﻿ECONOMIC 
  GEOLOGY 
  

  

  215 
  

  

  species 
  and 
  varieties. 
  The 
  following 
  tabular 
  arrangement 
  shows 
  

   the 
  natural 
  grouping 
  of 
  the 
  species 
  : 
  

  

  Chemical 
  name 
  Mineralogical 
  species 
  and 
  common 
  names 
  

  

  ^T^ 
  . 
  J 
  ^ 
  . 
  -, 
  r 
  Magnetite. 
  

  

  ^ 
  h 
  erne 
  and 
  ferrous 
  oxides. 
  ® 
  

  

  -r, 
  ^ 
  . 
  • 
  1 
  X 
  • 
  "! 
  Magnetic 
  iron 
  ore. 
  

  

  Proto-sesquioxide 
  of 
  iron, 
  i 
  ^ 
  

  

  ^Titaniferous 
  iron 
  ore. 
  

  

  /^Hematite. 
  

   I 
  Eed 
  hematite. 
  

  

  72.4 
  % 
  of 
  iron. 
  

  

  .^ 
  . 
  , 
  J 
  Anhydrous 
  ferric 
  oxide, 
  j 
  Specular 
  ore. 
  

  

  Sesquioxide 
  of 
  iron. 
  | 
  Clinton 
  ore. 
  — 
  Fossil 
  ore. 
  

  

  70 
  % 
  of 
  iron. 
  [ 
  Eed 
  ochre. 
  

  

  Hydrated 
  ferric 
  oxide. 
  

  

  Sesquioxide 
  of 
  iron. 
  

   60 
  % 
  of 
  iron. 
  

  

  Ferrous 
  carbonate. 
  

  

  Carbonates 
  

  

  f 
  Limonite. 
  

   ! 
  Brown 
  hematite. 
  

   I 
  Brown 
  ochre. 
  

   I 
  Bog 
  iron 
  ore. 
  

  

  f 
  Siderite. 
  

  

  I 
  Carbonate 
  ore. 
  

  

  Carbonate 
  of 
  iron. 
  Spathic 
  i 
  Clay 
  iron 
  stone. 
  

   48% 
  of 
  iron. 
  Iron 
  ore 
  I 
  

  

  I 
  ^ 
  White 
  Horse.' 
  

  

  A 
  general 
  law 
  of 
  occurrence 
  of 
  iron 
  ores 
  is 
  that 
  certain 
  species 
  

   occur 
  in, 
  or 
  are 
  characteristic 
  of, 
  definite 
  geological 
  horizons. 
  

   For 
  example, 
  the 
  magnetic 
  iron 
  ores 
  and 
  the 
  red 
  hematite 
  are 
  

   found 
  in 
  the 
  crystalline 
  rock 
  areas 
  of 
  the 
  Pre-cambrian 
  ; 
  the 
  

   fossil 
  ore, 
  the 
  limonite 
  or 
  brown 
  hematite 
  and 
  the 
  carbonate 
  are 
  

   found 
  in 
  the 
  Palaeozoic 
  rocks; 
  and 
  the 
  bog 
  iron 
  ore 
  in 
  the 
  more 
  

   recent 
  formations 
  of 
  Tertiary 
  and 
  Post 
  Tertiary 
  ages. 
  There 
  are, 
  

   as 
  might 
  be 
  expected, 
  many 
  exceptions; 
  but 
  in 
  the 
  greater 
  num- 
  

   ber 
  of 
  these 
  apparently 
  exceptional 
  cases, 
  the 
  surface 
  alteration, 
  

   due 
  to 
  weathering 
  or 
  other 
  atmospheric 
  agencies, 
  explains 
  the 
  

   occurrence. 
  

  

  This 
  relation 
  between 
  the 
  geological 
  formation 
  and 
  the 
  mineral- 
  

   ogical 
  species 
  or 
  kinds 
  of 
  iron 
  ore 
  indicates 
  the 
  areas 
  in 
  which 
  

   they 
  may 
  occur, 
  and 
  determines 
  roughly 
  their 
  limits. 
  Hence, 
  a 
  

   geological 
  map 
  of 
  the 
  state 
  shows 
  approximately 
  correct 
  bound- 
  

   aries 
  of 
  the 
  several 
  iron-ore 
  districts, 
  and 
  is, 
  as 
  it 
  were, 
  an 
  iron 
  

  

  