﻿J. 
  J. 
  Stevenson 
  — 
  Origin 
  of 
  FormJcofde. 
  217 
  

  

  in 
  tar 
  and 
  bitumen 
  than 
  the 
  adjoining 
  coal, 
  which 
  is 
  recognized 
  

   by 
  that 
  author 
  as 
  autochthonous. 
  He 
  finds 
  that 
  the 
  alleged 
  

   separation 
  of 
  original 
  materials 
  according 
  to 
  specific 
  gravity 
  

   has 
  not 
  taken 
  place, 
  the 
  specifically 
  lighter 
  coal 
  being 
  for 
  the 
  

   most 
  part 
  in 
  the 
  lower 
  part 
  of 
  the 
  coal 
  deposit. 
  In 
  districts 
  

   with 
  Klarkohle, 
  bitumen-rich 
  and 
  bitumen-poor 
  coal 
  alternate 
  

   just 
  as 
  they 
  do 
  in 
  districts 
  containing 
  knorpelig 
  coal. 
  Even 
  

   in 
  the 
  Emma 
  mine, 
  the 
  pyropissite 
  layers 
  are 
  regular. 
  Still 
  

   more 
  important 
  is 
  the 
  fact 
  that 
  on 
  the 
  southeastern 
  side 
  of 
  the 
  

   region, 
  on 
  the 
  outcrop 
  of 
  the 
  beds 
  in 
  that 
  direction, 
  as 
  well 
  as 
  

   in 
  independent 
  basins, 
  analogous 
  to 
  those 
  of 
  the 
  northwestern 
  

   side, 
  one 
  finds 
  a 
  bitumen-rich 
  coal 
  with 
  nests 
  of 
  pyropissite. 
  

  

  Raefler 
  believes 
  that 
  wax-producing 
  plants 
  gave 
  the 
  pyropis- 
  

   site 
  material 
  ; 
  by 
  decay 
  of 
  cellulosic 
  and 
  other 
  constituents, 
  

   there 
  would 
  be 
  enrichment 
  of 
  waxy 
  matter, 
  but 
  unless 
  the 
  wax 
  

   were 
  already 
  present 
  no 
  pyropissite 
  or 
  Schwelkohle 
  could 
  be 
  

   formed. 
  The 
  careful 
  chemical 
  studies 
  by 
  Graefe* 
  are 
  import- 
  

   ant 
  in 
  this 
  connection. 
  The 
  prevalent 
  opinion 
  has 
  been 
  that 
  

   pyropissite 
  is 
  probably 
  a 
  fossil 
  resin 
  ; 
  but 
  in 
  consequence 
  of 
  the 
  

   contrast 
  between 
  that 
  substance 
  and 
  retinite, 
  Graefe 
  cannot 
  

   regard 
  resin 
  as 
  the 
  source 
  of 
  bitumen. 
  After 
  consideration 
  of 
  

   the 
  gravity, 
  fusion 
  point, 
  optical 
  conduct, 
  the 
  characteristics 
  of 
  

   the 
  tar-output 
  and 
  of 
  the 
  acids, 
  he 
  concludes 
  that 
  wax-like 
  

   secretions 
  were 
  in 
  chief 
  part 
  the 
  original 
  material 
  of 
  pyropissite. 
  

  

  Potonie's 
  hypothesis 
  is 
  an 
  assertion 
  that 
  by 
  structure 
  and 
  

   composition 
  Rieselkohle 
  — 
  Form- 
  or 
  Klarkohle 
  — 
  is 
  proved 
  to 
  

   be 
  autochthonous 
  material 
  transported 
  by 
  running 
  water 
  and 
  

   redeposited, 
  measurably 
  under 
  selective 
  influence 
  of 
  gravity. 
  

  

  Running 
  water, 
  aided 
  by 
  gravity, 
  does 
  exercise 
  selective 
  

   influence 
  upon 
  transported 
  materials. 
  The 
  process 
  is 
  continu- 
  

   ous 
  along 
  streams, 
  and 
  it 
  is 
  so 
  characteristic 
  that 
  one 
  finds 
  no 
  

   difficulty 
  in 
  recognizing 
  stream-action, 
  even 
  the 
  courses 
  of 
  

   streams 
  in 
  the 
  older 
  rocks. 
  Particles 
  of 
  coal 
  are 
  like 
  other 
  

   debris. 
  The 
  writer, 
  in 
  following 
  streams 
  within 
  areas 
  of 
  coal 
  

   mining, 
  has 
  often 
  seen 
  patches 
  of 
  mud 
  and 
  sand 
  with 
  much 
  

   fine 
  coal, 
  which 
  had 
  accumulated 
  in 
  the 
  curves. 
  Students 
  of 
  

   coal- 
  bearing 
  rocks, 
  in 
  every 
  period, 
  have 
  observed 
  fragments 
  

   of 
  coal 
  in 
  sandstones, 
  clays, 
  even 
  in 
  limestones. 
  But 
  such 
  

   occurrences 
  have 
  no 
  significance 
  in 
  this 
  connection, 
  for 
  here 
  

   one 
  has 
  to 
  consider 
  great 
  deposits 
  of 
  commercially 
  clean 
  coal, 
  

   not 
  patches 
  of 
  sand 
  or 
  clay 
  containing 
  more 
  or 
  less 
  of 
  distinctly 
  

   transported 
  coal. 
  

  

  The 
  accumulation 
  of 
  Knorpel- 
  and 
  Eormkohle 
  was 
  contem- 
  

   poraneous, 
  in 
  the 
  strictest 
  sense 
  of 
  that 
  term, 
  at 
  many 
  places 
  in 
  

   Sachsen. 
  Both 
  types, 
  at 
  times, 
  are 
  continuous 
  in 
  a 
  bed 
  or 
  

   bench, 
  passage 
  from 
  one 
  to 
  the 
  other 
  being 
  so 
  gradual 
  that 
  

  

  *E. 
  Graefe, 
  "Bitumen 
  und 
  Ketinit," 
  Braunkohle, 
  vol. 
  vi, 
  p. 
  226. 
  

  

  