﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  47 
  

  

  ing 
  the 
  color 
  as 
  beyond 
  question 
  original. 
  The 
  red 
  color 
  which 
  so 
  

   many 
  feldspars 
  possess 
  is 
  usually 
  ascribed 
  to 
  ferric 
  oxid, 
  though 
  in 
  

   general 
  without 
  any 
  definite 
  proof 
  in 
  the 
  matter. 
  In 
  such 
  case 
  the 
  

   loss 
  of 
  color 
  might 
  be 
  ascribed 
  to 
  simple 
  reduction 
  of 
  the 
  iron, 
  but 
  

   what 
  reducing 
  agent 
  the 
  limestone 
  might 
  furnish 
  is 
  a 
  difficult 
  prob- 
  

   lem 
  and 
  greenish, 
  rather 
  than 
  white, 
  feldspar 
  would 
  likely 
  result. 
  

   Analyses 
  of 
  both 
  white 
  and 
  red 
  granites 
  are 
  given 
  on 
  a 
  later 
  page, 
  

   where 
  the 
  matter 
  will 
  be 
  somewhat 
  further 
  discussed. 
  The 
  chemical 
  

   differences 
  between 
  the 
  two 
  rocks 
  are 
  but 
  slight, 
  and 
  we 
  are 
  in 
  

   doubt 
  whether 
  in 
  any 
  recognizable 
  respect 
  they 
  are 
  due 
  to 
  influence 
  

   of 
  the 
  limestone. 
  The 
  field 
  relations 
  are, 
  however, 
  perfectly 
  clear, 
  

   and 
  susceptible 
  of 
  no 
  other 
  explanation. 
  

  

  Mixed 
  rocks. 
  Rocks 
  which 
  seem 
  definitely 
  of 
  intermediate 
  com- 
  

   position 
  between 
  the 
  intrusive 
  and 
  a 
  sediment, 
  to 
  be 
  due 
  to 
  the 
  

   intimate 
  penetration 
  and 
  final 
  digestion 
  of 
  the 
  latter 
  by 
  the 
  former, 
  

   and 
  which 
  show 
  all 
  stages 
  in 
  the 
  process, 
  occur- 
  as 
  the 
  result 
  of 
  action 
  

   of 
  granite 
  upon 
  amphibolite 
  and 
  upon 
  quartzite. 
  In 
  the 
  former 
  the 
  

   action 
  is 
  chiefly 
  seen 
  in 
  the 
  case 
  of 
  the 
  amphibolite 
  inclusions 
  which 
  

   so 
  abound 
  in 
  the 
  granite 
  gneiss, 
  and 
  which 
  are 
  found 
  in 
  all 
  stages 
  of 
  

   being 
  first 
  penetrated 
  by 
  films 
  of 
  the 
  granite 
  and 
  later 
  slowly 
  

   absorbed 
  by 
  it. 
  The 
  process 
  has 
  already 
  been 
  described 
  ; 
  so 
  has 
  the 
  

   gradation 
  of 
  granite 
  into 
  quartzite 
  which 
  is 
  found 
  in 
  some 
  localities 
  

   and 
  which 
  seems 
  only 
  explainable 
  on 
  the 
  assumption 
  of 
  production 
  

   of 
  a 
  border 
  zone 
  of 
  true 
  mixed 
  rock 
  between 
  the 
  two. 
  

  

  Contact 
  rocks. 
  These, 
  as 
  here 
  understood, 
  result 
  from 
  the 
  injec- 
  

   tion 
  into 
  the 
  sediment 
  of 
  fluids 
  from 
  the 
  igneous 
  rock 
  which 
  contain 
  

   only 
  certain 
  of 
  its 
  constituents 
  instead 
  of 
  all, 
  and 
  which 
  may, 
  and 
  

   often 
  do, 
  dififer 
  very 
  materially 
  in 
  composition 
  from 
  the 
  rock 
  itself. 
  

   The 
  injection 
  is 
  apt 
  to 
  be 
  more 
  or 
  less 
  local, 
  here 
  much, 
  there 
  Httle, 
  

   or 
  none 
  at 
  all; 
  the 
  injected 
  fluid 
  may 
  dififer 
  in 
  composition 
  at 
  

   different 
  points 
  along 
  the 
  border 
  of 
  the 
  igneous 
  mass; 
  the 
  bordering 
  

   rocks 
  themselves 
  differ 
  from 
  place 
  to 
  place, 
  and 
  finally 
  the 
  various 
  

   igneous 
  masses 
  are 
  quite 
  sure 
  to 
  differ 
  among 
  themselves 
  in 
  the 
  

   character 
  of 
  their 
  mineralizing 
  fluids. 
  Since 
  we 
  have 
  here 
  three 
  

   separate 
  granite 
  bathyliths, 
  to 
  say 
  nothing 
  of 
  the 
  syenites 
  and 
  smaller 
  

   granite 
  masses, 
  and 
  Grenville 
  rocks 
  of 
  great 
  variety 
  of 
  composition, 
  

   the 
  opportunity 
  for 
  contact 
  action 
  o'f 
  diverse 
  sorts 
  is 
  exceedingly 
  

   good. 
  

  

  Green 
  schists 
  in 
  Alexandria. 
  Reference 
  to 
  the 
  geologic 
  map 
  of 
  

   the 
  Alexandria 
  quadrangle 
  will 
  show, 
  to 
  the 
  south 
  and 
  southwest 
  

   of 
  Alexandria 
  Bay, 
  three 
  northeast-southwest 
  ridges 
  of 
  Grenville 
  

   schists. 
  These 
  are 
  cut 
  out 
  on 
  the 
  north 
  by 
  the 
  granite 
  of 
  the 
  

  

  