﻿1 
  8 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  furnishes 
  a 
  clew 
  to 
  the 
  derivation 
  of 
  such 
  amphibolites, 
  in 
  distinction 
  

   from 
  those 
  which 
  are 
  of 
  sedimentary 
  origin. 
  

  

  Syenite. 
  The 
  Adirondack 
  syenite 
  constitutes 
  an 
  abnormal 
  

   variety 
  of 
  that 
  rock, 
  and 
  was 
  not 
  recognized 
  as 
  such 
  until 
  recently. 
  

   Mineralogically 
  it 
  occupies 
  a 
  middle 
  place 
  between 
  the 
  gabbroic 
  

   rocks 
  and 
  the 
  granites. 
  A 
  green 
  augite 
  is 
  nearly 
  always 
  the 
  chief 
  

   dark 
  constituent, 
  but 
  hornblende 
  and 
  hypersthene 
  may 
  be 
  present. 
  

   The 
  feldspar 
  is 
  commonly 
  microperthite. 
  Orthoclase, 
  oligoclase, 
  

   quartz 
  and 
  magnetite 
  are 
  the 
  more 
  important 
  of 
  the 
  other 
  minerals. 
  

   The 
  rock 
  nearly 
  always 
  has 
  a 
  greenish 
  color, 
  varying 
  from 
  light 
  to 
  

   dark 
  shades. 
  When 
  there 
  is 
  a 
  considerable 
  proportion 
  of 
  the 
  dark 
  

   constituents, 
  it 
  resembles 
  the 
  gabbro 
  so 
  much 
  as 
  to 
  be 
  hardly 
  dis- 
  

   tinguished 
  in 
  the 
  field, 
  a 
  resemblance 
  which 
  is 
  even 
  closer 
  in 
  com- 
  

   paring 
  gneissoid 
  varieties 
  of 
  the 
  two 
  rocks. 
  With 
  the 
  increase 
  of 
  

   those 
  minerals 
  there 
  is 
  apt 
  to 
  be 
  a 
  change 
  also 
  in 
  the 
  feldspars 
  

   shown 
  by 
  the 
  preponderance 
  of 
  the 
  oligoclase 
  over 
  the 
  alkali 
  feld- 
  

   spars. 
  It 
  is 
  not 
  apparent, 
  however, 
  that 
  the 
  syenite 
  ever 
  merges 
  

   completely 
  into 
  the 
  gabbro, 
  the 
  evidence 
  tending 
  to 
  show 
  that 
  the 
  

   two 
  are 
  separate 
  and 
  distinct 
  intrusions. 
  On 
  the 
  other 
  hand 
  the 
  

   acid 
  types 
  of 
  the 
  syenite 
  pass 
  into 
  typical 
  granite, 
  as 
  was 
  first 
  

   demonstrated 
  by 
  Professor 
  Smyth. 
  

  

  The 
  syenite 
  occurs 
  in 
  local 
  intrusions 
  all 
  through 
  the 
  Adiron- 
  

   dacks 
  outside 
  of 
  the 
  anorthosite 
  area. 
  It 
  is 
  developed 
  in 
  great 
  

   force 
  in 
  the 
  northern 
  section, 
  specially 
  in 
  Franklin 
  county, 
  and 
  is 
  

   common 
  in 
  the 
  eastern 
  part 
  though 
  the 
  different 
  areas 
  here 
  have 
  

   not 
  yet 
  been 
  delimited. 
  On 
  the 
  south 
  side 
  the 
  Precambric 
  outlier 
  

   near 
  Little 
  Falls 
  consists 
  of 
  syenite. 
  The 
  Diana-Pit 
  cairn 
  area 
  on 
  

   the 
  northwest, 
  described 
  by 
  Professor 
  Smyth, 
  deserves 
  mention 
  

   as 
  affording 
  the 
  first 
  evidence 
  of 
  the 
  intrusive 
  character 
  of 
  the 
  

   rock 
  and 
  its 
  lithologic 
  relations. 
  

  

  Granite. 
  The 
  granites, 
  with 
  the 
  derived 
  gneisses, 
  are 
  the 
  most 
  

   frequent 
  of 
  all 
  the 
  intrusives. 
  They 
  are 
  closely 
  involved 
  with 
  the 
  

   Grenville 
  series 
  and 
  over 
  large 
  districts 
  are 
  the 
  only 
  igneous 
  forma- 
  

   tion 
  present. 
  It 
  has 
  already 
  been 
  pointed 
  out 
  that 
  they 
  constitute 
  

   an 
  important 
  factor 
  in 
  the 
  belt 
  of 
  Saranac 
  gneisses. 
  

  

  The 
  granites 
  are 
  prevailingly 
  light 
  colored, 
  gray 
  or 
  reddish 
  rocks. 
  

   Feldspar 
  and 
  quartz 
  always 
  predominate 
  and 
  may 
  be 
  practically 
  

   the 
  only 
  minerals 
  present. 
  Hornblende 
  granite 
  seems 
  to 
  be 
  more 
  

   common 
  than 
  the 
  mica 
  varieties, 
  while 
  augite 
  granite 
  occurs 
  as 
  a 
  

   variation 
  of 
  the 
  syenite. 
  It 
  is 
  only 
  rarely 
  that 
  the 
  intrusions 
  have 
  

   preserved 
  their 
  original 
  massive 
  character, 
  a 
  granulated 
  cataclastic 
  

   and 
  gneissoid 
  texture 
  being 
  the 
  rule. 
  In 
  regions 
  where 
  compression 
  

  

  