﻿28 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  reality 
  a 
  marginal 
  part 
  of 
  the 
  same 
  intrusion, 
  or 
  a 
  separate 
  in- 
  

   trusion. 
  1 
  The 
  porphyritic 
  border 
  phases 
  of 
  the 
  rock 
  as 
  they 
  occur 
  

   about 
  Saratoga, 
  where 
  the 
  relation 
  to 
  the 
  main 
  rock 
  is 
  certain, 
  

   are 
  so 
  precisely 
  like 
  this 
  porphyritic 
  rock 
  from 
  Alexandria 
  as 
  to 
  

   leave 
  no 
  doubt 
  in 
  our 
  mind 
  that 
  this 
  is 
  also 
  a 
  border 
  phase 
  of 
  

   the 
  syenite 
  intrusion. 
  Such 
  border 
  phases 
  of 
  the 
  rock, 
  of 
  por- 
  

   phyritic 
  nature, 
  are 
  proving 
  a 
  quite 
  normal 
  feature 
  of 
  the 
  syenite 
  

   of 
  the 
  region. 
  

  

  The 
  rock 
  here 
  varies 
  about 
  as 
  it 
  does 
  elsewhere 
  except 
  that 
  the 
  

   more 
  basic 
  phases 
  are 
  lacking. 
  Granitic 
  varieties, 
  however, 
  are 
  

   abundant. 
  This 
  seems 
  to 
  us 
  likely 
  due 
  to 
  the 
  fact 
  that 
  the 
  sur- 
  

   rounding 
  rocks 
  in 
  the 
  quadrangle 
  are 
  mostly 
  of 
  siliceous 
  nature. 
  

   Much 
  more 
  than 
  in 
  the 
  case 
  of 
  the 
  other 
  intrusives 
  of 
  the 
  region 
  

   there 
  is 
  found 
  for 
  the 
  syenite 
  a 
  usual 
  relation 
  between 
  the 
  nature 
  

   of 
  its 
  border 
  phase 
  and 
  the 
  character* 
  of 
  the 
  neighboring 
  rock 
  ; 
  

   such 
  a 
  relation 
  as 
  indicated 
  by 
  Kemp 
  for 
  the 
  occurrences 
  of 
  the 
  

   Elizabethtown 
  quadrangle, 
  and 
  by 
  the 
  writer 
  for 
  the 
  Long 
  Lake 
  

   quadrangle. 
  2 
  

  

  But 
  one 
  variety 
  of 
  syenite 
  on 
  the 
  quadrangle 
  seems 
  sufficiently 
  

   novel 
  to 
  merit 
  special 
  notice. 
  In 
  the 
  quarry 
  by 
  the 
  Hudson 
  near 
  

   Spiers 
  dam, 
  is 
  a 
  very 
  gneissoid 
  dark 
  green 
  variety 
  of 
  syenite, 
  one 
  

   of 
  the 
  many 
  varieties 
  occurring 
  there, 
  which 
  is 
  really 
  not 
  a 
  syenite 
  

   at 
  all, 
  but 
  diorite, 
  80 
  per 
  cent 
  of 
  its 
  feldspar 
  being 
  andesine 
  (about 
  

   Ab 
  3 
  An 
  2 
  ). 
  Pyroxene, 
  hornblende, 
  biotite, 
  magnetite, 
  apatite 
  and 
  

   zircon 
  form 
  about 
  15 
  per 
  cent 
  of 
  the 
  rock, 
  some 
  7 
  per 
  cent 
  is 
  

   quartz, 
  and 
  the 
  remainder 
  feldspar. 
  The 
  excellent 
  exhibit 
  of 
  the 
  

   rock 
  shown 
  in 
  the 
  quarry 
  shows 
  rapid 
  and 
  great 
  range 
  in 
  com- 
  

   position, 
  bands 
  of 
  granite, 
  syenite 
  and 
  diorite 
  appearing. 
  All 
  are 
  

   plainly 
  varieties 
  of 
  the 
  one 
  rock 
  type. 
  The 
  material 
  is 
  almost 
  pre- 
  

   cisely 
  like 
  the 
  syenite 
  at 
  Little 
  Falls 
  in 
  appearance 
  and 
  in 
  variation, 
  

   except 
  that 
  at 
  Little 
  Falls 
  the 
  variation 
  between 
  extreme 
  types 
  is 
  

   not 
  usually 
  so 
  rapid. 
  In 
  these 
  very 
  gneissoid 
  syenites 
  of 
  the 
  east, 
  

   garnet 
  is 
  a 
  more 
  common 
  mineral 
  than 
  in 
  the 
  mid-Adirondacks 
  or 
  

   on 
  the 
  west. 
  There 
  it 
  is 
  usually 
  confined 
  to 
  the 
  basic, 
  border 
  

   phases, 
  or 
  to 
  the 
  narrow 
  dikes, 
  whereas 
  here 
  it 
  comes 
  quite 
  fre- 
  

   quently 
  as 
  a 
  constituent 
  of 
  the 
  normal 
  and 
  the 
  acid 
  varieties. 
  

  

  Diabase 
  dikes 
  of 
  late 
  Precambric 
  age. 
  Nearly 
  everywhere 
  in 
  

   the 
  Adirondacks 
  all 
  the 
  other 
  Precambric 
  rocks 
  are 
  found 
  cut 
  by 
  

  

  1 
  N. 
  Y. 
  State 
  Mus. 
  Bui. 
  145, 
  p. 
  39-40, 
  182-84. 
  

  

  2 
  N. 
  Y. 
  State 
  Mus. 
  Bui. 
  138, 
  p. 
  81; 
  N. 
  Y. 
  State 
  Mus. 
  Mul. 
  115, 
  p. 
  478-79. 
  

  

  