﻿ADIRONDACK 
  MAGNETIC 
  IRON 
  ORES 
  15 
  

  

  being 
  interbedded 
  with 
  limestone 
  and 
  hornblende, 
  mica 
  and 
  

   pyroxene 
  schists. 
  The 
  St 
  Lawrence 
  county 
  quartzites 
  contain 
  

   feldspar 
  and 
  mica, 
  but 
  are 
  not 
  so 
  graphitic 
  as 
  those 
  of 
  Essex 
  

   county, 
  where 
  they 
  have 
  been 
  exploited. 
  

  

  The 
  quartzites 
  are 
  no 
  doubt 
  ancient 
  sandstones 
  that 
  have 
  been 
  

   hardened 
  by 
  recrystallization 
  of 
  the 
  quartz 
  particles; 
  they 
  may 
  be 
  

   considered, 
  therefore, 
  to 
  represent 
  the 
  extreme 
  silicious 
  phase 
  of 
  

   Precambric 
  sedimentation. 
  

  

  Gneisses 
  of 
  undetermined 
  relationship. 
  The 
  recent 
  work 
  in 
  the 
  

   Adirondack 
  region 
  has 
  disclosed 
  the 
  existence 
  of 
  certain 
  gneisses 
  

   of 
  obscure 
  character. 
  While 
  more 
  detailed 
  investigation 
  may 
  

   resolve 
  them 
  into 
  elements 
  which 
  can 
  be 
  classed 
  with 
  the 
  igneous 
  

   or 
  sedimentary 
  series, 
  they 
  have 
  been 
  found 
  so 
  far 
  to 
  have 
  no 
  well 
  

   defined 
  connection 
  with 
  either. 
  

  

  Saranac 
  formation. 
  The 
  principal 
  area 
  of 
  these 
  gneisses 
  seems 
  

   to 
  be 
  on 
  the 
  northern 
  borders 
  in 
  Clinton 
  and 
  Franklin 
  counties. 
  

   Professor 
  Cushing 
  has 
  described 
  a 
  belt 
  that 
  extends 
  along 
  the 
  

   Paleozoic 
  contact 
  for 
  a 
  distance 
  of 
  70 
  miles. 
  The 
  rocks 
  are 
  mainly 
  

   red 
  acid 
  gneisses, 
  composed 
  of 
  alkali 
  feldspar, 
  which 
  is 
  usually 
  

   microperthite, 
  and 
  quartz, 
  with 
  small 
  amounts 
  of 
  hornblende 
  and 
  

   biotite. 
  They 
  are 
  thus 
  mineralogically 
  related 
  to 
  the 
  granites, 
  but 
  

   differ 
  from 
  the 
  latter 
  in 
  their 
  textures 
  which 
  are 
  often 
  finely 
  gran- 
  

   ular 
  or 
  without 
  the 
  definite 
  arrangement 
  that 
  characterizes 
  igneous 
  

   rocks 
  in 
  their 
  original 
  state 
  of 
  consolidation 
  from 
  a 
  molten 
  condi- 
  

   tion. 
  Besides 
  the 
  acid 
  gneisses 
  a 
  gray 
  variety 
  consisting 
  of 
  pyrox- 
  

   ene 
  and 
  feldspar 
  (orthoclase 
  and 
  plagioclase) 
  and 
  dark 
  hornblende 
  

   gneisses 
  or 
  amphibolites 
  occur 
  as 
  bands 
  or 
  larger 
  masses. 
  Of 
  the 
  

   Grenville 
  rocks 
  there 
  are 
  very 
  few 
  exposures 
  throughout 
  the 
  entire 
  

   belt. 
  The 
  gneisses 
  as 
  a 
  whole 
  correspond 
  in 
  composition 
  quite 
  

   closely 
  to 
  a 
  series 
  of 
  igneous 
  rocks 
  grading 
  from 
  granites 
  through 
  

   syenites 
  and 
  diorites 
  to 
  gabbros, 
  though 
  the 
  comparison 
  has 
  not 
  

   been 
  substantiated 
  fully 
  by 
  chemical 
  analyses. 
  

  

  Professor 
  Cushing 
  is 
  inclined 
  to 
  regard 
  them 
  as 
  an 
  older 
  series 
  

   than 
  the 
  recognized 
  intrusives 
  and 
  has 
  proposed 
  to 
  group 
  them 
  

   collectively 
  as 
  the 
  Saranac 
  formation, 
  a 
  name 
  suggested 
  by 
  their 
  

   occurrence 
  along 
  Saranac 
  river. 
  Concerning 
  their 
  possible 
  posi- 
  

   tion 
  among 
  the 
  Precambric 
  rocks 
  of 
  the 
  Adirondacks, 
  Professor 
  

   Cushing 
  points 
  to 
  the 
  similarity 
  which 
  they 
  show 
  to 
  the 
  basal 
  

   gneisses 
  in 
  other 
  regions 
  and 
  more 
  specially 
  the 
  so 
  called 
  Ottawa 
  

   gneiss 
  of 
  Canada; 
  while 
  he 
  seems 
  to 
  favor 
  the 
  view 
  that 
  they 
  

   represent 
  the 
  original 
  floor 
  on 
  which 
  the 
  Grenville 
  rocks 
  have 
  been 
  

   deposited, 
  he 
  does 
  not 
  regard 
  the 
  proofs 
  for 
  this 
  explanation 
  to 
  

   be 
  fully 
  established. 
  

  

  