592  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.  [bull.  260. 
reduction  of  gypsum.  The  origin  of  sulphur  has  been  accounted  for 
by  considering  that  organic  matter  reduces  gypsum  to  calcium  sul- 
phide, which,  being  acted  on  by  carbonic-acid  waters,  yields  calcium 
carbonate  and  hydrogen  sulphide,  and  from  the  latter  sulphur  is 
formed  by  oxidation.  Gypsum,  however,  is  a  stable  compound,  and 
though  it  can  be  reduced  by  the  application  of  heat  its  reduction  at 
ordinary  temperatures,  except  through  the  life  activity  of  algeo  or 
bacteria,  has  not  been  established.  Possibly  such  favorable  condi- 
tions existed  during  the  formation  of  some  of  the  sulphur  under  con- 
sideration, which  apparently  was  formed  at  or  near  the  surface. 
Hydrogen  sulphide,  though  its  source  is  not  clear,  is  widespread 
throughout  the  area  under  consideration,  and  it  is  a  familiar  fact 
that  native  sulphur  is  formed  by  the  oxidation  of  this  gas.  By  such 
a  reaction  sulphur  is  now  being  deposited  in  Delaware  Creek,  where 
water  from  a  sulphur  spring  mingles  with  water  from  Delaware 
Springs.  The  surficial  rust-like  coating  of  sulphur  on  gypsum  head 
iMaverick  Spring  may  be  accounted  for  by  the  oxidation  of  hydrogen 
sulphide  contained  in  water  trickling  over  the  gypsum.  Throughout 
this  region,  each  occurrence  having  its  own  characteristics,  in  the  final 
reaction  the  sulphur  may  have  been  formed  by  the  oxidation  of 
hydrogen  sulphide,  but  the  ultimate  source  of  this  gas  needs  further 
investigation,  both  in  the  field  and  in  the  laboratory. 
