﻿50 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  being 
  in 
  the 
  amount 
  of 
  calcite, 
  and 
  that 
  a 
  very 
  slow 
  and 
  gradual 
  

   change), 
  seem 
  more 
  suggestive 
  of 
  regional 
  than 
  of 
  contact 
  meta- 
  

   morphism. 
  On 
  this 
  view 
  the 
  belt 
  would 
  consist 
  of 
  original 
  impure 
  

   limestones 
  and 
  calcareous 
  shales, 
  metamorphosed 
  to 
  the 
  pyroxene- 
  

   feldspar-calcite 
  combination, 
  and 
  with 
  the 
  tourmalin, 
  actinolite 
  and 
  

   epidote 
  alone 
  due 
  to 
  the 
  later 
  contact 
  action. 
  While 
  unable 
  to 
  

   definitely 
  decide 
  between 
  the 
  two, 
  the 
  first 
  seems 
  to 
  us 
  the 
  more 
  

   probable. 
  It 
  is 
  possible 
  that 
  the 
  granite 
  is 
  close 
  in 
  place 
  under- 
  

   neath 
  the 
  whole 
  belt. 
  In 
  our 
  view, 
  then, 
  the 
  belt 
  is 
  due 
  to 
  the 
  con- 
  

   tact 
  action 
  of 
  an 
  especial 
  granite, 
  its 
  localization 
  being 
  thus 
  ex- 
  

   plained, 
  acting 
  upon 
  a 
  limestone 
  series 
  of 
  considerable 
  thickness, 
  

   and 
  certainly 
  somewhat 
  impure 
  at 
  least, 
  as 
  shown 
  by 
  the 
  bands 
  of 
  

   quartzite, 
  amphibolite 
  and 
  mica 
  gneiss 
  within 
  it. 
  Part 
  of 
  the 
  reg- 
  

   ular 
  Grenville 
  succession 
  of 
  the 
  area 
  consists 
  of 
  alternating 
  thin 
  

   beds 
  of 
  limestone*, 
  various 
  schists 
  and 
  an 
  occasional 
  quartzite, 
  and 
  

   it 
  would 
  seem 
  as 
  if 
  such 
  a 
  combination 
  might 
  well 
  be 
  turned 
  over 
  

   into 
  a 
  group 
  like 
  that 
  of 
  the 
  green 
  schists 
  by 
  contact 
  metamorphism. 
  

   This 
  would 
  be 
  all 
  the 
  more 
  likely 
  if 
  acted 
  upon 
  by 
  two 
  successive, 
  

   granite 
  injections 
  as 
  is 
  supposed 
  to 
  be 
  the 
  case 
  here, 
  since 
  dikes 
  of 
  

   Picton 
  granite 
  are 
  believed 
  to 
  be 
  present. 
  

  

  The 
  coarse 
  pegmatite 
  dikes 
  of 
  the 
  north 
  schist 
  ridge, 
  which 
  furnish 
  

   well 
  crystallized 
  specimens 
  of 
  orthoclase 
  and 
  specular 
  hematite, 
  to 
  

   be 
  found 
  in 
  many 
  mineral 
  collections, 
  have 
  already 
  been 
  described 
  

   by 
  Smyth. 
  ^ 
  

  

  Tourmalin 
  contact 
  zones 
  in 
  Alexandria. 
  The 
  Picton 
  granite 
  is 
  

   found 
  cutting 
  Grenville 
  quartzite 
  and 
  amphibolite, 
  but 
  no 
  other 
  

   members 
  of 
  the 
  series, 
  and 
  the 
  same 
  is 
  true 
  of 
  its 
  known 
  dikes 
  ; 
  that 
  

   dik&s 
  suspected 
  to 
  belong 
  to 
  it 
  cut 
  other 
  members 
  has 
  just 
  been 
  

   seen. 
  This 
  granite 
  seems 
  to 
  have 
  been 
  much 
  more 
  potent 
  in 
  tour- 
  

   malin-forming 
  capacity 
  than 
  any 
  other 
  granite 
  of 
  the 
  region 
  and 
  

   its 
  contacts 
  with 
  the 
  Grenville 
  on 
  Grindstone 
  and 
  Wellesley 
  islands 
  

   are 
  characterized 
  by 
  narrow 
  tourmalinized 
  zones 
  which 
  Smyth 
  

   has 
  clearly 
  described, 
  as 
  follows 
  : 
  

  

  Along 
  their 
  margins 
  these 
  dikes 
  frequently 
  show 
  much 
  black 
  

   tourmalin 
  and 
  this 
  is 
  usually 
  most 
  abundant 
  in 
  the 
  very 
  narrow 
  

   ones, 
  in 
  which 
  the 
  imperfect 
  crystals 
  of 
  tourmalin 
  interlock 
  across 
  

   the 
  entire 
  width. 
  At 
  the 
  same 
  time 
  the 
  schists 
  along 
  the 
  contact 
  

   become 
  impregnated 
  with 
  fine, 
  granular 
  tourmalin, 
  producing 
  

   strips 
  and 
  irregular 
  areas 
  of 
  a 
  lustrous 
  black 
  rock. 
  The 
  remarkable 
  

   feature 
  about 
  these 
  contact 
  zones 
  in 
  the 
  schist 
  is 
  their 
  extreme 
  ir- 
  

   regularity 
  in 
  form 
  and 
  extent, 
  and 
  their 
  entire 
  independence 
  of 
  the 
  

   magnitude 
  of 
  the 
  accompanying 
  dike. 
  A 
  dike 
  of 
  granite 
  a 
  foot 
  wide 
  

  

  J 
  op 
  cit. 
  p. 
  r94. 
  

  

  