﻿232 
  J. 
  P. 
  Kimball 
  — 
  Genesis 
  of 
  Iron-ores 
  by 
  Isomorphous 
  

  

  place, 
  nor 
  vicariously 
  developed, 
  form 
  as 
  such 
  a 
  separate 
  class. 
  

   These, 
  however, 
  as 
  commonly 
  understood, 
  are 
  products 
  of 
  like 
  

   reactions 
  between 
  solutions 
  of 
  the 
  same 
  salts 
  in 
  circulating 
  

   acidulous 
  waters. 
  These 
  products, 
  though 
  sometimes 
  accumu- 
  

   lated 
  under 
  favorable 
  conditions 
  of 
  environment 
  and 
  topog- 
  

   raphy, 
  are 
  more 
  commonly 
  dissipated. 
  

  

  But 
  for 
  the 
  instability 
  of 
  hydrous 
  ferrous 
  carbonate, 
  it 
  might 
  

   be 
  assumed 
  to 
  be 
  transiently 
  produced 
  through 
  reactions 
  of 
  

   ferrous 
  salts 
  and 
  alkaline 
  mono-carbonates 
  in 
  solution, 
  not 
  far 
  

   from 
  loci 
  of 
  replacement 
  of 
  calcic 
  carbonate 
  by 
  siderite, 
  as 
  the 
  

   result 
  of 
  transmission 
  of 
  solutions 
  beyond 
  range 
  of 
  reducing 
  or 
  

   preserving 
  gases. 
  Visible 
  results 
  of 
  precipitation 
  and 
  sponta- 
  

   neous 
  oxidation 
  of 
  this 
  salt 
  into 
  ferric 
  hydrate 
  in 
  these 
  circum- 
  

   stances 
  on 
  the 
  one 
  hand, 
  and 
  direct 
  precipitation 
  of 
  ferric 
  

   hydrate 
  through 
  oxidation 
  on 
  the 
  other 
  hand, 
  are 
  identical. 
  

   Hence 
  the 
  two 
  processes 
  in 
  nature 
  can 
  seldom 
  be 
  distinguished. 
  

   The 
  general 
  proposition 
  may 
  now 
  be 
  advanced 
  — 
  that 
  de- 
  

   posits 
  of 
  concentrated 
  iron-ores 
  occur 
  far 
  more 
  extensively 
  as 
  

   pseudomorphous 
  replacements 
  than 
  has 
  hitherto 
  been 
  made 
  to 
  

   appear 
  ; 
  and 
  far 
  more 
  extensively 
  than 
  by 
  original 
  sedimenta- 
  

   tion 
  of 
  ferric 
  hydrate 
  in 
  hydrographic 
  basins 
  (if 
  indeed 
  impor- 
  

   tant 
  deposits 
  have 
  ever 
  been 
  formed 
  in 
  this 
  way), 
  followed 
  by 
  

   chemical 
  transmutations 
  so 
  far 
  as 
  essential 
  to 
  their 
  plausible 
  

   explanation 
  upon 
  theories 
  of 
  such 
  a 
  common 
  genesis. 
  In 
  the 
  

   present 
  place, 
  suffice 
  it 
  to 
  indicate 
  the 
  impracticability 
  of 
  con- 
  

   ceiving 
  of 
  sedimentation 
  of 
  ferriferous 
  material 
  without 
  sili- 
  

   ceous 
  alternations; 
  or 
  of 
  great 
  accumulations 
  of 
  non-ferrugin- 
  

   ous, 
  non-siliceous 
  sediments 
  at 
  all, 
  except 
  in 
  the 
  case 
  of 
  marine 
  

   limestones. 
  These 
  are 
  preeminently 
  the 
  habitat 
  or 
  reposi- 
  

   tories 
  of 
  massive 
  and 
  stratiform 
  iron-ores 
  of 
  all 
  descriptions. 
  

   Occurrences 
  of 
  iron-ores 
  in 
  this 
  relation 
  are 
  often, 
  and 
  indeed 
  

   generally, 
  without 
  transitions. 
  On 
  the 
  other 
  hand, 
  it 
  is 
  easy 
  

   to 
  conceive, 
  and 
  in 
  numerous 
  instances 
  to 
  prove, 
  effective 
  

   replacement 
  of 
  limestones 
  of 
  all 
  geologic 
  periods. 
  Among 
  the 
  

   great 
  number 
  of 
  important 
  stratiform 
  occurrences 
  of 
  iron-ores 
  

   — 
  that 
  stratified 
  ores 
  exist, 
  there 
  seems 
  to 
  me 
  much 
  reason 
  to 
  

   doubt 
  — 
  that 
  is, 
  homogeneous, 
  non-laminated 
  ores, 
  formed 
  in 
  

   thu 
  natural 
  order 
  of 
  succession 
  of 
  strata 
  between 
  which 
  they 
  

   are 
  enclosed, 
  and 
  along 
  with 
  which 
  they 
  are 
  commonly 
  as- 
  

   sumed, 
  prima 
  facie, 
  to 
  be 
  imbedded. 
  

  

  (1.) 
  As 
  deep-sea 
  chemical 
  precipitation 
  of 
  ferric 
  hydrate 
  is 
  out 
  

   of 
  the 
  question, 
  the 
  circumstance 
  of 
  the 
  presence 
  in 
  limestone 
  

   of 
  important 
  lenticular 
  deposits 
  of 
  this 
  material 
  or 
  its 
  deriva- 
  

   tives, 
  including 
  siderite 
  upon 
  one 
  theory 
  of 
  its 
  genesis, 
  would 
  

   suffice 
  to 
  prove 
  the 
  invasion 
  of 
  mid-sea 
  or 
  calcareous 
  sediments 
  

   by 
  at 
  least 
  suspended 
  material 
  from 
  sub- 
  serial 
  rock-decay. 
  

   This 
  condition 
  is 
  obviously 
  incompatible 
  with 
  the 
  more 
  impor- 
  

   tant 
  developments 
  of 
  Palaeozoic 
  iron-ores, 
  whose 
  relations 
  in 
  

  

  