164         CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART   II. 
Glenrock  and  Big  Muddy  mines.  This  includes  all  the  coal  used  by 
ranchmen  and  others,  and  much  of  this  amount  was  not  sold,  but 
mined  by  consumers. 
The  market  for  the  coal  is  found  in  towns  along  the  Chicago  and 
Northwestern  Railway  in  this  field,  and  to  the  east  far  into  Nebraska. 
The  coal  has  not  been  used  by  the  railroad,  because  it  decrepitates 
and  is  blown  out  of  the  smokestack  by  the  heavy  fire  and  draft  of  the 
locomotive.  However,  as  similar  coals  are  being  used  by  other  rail- 
roads, it  seems  probable  that  in  time  locomotives  will  be  so  modi- 
fied as  to  burn  coal  from  the  Glenrock  field.  At  present  much  more 
than  half  of  the  product  goes  to  Nebraska,  where  it  is  used  as  steam 
and  domestic  fuel. 
FUTURE   OF  THE  FIELD. 
The  reasons  why  so  little  is  being  done  with  the  coal  in  the  Glen- 
rock field  seem  to  be  (1)  the  scarcity  of  thick  beds;  (2)  the  high  cost 
of  mining  due  to  thinness  of  bed,  high  price  of  labor  and  timber,  poor 
roof,  and  presence  of  water;  and  (3)  the  inability  to  utilize  the  coal 
as  locomotive  fuel. 
Nevertheless,  this  field,  like  all  other  areas  containing  coal,  is  one 
of  growing  importance,  because  of  the  growing  population  and  the 
increasing  demand  for  fuel.  At  present  there  is  much  coal  in  the 
field  which  can  not  be  worked  with  profit,  but  it  is  probable  that  in 
the  future  more  and  more  of  this  will  be  mined.  The  coal  beds  are 
generally  lenticular,  and  they  vary  in  quality  from  place  to  place, 
but  careful  prospecting  would  reveal  many  localities  where  even  at 
the  present  time  the  coal  could  be  worked  with  profit. 
