﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  1 
  87 
  

  

  ages 
  of 
  this 
  amphibolite, 
  and 
  column 
  4 
  a 
  calculated 
  mixture 
  of 
  

   granite 
  and 
  amphibolite 
  in 
  the 
  ratio 
  of 
  24^ 
  of 
  the 
  former 
  and 
  'j^'f) 
  

   of 
  the 
  latter. 
  The 
  agreement 
  in 
  this 
  case 
  is 
  not 
  so 
  close 
  as 
  in 
  the 
  

   former 
  one, 
  but 
  in 
  large 
  part 
  the 
  differences 
  can 
  be 
  ascribed 
  to 
  the 
  

   fact 
  that 
  the 
  granite 
  here 
  is 
  not 
  normal, 
  but 
  of 
  the 
  pegmatitic 
  type, 
  

   higher 
  in 
  mineralizers 
  and 
  in 
  iron, 
  and 
  poorer 
  in 
  alumina, 
  lime 
  and 
  

   magnesia 
  than 
  the 
  normal 
  rock. 
  Comparison 
  of 
  analyses 
  3 
  and 
  4 
  

   seems 
  definitely 
  to 
  suggest 
  this, 
  the 
  iron 
  being 
  higher 
  in 
  the 
  grani- 
  

   tized 
  rock 
  than 
  in 
  the 
  amphibolite, 
  and 
  the 
  lime 
  and 
  magnesia 
  much 
  

   lower. 
  It 
  is 
  thought 
  that 
  if 
  an 
  analysis 
  of 
  the 
  neighboring 
  granite 
  

   was 
  available 
  for 
  use 
  in 
  the 
  computation, 
  the 
  agreement 
  would 
  be 
  

   much 
  closer. 
  But 
  the 
  result 
  is 
  somewhat 
  disappointing, 
  and 
  the 
  

   importance 
  to 
  be 
  assigned 
  to 
  the 
  discrepancies 
  a 
  debatable 
  matter, 
  

   likely 
  to 
  vary 
  with 
  the 
  personal 
  equation 
  of 
  the 
  reader. 
  Consider- 
  

   ing 
  all 
  the 
  circumstances 
  the 
  agreement 
  seems 
  to 
  us 
  as 
  close 
  as 
  

   could 
  be 
  hoped 
  for, 
  and 
  indicative 
  of 
  the 
  correctness 
  of 
  interpreta- 
  

   tion 
  of 
  the 
  field 
  evidence, 
  namely, 
  that 
  these 
  are 
  true 
  mixed 
  rocks. 
  

  

  