150        CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART  II. 
suddenly  heated.  The  small  particles  of  coal  that  are  thrown  off  by 
the  sudden  application  of  strong  heat  are  in  large  part  either  blown 
out  of  the  stack  or  fall  between  the  grate  bars  used  in  the  ordinary 
fire  box  of  locomotives  and  other  engines. 
The  Burlington  Railroad  began  a  series  of  tests  of  the  Sheridan 
coals  in  its  locomotives  in  1900.  By  the  use  of  specially  constructed 
grates  of  large  area,  with  modified  fire  boxes  and  stacks,  the  Sheridan 
coal  is  said  to  produce  very  satisfactory  results.  Coal  from  all  the 
beds  now  mined  is  used  extensively  in  locomotives  and  stationary 
engines. 
A  large  part  of  the  production  of  coal  in  the  Sheridan  district  is 
used  by  the  Burlington  Railroad.  It  is  marketed  in  Wyoming  and 
Nebraska  as  far  east  as  Omaha;  in  the  Black  Hills  region;  at 
Billings,  Butte,  and  other  points  in  Montana,  and  as  far  west  as 
Idaho  and  Washington. 
