
  west 
  bank 
  of 
  the 
  river. 
  It 
  may 
  have 
  considerable 
  extent 
  

   under 
  the 
  adjacent 
  sandstone 
  but 
  with 
  the 
  most 
  generous 
  possible 
  

   allowance 
  for 
  such 
  extension 
  the 
  mass 
  would,still 
  have 
  to 
  be 
  rated 
  

   as 
  a 
  stock 
  of 
  no 
  great 
  size. 
  

  

  Picton 
  graniteJ 
  The 
  most 
  extensive 
  and 
  important 
  of 
  these 
  

   younger 
  Precambric 
  intrusives 
  is 
  the 
  coarse 
  red 
  granite 
  which 
  out- 
  

   crops 
  widely 
  on 
  Grindstone, 
  Wellesley 
  and 
  some 
  of 
  the 
  smaller 
  

  

  iThe 
  most 
  considerable 
  outcrops 
  of 
  this 
  rock 
  within 
  the 
  State 
  are 
  on 
  

   Grindstone 
  island, 
  but 
  the 
  name 
  of 
  Grindstone 
  granite 
  would 
  perhaps 
  be 
  

   misleading, 
  and 
  Grindstone 
  Island 
  granite 
  is 
  too 
  long 
  a 
  name. 
  The 
  smaller 
  

   Picton 
  island 
  is 
  however 
  the 
  seat 
  of 
  the 
  chief 
  quarries 
  at 
  the 
  present 
  time 
  

   and 
  the 
  name 
  would 
  be 
  wholly 
  appropriate 
  except 
  for 
  the 
  fact 
  that 
  the 
  

   island 
  appears 
  on 
  the 
  maps 
  as 
  Robbins 
  island. 
  It 
  is 
  universally 
  called 
  

   Picton 
  island 
  by 
  residents, 
  many 
  of 
  whom 
  have 
  no 
  knowledge 
  of 
  any 
  such 
  

   nam.e 
  as 
  Robbins 
  island. 
  

  

  