﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  37 
  

  

  thus 
  becomes 
  a 
  conspicuous 
  constituent. 
  The 
  rock 
  changes 
  from 
  

   deep 
  red 
  through 
  lighter 
  shades 
  to 
  nearly 
  white. 
  It 
  varies 
  also 
  

   much 
  in 
  texture, 
  from 
  throughly 
  solid 
  looking, 
  crystalline 
  appear- 
  

   ance 
  to 
  varieties 
  which 
  weather 
  to 
  a 
  sugary, 
  granular 
  aspect. 
  

  

  As 
  usual 
  in 
  the 
  Laurentian, 
  inclusions 
  albound, 
  and 
  as 
  usual 
  

   the 
  bulk 
  of 
  these 
  are 
  of 
  amphibolite. 
  Quartzite 
  inclusions 
  

   also 
  occur, 
  but 
  infrequently, 
  limestone 
  inclusions 
  never. 
  The 
  

   amphibolite 
  inclusions 
  are 
  found 
  everywhere 
  but 
  always 
  most 
  

   abundantly 
  near 
  the 
  margins, 
  where 
  they 
  abound. 
  In 
  fact 
  a 
  

   sharp 
  boundary 
  line 
  between 
  the 
  granite 
  gneiss 
  and 
  the 
  adjacent 
  

   Granville 
  rocks 
  can 
  not 
  be 
  drawn. 
  In 
  passing 
  from 
  granite 
  to 
  

   sediments 
  the 
  inclusions 
  show 
  steady 
  increase 
  in 
  number 
  until 
  

   they 
  come 
  to 
  constitute 
  50^ 
  of 
  the 
  rock, 
  beyond 
  which 
  we 
  find 
  

   sediments 
  cut 
  by 
  granite 
  dikes 
  rather 
  than 
  granite 
  holding 
  inclu- 
  

   sions 
  of 
  sediments. 
  This 
  reduces 
  boundary 
  mapping 
  to 
  a 
  matter 
  

   of 
  estimating 
  equality 
  or 
  inequality 
  in 
  amount 
  of 
  the 
  two 
  rocks, 
  

   or 
  in 
  drawing 
  a 
  boundary 
  where 
  no 
  real 
  one 
  exists. 
  An 
  attempt, 
  

   however, 
  has 
  been 
  made 
  to 
  indicate, 
  by 
  convention, 
  on 
  the 
  maps, 
  

   the 
  actual 
  state 
  of 
  things 
  found 
  in 
  the 
  field. 
  

  

  The 
  granite 
  dikes 
  usually 
  represent 
  the 
  extreme 
  acid 
  state 
  of 
  

   the 
  rock. 
  The 
  main 
  mass 
  averages 
  less 
  acid, 
  chiefly 
  because 
  of 
  

   the 
  inclusions 
  and 
  of 
  the 
  attack 
  of 
  the 
  granite 
  upon 
  them. 
  In 
  

   its 
  preliminary 
  stages 
  this 
  usually 
  takes 
  the 
  form 
  of 
  an 
  injection 
  

   of 
  the 
  granite 
  in 
  thin 
  sheets 
  along 
  the 
  foliation 
  planes 
  of 
  the 
  

   amphibolite, 
  the 
  so 
  called 
  '' 
  lit-par-lit," 
  or 
  leaf 
  type 
  of 
  injection, 
  

   producing 
  a 
  banded 
  rock 
  of 
  alternations 
  of 
  igneous 
  and 
  sedi- 
  

   mentary 
  material. 
  Then, 
  here 
  and 
  there, 
  the 
  granite 
  breaks 
  out 
  

   from 
  the 
  foliation 
  planes 
  and 
  spreads 
  through 
  the 
  rock 
  adjacent, 
  

   forcing 
  its 
  grains 
  apart 
  by 
  the 
  injection 
  of 
  a 
  thin 
  film 
  of 
  granite 
  

   between. 
  This 
  process 
  becomes 
  more 
  and 
  more 
  pronounced, 
  

   until 
  much 
  of 
  the 
  rock 
  is 
  broken 
  up 
  into 
  a 
  granular 
  mosaic 
  of 
  

   particles 
  cemented 
  together 
  by 
  granite 
  films, 
  producing 
  what 
  

   may 
  be 
  called 
  the 
  mosaic 
  type 
  of 
  injection, 
  as 
  distinguished 
  from 
  

   the 
  leaf 
  type. 
  A 
  fine 
  example 
  of 
  injection 
  of 
  this 
  type 
  is 
  shown 
  

   in 
  plates 
  4 
  and 
  5. 
  The 
  injected 
  rock 
  is 
  not 
  amphibolite, 
  but 
  is 
  green 
  

   schist, 
  a 
  closely 
  related 
  rock, 
  and 
  the 
  type 
  of 
  injection 
  is 
  identical. 
  

   A/^-'iSi 
  further 
  stage, 
  in 
  both 
  types 
  of 
  injection, 
  the 
  sharp 
  bound- 
  

   aries 
  become 
  blurred, 
  and 
  this 
  shading 
  of 
  the 
  two 
  rocks 
  into 
  one 
  

   another 
  becomes 
  more 
  and 
  more 
  prominent 
  until 
  finally 
  rocks 
  

   result 
  which 
  seem 
  unquestionably 
  to 
  be 
  due 
  to 
  the 
  complete 
  

   digestion 
  of 
  the 
  amphibolite 
  by 
  the 
  granite, 
  gray 
  gneisses 
  of 
  

   distinctly 
  intermediate 
  composition. 
  As 
  would 
  be 
  expected 
  

  

  