COAL    OF    NORTHEAST    SIDE    OF    BIGHORN    BASIN,     WTO.  195 
As  the  roof  is  excellent  and  the  floor  rather  soft  and  easily  picked, 
the  mining  of  this  coal  could  perhaps  be  carried  on  with  profit  in  the 
future. 
The  following  note  on  the  prospect  at  Carbonado,  on  the  Red  Lodge 
branch  of  the  Northern  Pacific  Railway,  8  miles  west  of  Joliet,  is 
quoted  from  N.  H.  Darton:a 
Several  years  ago  a  large  shaft  was  sunk  at  Carbonado  station  to  reach  the  Bridger 
coal  bed.  A  preliminary  drill  hole  was  bored,  which  gave  promise  of  a  thick  bed, 
but  in  the  shaft  the  coal  has  a  thickness  of  4  feet  with  a  parting,  and  occurs  at  a  depth 
of  about  980  feet.  The  enterprise  belonged  to  the  late  Marcus  Daly  and  was  equipped 
for  extensive  workings.  A  very  large  amount  of  water  was  encountered,  and  as  the 
bed  was  not  satisfactory  the  project  was  abandoned. 
QUALITY  OF  THE  COAL. 
The  coals  of  the  fields  treated  in  this  paper  are  all  of  the  subbitu- 
minous  class,  often  called  black  lignite,  intermediate  between  true 
lignite  and  bituminous  coal.  They  show  no  trace  of  woody  structure. 
The  Eagle  coal  compares  favorably  with  other  subbituminous  coals 
of  the  Rocky  Mountain  region.  The  Laramie  and  Fort  Union  coals 
of  the  Bighorn  Basin  are  of  poorer  quality. 
PHYSICAL    PROPERTIES. 
The  coal  of  the  Eagle  sandstone  has  similar  physical  properties 
in  all  parts  of  the  field.  The  coals  of  the  Laramie  and  Fort  LTnion 
formations  are  variable  in  physical  properties  and  differ  markedly 
as  a  group  from  the  Eagle  coal.  In  general  the  Eagle  coal  is  harder 
and  more  compact  than  the  Laramie-Fort  Union  coals.  As  the 
coals  contain  practically  equal  amounts  of  water,  the  better  keeping 
quality  of  the  Eagle  coal  may  be  in  part  due  to  this  superior  hard- 
ness and  compactness.  The  difference  in  hardness  affects  mining 
by  making  it  necessary  to  blast  all  the  coal  that  is  removed.  No 
coal  can  be  removed  by  picking  alone,  as  is  done  in  some  mines  that 
work  the  higher  beds.  At  the  working  face  of  the  Bridger  mine,  on 
the  Eagle  coal,  a  strong  blow  of  the  pick  results  merely  in  shattering 
a  little  coal  about  the  point  struck.  It  is  not  possible  to  drive  the 
pick  on  cleats  and  partings  and  pry  out  the  blocks  of  coal.  The 
Eagle  coal  is  more  brittle  and  less  tough  than  the  higher  coals  in  the 
Laramie  and  Fort  Union  formations.  The  coals  of  both  groups  are 
about  equally  dirty  to  handle,  leaving  considerable  smut  <>n  the 
fingers. 
One  of  the  most  important  physical  differences  between  coals  lies 
in  their  minute  jointing — a  property  whose  value  in  distinguishing 
coals  of  different  quality  has  not  been  sufficiently  recognized.     The 
«Bull.  r.  s.  Geol.  Survey  No.  316,  1907,  P.  192. 
