﻿J. 
  J. 
  Stevenson 
  — 
  Oi'igin 
  of 
  Formkohle. 
  211 
  

  

  Art. 
  XIX. 
  — 
  Origin 
  of 
  Fornikohle 
  ; 
  by 
  John. 
  J. 
  Stevenson. 
  

  

  A 
  peculiar 
  type 
  of 
  brown 
  coal, 
  called 
  Form-, 
  Fein-, 
  Klar- 
  

   or 
  Kieselkohle, 
  occurs 
  in 
  parts 
  of 
  Sachsen, 
  Brandenburg, 
  as 
  

   well 
  as 
  in 
  the 
  Cologne 
  region, 
  and 
  similar 
  coal 
  is 
  found 
  in 
  

   Texas. 
  It 
  is 
  an 
  incoherent 
  brown 
  coal, 
  apparently 
  without 
  

   cementing 
  material; 
  it 
  may 
  constitute 
  the 
  whole 
  of 
  a 
  bed 
  at 
  

   one 
  locality, 
  while 
  elsewhere 
  in 
  the 
  same 
  bed 
  only 
  Knabben- 
  or 
  

   Knorpelkohle, 
  lump 
  coal, 
  is 
  found 
  ; 
  or 
  it 
  may 
  be 
  confined 
  to 
  a 
  

   single 
  bench, 
  even 
  to 
  a 
  portion 
  of 
  a 
  bench. 
  Usually 
  it 
  is 
  con- 
  

   verted 
  into 
  briquets 
  for 
  fuel, 
  but 
  in 
  Sachsen 
  it 
  is 
  associated 
  

   with 
  pyropissite, 
  which 
  is 
  utilized 
  in 
  the 
  paraffin 
  industry. 
  

   This 
  type 
  of 
  brown 
  coal 
  has 
  acquired 
  new 
  interest 
  to 
  geologists 
  

   because 
  of 
  recent 
  discussions 
  respecting 
  its 
  origin 
  and 
  mode 
  of 
  

   accumulation. 
  Potonie* 
  has 
  asserted 
  that 
  it 
  is 
  secondarily- 
  

   allochthonous 
  in 
  origin, 
  signifying 
  by 
  that 
  term 
  that 
  it 
  must 
  % 
  

   be 
  regarded 
  as 
  an 
  autochthonous 
  coal, 
  removed 
  from 
  its 
  original 
  

   place 
  of 
  accumulation 
  and 
  redeposited. 
  The 
  transporting 
  agent 
  

   was 
  running 
  water 
  and 
  the 
  process 
  of 
  redeposition 
  was 
  affected 
  

   by 
  selective 
  influence 
  of 
  gravity. 
  

  

  Potonie 
  remarks 
  that 
  autochthonous 
  and 
  primarily-allochthon- 
  

   ous 
  coals 
  are 
  hard 
  and 
  homogeneous 
  ; 
  if 
  they 
  have 
  numerous 
  

   cracks, 
  they 
  be 
  Rieselkohle, 
  but 
  in 
  that 
  case 
  the 
  fragments 
  fit 
  

   together 
  as 
  in 
  a 
  mosaic 
  and 
  the 
  clefts 
  are 
  commonly 
  filled 
  with 
  

   inorganic 
  material, 
  such 
  as 
  calcite. 
  The 
  coal 
  had 
  been 
  Knab- 
  

   benkohle 
  ; 
  he 
  had 
  seen 
  such 
  coal 
  in 
  the 
  Oligocene 
  of 
  Sachsen. 
  

   The 
  condition 
  is 
  wholly 
  different 
  in 
  coal 
  of 
  secondarily- 
  

   allochthonous 
  origin, 
  as 
  is 
  seen 
  in 
  the 
  Emma 
  mine, 
  near 
  

   Streckau 
  in 
  Sachsen. 
  There 
  the 
  individual 
  pieces 
  are 
  less 
  

   closely 
  united 
  and 
  the 
  larger 
  ones 
  are 
  embedded 
  in 
  fine 
  

   material, 
  so 
  that, 
  when 
  struck 
  by 
  a 
  pick, 
  the 
  mass 
  falls 
  into 
  a 
  

   dustlike 
  or 
  crumblike 
  heap. 
  Pebbles 
  of 
  coal 
  are 
  rare 
  in 
  such 
  

   deposits, 
  because 
  the 
  brittle 
  coal 
  would 
  break 
  into 
  angular 
  

   fragments 
  during 
  transport. 
  This 
  is 
  proved 
  by 
  the 
  constant 
  

   occurrence 
  of 
  crumb 
  or 
  dust 
  coal. 
  The 
  farther 
  the 
  coal 
  w 
  T 
  as 
  

   transported, 
  by 
  so 
  much 
  finer 
  would 
  be 
  the 
  particles 
  ; 
  thus 
  one 
  

   finds 
  at 
  times, 
  as 
  at 
  the 
  Voss 
  stripping 
  near 
  Deuben, 
  very 
  fine 
  

   coal 
  throughout, 
  evidently 
  dustlike 
  when 
  deposited. 
  In 
  this 
  

   connection, 
  Potonie 
  remarks 
  that 
  this 
  specific 
  structure 
  would 
  

   disappear 
  with 
  increasing 
  age 
  of 
  the 
  coal, 
  as 
  advancing 
  self- 
  

   decomposition 
  would 
  induce 
  homogeneity. 
  

  

  To 
  determine 
  whether 
  or 
  not 
  a 
  coal 
  is 
  secondarily-allochthon- 
  

   ous 
  in 
  origin, 
  one 
  must 
  have 
  an 
  unweathered 
  pile 
  for 
  study, 
  

   since 
  weathered 
  autochthonous 
  is 
  very 
  similar 
  to 
  the 
  other. 
  

  

  *H. 
  Potonie, 
  "Die 
  Entstehung 
  der 
  Steinkohle," 
  5te 
  Aufl. 
  1910, 
  pp. 
  137- 
  

   142, 
  205-211. 
  

  

  