﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  WESTERN 
  ADIRONDACK 
  REGION 
  483 
  

  

  occurs 
  just 
  north 
  of 
  Cranberry 
  lake. 
  At 
  Clifton 
  mine 
  the 
  schists 
  

   and 
  lean 
  ore 
  are 
  of 
  such 
  a 
  character 
  as 
  to 
  indicate 
  that 
  they 
  

   belong 
  to 
  the 
  limestone 
  series, 
  though 
  no 
  actual 
  limestone 
  was 
  

   found. 
  That 
  a 
  more 
  detailed 
  study 
  of 
  the 
  region 
  will 
  show 
  the 
  

   presence 
  of 
  small, 
  scattered 
  areas 
  of 
  the 
  limestone 
  series 
  is 
  prac- 
  

   tically 
  certain. 
  But 
  the 
  region 
  as 
  a 
  whole 
  is 
  gneissic 
  and 
  affords 
  

   a 
  good 
  illustration 
  of 
  the 
  large 
  scale 
  on 
  which 
  the 
  gneisses 
  

   of 
  plutonic 
  habit 
  occur. 
  Throughout 
  the 
  whole 
  area 
  with 
  the 
  

   exceptions 
  already 
  noted 
  the 
  gneisses 
  exhibit 
  their 
  usual 
  char- 
  

   acter, 
  being 
  quite 
  uniform, 
  massive, 
  with 
  almost 
  no 
  banding 
  

   and 
  the 
  foliation 
  striking 
  northeast 
  and 
  dipping 
  north. 
  

  

  While 
  it 
  is 
  probable 
  that 
  small 
  isolated 
  intrusions 
  of 
  gabbro 
  

   occur, 
  the 
  absence 
  of 
  any 
  large 
  areas 
  of 
  this 
  rock 
  is 
  noticeable 
  

   and 
  of 
  considerable 
  importance, 
  as 
  will 
  be 
  noted 
  below. 
  ^ 
  

  

  Before 
  passing 
  to 
  the 
  consideration 
  of 
  other 
  topics 
  it 
  may 
  be 
  

   well 
  to 
  ^sum 
  up 
  the 
  important 
  points 
  which 
  make 
  the 
  syenite 
  of 
  

   particular 
  interest. 
  It 
  is 
  a 
  rock 
  of 
  considerable 
  extent, 
  covering 
  

   not 
  less 
  than 
  75 
  square 
  miles, 
  is 
  of 
  igneous 
  origin 
  and 
  younger 
  

   than 
  the 
  limestone. 
  But 
  while 
  its 
  " 
  habit 
  " 
  is 
  usually 
  igneous 
  

   and 
  its 
  origin 
  would 
  be 
  suspected 
  aside 
  from 
  all 
  structural 
  data, 
  

   the 
  syenite 
  is 
  nearly 
  always 
  gneissoid 
  and 
  passes 
  over 
  into 
  a 
  

   typical 
  hornblende 
  gneiss, 
  unquestionably 
  a 
  product 
  of 
  dynamic 
  

   metamorphism. 
  Though 
  commonly 
  gneissoid, 
  the 
  syenite 
  lacks 
  

   distinct 
  banding 
  except 
  in 
  a 
  few 
  localities, 
  where 
  this 
  structure 
  

   is 
  associated 
  with 
  basic 
  segregation 
  or 
  with 
  inclusions. 
  While 
  

   the 
  rock 
  is 
  somewhat 
  variable 
  in 
  composition, 
  the 
  variations 
  take 
  

   place 
  very 
  gradually 
  and 
  on 
  the 
  whole 
  the 
  composition 
  is 
  quite 
  

   fixed 
  over 
  wide 
  areas. 
  

  

  All 
  of 
  these 
  phenomena 
  are 
  what 
  would 
  be 
  expected 
  in 
  a 
  

   gneiss 
  of 
  igneous 
  origin, 
  and 
  it 
  is 
  important 
  to 
  find 
  them 
  so 
  well 
  

   exemplified 
  in 
  this 
  rock 
  whose 
  origin 
  is 
  clear. 
  

  

  In 
  gneisses 
  of 
  sedimentary 
  origin 
  on 
  the 
  other 
  hand, 
  pro- 
  

   nounced 
  banding 
  with 
  frequent 
  and 
  sudden 
  changes 
  of 
  composi- 
  

   tion 
  at 
  right 
  angles 
  to 
  the 
  strike 
  are 
  to 
  be 
  expected. 
  The 
  lime- 
  

   stone 
  formation 
  furnishes 
  abundant 
  examples 
  of 
  the 
  latter 
  class, 
  

   while, 
  as 
  stated 
  in 
  a 
  previous 
  report, 
  tbe 
  wide 
  areas 
  of 
  gneiss 
  so 
  

  

  