﻿ADIRONDACK 
  MAGNETIC 
  IRON 
  ORES 
  1 
  7 
  

  

  limestone 
  within 
  the 
  area, 
  probably 
  entangled 
  masses 
  borne 
  up 
  

   01 
  the 
  surface 
  of 
  the 
  intrusion, 
  but 
  in 
  the 
  main 
  the 
  anorthosite 
  

   is 
  unbroken 
  by 
  other 
  rocks. 
  Small 
  outlying 
  exposures 
  of 
  anor- 
  

   thosite 
  have 
  beeen 
  found 
  on 
  the 
  northern 
  and 
  southern 
  borders, 
  

   the 
  most 
  remote 
  being 
  the 
  Rand 
  hill 
  intrusion 
  near 
  Dannemora, 
  

   Clinton 
  co., 
  and 
  the 
  one 
  near 
  Bakers 
  Mills, 
  Warren 
  co., 
  both 
  of 
  

   which 
  lie 
  some 
  20 
  miles 
  distant 
  from 
  the 
  proximate 
  portion 
  of 
  

   the 
  principal 
  area. 
  

  

  In 
  its 
  normal 
  development 
  the 
  anorthosite 
  consists 
  of 
  little 
  else 
  

   than 
  feldspar 
  which 
  is 
  generally 
  a 
  blue 
  labradorite. 
  This 
  mineral 
  

   occurs 
  as 
  a 
  rule 
  in 
  large 
  interlocking 
  crystals, 
  giving 
  the 
  rock 
  a 
  

   very 
  coarse 
  texture 
  like 
  that 
  of 
  porphyritic 
  granites. 
  The 
  acces- 
  

   sory 
  minerals 
  include 
  augite, 
  hypersthene, 
  hornblende, 
  ilmenite 
  

   and 
  magnetite. 
  While 
  usually 
  constituting 
  a 
  small 
  percentage 
  of 
  

   the 
  rock, 
  the 
  ferromagnesian 
  silicates 
  may 
  assume 
  such 
  importance 
  

   as 
  to 
  mark 
  a 
  gradation 
  toward 
  or 
  even 
  a 
  complete 
  transition 
  into 
  

   the 
  gabbros. 
  With 
  the 
  increase 
  in 
  the 
  proportion 
  of 
  these 
  min- 
  

   erals, 
  there 
  is 
  also 
  a 
  change 
  in 
  the 
  texture, 
  which 
  becomes 
  finer 
  

   by 
  diminishing 
  the 
  size 
  of 
  the 
  feldspar 
  and 
  shows 
  the 
  characteristic 
  

   mottled 
  aspect 
  of 
  gabbroic 
  rocks. 
  There 
  are 
  innumerable 
  places 
  

   within 
  the 
  area 
  where 
  this 
  variation 
  is 
  to 
  be 
  found. 
  The 
  gabbro 
  

   type, 
  however, 
  falls 
  far 
  short 
  of 
  the 
  wide 
  distribution 
  of 
  the 
  felds- 
  

   pathic 
  phase, 
  being 
  limited 
  to 
  patches 
  and 
  dikelike 
  bands 
  in 
  the 
  

   latter. 
  By 
  compression 
  the 
  anorthosite 
  has 
  become 
  laminated, 
  

   specially 
  in 
  the 
  bordering 
  zones 
  where 
  it 
  often 
  shows 
  a 
  thoroughly 
  

   gneissoid 
  appearance. 
  The 
  feldspar 
  crushes 
  down 
  to 
  a 
  white 
  mass 
  

   of 
  granules, 
  in 
  which 
  remnants 
  of 
  the 
  original 
  blue 
  feldspar 
  may 
  

   usually 
  be 
  seen. 
  The 
  granulation 
  is 
  accompanied 
  by 
  the 
  develop- 
  

   ment 
  of 
  garnet 
  in 
  the 
  form 
  of 
  pink 
  crystals 
  surrounding 
  the 
  dark 
  

   silicates. 
  

  

  Gabbro. 
  This 
  rock 
  stands 
  in 
  close 
  relation 
  to 
  the 
  anorthosite. 
  

   It 
  is 
  abundant 
  only 
  within 
  the 
  area 
  occupied 
  by 
  the 
  latter 
  or 
  in 
  

   close 
  proximity 
  thereto. 
  The 
  gabbro 
  is 
  a 
  black, 
  very 
  dense 
  aggre- 
  

   gate 
  of 
  labradorite, 
  augite, 
  hypersthene 
  and 
  ilmenite 
  or 
  magnetite, 
  

   with 
  olivine 
  as 
  a 
  somewhat 
  uncommon 
  constituent. 
  It 
  seems 
  to 
  

   have 
  been 
  a 
  later 
  differentiation 
  of 
  the 
  magma 
  which 
  has 
  given 
  

   rise 
  to 
  the 
  anorthosite 
  as 
  it 
  sometimes 
  cuts 
  the 
  latter 
  intrusively. 
  

   The 
  gabbro 
  inclusions 
  which 
  grade 
  into 
  the 
  anorthosite 
  are, 
  how- 
  

   ever, 
  contemporaneous 
  segregations. 
  

  

  The 
  limited 
  masses 
  of 
  gabbro 
  have 
  sometimes 
  been 
  so 
  thoroughly 
  

   metamorphosed 
  as 
  to 
  assume 
  the 
  character 
  of 
  amphibolites. 
  The 
  

   presence 
  of 
  unchanged 
  pyroxene 
  and 
  basic 
  plagioclase 
  feldspar 
  

  

  