310  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
cipal  occurrences  are  on  the  sides  of  the  uplift  which  rises  east  of  South  Fork  of  Powder 
River,  in  T.  38,  R.  82,  and  T.  40,  R.  79,  the  latter  being  in  the  valley  of  Salt  Creek.  Details 
regarding  these  occurrences  are  given  in  bulletins  by  the  late  Prof.  W.  C.  Knight. « 
Nine  wells  have  been  sunk  on  Salt  Creek  to  depths  of  from  800  to  1,200  feet,  some  of 
which  yield  oil.  The  output  of  this  field  in  1905  averaged  35  barrels  a  day,  which  has  to 
be  hauled  50  miles  to  Casper  at  a  cost  of  $2.80  a  barrel.  It  sells  at  an  average  rate  of  $7 
a  barrel.  The  horizon  appears  to  be  sandstone  at  the  base  of  the  Pierre,  or  possibly  the 
next  sandstone  stratum  below,  in  the  upper  part  of  the  Niobrara. 
Oil  springs  of  small  volume  occur  in  the  vicinity  of  Bonanza,  but  a  number  of  wells  sunk 
in  that  field  have  failed  to  obtain  a  supply.  The  oil  in  the  springs  is  from  a  horizon  in  the 
lower  portion  of  the  Benton. 
ASPHALTUM. 
A  deposit  of  asphalt  occurs  in  the  Tensleep  sandstone,  on  the  west  slope  of  the  Bighorn 
Mountains,  in  sees.  28,  29,  32,  and  33,  T.  52,  R.  89.  The  thickness  is  stated  to  be  6  feet, 
but  the  area  has  not  been  ascertained.  The  material  consists  largely  of  asphalt  intimately 
mixed  with  coarse  sand. 
a  University  of  Wyoming  Bulletins,  Petroleum  series,  Nos.  1  and  4. 
