HISTORY  OF  PETROLEUM  OR  ROCK  OIL. 
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The  sources  of  petroleum  and  mineral  pitch  in  Europe  and 
in  Asia  are  for  the  most  part,  like  those  just  named,  confined 
to  rocks  of  newer  secondary  and  tertiary  age,  though  they  are 
not  wanting  in  the  palaeozoic  strata,  which  in  Canada  and  the 
United  States  furnish  such  abundant  supplies  of  petroleum.  In 
the  great  palaeozoic  basin  of  North  America,  bitumen,  either  in 
a  liquid  or  solid  state,  is  found  in  the  strata  at  several  different 
horizons.    The  forms  in  which  it  now  occurs  depend  in  great 
measure  upon  the  presence  or  absence  of  atmospheric  oxygen, 
since  by  oxidation  and  volatilisation  the  naphtha  or  petroleum,  as 
we  have  already  explained,  becomes  slowly  changed  into  asphalt 
or  mineral  pitch,  which  is  solid  at  ordinary  temperature.  It 
would  even  appear  that  by  a  continuance  of  the  same  action  the 
bitumen  may  lose  its  fusibility  and  solubility,  and  become  con- 
verted into  a  coal- like  matter.     Thus,  in  the  calciferous  sand- 
rock  in  New  York  a  black  substance,  which  has  been  called  an- 
thracite, occurs  in  cavities  with  crystals  of  bitter  spar  and 
quartz.    It  sometimes  coats  these  crystals  or  the  walls  of  the 
cavities,  and  at  other  times  appears  in  the  form  of  buttons 
or  drops,  evidently,  according  to  Mr.  Vanuxem,  having  been 
introduced  into  these  cavities  in   a  liquid  state,  and  subse- 
quently hardened  as  a  layer  above  the  crystals  which  have  con- 
formed to  them,  showing  that  this  coal-like  matter  was  once  in 
a  plastic  state.     It  is  very  pulverulent,  brittle,  of  a  shining 
black,  and  according  to  Vanuxem,  yielded  but  little  ash  and  11  £ 
per  cent,  of  volatile  matter,  which  he  regarded  as  water  (Van- 
uxem, Geology  of  New  York,  iii.  33.)    A  similar  material 
occurs  in  the  Quebec  group  in  Canada,  the  equivalent  of  the 
calciferous  sandrock,  and  fills  cavities  and  fissures  in  the  lime- 
stones, sandstones,  and  even  in  the  accompanying  trap  rocks,  as 
at  Quebec,  Orleans  Island,  Point  Levis,  and  at  Acton,  present- 
ing mamillary  surfaces,  as  noticed  by  Vanuxem,  which  evidently 
show  that  it  has  once  been  semi-fluid.    This  matter  from  the 
first  two  localities  is  completely  infusible,  and  insoluble  in  benzol; 
it  readily  crumbles  between  the  fingers,  and  gives  a  very  black 
powder.  When  exposed  to  a  high  temperature  it  gives  off  abun. 
dance  of  inflammable  strong-smelling  vapors,  which  condense 
into  a  tarry  oil,  and  leave  a  black  residue,  which  when  heated 
slowly  burns  away,  leaving  only  a  trace  of  ash.    The  volatile 
