fbxngman.]  OIL    FIELDS    OF    TEXAS-LOUISIANA    COAST.  463 
plains  and  terraces  of  San  Marcos  River  are  numerous  mud  volca- 
noes. Wells  at  this  place  found  considerable  gas,  but  have  not  as 
yet  reached  oil  in  commercial  quantities.  The  conditions  at  Suther- 
land Springs  are  similar  to  those  at  Ottine,  but  no  active  mud 
volcanoes  are  found.  At  Humble,  16  miles  north  of  Houston,  the 
emission  of  gases  has  caused  the  presence  of  oil  to  be  suspected  for  a 
long  time.  The  first  Avells  drilled  in  this  field  were  ruined  by  violent 
eruptions  of  gas.  Recently,  however,  it  is  understood  that  at  least 
one  well  has  been  successful  in  reaching  a  body  of  oil  and  is  now 
pumping. 
SURFACE  INDICATIONS. 
Gas  and  oil  seeps. — The  surface  indications  which  have  led  to  the 
exploiting  of  the  several  fields  are  various.     In  a  general  way  they 
may  be  subdivided  into  two  classes,  those  which  are  common  to  this 
and  other  oil  fields  and  those  which  depend  for  their  significance 
upon  the  peculiar  relations  of  the  Coastal  Plain  oils.     Of  the  indica- 
tions common  to  this  and  to  other  fields  a  seepage  of  oil  is  the  best. 
This  evidence  has  been   found   in  a  considerable  number  of  fields 
named  above.     It  may,  however,  be  confused,  as  it  frequently  has 
been,  with  another  phenomenon  which  bears  no  relation  to  oil — the 
appearance  pf  a  scum  of  iron  oxide  on  stagnant  water  in  regions 
where  the  soil  is  strongly  colored  with  limonite.     This  appearance  is 
very   common   in   the   red-soil   districts   of   eastern   Texas.     Closely 
related  to  a  seepage  of  oil  is  the  asphaltic  substance  sometimes  found 
impregnating  the  soil  at  shallow  depths.     This  evidence  is  not  so 
widespread  as  are  oil  seepages  in  the  Coastal  Plain.     It  is  well  illus- 
trated at  Anse  la  Butte,  and  there  are  so-called  "  tar  springs  "  in  the 
northwestern  part  of  Jasper  County,  Tex.     Far  the  most  common 
of  all  evidences  is  the  escape  of  gases.     Indeed,  this  phenomenon  is  so 
jwidespread  that  it  is  entirely  unsatisfactory  as  an  indication  of  the 
lace  where  drilling  should  begin.     In  this,  again,  the  phenomena  of 
importance  are  frequently  confused  with  those  which  have  no  signifi- 
ance  whatever.     To  the  latter  class  belongs  the  escape  of  marsh  gas 
rom  recently  buried  sediments.     A  very  simple  distinction  having 
ome  significance  is  that  based  upon  the  leaving  of  an  oily  film  on  the 
ater  after  the  breaking  of  a  bubble. 
Indications  based  on  local  conditions. — Of  the  class  of  surface 
ndications  depending  upon  the  peculiar  relations  of  the  Coastal 
lain  oil  deposits,  probably  the  escape  of  hydrogen  sulphide  gas  is 
-he  one  deserving  the  most  consideration.  At  places  the  bubbling  up 
)f  the  gas  itself  through  stagnant  water  is  all  that  is  to  be  seen.  At 
kher  places  the  waters  have  become  more  or  less  strongly  sulphu- 
Jreted.  In  some  districts,  around  the  mouths  of  shallow  wells,  an 
ncrustation  of  pure  sulphur  is  continuously  forming.    Closely  related 
