Whaler/]  MUSCOGEE    OIL   FIELD,    INDIAN    TERRITORY.  445 
and  southeast  of  Muscogee  its  collection  into  pools  would  be  influ- 
enced by  the  location  of  the  upward  folds.  If  the  oil  should  occur 
in  the  Silurian  or  Ordovician  rocks,  the  interpretation  of  the  struc- 
tural conditions  governing  its  occurrence  would  be  more  difficult,  for 
but  little  is  known  of  the  folding  produced  in  these  rocks  before  the 
formation  of  the  Mississippian  limestone.  These  older  rocks  are 
exposed  at  several  places  in  the  valleys  of  Illinois  River  and  Sallisaw 
Creek,  and  were  penetrated  in  the  well  at  Fort  Gibson  below  a  depth 
of  850  feet.  The  data  obtained  indicate  that  they  are  tilted  west- 
ward and  southward  at  a  greater  inclination  than  are  the  overlying 
rocks.  Should  this  structure  continue  westward,  successively  higher 
beds  of  the  Silurian  would  be  found  toward  Muscogee.  Should  oil 
occur  in  the  Silurian  rocks,  it  would  be  led  upward  against  the  flat- 
lying  Mississippian  limestones.  The  fact,  however,  that  the  oil  sand 
beneath  Muscogee  lies  practically  flat  argues  in  favor  of  its  being 
above  the  base  of  the  Mississippian  series. 
