LEWISTOWN   COAL   FTELD,   MONT  119 
greater  than  that  received  in  others.  This  higher  price  is  due  partly 
to  the  fact  that  coal  is  not  readily  obtained  from  other  fields,  but 
chiefly  because  local  conditions  are  not  conducive  to  cheap  mining. 
CHARACTER  OF  THE   COAL. 
PHYSICAL    CHARACTER. 
The  coal  of  the  Lewistown  field  has  certain  physical  characteristics 
which  differentiate  it  in  a  measure  from  other  coals  of  the  State, 
with  the  exception  of  that  from  the  Great  Falls  field,  to  the  west. 
The  coal  is  persistently  banded  in  appearance,  with  alternating  layers 
of  bright  and  dull  luster,  the  latter  predominating.  In  general,  there- 
fore, the  coal  is  dull  or  grayish  black  in  color.  The  bright  bands 
are  thin,  ranging  from  a  mere  film  to  one-fourth  inch  in  thickness. 
The  dull  bands  owe  their  appearance  chiefly  to  the  presence  of  mineral 
charcoal.  Even  in  these  bands,  which  at  first  sight  appear  to  be 
entirely  lusterless,  closer  examination  shows  that  very  minute  lenses 
of  bright  coal  are  present.  Sulphur  in  the  form  of  iron  pyrites 
(FeS2)  is  more  or  less  abundant,  occurring  usually  in  the  form  of  small 
nodules  or  lenses,  although  it  is  present  also  as  a  thin  incrustation 
between  layers  or  along  joint  planes. 
The  coal  in  the  Spring  Creek  and  neighboring  mines  has  near  -the 
bottom  of  the  bed  several  thin  partings  which  at  first  glance  appear 
to  be  similar  to  the  bright  bands  previously  mentioned.  This  mate- 
rial will  not  burn  readily,  however,  and  is  thrown  aside  as  waste.  It 
is  termed  "black  jack"  by  the  miners.  A  sample  obtained  at  the 
Spring  Creek  mine  and  analyzed  at  the  laboratory  of  the  fuel-testing 
plant  at  Pittsburg  carried  31.84  per  cent  of  ash.  In  several  localil  ies, 
notably  in  the  Mace  mine  on  Warm  Spring  Creek,  a  dull,  lusterless 
variety  of  coal,  resembling  cannel,  was  noted.  It  occurs  in  the  Mace 
mine  as  lenses  of  considerable  extent  in  the  bed,  the  largest  being 
200  feet  in  length. 
CHEMICAL    CHARACTER. 
Chemical  analyses  of  the  coal  show  that  it  is  to  be  classed  as  medium- 
grade  bituminous.  That  there  is  a  considerable  range  in  quality  is 
indicated  by  the  heat-value  determinations.  A  sample  of  coal  was 
obtained  from  each  working  mine  in  the  field  by  cutting  a  channel 
across  the  bed  from  roof  to  floor,  exclusive  of  partings  discarded  in 
mining. 
The  results  of  the  analyses,  given  in  the  following  table,  are  in  two 
sets,  one  showing  analyses  of  the  sain | >les  as  received  in  the  laboratory 
and  the  other  on  an  air-dried  basis.  The  latter  more  Dearly  represent 
the  coal  as  it  is  used  commercially. 
