﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  5 
  1 
  

  

  may 
  have 
  no 
  contact 
  zone, 
  while 
  a 
  mere 
  thread 
  of 
  granite 
  a 
  few 
  

   feet 
  distant, 
  may 
  be 
  bounded 
  on 
  each 
  side 
  by 
  a 
  band 
  of 
  the 
  

   tourmaHn 
  rock 
  2 
  or 
  3 
  inches 
  wide. 
  Again, 
  the 
  tourmalin, 
  in- 
  

   stead 
  of 
  forming 
  a 
  continuous 
  band, 
  appears 
  in 
  lumps 
  and 
  bunches 
  

   of 
  every 
  conceivable 
  shape, 
  irregularly 
  scattered 
  along 
  a 
  dike, 
  and 
  

   sometimes 
  extending 
  several 
  inches 
  away, 
  at 
  right 
  angles 
  to 
  the 
  

   course 
  of 
  the 
  dike.^ 
  

  

  Tourmalin 
  is 
  also 
  at 
  times 
  developed 
  in 
  the 
  quartzite 
  as 
  well 
  as 
  

   the 
  schists, 
  but 
  not 
  in 
  the 
  same 
  definite 
  manner. 
  It 
  is 
  not 
  at 
  all 
  

   certain 
  that 
  dikes 
  from 
  the 
  Alexandria 
  bathylith 
  are 
  excluded 
  from 
  

   the 
  category 
  of 
  rocks 
  producing 
  this 
  contact 
  effect. 
  In 
  many 
  cases 
  

   the 
  dikes 
  from 
  the 
  two 
  bathyliths 
  can 
  by 
  no 
  possibility 
  be 
  distin- 
  

   guished 
  from 
  one 
  another. 
  In 
  addition 
  to 
  these 
  bands 
  and 
  bunches 
  

   of 
  abundant 
  tourmalin, 
  developed 
  in 
  this 
  localized 
  fashion, 
  more 
  

   scattered 
  crystals 
  of 
  tourmalin, 
  of 
  the 
  same 
  evident 
  origin, 
  range 
  

   much 
  more 
  widely 
  through 
  the 
  rocks. 
  

  

  Smyth 
  dissents 
  from 
  the 
  view 
  that 
  the 
  Picton 
  granite 
  was 
  espe- 
  

   cially 
  influential 
  in 
  the 
  formation 
  of 
  these 
  tourmalin 
  zones, 
  and 
  in 
  

   other 
  contact 
  phenomena. 
  He 
  points 
  out 
  that, 
  in 
  his 
  belief, 
  the 
  

   tourmalin 
  zones 
  are 
  most 
  abundant 
  at 
  the 
  extreme 
  east 
  end 
  of 
  

   Wellesley 
  island, 
  quite 
  remote 
  from 
  the 
  Picton 
  granite, 
  though 
  

   with 
  the 
  Alexandria 
  bathyhth 
  near 
  at 
  hand; 
  also 
  that 
  the 
  Alex- 
  

   andria 
  bathylith 
  is 
  much 
  nearer 
  the 
  Alexandria 
  green 
  schists 
  than 
  

   the 
  Picton. 
  He 
  therefore 
  regards 
  the 
  Alexandria 
  bathylith 
  as 
  

   the 
  most 
  important 
  granite 
  of 
  the 
  region 
  in 
  producing 
  contact 
  ef- 
  

   fects. 
  We 
  are 
  not 
  sufficiently 
  certain 
  of 
  the 
  truth 
  of 
  the 
  opposite 
  

   view 
  to 
  urge 
  it, 
  and 
  simply 
  chronicle 
  the 
  matter 
  as 
  one 
  on 
  which 
  

   we 
  mildly 
  disagree. 
  It 
  is 
  not 
  a 
  matter 
  of 
  great 
  importance 
  in 
  the 
  

   interpretation 
  of 
  the 
  geology 
  of 
  the 
  region, 
  on 
  the 
  general 
  features 
  

   of 
  which 
  we 
  are 
  in 
  absolute 
  agreement. 
  

  

  Contact 
  amphibolites. 
  Adams 
  has 
  recently 
  shown 
  conclusively 
  

   that, 
  in 
  central 
  Ontario, 
  amphibolite 
  occurs 
  as 
  a 
  result 
  of 
  intense 
  

   contact 
  alteration 
  of 
  Grenville 
  limestone 
  by 
  granite, 
  limestones 
  pass- 
  

   ing 
  into 
  rocks 
  in 
  which 
  pyroxene, 
  hornblende, 
  feldspars 
  and 
  scapo- 
  

   lite 
  appear 
  in 
  increasing 
  quantity 
  up 
  to 
  final 
  disappearance 
  of 
  cal- 
  

   cite, 
  and 
  with 
  final 
  entire 
  replacement 
  of 
  pyroxene 
  by 
  hornblende 
  

   and 
  scapolite 
  by 
  f 
  eldspar.^ 
  We 
  have 
  had 
  the 
  privilege 
  of 
  going 
  over 
  

   his 
  territory 
  with 
  him, 
  and 
  fully 
  agree 
  in 
  his 
  conclusions. 
  Per- 
  

   haps 
  the 
  chief 
  interest 
  attaching 
  to 
  his 
  work 
  is 
  the 
  explanation 
  

   thereby 
  afforded 
  of 
  the 
  abundance 
  of 
  inclusions 
  of 
  amphibolite 
  in 
  

   the 
  Laurentian 
  granite 
  gneisses, 
  where 
  cutting 
  the 
  Grenville 
  rocks, 
  

  

  1 
  op 
  cit. 
  p. 
  rgo. 
  

  

  2 
  Adams, 
  F. 
  D. 
  Jour. 
  Geol. 
  17:7-18. 
  

  

  