﻿214 
  J. 
  J. 
  Stevenson 
  — 
  Origin 
  of 
  Formkolile. 
  

  

  merit 
  in 
  recent 
  peats. 
  "When 
  the 
  upper 
  part 
  of 
  an 
  already 
  

   hard 
  bed 
  of 
  brown 
  coal 
  is 
  so 
  exposed 
  to 
  the 
  atmosphere 
  that 
  a 
  

   greater 
  decomposition 
  becomes 
  possible 
  and 
  the 
  coal 
  becomes 
  

   a 
  Schmierkohle, 
  an 
  enrichment 
  of 
  the 
  same 
  kind 
  must 
  occur. 
  

   But 
  in 
  so 
  far 
  as 
  Potonie* 
  has 
  investigated 
  the 
  conditions, 
  evidence 
  

   favors 
  the 
  belief, 
  that 
  separation 
  of 
  the 
  substances 
  by 
  running 
  

   water 
  under 
  influence 
  of 
  gravity 
  explains 
  the 
  difference 
  in 
  

   structure 
  and 
  composition. 
  

  

  Potonie's 
  conclusions 
  were 
  opposed 
  by 
  Raefler,* 
  who 
  based 
  

   his 
  arguments 
  upon 
  a 
  close 
  study 
  of 
  more 
  than 
  one 
  hundred 
  

   mines 
  and 
  strippings 
  within 
  that 
  part 
  of 
  Sachsen 
  whence 
  

   Potonie 
  had 
  drawn 
  his 
  illustrations. 
  He 
  recognizes 
  that 
  when 
  

   one 
  considers 
  the 
  characteristics 
  of 
  Potonie's 
  typical 
  autoch- 
  

   thonous 
  coal 
  and 
  contrasts 
  them 
  with 
  those 
  of 
  that 
  author's 
  

   secondarily-allochthonous, 
  the 
  temptation 
  to 
  seek 
  different 
  

   modes 
  of 
  origin 
  is 
  very 
  great 
  ; 
  but 
  he 
  maintains 
  that 
  one 
  must 
  

   not 
  neglect 
  consideration 
  of 
  certain 
  agents 
  which 
  are 
  efficient 
  

   in 
  causing 
  changes 
  in 
  structure. 
  

  

  The 
  character, 
  constitution 
  and 
  thickness 
  of 
  materials 
  cover- 
  

   ing 
  the 
  coal 
  are 
  very 
  important. 
  There 
  is 
  one 
  workable 
  coal 
  

   bed 
  in 
  the 
  district 
  under 
  review, 
  with 
  extreme 
  thickness 
  of 
  15 
  

   to 
  20 
  meters 
  and 
  accompanied 
  locally 
  by 
  one 
  or 
  more 
  beds 
  

   higher 
  in 
  the 
  section. 
  The 
  whole 
  region 
  is 
  covered 
  with 
  

   Diluvium, 
  which 
  rests 
  now 
  on 
  Lower 
  Oligocene 
  sands 
  and 
  

   clays, 
  but 
  again 
  directly 
  on 
  the 
  coal. 
  Under 
  clay 
  cover, 
  the 
  

   coal 
  is 
  Knorpel, 
  L 
  e., 
  lump 
  coal 
  ; 
  under 
  sand, 
  it 
  is 
  Klar 
  or 
  in- 
  

   coherent 
  coal. 
  He 
  gives 
  many 
  instances 
  showing 
  the 
  con- 
  

   ditions 
  as 
  shown 
  in 
  a 
  single 
  stripping. 
  The 
  manner 
  in 
  which 
  

   the 
  roof 
  material 
  originated 
  is 
  important. 
  A 
  thick 
  cover 
  of 
  

   ice 
  had 
  serious 
  effect 
  on 
  coal 
  separated 
  from 
  it 
  by 
  only 
  a 
  thin 
  

   layer 
  of 
  Oligocene. 
  Pressure, 
  thrust 
  and 
  the 
  water 
  from 
  

   melting 
  ice 
  combined 
  to 
  bring 
  about 
  change. 
  The 
  proof 
  is 
  

   beyond 
  dispute 
  in 
  all 
  mines 
  where 
  the 
  coal 
  directly 
  underlies 
  

   Diluvium, 
  for 
  there 
  the 
  coal 
  is 
  very 
  different 
  from 
  that 
  in 
  

   those 
  where 
  Tertiary 
  beds 
  form 
  the 
  roof. 
  Even 
  in 
  the 
  Emma 
  

   stripping, 
  on 
  which 
  the 
  doctrine 
  of 
  origin 
  was 
  based, 
  coal 
  

   covered 
  by 
  Tertiary 
  rocks 
  is 
  Knorpel, 
  but 
  under 
  other 
  

   cover 
  it 
  is 
  not. 
  Following 
  from 
  south 
  to 
  north 
  the 
  gradual 
  

   disappearance 
  of 
  Tertiary 
  cover 
  in 
  that 
  great 
  open 
  work, 
  

   one 
  sees 
  the 
  equally 
  gradual 
  passage 
  from 
  lump 
  coal 
  to, 
  

   in 
  the 
  area 
  of 
  diluvial 
  contact, 
  a 
  typical 
  Pieselkohle. 
  The 
  

   same 
  condition 
  appears 
  in 
  other 
  mines 
  described 
  by 
  Raefler, 
  

   whose 
  notes 
  are 
  in 
  such 
  detail 
  as 
  to 
  leave 
  no 
  room 
  for 
  doubt. 
  

   Even 
  thickness 
  of 
  cover 
  seems 
  to 
  have 
  far 
  reaching 
  influence, 
  

   for 
  in 
  the 
  old 
  stripping 
  near 
  Fichtenhainichen 
  as 
  well 
  as 
  in 
  

  

  * 
  F. 
  Raefler, 
  " 
  Die 
  Ensteliung 
  der 
  Bratmkohlenlager 
  zwischen 
  Alteuburg 
  

   und 
  Weissenfels." 
  Jena, 
  1911, 
  pp. 
  9, 
  17-30, 
  50-70. 
  

  

  