254         CONTRIBUTIONS    TO    ECONOMIC   GEOLCGY,    1907,   PART   II. 
sintering  and  slumping  of  the  overlying  shaly  sandstone,  but  the 
dirty  coal  composing  the  lower  part  of  the  bed  is  apparently  not 
affected.  In  this  connection  attention  should  be  called  to  the  fact 
that  sample  No.  5299  in  the  table  above  was  taken  from  a  2-foot  bed 
separated  by  3  feet  of  shale  from  15  feet  of  burned  coal.  The  physical 
appearance  of  the  bed  sampled  was  not  altered  by  the  burning,  but 
the  chemical  analysis  shows  decided  differences  between  this  sample 
and  the  others  collected  from  the  same  zone;  notably,  increased  fuel 
value;  lower  air-drying  loss;  low  volatile  matter  and  high  fixed 
carbon,  giving  high  fuel  ratio;  and,  in  the  ultimate  analysis,  low 
hydrogen  and  oxygen  and  high  carbon.  Thus  this  coal  in  close 
proximity  to  a  burned  bed  has  by  alteration  become  of  considerably 
higher  grade  than  its  unaffected  neighbors. 
RELATIVE  VALUE. 
Unfortunately  there  are  in  this  field  no  openings  on  the  coals  of 
the  two  upper  members  of  the  upper  coal  group,  and  it  was  impossible 
to  procure  un weathered  samples  of  these  beds  for  analysis.  The 
samples,  all  from  the  three  low^er  coal-bearing  zones,  have  lowTer  fuel 
values  than  the  samples  from  the  same  zones  collected  by  Veatcha  in 
the  east-central  Carbon  County  fields  in  1906.  This  may  be  due  to 
the  greater  amount  of  folding  in  the  rocks  of  the  eastern  fields,  but  it 
must  be  borne  in  mind  that  most  of  the  samples  collected  in  eastern 
Carbon  County  were  from  working  mines  or  other  adequate  openings, 
whereas  of  the  samples  from  this  field  two  are  from  abandoned  mines 
and  the  remainder  from  prospects.  The  eastern  Carbon  County 
samples,  then,  represent  coal  which  is  much  fresher,  less  weathered, 
and  nearer  the  true  value  than  the  samples  from  this  field. 
With  the  exception  of  the  coal  No.  5299,  which  is  believed  to  have 
increased  in  value  by  the  burning  of  an  adjacent  bed,  the  coals  of  this 
field  decrease  in  value  from  the  lowest  to  the  highest  coal-bearing 
zones;  from  bituminous  coal  at  the  Dillon  mine  through  increasingly 
low-grade  subbituminous  almost  to  lignite  in  the  uppermost  member 
of  the  upper  coal  group. 
DEVELOPMENT. 
Development  in  the  area  has  been  confined  to  a  slight  amount 
of  prospecting  and  a  few  small  openings  to  supply  the  local  demand. 
The  Dillon  mine  (Mesaverde)  produced  good  coal  for  several  years 
prior  to  1900  or  1901.  M.  W.  Dillon,  the  original  owner  of  the  mine, 
says  the  mine  wTas  closed  down  by  the  people  to  whom  he  sold  it 
because  faults  were  encountered  in  the  rooms.  The  coal  was  used 
in  Rawlins,  3  miles  away,  as  was  also  that  of  the  Nebraska  mine 
(Laramie),  4  miles  southwest  of  the  Dillon  opening. 
a  Bull.  U.  S.  Geol.  Survey  No.  316,  1907,  pp.  253-258. 
