﻿14 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  portion 
  of 
  the 
  quadrangle 
  with 
  fine 
  exposures 
  between 
  Brant- 
  

   ingham 
  lake 
  and 
  Partridgeville 
  and 
  also 
  where 
  the 
  road 
  leaves 
  

   the 
  map 
  east 
  of 
  Brantingham 
  post 
  office. 
  The 
  area 
  between 
  

   Greig 
  and 
  Donnattsburg 
  show^s 
  many 
  large 
  outcrops 
  of 
  rock 
  

   which 
  here 
  as 
  well 
  as 
  around 
  Partridgeville 
  are 
  more 
  quartzose 
  

   than 
  usual. 
  Smaller 
  patches 
  of 
  rather 
  quartzose 
  syenite 
  are 
  

   show^n 
  at 
  Lyons 
  Falls 
  and 
  in 
  the 
  river 
  bottom 
  east 
  of 
  Glenfield. 
  

  

  The 
  rock 
  exposed 
  in 
  the 
  quarry 
  southeast 
  of 
  Denley 
  may 
  be 
  

   taken 
  as 
  typical 
  of 
  the 
  best 
  syenite 
  of 
  the 
  quadrangle 
  and 
  a 
  

   detailed 
  description 
  of 
  this 
  type 
  will 
  now 
  be 
  given. 
  In 
  thin 
  

   section 
  fresh 
  feldspar 
  is 
  seen 
  to 
  be 
  the 
  most 
  common 
  mineral 
  

   which 
  makes 
  up 
  75 
  to 
  Sofo 
  of 
  the 
  rock. 
  Much 
  of 
  the 
  feldspar 
  

   is 
  present 
  as 
  microperthite 
  usually 
  in 
  large 
  crystals 
  and 
  with 
  

   the 
  microperthitic 
  strticture 
  beautifully 
  exhibited. 
  There 
  is 
  also 
  

   a 
  considerable 
  percentage 
  of 
  another 
  feldspar, 
  presumably 
  anor- 
  

   thocliase, 
  which 
  is 
  characterized 
  by 
  a 
  sort 
  of 
  moire 
  or 
  clouded 
  

   appearance. 
  There 
  is 
  a 
  small 
  amount 
  of 
  plagioclase 
  feldspar 
  

   ranging 
  from 
  oligoclase 
  to 
  andesin. 
  The 
  second 
  most 
  common 
  

   mineral 
  is 
  quartz 
  of 
  which 
  there 
  is 
  12 
  or 
  15;^. 
  The 
  quartz 
  grains 
  

   are 
  very 
  variable 
  in 
  shape 
  and 
  size 
  and 
  are 
  frequently 
  broken 
  

   as 
  a 
  result 
  01 
  pressure. 
  Of 
  the 
  dark 
  colored 
  minerals 
  hornblende 
  

   and 
  biotite 
  make 
  up 
  about 
  ^^^ 
  of 
  the 
  rock. 
  The 
  hornblende 
  is 
  

   the 
  common 
  green 
  variety 
  with 
  usual 
  pleochroism 
  and 
  shows 
  

   frequent 
  alterations 
  to 
  chlorite, 
  i 
  or 
  2fo 
  of 
  magnetite, 
  some- 
  

   times 
  with 
  leucoxene 
  borders, 
  is 
  also 
  present. 
  Beside 
  these 
  a 
  

   few 
  small 
  crystals 
  of 
  zircon, 
  apatite, 
  and 
  zoisite 
  may 
  be 
  seen 
  nearly 
  

   always 
  as 
  inclusions. 
  

  

  A 
  study 
  of 
  the 
  thin 
  sections 
  from 
  the 
  different 
  syenite 
  locali- 
  

   ties 
  shows 
  a 
  range 
  of 
  minerals 
  as 
  follows 
  : 
  Feldspar 
  60 
  to 
  80^ 
  

   — 
  microperthite 
  always 
  abundant, 
  anorthoclase 
  none 
  to 
  20^, 
  

   oligoclase 
  none 
  to 
  10^; 
  quartz 
  15 
  to 
  30^; 
  hornblende 
  none 
  to 
  5^; 
  

   biotite 
  none 
  to 
  3^; 
  magnetite 
  none 
  to 
  3^ 
  and 
  zircon, 
  apatite 
  and 
  

   zoisite 
  are 
  nearly 
  always 
  present 
  in 
  very 
  small 
  amounts. 
  In 
  

   one 
  or 
  two 
  cases 
  a 
  little 
  garnet 
  has 
  been 
  noted. 
  The 
  cataclastic 
  

   structure 
  is 
  always 
  more 
  or 
  less 
  well 
  developed 
  in 
  the 
  syenite, 
  

   sometimes 
  being 
  very 
  prominent, 
  which 
  shows 
  that 
  the 
  rock 
  

   must 
  have 
  been 
  subjected 
  to 
  a 
  pretty 
  severe 
  dynamic 
  meta- 
  

   morphism. 
  

  

  In 
  Cushing's^ 
  typical 
  syenite 
  at 
  Loon 
  lake 
  and 
  Smyth's^ 
  typi- 
  

  

  . 
  ' 
  

  

  ^Geol. 
  Soc. 
  Am. 
  Bui. 
  1899. 
  10:177-92. 
  

  

  ' 
  loc. 
  cit. 
  p. 
  473. 
  

  

  