﻿702 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  erosion 
  brought 
  the 
  ore 
  body 
  more 
  within 
  reach 
  of 
  surface 
  waters. 
  

   The 
  passage 
  of 
  limonite 
  into 
  hematite 
  is 
  probably 
  often 
  spontane- 
  

   ous,* 
  but 
  in 
  the 
  present 
  instance 
  it 
  is 
  sufficiently 
  accounted 
  for 
  

   by 
  the 
  movements 
  to 
  which 
  the 
  ore 
  has 
  been 
  subjected 
  in 
  con- 
  

   nection 
  with 
  the 
  folding 
  of 
  the 
  overlying 
  Potsdam 
  sandstone, 
  

   and 
  very 
  probably 
  also 
  by 
  movements 
  of 
  earlier 
  date. 
  The 
  

   highly 
  crystalline 
  hematites, 
  of 
  which 
  specimens 
  are 
  seen 
  in 
  

   mineral 
  collections, 
  occur 
  in 
  small 
  pockets, 
  none 
  of 
  which 
  have 
  

   come 
  under 
  the 
  writer's 
  observation. 
  They 
  may 
  be 
  older 
  bodies 
  

   which 
  have 
  been 
  subjected 
  to 
  the 
  same 
  metamorphism 
  as 
  have 
  

   the 
  Oswegatchie 
  rocks, 
  or 
  may 
  have 
  resulted 
  from 
  some 
  peculiar 
  

   conditions 
  of 
  precipitation. 
  In 
  this 
  connection 
  it 
  is 
  interesting 
  to 
  

   note 
  that 
  the 
  cavities 
  of 
  the 
  Old 
  Sterling 
  ore 
  are 
  lined 
  with 
  

   tabular 
  crystals 
  having 
  the 
  form 
  and 
  appearance 
  of 
  hematite. 
  

   Examination 
  of 
  a 
  large 
  number 
  of 
  specimens 
  has 
  shown 
  that 
  

   these 
  crystals 
  are 
  often 
  strongly 
  attracted 
  by 
  the 
  magnet 
  and 
  

   have 
  a 
  jet 
  black 
  streak. 
  They 
  dissolve 
  quite 
  readily 
  in 
  hydro- 
  

   chloric 
  acid, 
  and 
  the 
  solution 
  gives 
  a 
  nearly 
  black 
  precipitate 
  

   with 
  ammonic 
  hydrate.f 
  These 
  facts 
  indicate 
  that 
  the 
  crystals 
  

   are 
  pseudomorphs 
  of 
  magnetite 
  after 
  hematite. 
  This 
  change 
  has 
  

   doubtless 
  been 
  effected 
  by 
  solutions 
  of 
  a 
  reducing 
  nature, 
  which 
  

   have 
  also 
  deposited 
  rhombohedrons 
  of 
  siderite 
  and 
  the 
  well-known 
  

   millerite 
  within 
  the 
  cavities. 
  

  

  The 
  theory 
  of 
  ore 
  formation 
  thus 
  outlined, 
  points 
  to 
  a 
  source 
  

   of 
  iron, 
  explains 
  its 
  common 
  accumulation 
  on 
  bodies 
  of 
  granite, 
  

   and 
  gives 
  a 
  cause 
  for 
  the 
  alteration 
  of 
  the 
  granite. 
  It 
  also 
  

   accounts 
  for 
  the 
  structure 
  and 
  variation 
  of 
  the 
  ore 
  ; 
  and 
  not 
  only 
  

   for 
  the 
  irregular 
  shape 
  of 
  the 
  ore 
  bodies 
  but 
  also 
  for 
  their 
  linear 
  

   distribution 
  along 
  the 
  strike, 
  the 
  former 
  resulting 
  from 
  their 
  

   mode 
  of 
  concentration, 
  the 
  latter 
  from 
  their 
  derivation 
  from 
  the 
  

   apparently 
  interbedded 
  pyritiferous 
  layers. 
  

  

  With 
  the 
  form, 
  structure 
  and 
  distribution 
  of 
  the 
  ore 
  bodies 
  and 
  

   their 
  association 
  with 
  altered 
  granite 
  accounted 
  for, 
  there 
  remains 
  

   to 
  be 
  explained 
  only 
  the 
  constant 
  presence 
  of 
  sandstone 
  resting 
  

   upon 
  the 
  ore. 
  To 
  find 
  a 
  reason 
  for 
  this 
  it 
  is 
  necessary 
  to 
  con- 
  

   sider 
  what 
  were 
  the 
  topographic 
  conditions 
  at 
  the 
  beginning 
  of 
  

   the 
  Potsdam 
  period. 
  The 
  region 
  was 
  doubtless 
  of 
  rather 
  low 
  

  

  *W. 
  O. 
  Crosby, 
  Amer. 
  Geologist, 
  VIII, 
  p. 
  72. 
  

  

  t 
  Compare 
  Tschermak'a 
  Lehrbuch 
  der 
  Mineralogie, 
  p. 
  418. 
  

  

  