﻿474 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  tion 
  taken 
  in 
  conjunction 
  with 
  the 
  extreme 
  fineness 
  often 
  shown 
  

   by 
  the 
  microperthite 
  recalls 
  very 
  forcibly 
  the 
  explanation 
  of 
  

   anorthoclase 
  as 
  an 
  ultramicroscopic 
  intergrowth 
  of 
  potash 
  and 
  

   soda 
  feldspars. 
  ' 
  

  

  As 
  the 
  more 
  basic, 
  gabbroitic 
  variety 
  has 
  been 
  found 
  to 
  be 
  the 
  

   exception 
  and 
  the 
  syenitic 
  variety 
  the 
  prevailing 
  type, 
  in 
  the 
  

   following 
  pages 
  the 
  term 
  syenite 
  will 
  be 
  used 
  for 
  the 
  rock 
  as 
  a 
  

   whole, 
  though 
  its 
  wide 
  range 
  in 
  composition 
  is 
  to 
  be 
  kept 
  con- 
  

   stantly 
  in 
  view.® 
  While 
  no 
  extended 
  petrographic 
  investigation 
  

   of 
  the 
  rock 
  under 
  discussion 
  has 
  been 
  attempted 
  such 
  data 
  have 
  

   been 
  sought 
  as 
  might 
  shed 
  light 
  on 
  the 
  question 
  of 
  its 
  origin, 
  

   though 
  on 
  strictly 
  petrographic 
  data 
  but 
  little 
  reliance 
  has 
  

   been 
  placed. 
  The 
  structural 
  relations 
  existing 
  between 
  the 
  

   syenite 
  and 
  the 
  other 
  rocks 
  of 
  the 
  region 
  have 
  been 
  studied 
  as 
  

   carefully 
  as 
  time 
  would 
  permit, 
  and 
  on 
  them 
  almost 
  entirely 
  have 
  

   been 
  based 
  all 
  conclusions 
  as 
  to 
  the 
  true 
  nature 
  and 
  history 
  of 
  

   the 
  syenite. 
  

  

  The 
  study 
  of 
  this 
  particular 
  rock 
  was 
  taken 
  up 
  because 
  it 
  was 
  

   thought 
  to 
  afford 
  a 
  connecting 
  link 
  between 
  some 
  rocks 
  of 
  certain 
  

   and 
  others 
  of 
  doubtful 
  origin. 
  As 
  shown 
  in 
  an 
  earlier 
  report 
  

   some 
  areas 
  of 
  gneiss 
  in 
  the 
  western 
  Adirondack 
  region 
  are 
  with- 
  

   out 
  doubt 
  of 
  sedimentary 
  origin 
  and 
  others 
  are 
  as 
  certainly 
  

   igneous. 
  Small 
  areas 
  of 
  gneiss 
  of 
  composite 
  origin 
  are 
  known, 
  

   and 
  larger 
  areas 
  are 
  probably 
  igneous, 
  while 
  still 
  others 
  are 
  of 
  

   wholly 
  problematic 
  origin. 
  

  

  The 
  rock 
  under 
  consideration 
  has 
  been 
  thought 
  to 
  afford 
  a 
  clue 
  

   which 
  may 
  be 
  of 
  service 
  in 
  making 
  more 
  definite 
  our 
  knowledge 
  

   of 
  these 
  gneisses 
  and 
  it 
  was 
  for 
  this 
  purpose 
  that 
  its 
  study 
  was 
  

   begun. 
  But 
  as 
  already 
  stated 
  this 
  study 
  was 
  left 
  very 
  incom- 
  

   plete 
  and 
  from 
  the 
  facts 
  gathered 
  it 
  is 
  impossible 
  to 
  draw 
  con- 
  

   clusions 
  as 
  far-reaching 
  as 
  it 
  had 
  been 
  hoped 
  to 
  reach. 
  

  

  The 
  structural 
  data 
  bearing 
  upon 
  the 
  question 
  of 
  the 
  origin 
  of 
  

   the 
  syenite 
  were 
  presented 
  in 
  the 
  former 
  paper 
  6 
  and 
  in 
  the 
  

  

  a 
  Since 
  the 
  foregoing 
  was 
  written 
  Prof. 
  Cushing 
  has 
  described 
  similar 
  augite-syenite 
  

   occurring 
  in 
  Franklin 
  co. 
  in 
  close 
  association 
  with 
  gabbro, 
  of 
  which 
  the 
  syenite 
  is 
  

   thought 
  to 
  be 
  an 
  acid 
  phase. 
  The 
  two 
  cases 
  are 
  closely 
  parallel 
  but 
  with 
  the 
  quantita- 
  

   tive 
  relations 
  of 
  the 
  rock 
  varieties 
  reversed. 
  

  

  b 
  Crystalline 
  limestones 
  and 
  associated 
  rockf 
  of 
  the 
  northwestern 
  Adirondack 
  region. 
  

   Sull. 
  geol. 
  soc. 
  6:276. 
  

  

  