﻿32 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  results. 
  Of 
  these 
  the 
  influence 
  of 
  highly 
  heated 
  vapors 
  and 
  waters 
  

   arising 
  from 
  the 
  igneous 
  mass 
  has 
  been 
  most 
  important. 
  The 
  occur- 
  

   rence 
  of 
  fluorite, 
  apatite, 
  hornblende 
  etc., 
  intercrystallized 
  with 
  

   the 
  magnetite, 
  is 
  suggestive 
  in 
  that 
  line, 
  as 
  well 
  as 
  the 
  frequent 
  

   accompaniments 
  of 
  pegmatite 
  and 
  vein 
  quartz. 
  This 
  agency 
  would 
  

   be 
  specially 
  active 
  in 
  the 
  final 
  stages 
  of 
  cooling 
  and 
  consolidation 
  

   of 
  the 
  wall 
  rocks. 
  In 
  some 
  cases 
  it 
  may 
  have 
  been 
  the 
  determina- 
  

   tive 
  factor 
  in 
  bringing 
  the 
  iron 
  minerals 
  into 
  their 
  present 
  position. 
  

   The 
  ore 
  bodies 
  thus 
  formed 
  would 
  be 
  comparable 
  in 
  a 
  way 
  to 
  

   pegmatite 
  dikes. 
  

  

  Some 
  authorities 
  are 
  inclined 
  to 
  doubt 
  the 
  efficacy 
  of 
  magmatic 
  

   differentiation 
  as 
  applied 
  to 
  the 
  formation 
  of 
  ore 
  bodies 
  in 
  rocks 
  of 
  

   acid 
  composition. 
  There 
  seems 
  to 
  be 
  no 
  valid 
  reason 
  for 
  thus 
  limit- 
  ' 
  

   ing 
  it 
  to 
  the 
  gabbros 
  and 
  anorthosites 
  of 
  the 
  Adirondacks. 
  The 
  

   relative 
  acidity 
  of 
  the 
  rocks 
  appears 
  to 
  the 
  writer 
  not 
  so 
  important 
  

   as 
  the 
  relation 
  between 
  the 
  iron 
  and 
  lime-magnesia 
  percentages. 
  

   With 
  a 
  large 
  excess 
  of 
  iron 
  over 
  the 
  amounts 
  required 
  for 
  combina- 
  

   tion 
  with 
  the 
  latter 
  to 
  form 
  augite, 
  hornblende 
  and 
  biotite, 
  the 
  

   segregation 
  of 
  iron 
  minerals 
  might 
  well 
  be 
  expected. 
  This 
  -is 
  exactly 
  

   the 
  condition 
  presented 
  by 
  the 
  wall 
  rocks 
  of 
  the 
  ores. 
  From 
  the 
  

   analyses 
  that 
  have 
  been 
  given 
  on 
  a 
  preceding 
  page, 
  it 
  will 
  be 
  seen 
  

   that 
  even 
  the 
  more 
  acid 
  of 
  the 
  intrusives 
  carry 
  relatively 
  high 
  

   percentages 
  of 
  free 
  iron. 
  The 
  amounts 
  of 
  magnetite 
  calculated 
  for 
  

   the 
  rocks, 
  all 
  of 
  which 
  are 
  from 
  localities 
  outside 
  of 
  the 
  mine 
  dis- 
  

   tricts, 
  run 
  from 
  1.58 
  to 
  6.57 
  per 
  cent. 
  Higher 
  percentages 
  would 
  be 
  

   found, 
  undoubtedly, 
  in 
  specimens 
  taken 
  from 
  the 
  actual 
  wall 
  rocks. 
  

   With 
  5 
  or 
  6 
  per 
  cent 
  of 
  magnetite 
  a 
  concentration 
  of 
  10 
  to 
  1 
  would 
  

   produce 
  the 
  leaner 
  ores 
  that 
  are 
  mined 
  in 
  this 
  region. 
  

  

  The 
  granites 
  and 
  syenites 
  of 
  the 
  Adirondack 
  iron 
  ore 
  districts 
  

   constitute 
  a 
  group 
  that 
  has 
  some 
  elements 
  of 
  relationship 
  with 
  

   the 
  gabbros 
  and 
  anorthosites. 
  This 
  is 
  manifested 
  by 
  a 
  similarity 
  

   in 
  important 
  features 
  of 
  chemical 
  composition 
  and 
  by 
  the 
  existence 
  

   of 
  transition 
  types. 
  The 
  ores 
  they 
  inclose 
  differ 
  mainly 
  in 
  the 
  

   titanium 
  content. 
  In 
  the 
  silicious 
  rocks, 
  the 
  titanium 
  has 
  com- 
  

   bined 
  with 
  lime 
  and 
  silica 
  to 
  form 
  titanite 
  which 
  has 
  been 
  held 
  

   mainly 
  in 
  the 
  body 
  of 
  the 
  rock 
  mass. 
  With 
  the 
  basic 
  magmas, 
  

   the 
  silica 
  has 
  been 
  entirely 
  taken 
  up 
  by 
  the 
  feldspathic 
  and 
  ferro- 
  

   magnesian 
  constituents 
  and 
  the 
  titanium 
  consequently 
  united 
  

   with 
  the 
  iron 
  and 
  has 
  been 
  concentrated 
  with 
  it 
  in 
  the 
  ore 
  bodies. 
  

   The 
  ores 
  in 
  the 
  acid 
  rocks 
  commonly 
  contain 
  a 
  fraction 
  of 
  one 
  per 
  

   cent 
  or 
  so 
  of 
  titanium 
  in 
  the 
  form 
  of 
  titanite. 
  

  

  The 
  pyritic 
  ores 
  that 
  are 
  found 
  in 
  the 
  Grenville 
  gneisses 
  con- 
  

   stitute 
  of 
  course 
  a 
  distinct 
  class. 
  They 
  may 
  be 
  ascribed 
  possibly 
  

  

  