kichardson.]      SALT,    PETROLEUM,    ETC.,    IN    TRANS-PECOS    TEXAS.      577 
the  steeper-dipping  western  limb.     Faulting  of  undetermined  throw 
appears  to  be  associated  with  this  fold. 
In  the  Guadalupe-Delaware  Mountains  arc  developed  a  consider- 
able thickness  of  Permian  strata,  which  do  not  occur  west  of  Salt 
basin.  In  the  Guadalupe  Mountains  the  following  generalized  sec- 
tion is  plainly  exposed. 
Section  of  rocks  in  Guadalupe  Mountains. 
Feet. 
Massive  white  magnesian  limestone 1,800 
Interbedded  buff  sandstone  and  gray  limestone 2,000 
Blue-black  limestone,  locally  shaly 200 
Farther  south,  in  the  Delaware  Mountains,  the  upper  white  lime- 
stone is  missing,  the  rocks  exposed  belonging  to  the  middle  formation, 
sandstone  predominating  in  the  northern  and  limestone  in  the  south- 
ern part  of  the  mountains.  As  mentioned  above,  the  structure  of  the 
range  is  a  low  east-dipping  monocline.  These  rocks  contain  an 
abundant  and  unique  Permian  fauna,  which  is  being  studied  by  Dr. 
G.  H.  Girty. 
Midway  between  the  mountains  and  Pecos  River  lies  a  broad  belt 
of  bedded  gypsum,  which  rests  unconformably  on  the  rocks  exposed 
in  the  Delaware  Mountains  and  apparently  maintains  the  prevailing 
ow  eastward  dip.  The  width  of  the  belt  averages  about  15  miles, 
though  at  the  New  Mexico-Texas  boundary  it  is  30  miles.  This 
gypsum  belt  begins  15  miles  north  of  the  Texas  and  Pacific  Rail- 
oad  and  extends  into  New  Mexico. 
The  gypsum  is  unconformably  overlain  in  the  Screwbean-Rustler 
Hills  by  buff  sandstone,  which  is  wholly  conglomeratic,  and  white 
nagnesian  limestone,  aggregating  about  200  feet  in  thickness.  Only 
i  few  indeterminable  fossils  were  found  in  these  rocks,  which,  with 
he  gypsum,  are  provisionally  assigned  to  the  Permian.  They  like- 
vise,  with  minor  undulations,  conform  to  the  general  low  eastward 
ip,  at  least  as  far  as  Toyah  basin,  where  they  are  covered  by  Pleisto* 
ene  deposits. 
Outlying  exposures  of  horizontal  or  gently  inclined  calcereous 
hale,  thin-bedded  limestone,  and  occasional  beds  of  sandstone 
>elonging  to  the  Washita  group  of  the  Comanche  Cretaceous,  occur 
urrounded  by  the  Toyah  basin  deposits  in  low  hills  in  the  western 
Dart  of  the  basin,  and  also  adjacent  to  Pecos  River,  about  20  miles 
south  of  the  State  boundary. 
Toyah  basin,  like  Salt  basin,  is  strewn  with  unconsolidated  mate- 
ial  derived  from  the  bordering  highlands.  At  Toyah  a  well  832 
eet  deep  has  been  bored  in  these  deposits  without  reaching  bed  rock, 
he  depth  to  which  is  not  known.    Practically  all  of  the  surface  cov- 
