58  CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,   1907,   PART   II. 
woody  texture  and  are  tough;  the  lower  coals  have  more  the  texture 
of  higher-grade  coals,  though  nearly  all  the  beds  contain  some  woody 
material.  Joints  have  been  observed  in  all  the  beds  wherever  they 
are  well  exposed.  The  joint  planes  are  invariably  wide  apart,  but 
are  of  considerable  importance  in  mining,  and  for  blasting  the  holes 
are  usually  bored  parallel  to  them.  The  lumps  of  coal  produced  are 
generally  of  irregular  shape.  They  begin  to  crackle  and  lose  moisture 
immediately  after  mining  and  finally  slack  to  fine  flaky  powder  under 
atmospheric  influences. 
In  burning  the  coals  decrepitate  rapidly,  and  if  disturbed  the  fire  is 
easily  smothered.  To  obtain  the  greatest  efficiency,  the  coal  must  be 
spread  thinly  over  wide  grates.  It  burns  with  a  long,  yellow  flame, 
but  does  not  produce  much  smoke. 
CHEMICAL   PROPERTIES. 
All  the  samples  of  this  coal  which  have  been  analyzed  contain  more 
than  29  per  cent  of  moisture  as  they  come  from  the  mine,  and  after 
air  drying  they  still  retain  from  10  to  18  per  cent.  The  coals  from 
the  upper  member  usually  contain  from  8  to  10  per  cent  of  ash  and 
are  apparently  more  impure  than  those  from  the  lower  member. 
The  relative  proportion  of  fixed  carbon  in  the  coal  from  the  former  is 
higher  than  in  that  from  the  latter.  The  fuel  ratios  (percentage  of 
fixed  carbon  divided  by  percentage  of  volatile  matter)  of  the  lower 
coals  average  1.20;  those  of  the  lignites  higher  in  the  section  are 
considerably  less.  In  efficiency  the  lower  coals  are  greater  than  the 
higher  lignites.  From  their  obvious  physical  and  chemical  properties 
the  former  are  classed  as  subbituminous  and  the  latter  as  lignite. 
Owing  to  the  primitive  nature  of  the  developments  in-  tins  field, 
only  seven  representative  samples  of  unweathered  coal  were  obtained 
for  chemical  analysis.  These  were  collected  from  mines  according  to 
the  method  prescribed  by  the  United  States  Geological  Survey 
fuel-testing  plant,  as  noted  on  pages  12-13. 
Sample  No.  5962  was  collected  near  the  outcrop  where  the  lignite 
showed  some  indications  of  weathering.  All  the  other  samples  rep- 
resent unweathered  coal.  The  samples  collected  last  summer  were 
not  analyzed  until  several  months  after  they  were  obtained,  but  all 
of  them  were  sealed  in  air-tight  cans.  Before  analyzing  they  were 
reduced  to  a  uniform  basis  by  exposing  them  to  dry  air,  and  the  loss 
of  moisture  on  air  drying  was  determined.  The  analyses  of  the 
samples  both  as  received  and  after  air  drying  are  given,  but  for  pur- 
poses of  comparison  the  analysis  of  the  air-dried  sample  is  preferable, 
as  it  represents  more  nearly  the  condition  in  which  the  coal  would 
reach  the  consumer. 
