536 
HISTORY  OF  PETROLEUM  OR  ROCK  OIL. 
mines.  A  curious  circumstance  is,  however,  noticed  by  Mr. 
Robb;  the  gas  which  accumulates  in  the  oil  pits  becomes 
charged  with  vapors  which  produces  upon  the  workmen  a  sort  of 
intoxication  like  nitrous  oxide.  This  is  not  surprising  when  we 
remember  that  volatile  hydrocarbons,  like  amylene,  closely  re- 
lated to  the  hydrocarbons  of  petroleum,  produce  similar  effects 
when  their  vapor  is  respired. 
The  oil  wells  of  the  United  States  are  for  the  most  part  sunk 
in  the  sandstones  which  form  the  summit  of  the  Devonian  series  ; 
but  the  oils  of  Western  Virginia  and  Southern  Ohio  rise  through 
the  coal  measures  which  overlie  the  Devonian  strata,  while  the 
wells  of  Enniskillen  are  situated  much  lower,  and  are  sunk  in 
the  Hamilton  shales,  which  immediately  overlie  the  Corniferous 
or  Devonian  limestone.  It  is  not  impossible  that  in  Ohio  some 
of  the  higher  strata,  such  as  the  sandstone,  were  originally  im- 
pregnated with  bitumen,  but  in  Canada,  from  the  absence  of 
this  substance  diffused  through  the  shales  in  question,  we  are 
forced  to  assign  it  to  a  lower  horizon,  which  is  doubtless  that  of 
the  bituminous  Devonian  limestone.  This  view  I  have  for  some 
time  maintained  in  opposition  to  those  who  conceive  the  bitumen 
to  be  derived  from  the  black  pyroschists  ;  (see  my  lecture 
before  the  Board  of  Arts  reported  in  the  Montreal  Gazette 
of  March  1,  where  I  asserted  that  the  source  of  the  petroleum 
was  to  be  sought  in  the  bituminous  Devonian  and  Silurian  lime- 
stones;) besides  the  Corniferous  limestone  (Devonion,)  we  have 
shown  that  both  the  Niagara  and  the  Trenton  (of  Upper  and 
Lower  Silurian  age)  contain  petroleum.  The  question  of  the 
extent  of  the  supply  of  petroleum  is  not  easily  answered  ;  the 
oil  now  being  wrought  is  the  accumulated  drainings  of  ages,  con- 
centrated along  certain  lines  of  elevation,  and  the  experience  of 
other  regions  has  shown  that  these  sources  are  sooner  or  later 
exhausted ;  but  though  the  springs  of  Agrigentum,  like  those  of 
Derbyshire,  have  nearly  ceased  to  flow,  those  of  Burmah  and 
Persia  still  furnish,  as  they  have  for  ages  past,  immense  quan- 
tities of  oil,  nothing  but  experience  can  tell  us  the  richness  of 
the  subterranean  reservoirs.  It  is  not  probable  that  the  Devonian 
limestone  is  equally  rich  in  petroleum  throughout  its  whole  dis- 
tribution, but  the  exposures  of  it  in  the  west  are  too  few  to  ena- 
ble us  as  yet  to  say  in  what  portions  the  petroleum  predomi- 
