﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  WESTERN 
  ADIRONDACK 
  REGION 
  485 
  

  

  and 
  this 
  is 
  sometimes 
  accompanied 
  by 
  a 
  beautiful 
  blue 
  color. 
  

   Less 
  often 
  though 
  by 
  no 
  means 
  rarely, 
  typical 
  contact 
  zones, 
  in 
  

   which 
  pyroxene 
  is 
  the 
  most 
  abundant 
  mineral, 
  are 
  developed. 
  

   Occasionally 
  inclusions 
  of 
  the 
  fine 
  pyroxenic 
  gneisses 
  of 
  the 
  lime- 
  

   stone 
  formation 
  may 
  be 
  found 
  analogous 
  to 
  those 
  shown 
  in 
  the 
  

   syenite. 
  Abundant 
  veins 
  of 
  pegmatite 
  and 
  quartz 
  doubtless 
  rep- 
  

   resent 
  the 
  last 
  stages 
  of 
  igneous 
  activity 
  at 
  this 
  point. 
  

  

  Half 
  a 
  mile 
  west 
  of 
  this 
  locality, 
  across 
  the 
  Oswegatchie 
  river 
  

   is 
  a 
  bold 
  hill 
  made 
  up 
  chiefly 
  of 
  gabbro 
  which 
  was 
  described 
  at 
  

   some 
  length 
  three 
  years 
  since." 
  

  

  This 
  same 
  rock 
  has 
  been 
  found 
  in 
  scattered 
  areas 
  of 
  smaller 
  

   extent 
  two 
  miles 
  or 
  more 
  to 
  the 
  westward. 
  In 
  these 
  occurrences 
  

   it 
  is 
  often 
  extremely 
  coarse 
  and 
  very 
  basic, 
  looking 
  almost 
  black 
  

   at 
  a 
  short 
  distance. 
  In 
  the 
  field 
  it 
  would 
  be 
  taken 
  for 
  a 
  basic 
  

   diorite, 
  but 
  in 
  thin 
  section 
  shows 
  prevailing 
  pyroxene, 
  though 
  

   hornblende 
  is 
  always 
  present 
  and 
  sometimes 
  in 
  preponderance. 
  

   These 
  outcrops 
  usually 
  show 
  a 
  marked 
  gneissoid 
  structure 
  and 
  

   the 
  true 
  nature 
  of 
  the 
  rock 
  might 
  be 
  a 
  matter 
  of 
  doubt 
  but 
  for 
  

   the 
  outcrops 
  referred 
  to 
  above 
  where 
  the 
  intrusive 
  character 
  is 
  

   plain. 
  The 
  tendency 
  of 
  these 
  intrusions 
  to 
  assume 
  the 
  form 
  of 
  

   greatly 
  elongated 
  lenses 
  or 
  schists, 
  combined 
  with 
  the 
  gneissic 
  

   structure 
  of 
  the 
  rocks, 
  is 
  apt 
  to 
  lead 
  to 
  confusion 
  in 
  distinguish- 
  

   ing 
  between 
  intrusive 
  and 
  interbedded 
  gneisses. 
  

  

  A 
  good 
  illustration 
  of 
  this 
  difficulty 
  is 
  afforded 
  by 
  a 
  section 
  

   shown 
  just 
  south 
  of 
  the 
  new 
  sawmill 
  a 
  half 
  mile 
  west 
  of 
  Gier's. 
  

  

  The 
  actual 
  outcrops 
  cover 
  about 
  one 
  eighth 
  of 
  a 
  mile, 
  the 
  whole 
  

   section 
  being 
  about 
  one 
  half 
  mile 
  in 
  length. 
  Starting 
  on 
  the 
  

   north 
  there 
  is 
  a 
  heavy 
  well-banded 
  garnetiferous 
  gneiss 
  with 
  a 
  

   lens 
  of 
  gneissoid 
  gabbro. 
  Below 
  this 
  is 
  limestone 
  with 
  lenses 
  of 
  

   granite 
  sometimes 
  massive 
  and 
  sometimes 
  extremely 
  gneissoid. 
  

   Whether 
  there 
  is 
  some 
  fine, 
  acid 
  gneiss 
  of 
  different 
  origin 
  here 
  

   too, 
  or 
  whether 
  it 
  is 
  all 
  granite, 
  is 
  open 
  to 
  question. 
  After 
  a 
  

   wide 
  break 
  another 
  large 
  mass 
  of 
  gneissoid 
  gabbro 
  appears. 
  

  

  In 
  this 
  section 
  the 
  limestone 
  and 
  granite 
  are 
  readily 
  classed 
  

   as 
  sedimentary 
  and 
  igneous 
  respectively, 
  but 
  with 
  doubt 
  as 
  to 
  

  

  a 
  Crystalline 
  limestones 
  and 
  associated 
  rocks 
  of 
  the 
  northwestern 
  Adirondack 
  region. 
  

   Bull. 
  geol. 
  soc. 
  6:268-70. 
  

  

  