﻿J. 
  J. 
  Stevenson 
  — 
  Origin 
  of 
  Formkohle. 
  221 
  

  

  The 
  hypothesis 
  that 
  Formkohle 
  is 
  transported 
  coal 
  or 
  peat 
  

   appears 
  to 
  be 
  a 
  generalization 
  based 
  on 
  conditions 
  in 
  portions 
  

   of 
  a 
  few 
  mines. 
  It 
  is 
  supported 
  merely 
  by 
  a 
  priori 
  reasoning 
  

   dependent 
  on 
  postulates, 
  which 
  themselves 
  are 
  hypothetical. 
  

   No 
  evidence 
  is 
  presented 
  to 
  show 
  that 
  the 
  supposed 
  process 
  of 
  

   removal 
  and 
  redeposition 
  is 
  probable, 
  though 
  such 
  evidence 
  is 
  

   necessary 
  ; 
  since 
  this 
  supposed 
  process 
  is 
  not 
  only 
  unlike 
  any- 
  

   thing 
  known 
  in 
  the 
  present 
  era 
  but 
  also 
  is 
  contradicted 
  by 
  all 
  

   that 
  is 
  known. 
  The 
  author 
  appears 
  to 
  have 
  been 
  so 
  convinced 
  

   by 
  his 
  logic 
  as 
  to 
  suppose 
  that 
  nothing 
  was 
  essential 
  beyond 
  

   mere 
  assertion 
  in 
  order 
  to 
  secure 
  immediate 
  acceptance. 
  But 
  

   one 
  should 
  be 
  grateful 
  for 
  the 
  delicate 
  reminder 
  that 
  sand 
  is 
  

   not 
  necessarily 
  autochthonous 
  when 
  it 
  happens 
  to 
  be 
  covered 
  

   by 
  a 
  forest 
  of 
  firs. 
  

  

  There 
  are 
  features 
  in 
  Formkohle 
  that 
  are 
  perplexing 
  and 
  no 
  

   one 
  explanation, 
  thus 
  far, 
  seems 
  to 
  be 
  sufficient. 
  But 
  it 
  is 
  cer- 
  

   tain 
  that 
  some 
  are 
  explicable 
  by 
  the 
  well-known 
  process 
  of 
  

   weathering, 
  which 
  is 
  protean 
  in 
  manifestations. 
  Potonie 
  well 
  

   says 
  that 
  for 
  determination 
  one 
  must 
  have 
  a 
  pile 
  of 
  freshly 
  

   mined 
  coal, 
  since 
  exposure 
  to 
  the 
  weather 
  changes 
  lump 
  to 
  fine 
  

   coal. 
  Weathering 
  may 
  be 
  induced 
  by 
  change 
  in 
  character 
  or 
  

   thickness 
  of 
  cover 
  as 
  well 
  as 
  by 
  disturbance, 
  which 
  by 
  crush- 
  

   ing 
  increases 
  the 
  porosity 
  and 
  aids 
  access 
  of 
  surface 
  water. 
  

   The 
  Emma 
  mine 
  in 
  the 
  Zeitz 
  district 
  is 
  that 
  on 
  which 
  the 
  

   transport 
  hypothesis 
  had 
  its 
  birth 
  ; 
  but 
  even 
  there 
  the 
  influence 
  

   of 
  changing 
  cover 
  and 
  of 
  increasing 
  disturbance 
  is 
  distinct. 
  

   Where 
  the 
  cover 
  is 
  only 
  slightly 
  pervious 
  clay, 
  the 
  coal 
  is 
  

   lump 
  ; 
  but 
  pulverulent 
  coal 
  appears 
  in 
  greater 
  and 
  greater 
  pro- 
  

   portion 
  with 
  change 
  of 
  roof 
  to 
  pervious 
  diluvium 
  and 
  with 
  

   increasing 
  disturbance. 
  The 
  relations 
  are 
  exposed 
  fully 
  in 
  that 
  

   extensive 
  stripping. 
  Stohr's 
  section 
  is 
  equally 
  to 
  the 
  point. 
  

   The 
  upper 
  bench 
  is 
  lump 
  coal 
  and 
  has 
  a 
  roof 
  of 
  clay 
  to 
  sand- 
  

   stone 
  ; 
  it 
  is 
  best 
  under 
  the 
  clay. 
  The 
  lower 
  bench, 
  separated 
  

   by 
  a 
  parting, 
  is 
  fine 
  coal. 
  Its 
  cover 
  is 
  very 
  thin 
  and 
  represents 
  

   a 
  period 
  during 
  which 
  the 
  underlying 
  coal 
  or 
  peat 
  was 
  exposed 
  

   to 
  the 
  action 
  of 
  leaching 
  waters. 
  Heusler,* 
  in 
  describing 
  the 
  

   Cologne 
  area, 
  says 
  that 
  the 
  coal 
  often 
  has 
  a 
  diluvial 
  cover, 
  

   through 
  which 
  pluvial 
  waters 
  gain 
  access 
  and 
  pass 
  even 
  to 
  the 
  

   bottom 
  of 
  the 
  mass, 
  affecting 
  the 
  quality. 
  In 
  that 
  region, 
  the 
  

   top 
  portion 
  of 
  the 
  deposit 
  has 
  been 
  converted 
  into 
  Schmier- 
  

   kohle, 
  a 
  soft, 
  greasy 
  substance, 
  which 
  is 
  said 
  to 
  yield 
  a 
  greater 
  

   proportion 
  of 
  distillation 
  products 
  than 
  is 
  obtained 
  from 
  the 
  

   underlying 
  coal. 
  Potonie 
  has 
  suggested 
  that 
  this 
  Schmier- 
  

   kohle 
  is 
  allied 
  to 
  Schwelkohle 
  ; 
  but 
  it 
  is 
  unquestionably 
  due 
  to 
  

   weathering 
  and 
  the 
  ash 
  as 
  well 
  as 
  moisture 
  content 
  decreases 
  

  

  *C. 
  Heusler, 
  " 
  Be'schreibung 
  des 
  Bergreviers 
  Briihl-Unkel 
  .und 
  des 
  Nieder- 
  

   rheinischen 
  Braunkohlen-beckens," 
  Bonn, 
  1897, 
  pp. 
  149, 
  163. 
  

  

  