590  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.  [bull.  260. 
rounded  quartz  pebbles  that  average  about  one-half  inch  in  diameter. 
The  gypsum  is  impure  and  earthy,  and  besides  predominating  granu- 
lar gypsum  consists  of  small  selenite  crystals,  with  which  are  asso- 
ciated some  sand,  occasional  quartz  pebbles,  and  bits  of  organic  mat- 
ter. Apparently  this  gypsum  is  of  secondary  origin,  derived  from  the 
near  by  bedded  deposits  in  several  ways,  including  evaporation  of 
ground  water  solutions  of  calcium  sulphate  and  transportation  by 
wind  and  streams.  The  quartz  pebbles  can  be  traced  to  conglomeratic 
sandstone  in  the  Screwbean-Rustler  Hills. 
Sulphur  occurs  here  in  different  ways.  Sometimes  it  is  surficially 
developed  on  the  gypsum  as  a  thin  amorphous  film.  Again  it  is 
rather  minutely  disseminated  throughout  the  mass  of  gypsum.  One 
broad  strip  exposes  a  bed  of  brownish  earth  about  3  feet  thick,  highly 
impregnated  with  undeterminable  organic  matter,  having  a  peculiar 
sulphurous  odor  and  containing  considerable  disseminated  minute  sul- 
phur crystals.  Small  sulphur  crystals  also  occur  locally  in  linear 
vein-like  arrangement  through  the  earthy  gypsum.  A  cut  in  this 
vicinity  exposes  about  2  feet  of  rather  compact  amorphous  sulphur, 
which  also  contains  small  pebbles. 
This  is  the  only  locality  where  considerable  prospecting  has  been 
done,  though  no  sulphur  has  been  shipped  from  it.  Mr.  E.  M.  Skeats 
reports  a  pit  section  41  feet  deep  in  gypsum,  sand,  and  gravel,  situated 
about  5  miles  northwest  of  Maverick  Spring.  Samples  were  taken 
every  few  feet,  an  average  of  which  gave  26  per  cent  of  free  sulphur, 
though  some  tests  went  as  high  as  46  per  cent.  Mr.  Skeats  reports 
the  presence  of  free  sulphuric  acid  in  the  waters  associated  with  the 
sulphur  deposits,  and  he  mentions  that  a  21-foot  bore  hole  struck  a 
mixture  of  gas  which  burned  for  several  days. 
The  most  extensive  development  work  has  been  done  about  6  miles 
north  of  Rustler  Springs,  in  the  bedded  gypsum  belt.  It  is  reported 
that  four  or  five  years  ago  100  men  or  more  were  employed  here  for 
several  months.  A  number  of  acres  were  stripped,  a  furnace  was 
erected  for  treating  the  ore  by  the  superheated  steam  process,  and  two 
or  three  carloads  of  refined  sulphur  were  shipped  from  Guadalupe. 
The  strippings  show  at  the  surface  from  2  to  3  feet  of  porous,  earthy 
gypsum,  containing  a  few  rounded  pebbles  of  quartz,  overlying  the 
ore,  which  averages  about  4  feet  in  thickness.  The  ore  is  a  brownish, 
porous  substance,  containing  disseminated  sulphur  crystals.  An 
analysis  by  Mr.  George  Steiger,  of  the  United  States  Geological  Sur- 
vey, shows  that  the  bulk  of  the  ore  is  silica,  with  a  little  alumina, 
and  that  no  calcium,  sulphuric  acid,  or  carbon  dioxide  is  present. 
This  ore  contains  considerable  organic  matter  of  an  undetermined 
nature  and  18.36  per  cent  of  free  sulphur.  Geodes  consisting  of  hol- 
low spherical  masses  of  gypsum,  lined  with  small  sulphur  crystals, 
have  been  reported  from  this  vicinity. 
