﻿1 
  6 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  order 
  to 
  distinguish 
  the 
  granitic 
  syenite 
  from 
  the 
  normal 
  syenite 
  

   several 
  features, 
  given 
  in 
  the 
  following 
  description, 
  must 
  be 
  

   considered. 
  

  

  The 
  rock 
  is 
  not 
  only 
  clearly 
  gneissoid 
  but 
  also 
  distinctly 
  

   banded. 
  The 
  rock 
  bands 
  are 
  straight 
  and 
  rather 
  persistent 
  and 
  

   the 
  minerals 
  are 
  commonly 
  arranged 
  with 
  their 
  long 
  axes 
  paral- 
  

   lel 
  to 
  the 
  foliation. 
  Frequently 
  the 
  " 
  leaf 
  gneiss 
  " 
  effect 
  is 
  beau- 
  

   tifully 
  shown 
  because 
  of 
  the 
  flattening 
  out 
  of 
  the 
  quartz 
  and 
  

   feldspar 
  crystals. 
  The 
  color 
  of 
  the 
  typical 
  rock 
  is 
  red 
  although 
  

   at 
  times 
  gray 
  bands 
  are 
  present. 
  The 
  size 
  of 
  the 
  grain 
  is 
  rather 
  

   variable 
  but 
  mostly 
  pretty 
  coarse. 
  At 
  times 
  the 
  quartz 
  and 
  

   feldspar 
  crystals 
  are 
  almost 
  porphyritic. 
  The 
  average 
  quartz 
  

   content 
  is 
  noticeably 
  higher 
  than 
  in 
  the 
  normal 
  syenite 
  and 
  com- 
  

   monly 
  the 
  more 
  weathered 
  surfaces 
  show 
  numerous 
  projecting 
  

   quartz 
  crystals; 
  often 
  the 
  rock 
  might 
  well 
  be 
  called 
  granite. 
  

   The 
  granitic 
  syenite 
  also 
  lacks 
  the 
  homogeneity 
  of 
  the 
  ordinary 
  

   syenite. 
  In 
  the 
  larger 
  exposures 
  of 
  the 
  typical 
  red 
  quartzose 
  

   gneisses 
  there 
  are 
  occasional 
  bands 
  of 
  gray, 
  less 
  quartzose 
  

   gneisses 
  very 
  similar 
  to 
  the 
  normal 
  syenite. 
  

  

  Another 
  noteworthy 
  feature 
  is 
  the 
  presence 
  of 
  long, 
  narrow 
  

   patches 
  or 
  inclusions 
  much 
  like 
  those 
  sparingly 
  present 
  in 
  the 
  

   ordinary 
  syenite, 
  but 
  they 
  are 
  here 
  much 
  larger 
  and 
  more 
  numer- 
  

   ous. 
  They 
  are 
  always 
  drawn 
  out 
  perfectly 
  parallel 
  to 
  the 
  folia- 
  

   tion 
  planes 
  but 
  they 
  are 
  seldom 
  more 
  than 
  30 
  or 
  40 
  feet 
  in 
  

   length. 
  They 
  are 
  composed 
  of 
  about 
  equal 
  parts 
  of 
  badly 
  de- 
  

   composed 
  basic 
  plagioclase 
  and 
  brown 
  hornblende 
  with 
  which 
  

   are 
  associated 
  thin 
  layers 
  of 
  almost 
  pure 
  biotite. 
  These 
  biotite 
  

   layers 
  often 
  give 
  the 
  rock 
  a 
  decidedly 
  schistose 
  appearance. 
  

   The 
  presence 
  of 
  these 
  basic 
  patches 
  has 
  doubtless 
  aided 
  in 
  the 
  

   production 
  of 
  the 
  distinct 
  banding 
  of 
  the 
  granitic 
  gneiss 
  during 
  

   the 
  process 
  of 
  dynamic 
  metamorphism. 
  In 
  this 
  connection 
  the 
  

   writer 
  has 
  read 
  the 
  recent 
  paper^ 
  by 
  Professor 
  Adams 
  which 
  

   deals 
  with 
  the 
  origin 
  of 
  the 
  amphibolites 
  in 
  the 
  Glamorgan 
  gran- 
  

   ite 
  of 
  Ontario, 
  Canada. 
  He 
  says: 
  ''Here 
  the 
  limestone 
  (Gren- 
  

   ville), 
  toward 
  the 
  granitic 
  contact, 
  passes 
  gradually 
  over 
  into 
  

   amphibolite, 
  the 
  latter 
  being 
  undoubtedly 
  produced 
  by 
  the 
  alter- 
  

   ation 
  of 
  the 
  former. 
  . 
  . 
  The 
  granite, 
  furthermore, 
  not 
  only 
  

   penetrates 
  the 
  (limestone) 
  series, 
  but 
  floats 
  off 
  masses 
  of 
  the 
  

   altered 
  rock 
  which 
  in 
  the 
  form 
  of 
  bands, 
  streaks, 
  and 
  isolated 
  

   shreds 
  are 
  seen 
  thickly 
  scattered 
  through 
  the 
  granite 
  in 
  the 
  

  

  ^Jour. 
  Geol. 
  1909. 
  17:8. 
  

  

  