﻿40 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  finally 
  we 
  get 
  a 
  rock 
  in 
  Avhich 
  but 
  few 
  iinmashed 
  feldspar 
  centers 
  

   remain, 
  the 
  hornblende 
  has 
  entirely 
  disappeared, 
  and 
  the 
  rock 
  

   is 
  a 
  finely 
  granular 
  aggregate 
  of 
  feldspars, 
  mica 
  scales, 
  and 
  

   some 
  quartz. 
  

  

  Of 
  accessory 
  minerals, 
  apatite 
  and 
  titanite 
  are 
  prominent, 
  the 
  

   former 
  being 
  abundant 
  for 
  this 
  mineral, 
  and 
  of 
  good 
  size, 
  the 
  

   latter 
  usually 
  rimming 
  the 
  magnetite, 
  as 
  well 
  as 
  occurring 
  away 
  

   from 
  it. 
  The 
  feldspars 
  comprise 
  microcline, 
  microperthite 
  and 
  

   plagioclase 
  (oligoclase-andesine), 
  with 
  the 
  latter 
  somewhat 
  in 
  

   excess 
  when 
  the 
  plagioclase 
  in 
  the 
  microperthite 
  is 
  included 
  with 
  

   it. 
  The 
  quantity 
  of 
  the 
  two, 
  however, 
  is 
  not 
  far 
  from 
  equal 
  in 
  

   most 
  cases. 
  There 
  is 
  little 
  or 
  no 
  quartz 
  in 
  the 
  least 
  mashed 
  rock, 
  

   and 
  the 
  quantity 
  steadily 
  increases 
  in 
  the 
  gneissoid 
  varieties. 
  

   Some 
  of 
  this 
  increase 
  is 
  certainly 
  due 
  to 
  reactions 
  during 
  recrys- 
  

   tallization 
  since 
  quartz 
  commences 
  to 
  appear 
  with 
  the 
  appear- 
  

   ance 
  of 
  biotite. 
  On 
  the 
  other 
  hand 
  the 
  rock 
  varies 
  somewhat 
  

   in 
  acidity 
  and 
  some 
  of 
  the 
  quartz 
  is 
  unquestionably 
  primary. 
  

  

  The 
  coarse 
  aug"en 
  gneiss 
  at 
  the 
  south 
  has 
  much 
  the 
  same 
  

   mineralogy 
  as 
  the 
  remainder, 
  though 
  more 
  quartzose 
  and 
  acid, 
  

   approaching 
  a 
  granite 
  in 
  composition. 
  Smyth 
  holds 
  the 
  view 
  

   that 
  it 
  is 
  a 
  separate 
  intrusion 
  from 
  the 
  main 
  mass 
  of 
  the 
  syenite, 
  

   and 
  older, 
  having 
  noted 
  an 
  exposure 
  in 
  which 
  the 
  syenite 
  

   appeared 
  to 
  cut 
  the 
  augen 
  gneiss. 
  We 
  did 
  not 
  have 
  the 
  good 
  

   fortune 
  to 
  observe 
  any 
  such 
  exposure, 
  hence 
  his 
  positive 
  evidence 
  

   must 
  outweigh 
  our 
  lack 
  of 
  such. 
  Chemically 
  also 
  the 
  augen 
  

   gneiss 
  is 
  much 
  more 
  acid 
  than 
  the 
  syenite, 
  being 
  remarkably 
  

   like 
  the 
  Picton 
  granite 
  in 
  composition. 
  If 
  the 
  two 
  are 
  separate, 
  

   the 
  augen 
  gneiss 
  is 
  the 
  older, 
  and 
  both 
  are 
  younger 
  than 
  the 
  

   Laurentian, 
  while 
  the 
  Picton 
  holds 
  inclusions 
  of 
  the 
  augen 
  gneiss. 
  

  

  This 
  syenite 
  differs 
  considerably 
  from 
  the 
  usual 
  type 
  of 
  syenite 
  

   of 
  the 
  Adirondack 
  region, 
  represented 
  here 
  by 
  the 
  Theresa 
  

   syenite, 
  both 
  in 
  general 
  appearance 
  and 
  in 
  mineralogy. 
  Analyses 
  

   and 
  more 
  detailed 
  description 
  will 
  be 
  given 
  in 
  a 
  later 
  section 
  of 
  

   this 
  report. 
  It 
  is 
  more 
  gneissoid, 
  giving 
  the 
  appearance 
  of 
  

   greater 
  deformation 
  than 
  the 
  Theresa 
  syenite, 
  and 
  hence 
  it 
  is 
  

   tentatively 
  inferred 
  that 
  it 
  is 
  somewhat 
  older 
  than 
  that. 
  The 
  

   appearance 
  may 
  however 
  be 
  entirely 
  deceptive, 
  since 
  the 
  one 
  

   rock 
  gives 
  rise 
  to 
  abundant 
  mica 
  when 
  deformed, 
  and 
  the 
  other 
  

   furnishes 
  little 
  or 
  none, 
  nor 
  any 
  other 
  mineral 
  which 
  promotes 
  

   foliation. 
  Hence 
  the 
  same 
  amount 
  of 
  deformation 
  would 
  produce 
  

   a 
  better 
  foliated 
  rock 
  in 
  the 
  former 
  case 
  than 
  in 
  the 
  latter, 
  a 
  

   rock 
  which 
  would 
  appear 
  more 
  greatly 
  deformed. 
  

  

  