tenneman.]  OIL    FIELDS    OF    TEXAS-LOUISIANA    COAST.  467 
It  would  be  difficult  to  make  valuable  suggestions  for  the  further 
prospecting  of  the  oils  on  the  uneroded  part  of  the  Coastal  Plain. 
Nothing  definite  can  be  added  to  the  suggestions  of  topography  and 
surface  indications  already  being  followed  by  the  exploiting  com 
panies.  But  a  word  of  caution  is  necessary  with  regard  to  drilling  in 
supposed  mounds  on  that  part  of  the  Coastal  Plain  more  remote  from 
the  Gulf  and  already  somewhat  subjected  to  erosion.  The  true 
mounds  of  the  Spindletop  type  may  indeed  be  partially  preserved  on 
the  slightly  eroded  plain  (as,  for  example,  at  Jennings),  but  where 
erosion  has  advanced  somewhat  further,  surface  topography  offers 
no  suggestions  whatever,  and  the  first  question  to  be  answered  with 
regard  to  a  hill  in  which  it  is  proposed  to  drill  is  whether  this  hill 
is  of  the  mound  type  or  is  of  purely  erosional  origin.  It  is  highly 
probable  that  many  such  mounds  have  been  destroyed  by  erosion, 
and  that  could  their  sites  be  found,  drilling  would  reveal  the  char- 
acteristic internal  structure  and  materials,  perhaps  including  oil. 
In  view  of  the  character  of  the  Texas  and  Louisiana  Coastal  Plain 
oils,  it  was  formerly  supposed  that  they  would  be  in  small  demand 
for  refining.  Their  gravity  varies  from  16°  B.  to  27°  B.  (generally 
nearer  the  former  than  the  latter),  and  they  have  an  asphalt  base. 
While  still  used  largely  for  fuel,  improved  methods  of  refining  have 
succeeded  in  obtaining  from  Beaumont  crude  oil  17  per  cent  kerosene 
of  a  good  quality  and  15  per  cent  solar  oil.  Similar  proportions 
are  derived  from  the  crude  oils  of  the  neighboring  fields. 
