﻿20 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  feldspar 
  and 
  a 
  large 
  proportion 
  of 
  quartz 
  and 
  the 
  dark 
  colored 
  

   minerals. 
  Thus 
  a 
  specimen 
  from 
  along 
  the 
  railroad 
  2>^ 
  miles 
  

   north 
  of 
  Lyons 
  Falls 
  contains 
  75^ 
  of 
  microperthite; 
  2ofo 
  of 
  

   quartz; 
  5^ 
  of 
  magnetite, 
  biotite 
  and 
  hornblende, 
  together 
  with 
  

   a 
  little 
  zircon. 
  Another 
  from 
  ^ 
  of 
  a 
  mile 
  southwest 
  of 
  Goulds 
  

   Mill 
  contains 
  6y/c, 
  in 
  about 
  equal 
  amounts, 
  of 
  microcline, 
  micro- 
  

   perthite 
  and 
  plagioclase 
  (oligoclase 
  to 
  labradorite) 
  ; 
  25;^ 
  of 
  

   quartz 
  ; 
  and 
  10^ 
  of 
  biotite 
  and 
  magnetite. 
  North 
  of 
  Lyons 
  Falls, 
  

   along 
  the 
  railroad, 
  similar 
  rocks 
  often 
  carry 
  30 
  to 
  40/0 
  of 
  quartz 
  

   with 
  sometimes 
  a 
  little 
  anorthoclase 
  and 
  they 
  greatly 
  resemble 
  

   the 
  granitic 
  syenite. 
  

  

  2 
  Grenville 
  facies. 
  Small 
  exposures 
  often 
  show 
  very 
  pure 
  

   Grenville 
  as 
  for 
  example 
  at 
  the 
  river 
  dam 
  ^ 
  mile 
  north 
  of 
  Port 
  

   Leyden, 
  A 
  thin 
  section 
  from 
  here 
  shows 
  Sofo 
  quartz; 
  lofo 
  silli- 
  

   manite 
  ; 
  Sfc 
  magnetite 
  and 
  2/0 
  biotite, 
  together 
  with 
  a 
  little 
  zircon. 
  

   Again, 
  a 
  typical 
  pyroxene, 
  quartz 
  gneiss 
  is 
  associated 
  with 
  syen- 
  

   itic 
  rocks 
  i^ 
  miles 
  above 
  the 
  mouth 
  of 
  Miller 
  brook. 
  A 
  Grenville 
  

   facies 
  carrying 
  garnets 
  occurs 
  in 
  the 
  vicinity 
  of 
  the 
  paper 
  mill 
  at 
  

   Lyons 
  Falls. 
  

  

  3 
  Garnetiferous 
  gneisses 
  with 
  a 
  general 
  igneous 
  appearance 
  are 
  

   very 
  common. 
  Such 
  a 
  rock 
  2 
  miles 
  east 
  of 
  Port 
  Leyden 
  shows 
  6^^^ 
  

   of 
  microcline 
  and 
  microperthite; 
  20^ 
  of 
  quartz; 
  5^ 
  of 
  hornblende 
  

   and 
  biotite 
  and 
  lofo 
  of 
  augite, 
  magnetite, 
  garnet 
  and 
  zircon. 
  

   A 
  similar 
  type 
  much 
  richer 
  m 
  garnet 
  and 
  almost 
  free 
  from 
  dark 
  

   minerals 
  occurs 
  in 
  the 
  river 
  bed 
  at 
  Port 
  Leyden. 
  Another 
  type 
  

   from 
  2^ 
  miles 
  east-southeast 
  of 
  Greig 
  shows 
  65^ 
  of 
  plagioclase 
  

   (oligoclase 
  to 
  labradorite) 
  ; 
  30^ 
  of 
  quartz 
  and 
  5^ 
  of 
  biotite, 
  gar- 
  

   net, 
  magnetite 
  and 
  zircon. 
  The 
  origin 
  of 
  these 
  gneisses 
  is 
  doubt- 
  

   ful 
  but 
  they 
  may 
  have 
  been 
  formed 
  by 
  a 
  thorough 
  mixing 
  of 
  

   Grenville 
  masses 
  with 
  the 
  molten 
  syenite. 
  The 
  garnets 
  in 
  these 
  

   rocks 
  are 
  frequently 
  an 
  inch 
  or 
  more 
  across. 
  

  

  4 
  A 
  ver}^ 
  gneissoid, 
  rather 
  dark 
  rock, 
  which 
  is 
  fairly 
  common, 
  

   is 
  rich 
  in 
  plagioclase, 
  quartz 
  and 
  biotite. 
  An 
  example 
  from 
  ^ 
  

   mile 
  south 
  of 
  Lyons 
  Falls 
  contains 
  45^ 
  of 
  plagioclase 
  (oligoclase 
  

   to 
  andesin) 
  ; 
  40^ 
  of 
  quartz 
  ; 
  lofc 
  of 
  biotite 
  ; 
  2fo 
  of 
  hornblende 
  and 
  

   3^ 
  of 
  magnetite, 
  zircon 
  and 
  pyrite. 
  

  

  5 
  A 
  very 
  gneissoid, 
  dark 
  rock 
  from 
  i^ 
  miles 
  east 
  of 
  Port 
  

   Leyden 
  contains 
  50^ 
  of 
  microcline 
  and 
  plagioclase 
  (oligoclase 
  

   to 
  labradorite) 
  ; 
  20^ 
  of 
  quartz 
  and 
  lofo 
  each 
  of 
  green 
  augite, 
  biotite, 
  

   magnetite 
  and 
  a 
  very 
  little 
  garnet. 
  

  

  6 
  A 
  type 
  of 
  dark, 
  quartzless, 
  gabbroic 
  rock 
  such 
  as 
  that 
  at 
  

   Lyons 
  Falls 
  dam 
  contains 
  55^ 
  of 
  plagioclase 
  (oligoclase 
  to 
  labrador- 
  

  

  