COAL  ON  NORTHEAST  SIDE  OP  BIGHORN   BASIN,   WYO.  171 
The  coal  of  the  Eagle  sandstone  is  workable  only  in  the  northern 
part  of  the  area,  in  the  Clark  Fork  valley,  Montana,  and  in  the  Sil- 
vertip  coal  field,  near  the  State  line.  The  formation  contains  three 
coal  beds,  only  one  of  which  is  workable  at  any  one  point  in  the 
Clark  Fork  valley,  but  two  of  which  are  workable  at  many  places  in 
the  Silvertip  field.  South  of  the  Silvertip  field  the  coal  beds  dete- 
riorate and  are  replaced  by  black  carbonaceous  shale  which  contains 
thin  partings  of  coal  less  than  1  foot  thick.  These  partings  disap- 
pear a  short  distance  south  of  Shoshone  River.  Farther  south  the 
shale  is  less  carbonaceous,  and  at  the  crossing  of  Dry  Creek  it  is  a 
yellow  sandy  shale,  with  no  suggestion  of  coal  or  carbonaceous  mat- 
ter such  as  characterizes  it  farther  north.  The  beds  at  this  horizon 
maintain  this  character  in  the  southern  part  of  the  area  studied  in 
1907,  but  beyond  that  area,  in  the  southeastern  part  of  the  Bighorn 
Basin,  the  formation  again  contains  workable  coal. 
Coal  of  the  Laramie  formation  is  known  to  occur  at  the  south  end 
of  the  area,  on  Sand  Creek,  a  tributary  of  No  Wood  Creek.  From 
this  point  the  coal  beds — three  in  number — at  the  base  of  the  Laramie 
formation  may  be  traced  northwestward  across  Bighorn  River  to  a 
point  southwest  of  Basin,  where  they  disappear  beneath  the  surface 
wash.  Between  this  point  and  the  neighborhood  of  Garland,  45 
miles  northwest  of  Basin,  workable  coal  beds  have  not  been  discov- 
ered in  the  Laramie,  although  prospecting  has  been  thoroughly  done. 
Near  Garland  there  are  two  or  more  workable  beds  which  have  been 
traced  northward  about  10  miles  to  a  high  terrace,  on  which  the  out- 
crop of  the  coal  is  covered  by  gravel.  Where  the  bed  reappears  on 
the  north  side  of  this  terrace  the  coal  is  not  workable,  and  there  is 
no  point  in  Montana  within  the  field  studied  by  the  writer  where  the 
Laramie  coal  reaches  minable  thickness. 
Coal  occurs  in  the  Fort  Union  formation  at  several  horizons,  but 
the  coal  beds  are  not  persistent.  A  coal  in  this  formation  is  mined 
on  the  east  side  of  Bighorn  River,  10  miles  southeast  of  Basin,  Wyo. 
North  of  this  point  the  coal  is  probably  not  workable,  except  in  a 
small  district  southwest  of  Lovell,  where  there  is  about  2  feet  of 
coal,  and  possibly  at  one  locality  west  of  the  Silvertip  field,  where 
about  3  feet  of  coal  was  found  in  this  formation.  Near  the  latter 
locality  exposures  of  the  same  bed  showed  less  than  18  inches  of  coal. 
THE    COAL. 
Although  the  coal-bearing  formations  extend  continuously  from 
one  end  of  the  area  examined  to  the  other,  nevertheless  the  area  is 
divisible  into  four  distinct  fields,  which  contain  all  the  coal  of  economic 
importance.  These  fields  are  separated  by  larger  areas  within  which 
coal  is  either  absent  or  else  too  thin  to  be  mined.  Tin4  fields  are 
designated  as  follows:  (1)  The  Basin  coal  field,  south  of  Basin,  Wyo., 
