﻿22 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  a 
  contact 
  mineral. 
  Its 
  occurrence 
  in 
  the 
  pegmatites, 
  however, 
  sug- 
  

   gests 
  caution 
  in 
  ascribing 
  it 
  all 
  to 
  such 
  a 
  source. 
  

  

  The 
  granite 
  is 
  chiefly 
  found 
  thoroughly 
  interbanded 
  with 
  the 
  

   schists, 
  injected 
  into 
  them 
  parallel 
  with 
  their 
  foliation, 
  forming 
  

   apparent 
  beds 
  of 
  hard, 
  white 
  gneiss 
  which 
  alternate 
  with 
  those 
  

   of 
  schist. 
  The 
  beds 
  vary 
  in 
  thickness 
  from 
  a 
  few 
  feet 
  to 
  many. 
  

   It 
  is 
  only 
  in 
  exceptional 
  cases 
  that 
  the 
  granite 
  can 
  be 
  seen 
  to 
  cut 
  

   across 
  the 
  schist 
  foliation. 
  It 
  is 
  quite 
  otherwise 
  with 
  the 
  peg- 
  

   matite 
  dikes 
  from 
  the 
  granite 
  which 
  cut 
  it 
  and 
  the 
  schists 
  in 
  all 
  

   directions, 
  and 
  seldom 
  follow 
  the 
  foliation. 
  In 
  the 
  three 
  small 
  

   areas 
  which 
  we 
  have 
  mapped 
  as 
  granite, 
  the 
  rock 
  is 
  full 
  of 
  schist, 
  

   ranging 
  from 
  mere 
  films 
  to 
  bands 
  many 
  feet 
  thick. 
  These 
  are 
  

   all 
  thought 
  to 
  be 
  stretched 
  inclusions, 
  though 
  it 
  is 
  seldom 
  possible 
  

   to 
  demonstrate 
  this. 
  The 
  bordering 
  areas 
  mapped 
  as 
  schist 
  are 
  

   likewise 
  full 
  of 
  granite 
  and 
  pegmatite 
  dikes, 
  so 
  that 
  the 
  mapping 
  is 
  

   highly 
  conventional 
  and 
  merely 
  roughly 
  distinguishes 
  areas 
  in 
  which 
  

   granite 
  is 
  in 
  excess 
  from 
  those 
  in 
  which 
  the 
  schist 
  predominates. 
  

   But 
  the 
  relations 
  are 
  much 
  less 
  simple 
  and 
  obvious 
  than 
  in 
  the 
  

   Thousand 
  Islands 
  region 
  where 
  what 
  we 
  regard 
  as 
  similar 
  relations 
  

   between 
  Grenville 
  and 
  granite 
  obtain. 
  In 
  passing 
  across 
  the 
  

   Adirondacks 
  from 
  west 
  to 
  east 
  the 
  Precambric 
  rocks 
  show 
  a 
  steady 
  

   increase 
  in 
  complexity 
  because 
  of 
  ever 
  more 
  severe 
  metamorphism, 
  

   until 
  eventually, 
  in 
  the 
  extreme 
  east, 
  the 
  whole 
  series 
  has 
  been 
  so 
  

   enormously 
  compressed 
  and 
  stretched 
  that 
  it 
  is 
  no 
  longer 
  easy 
  to 
  

   recognize 
  inclusions 
  of 
  sediments 
  in 
  igneous 
  rocks, 
  or 
  dikes 
  of 
  

   igneous 
  rocks 
  in 
  sediments, 
  owing 
  to 
  the 
  apparent 
  interbanding. 
  

  

  There 
  has 
  also 
  been 
  much 
  intermediate 
  rock 
  produced 
  by 
  a 
  

   thorough 
  interpenetration 
  of 
  the 
  schist 
  by 
  the 
  granite. 
  The 
  exposed 
  

   granite 
  masses 
  are 
  small, 
  and 
  we 
  have 
  not 
  noted 
  the 
  evidence 
  of 
  

   the 
  actual 
  digestion 
  of 
  schist 
  by 
  granite, 
  with 
  production 
  of 
  rock 
  

   of 
  intermediate 
  character, 
  such 
  as 
  may 
  be 
  seen 
  in 
  the 
  cases 
  of 
  the 
  

   larger 
  batholiths 
  of 
  Laurentian 
  granite. 
  There 
  has 
  been 
  much 
  

   injection 
  of 
  schist 
  by 
  granite, 
  however, 
  both 
  along 
  the 
  foliation 
  

   planes 
  with 
  production 
  of 
  injection 
  gneiss, 
  and 
  also 
  of 
  the 
  mosaic 
  

   type 
  in 
  which 
  the 
  granite 
  minutely 
  penetrates 
  the 
  schist 
  everywhere. 
  

   In 
  many 
  bands 
  of 
  this 
  type 
  an 
  enormous 
  amount 
  of 
  garnet 
  has 
  

   developed. 
  

  

  The 
  pegmatites. 
  It 
  was 
  the 
  abundant 
  dikes 
  of 
  white 
  granite 
  

   pegmatite 
  that 
  first 
  suggested 
  the 
  igneous 
  nature 
  of 
  the 
  white 
  gneiss 
  

   and 
  furnishes 
  the 
  chief 
  evidence 
  for 
  it, 
  aside 
  from 
  the 
  chemical 
  

   composition. 
  They 
  cut 
  through 
  the 
  granite 
  everywhere 
  and 
  also 
  

  

  