584  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.  [bull.  200. 
mately  north-south  belt,  are  low  outcrops  of  coarse  and  fine  textured 
sandstone,  with  interbedded  limestone,  which  are  almost  buried  by  the 
surrounding  basin  deposits.  These  are  outlying  Cretaceous  rocks, 
belonging  to  the  Washita  group  of  the  Comanche  series. 
The  "  wash  "  of  Toyah  basin  extends  farther  west,  to  the  Rustler 
Hills,  in  which  sandstone  (Permian?)  and  limestone  outcrop.  West- 
ward these  strata  are  succeeded  by  the  belt  of  bedded  gypsum,  and 
finally  by  the  sandstones  (Permian?)  and  limestones  in  the  Delaware 
Mountains.  These  rocks  in  general  dip  low  to  the  east,  but  their 
structure,  depth,  and  extent  in  the  Toyah  basin  are  unknown  because 
of  the  cover  of  wash  and  the  erosion  that  occurred  previous  to  the 
deposition  of  the  basin  deposits. 
Reviewing  known  conditions  in  the  area  covered  by  the  recon- 
naissance in  1903,  the  following  may  be  noted  concerning  the  possible 
abundance  of  petroleum.  There  occurs  here  a  great  mass  of  little- 
disturbed  sedimentary  rocks,  some  of  which  are  bituminous.  There 
are  beds  of  porous  rock  to  serve  as  reservoirs.  Locally  the  strata  are 
gently  folded,  and  small  amounts  of  petroleum  are  widely  dissemi- 
nated. On  the  other  hand,  there  is  very  little  shale  in  this  region  to 
act  as  an  impervious  cap  to  prevent  the  escape  and  to  aid  in  the 
accumulation  of  oil.  However,  there  is  considerable  limestone,  which 
sometimes  is  an  effective  barrier.  There  is  no  general  system  of 
folds  to  provide  for  storage  and  the  accumulation  of  pools,  but  the 
beds  are  characteristically  lenticular,  and  there  may  be  lenses  of 
porous  rock  saturated  with  oil  that  is  preserved  by  contiguous 
impervious  beds.  Besides  chances  for  oil  in  the  older  rocks,  there  are 
possibilities,  in  the  wide  extent  of  the  unconsolidated  materials  of 
Toyah  basin,  for  a  combination  of  favorable  conditions  for  collecting 
disseminated  petroleum  and  for  its  storage.  Only  the  drill  can  de- 
termine whether  oil  exists  here  in  paying  quantities. 
GYPSUM. 
Within  Texas  the  bedded  gypsum  referred  to  above  covers  an  area 
of  about  600  square  miles.  This  great  gypsum  field  remains  com- 
mercially untouched.  The  nearest  part  of  the  deposit  lies  about  15 
miles  from  the  Texas  and  Pacific  Railroad,  and  adjacent  to  the 
New  Mexico-Texas  boundary  another  part  of  the  area  lies  contigu- 
ous to  the  Pecos  Valley  Railway. 
This  gypsum  is  a  massive,  white,  granular  variety.  It  is  compara- 
tively pure,  and  a  characteristic  sample,  analyzed  qualitatively  by 
Mr.  W.  T.  Schaller,  shows  it  to  be  of  no  unusual  composition.  Con- 
sidering its  great  extent  the  gypsum  is  remarkably  homogeneous, 
yet  it  varies  somewhat.  On  the  surface  generally  it  is  disintegrated 
and  earthy.     In  places  it  is  grayish  or  dark  in  color,  owing  to.  the 
