76  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1007,   PART   II. 
by  the  Republic  Coal  Company  of  a  well-equipped  mine  2  miles 
northeast  of  Roundup.  This  company  first  began  to  operate  during 
the  fall  of  1907,  and  its  shaft  is  probably  the  first  of  any  considerable 
size  ever  excavated  in  the  Bull  Mountain  field.  The  company 
attempted  to  reach  the  coal  bed  through  a  slope  extending  beneath 
Musselshell  River,  but  the  coarse  character  of  the  beds  through  which 
such  a  slope  must  extend  allowed  the  entrance  of  great  quantities  of 
water,  which  was  fatal  to  the  project.  Thereupon  a  shaft  was  sunk 
on  the  south  side  of  the  river  to  a  depth  of  more  than  100  feet.  The 
coal  bed  penetrated  by  the  shaft  is  possibly  the  Wildhorse,  and  it  is 
overlain  by  an  excellent  roof  of  heavy  sandstone.  The  floor  is  clay 
shale,  which  may  be  readily  removed  if  necessary  in  mining.  The 
coal  bed  is  reported  to  be  over  6  feet  thick,  and  it  is  said  that  at  the 
present  writing  150  tons  of  coal  are  removed  daily.  Some  of  the 
output  is  put  to  local  uses,  but  much  the  larger  part  is  utilized  for 
steam  purposes  on  the  new  line  of  railroad. 
The  further  development  of  this  field  will  be  to  some  extent  con- 
trolled by  the  topographic  features,  the  water  supply,  and  the  struc- 
ture of  the  rocks  or  lay  of  the  coal  beds.  The  accessibility  of  the  coals 
depends  largely  on  the  topography.  The  main  divide,  on  which  are 
situated  the  mesas  constituting  the  Bull  Mountains,  separates  the 
field  into  two  natural  portions — a  northern  slope  toward  the  Mussel- 
shell and  a  southern  slope  toward  the  Yellowstone.  Coals  outcrop- 
ping on  the  south  slope  are  most  accessible  from  that  direction,  for 
railroad  spurs  sufficient  to  tap  the  field  may  be  extended  from  the 
main  line  of  the  Northern  Pacific  Railway,  which  is  12  miles  from  the 
nearest  coal  bed.  The  coals  which  would  thus  be  mined  on  the  south 
slope  extend  through  the  divide  and  outcrop  on  the  north  slope.  '  This 
slope  has  the  advantage  of  a  more  plentiful  water  supply  and  closer 
proximity  to  railroad  facilities.  The  coal  which  is  at  least  12  miles 
from  the  Northern  Pacific  Railway  on  the  south  slope  outcrops  on  the 
north  slope  along  the  line  of  the  Chicago,  Milwaukee  and  St.  Paul 
Railway,  and  is  the  one  now  being  mined  at  Roundup.  Furthermore, 
for  the  higher  coal  beds  on  the  north  railroad  spurs  may  be  projected 
up  the  various  creeks  heading  in  the  Bull  Mountains. 
Water  is  notably  scarce  in  some  parts  of  the  field.  On  the  south 
side  of  the  mountains,  as  already  stated,  the  supply  is  very  scanty 
during  the  dry  season. (  On  the  north  side,  owing  to  the  general 
northward  dip  of  the  rocks,  springs  are  fairly  abundant  and  water 
may  be  had  by  drilling.  It  may  therefore  be  necessary  in  mining 
some  of  the  coals  in  this  region  to  use  electricity  generated  at  some 
distant  point,  possibly  along  Musselshell  or  Yellowstone  River. 
This  method  of  mining  is  probably  the  only  available  one  for  the 
coals  on  the  south  slope,  unless,  inasmuch  as  the  same  beds  outcrop 
on  both  sides  of  the  mountains,  the  coal  is  taken  out  by  mines  situated 
on  the  north  side. 
