HISTORY  OF  PETROLEUM  OR  ROCK  OIL. 
539 
la  nature  these  various  modes  of  decomposition  often  go 
on  together,  or  intervene  at  different  stages  in  the  decomposi- 
tion of  the  same  mass  ;  they  are,  besides,  seldom  so  complete 
as  we  have  represented  them.  The  first  process  results  in  the 
formation  of  vegetable  mould,  which  always  retains  portions  of 
carbon  and  hydrogen ;  while  the  incomplete  operation  of  the 
processes  II.,  III.  and  IV.  give  rise,  to  peat,  lignite,  brown 
coal,  bituminous  coal,  and  pyroschists,  in  all  of  which  the  pro- 
portion of  the  oxygen  is  much  less  than  the  hydrogen,  so  that 
their  composition  may  be  approximately  represented  by  mixtures 
of  hydrocarbons  with  vegetable  fibre.  The  following  results 
have  been  selected  from  a  great  number  of  analyses  by  various 
chemists,  and  are  for  the  most  part  taken  from  Bischof's 
"  Chemical  Geology"  (vol.  i.  cap.  xv.)  The  nitrogen,  which  in 
most  cases  was  included  in  the  oxygen  with  the  analysis,  has 
been  disregarded,  and  the  oxygen  and  hydrogen,  for  the  sake  of 
comparison,  have  been  calculated  for  twenty-four  equivalents  of 
carbon  : — 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
Vegetable  fibre  or  cellulose 
Wood,  mean  composition 
Peat  (Vaux)  .... 
Ditto  (Regnault) 
Brown  coal  (Schrotter) 
Ditto    do.  (Woskresensky) 
Lignite  (Vaux)  .... 
Do.,  passing  into  mineral  resin  (Regnault) 
Bituminous  coal         .       .  ditto 
Ditto  do.         .       .  ditto 
Ditto  do.         .       .  ditto 
Ditto  do.         .       .  ditto 
Ditto  do,  (Kiihnert  and  Grager) 
Ditto  do.  (mean  comp.)  (Johnston 
Albert  coal  (Wetherell) 
Asphalt,  Auvergne  .... 
Ditto,  Naples.  .... 
Ditto,  Bastennes  .... 
Elastic  bitumen,  Derbyshire  (Johnston) 
Bitumen  of  Idria  .... 
Petroleum  and  naphtha 
^24^-20^20 
^24^-18-4^16-4 
^24H144^10 
^24  ^14  4  ^96 
^24^14-3^10-6 
^24H13^7-6 
^24^11-3^6.4 
C74H150,3 
C24H10^3-3 
C24Hl(A-7 
C24H8-4^1-2 
C24H8^0'9 
^24H74^1-3 
C24H9^2-^4 
C24H159^1-6 
^24^17-7  ^22 
C24H14;602 
^24H16^0-7 
^24^-22^0-3 
C24H8 
^24H24 
