﻿ADIRONDACK 
  MAGNETIC 
  IRON 
  ORES 
  63 
  

  

  much 
  as 
  a 
  square 
  mile. 
  They 
  are 
  of 
  special 
  interest 
  because 
  they 
  

   contain 
  bodies 
  of 
  low-grade 
  titaniferous 
  magnetite 
  in 
  numerous 
  

   localities. 
  These 
  ore 
  deposits 
  have 
  received 
  some 
  practical 
  atten- 
  

   tion 
  and 
  will 
  be 
  mentioned 
  in 
  detail 
  later. 
  

  

  The 
  gabbros 
  and 
  their 
  hornblendic 
  derivatives 
  may 
  be 
  very 
  

   easily 
  confounded 
  with 
  the 
  basic 
  phases 
  of 
  the 
  syenites 
  to 
  be 
  next 
  

   described. 
  The 
  two 
  rocks 
  look 
  extraordinarily 
  alike. 
  Yet 
  under 
  

   the 
  microscope 
  at 
  least, 
  the 
  syenitic 
  varieties 
  display 
  abundant 
  

   orthoclase, 
  the 
  gabbros 
  plagioclase. 
  The 
  garnets 
  are 
  more 
  abun- 
  

   dant 
  in 
  the 
  gabbros, 
  although 
  they 
  do 
  not 
  entirely 
  fail 
  the 
  syenites. 
  

   The 
  granular 
  fracture 
  of 
  magnetite 
  is 
  more 
  in 
  evidence 
  in 
  the 
  

   gabbros, 
  but 
  when 
  all 
  is 
  said, 
  the 
  field 
  observer 
  may 
  often 
  be 
  in 
  

   much 
  doubt 
  when 
  confronted 
  with 
  the 
  dark, 
  basic 
  gneisses, 
  as 
  to 
  

   which 
  rock 
  he 
  is 
  dealing 
  with. 
  For 
  the 
  present 
  we 
  may 
  consider 
  

   them 
  distinct. 
  

  

  Augite 
  syenites 
  and 
  related 
  types, 
  more 
  or 
  less 
  gneissoid. 
  The 
  

   syenites, 
  now 
  that 
  they 
  are 
  well 
  understood, 
  are 
  proving 
  to 
  be 
  one 
  

   of 
  the 
  most 
  important 
  members 
  among 
  the 
  rocks 
  of 
  the 
  eastern 
  

   Adirondacks. 
  They 
  were 
  first 
  identified 
  in 
  the 
  west 
  and 
  north 
  

   by 
  C. 
  H. 
  Smyth 
  jr, 
  and 
  H. 
  P. 
  Cushing, 
  respectively, 
  for 
  although 
  

   gneissoid 
  members 
  with 
  the 
  corresponding 
  mineralogy 
  were 
  found 
  

   in 
  the 
  east, 
  they 
  were 
  at 
  the 
  outset 
  placed 
  with 
  the 
  doubtful 
  

   gneisses 
  and 
  were 
  not 
  recognized 
  as 
  distinct 
  eruptives. 
  The 
  

   diamond 
  drill 
  cores 
  at 
  Mineville 
  have 
  done 
  much 
  to 
  clear 
  up 
  their 
  

   identity, 
  and 
  as 
  they 
  afford 
  perfectly 
  fresh 
  rocks 
  in 
  definite 
  

   relationships, 
  they 
  are 
  in 
  the 
  highest 
  degree 
  illuminating. 
  For 
  

   several 
  years 
  they 
  have 
  been 
  carefully 
  saved 
  and 
  recorded 
  by 
  

   Witherbee, 
  Sherman 
  & 
  Co., 
  and 
  have 
  been 
  of 
  the 
  greatest 
  service 
  

   in 
  the 
  preparation 
  of 
  this 
  description. 
  

  

  The 
  syenite 
  is 
  an 
  extremely 
  variable 
  magma 
  which 
  must 
  have 
  

   been 
  sharply 
  differentiated 
  into 
  contrasted 
  products, 
  which 
  then 
  

   constituted 
  different 
  layers 
  in 
  the 
  fluid 
  mass 
  at 
  the 
  time 
  of 
  intru- 
  

   sion 
  into 
  the 
  older 
  rocks. 
  At 
  Mineville, 
  diamond 
  drill 
  cores 
  have 
  

   in 
  one 
  case 
  been 
  available 
  showing 
  a 
  continuous 
  section 
  of 
  nearly 
  

   1000 
  feet; 
  in 
  another 
  of 
  nearly 
  1400 
  feet, 
  and 
  in 
  many 
  others 
  of 
  

   less, 
  so 
  that 
  the 
  relationships 
  of 
  the 
  several 
  layers 
  can 
  be 
  carefully 
  

   studied. 
  

  

  The 
  typical 
  syenite 
  consists 
  of 
  microperthitic 
  orthoclase 
  — 
  that 
  

   is 
  of 
  orthoclase 
  filled 
  with 
  flattened 
  spindles 
  of 
  albite 
  — 
  of 
  emerald 
  

   green 
  augite, 
  which 
  looks 
  black 
  in 
  the 
  hand 
  specimen; 
  of 
  brown 
  

   hornblende, 
  and 
  of 
  less 
  abundant 
  hypersthene. 
  Magnetite 
  is 
  of 
  

   course 
  present 
  in 
  subordinate 
  amount, 
  and 
  titanite, 
  apatite 
  and 
  

  

  