MINERAL    RESOURCES    OF    BIGHORN    MOUNTAIN    REGION.        309 
Copper  minerals  have  been  recently  discovered  in  the  granite  area  in  the  uplift  of  the 
Bridger  Range,  a  few  miles  southwest  of  Deranch.  One  vein  has  been  opened  which  shows 
a  moderate-sized  body  of  high-grade  ore,  consisting  of  oxides  and  sulphides.  The  open- 
ings are  not  yet  sufficiently  developed  to  exhibit  fully  the  extent  and  value  of  the  deposit. 
As  stated  in  the  preceding  paragraph,  considerable  gold  occurs  with  the  copper  minerals 
of  this  locality. 
GYPSUM. 
The  gypsum  in  the  Chugwater  formation,  on  both  sides  of  the  mountain,  is  of  excellent 
quality,  in  every  way  suited  for  the  production  of  stucco  and  plaster  of  Paris.  This  prod- 
uct is  prepared  by  calcining  and  powdering  the  mineral,  which  is  a  combination  of  sulphate 
of  lime  and  water.  The  beds  of  gypsum  occur  generally  near  the  base  of  the  formation 
and  a  thickness  of  10  to  15  feet  is  usually  presented.  Much  of  the  material  is  of  pure 
white  color  and  is  nearly  pure.  Owing  to  the  lack  of  a  local  market  and  the  fact  that  the 
value  of  plaster  of  Paris  is  too  low  to  cover  freight  charges  for  long  shipments,  this  resource 
has  no  promise  of  development  at  present. 
BENTONITE. 
No  bentonite  has  been  observed  in  the  immediate  vicinity  of  the  Bighorn  Mountains, 
but  as  it  occurs  in  adjoining  areas  and  appears  generally  to  be  present  in  the  Benton  shale 
probably  it  will  eventually  be  found.  It  occurs  at  two  horizons,  one  below  and  the  other 
above  the  hard  shale  or  Mowry  member.  The  mineral  is  a  pale  greenish-buff  clay  of  com- 
pact texture  and  of  such  porous  structure  that  it  will  absorb  several  times  its  bulk  of  water,, 
On  account  of  this  absorbent  quality  it  has  a  moderate  market  value  for  several  uses. 
LIMESTONE. 
The  limestones  of  the  mountain  slopes  are  in  the  main  sufficiently  pure  for  lime  burning 
or  for  smelting  flux,  but  there  is  very  little  demand  for  these  products  in  the  region.  No 
analyses  have  been  made  to  ascertain  the  chemical  character  of  the  rocks. 
BUILDING  STONES. 
Many  of  the  rocks  in  the  mountain  portion  of  the  area  are  more  or  less  well  suited  for 
building  stone.  Some  of  the  granites  are  massive,  have  a  fine  appearance  when  polished, 
are  relatively  free  from  minerals  which  cause  stains  on  weathering,  and  may  at  some  time 
be  valuable  for  shipment  for  building.  Some  of  the  limestones  in  the  Madison  forma- 
tion are  of  very  satisfactory  texture  and  appearance  and  possibly  could  be  worked  for  mar- 
ble, especially  the  upper  member.  The  Tensleep  sandstone  is  usually  massive,  even  text- 
ured, and  of  white  or  light-buff  color,  so  that  if  nearer  to  markets  it  might  be  advanta- 
geously worked  as  a  freestone.  The  red  sandstones  of  the  Chugwater  formation  are  of  a 
very  pleasing  color,  but  they  are  mostly  too  soft  to  be  of  value  for  building.  Large  sup- 
plies of  rough  stones  for  foundations  and  similar  uses  are  obtainable  from  the  Piney,  De 
Smet,  Parkman,  and  Cloverly  sandstones  and  the  hard  ledges  in  the  Sundance  formation. 
PHOSPHATE. 
The  spherical  concretions  occurring  in  the  lower  portion  of  the  Benton  formation  consist 
mainly  of  phosphate  of  lime,  and  as  they  could  be  obtained  in  large  numbers  by  means  of 
suitable  excavating  machinery  they  may  at  some  time  be  utilized  as  a  source  of  phosphate. 
PETROLEUM. 
At  various  localities  along  the  sides  of  the  Bighorn  and  associated  uplifts  some  of  the 
sandstones  and  sandy  shales  contain  petroleum.  This  material  usually  appears  in  springs 
or  seeps  in  small  valleys,  and  so  far  has  been  found  only  in  limited  amounts.     The  prin- 
