THE  MILES  CITY  COAL  FIELD,  MONTANA. 
By  Arthur  J.  Collier  and  Carl  D.  Smith. 
INTRODUCTION. 
The  Miles  City  coal  field,  situated  in  the  northern  part  of  Custer 
County,  Mont.,  about  90  miles  west  of  the  North  Dakota  line,  is  a 
small  part  of  a  large  area  of  Tertiary  coal-bearing  rocks  which 
extends  from  eastern  Montana  southward  into  Wyoming,  northward 
into  Canada,  and  eastward  into  North  and  South  Dakota.  The 
area  as  here  described  comprises  about  1,000  square  miles.  Rocks 
and  coals  of  the  same  age  in  Carbon,  Dawson,  Rosebud,  and  Custer 
counties,  Mont.,  have  been  examined  and  described (/  in  previous 
reports  of  the  Geological  Survey,  and  detailed  studies  during  1907 
of  coal-bearing  rocks  of  the  same  age  in  the  Sentinel  Butte  field  of 
North  Dakota  and  Montana,  in  the  Bull  Mountain  and  Red  Lodge 
fields  of  Montana,  and  in  the  Sheridan  and  Glenrock  fields  of  Wyo- 
ming, are  reported  in  this  volume.  The  coals  are  generally  of  low 
grade  and  are  classed  as  subbituminous  and  lignite. 
The  present  report  is  a  preliminary  statement  intended  to  give 
advance  information  regarding  the  coal  resources  of  the  field,  leaving 
the  more  purely  scientific  questions  for  consideration  at  a  later  date, 
when  the  investigations  in  this  and  other  parts  of  the  region  shall 
have  been  completed.  It  is  based  on  a  season's  field  work  by  the 
writers,  who  were  assisted  by  Carroll  H.  Wegemann  and  Ralph  W. 
Howell.  Through  July  and  August  the  party  was  in  charge  of  Mr. 
Collier,  who  was  called  away  to  other  work  on  September  1 ;  at  that 
time  Mr.  Smith  suspended  his  work  in  the  Sentinel  Butte  field  and 
took  charge  of  the  party  at  Miles  City,  continuing  in  the  field  until 
November  1. 
The  purpose  of  the  investigation  was  primarily  to  ascertain  the 
limits  of  the  area  underlain  by  workable  coal  and  to  classify  the 
coal  lands.  With  these  objects  in  view,  copies  of  the  original  town- 
ship plats  were  used  as  a  base  for  geologic  mapping.     Although 
a  Leonard,  A.  G.,  Coal  in  Dawson,  Custer,  and  Rosebud  counties,  Montana:  Bull.  U.  S.  Geol.  Survey 
No.  310,  1907,  pp.  194-211.    Darton,  N.  H.,  Coals  in  Carbon  County,  Montana:  Idem,  pp.  174-193. 
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