SENTINEL    BUTTE   LIGNITE   FIELD,    N.    DAK.    AND    MONT.  29 
Ft.     in. 
Sandstone  and  clay  alternating 47 
Bed  D:  Lignite 5    6 
Sandstone  and  clay 10 
Lignite 4 
Sandstone  and  clay  alternating 20 
{Lignite 2    9 
Clay,  gray 11 
Lignite 4    3 
Sand  and  clay 35 
Bed  B:  Lignite 3     8 
Clay,  sandy 11 
Level  of  Beaver  Creek. 
Total  lignite 30    9 
On  Little  Beaver  Creek,  in  T.  141  N.,  R.  105  W.,  beds  C  and  E 
show  workable  thickness,  but  only  a  small  portion  of  the  outcrop  of 
bed  E  has  been  followed  out.  Toward  the  south  its  outcrop  is 
divided  by  a  number  of  partings  and  is  lost  in  the  grass-covered 
prairies. 
The  outcrop  of  bed  C  disappears  below  the  level  of  Little  Beaver 
Creek  about  one-half  mile  east  of  the  State  line,  where  it  is  about  6 
feet  thick. 
Two  mines  or  strip  pits  have  been  opened  on  bed  E,  one  in  the 
NW.  \  sec.  8  and  the  other  in  the  NW.  \  sec.  16.  Sections  of  the 
lignite  at  these  mines  follow: 
Section  of  bed  E  in  the  NW.  \  sec.  8,  T.  14 1  N.,  R.  105  W. 
Ft.    in. 
Lignite 6     6 
Clay,  sandy 8 
Lignite 3 
Total  lignite 9     6 
Section  of  bed  E  in  the  NW.  \  sec.  16,  T.  141  N,  R.  105  W. 
Ft.    in. 
Lignite 2     2 
Clay,  white 6 
Lignite 5 
Clay,  white 6 
Lignite 5    6 
Total  lignite 8    1 
In  T.  16  N.,  R.  60  E.,  Montana,  and  in  the  northwestern  part  of 
T.  142  N.,  R.  105  W.,  North  Dakota,  bed  C  is  thin  and  unworkable. 
Toward  the  south  its  outcrop  runs  through  T.  15  N.,  R.  60  E.,  rising 
gradually  above  the  level  of  Beaver  Creek.  Its  outcrop  is  nearly 
everywhere  marked  by  a  fringe  of  clinkered  material,  due  to  the 
burning  of  the  bed.  The  outcrop  was  not  mapped  farther  south 
than  the  northern  part  of  T.  14  N.,  R.  60  E.,  though  the  clinker 
occurs  in  the  prairies  to  the  southern  boundary  of  the  field. 
