ROCK    SPRINGS    COAL   FIELD,    WYOMING.  279 
700  tons.  The  mine  is  ventilated  by  an  exhaust  fan  and  provided 
with  electric  signals  throughout.  The  coal  is  considered  a  good 
smithing  coal,  but  does  not  coke.  It  burns  with  a  white  ash  and 
leaves  no  clinker.  The  bed  of  coal  is  from  7  feet  6  inches  to  9  feet 
thick,  with  a  band  of  bone  1  inch  to  1  foot  thick  about  2  feet  from  the 
roof. 
ud"  mine. 
The  "D"  mine  was  opened  April  19,  1906,  and  late  in  the  same  year 
closed  down;  mining  was  resumed  in  June,  1907,  and  continued  until 
February  1,  1908,  when  the  mine  was  again  closed.  This  mine  is  a 
drift  opening  on  No.  1  bed,  1,200  feet  long,  driven  on  the  strike  of  the 
coal.  The  coal  is  the  same  as  in  the  "C"  mine.  It  is  undermined 
and  all  shot  down  at  once  and  is  hauled  to  the  dump  in  the  same  way 
as  at  aA"  mine.  The  same  system  of  mining  and  ventilating  is  used 
as  at  the  "A"  and  UB"  mines.  The  rooms  are  timbered  and  in  the 
entries  a  coal  roof  is  left.     The  output  was  about  300  tons  per  day. 
ECONOMIC   CONSIDERATIONS. 
MINING  OPERATIONS. 
Up  to  the  present  time  coal-mining  operations  in  Sweetwater 
County  have  been  conducted  chiefly  by  the  Union  Pacific  Coal  Com- 
pany. At  present  this  company  operates  almost  wholly  for  the  pur- 
pose of  supplying  coal  to  the  Union  Pacific  Railroad.  At  Rock 
Springs  the  Central  Coal  and  Coke  Company  has  been  mining  coal  for 
commercial  markets  since  1889.  In  1868  Rock  Springs  produced  365 
tons  of  coal,  while  in  1906  the  yearly  output  of  the  mines  was  over 
2,100,000  tons.  The  Superior  mines  began  shipping  coal  in  1906,  and 
the  output  for  the  year  was,  in  round  numbers,  12,000  tons.  In  1907 
the  daily  output  of  the  four  mines  was  1,800  tons,  making  a  probable 
annual  production  of  500,000  to  600,000  tons.  The  shipments  of  coal 
from  other  localities  in  this  held  have  been  meager  and  never  exceeded 
a  few  hundred  tons  per  day.  Mines  at  present  are  being  opened  in 
the  vicinity  of  Point  of  Rocks  and  Black  Buttes,  and  in  the  future 
these  coals  may  be  mined  much  more  extensively. 
The  entire  region  from  Rock  Springs  northward  around  the  north 
end  of  the  dome  is  a  valuable  field  of  bituminous  and  subbituminous 
coal.  In  all  parts  of  the  coal  zones  there  are  several  coal  beds  that 
will  be  profitable  to  mine.  Coal  is  the  chief  mineral  product  of  Wyo- 
ming, and  Sweetwater  County  heads  the  list  of  all  the  counties  as  a 
coal  producer.  Uinta  County  is  a  close  second,  and  in  1906  produced 
2,078,772  tons,  as  compared  with  Sweetwater  County's  output  of 
2,121,546  tons,  all  of  which  came  from  the  Rock  Springs  field.  In 
1903  these  two  counties  produced  78  per  cent  of  the  coal  Output  of  the 
State  and  employed  69  per  cent  of  the  miners;  in  1906  they  produced 
