214        CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART  II. 
that  township  its  exact  location  was  not  determined,  and  conse- 
quently its  location  as  shown  on  PL  XI  is  only  relative. 
Dickie  mine  No.  1. — Dickie  mine  No.  1  is  on  the  north  side  of  the 
Grass  Creek  anticline,  in  the  NW.  \  sec.  2,  T.  46  N.,  R.  99  W.,  where 
the  strata  dip  19°  N.  The  bed  lies  below  a  massive  sandstone  and 
contains  40  inches  of  coal  in  the  lower  bench.  The  mine  consists  of  an 
entry  about  100  feet  long  with  one  room  opened  to  the  west.  About 
200  tons  of  coal  has  been  taken  out  to  supply  fuel  to  neighboring 
ranches.  The  physical  properties  of  the  coal  are  identical  with  those 
previously  described  from  the  Eagle  sandstone. 
Dickie  mine  No.  2. — Dickie  mine  No.  2,  locally  known  as  the  O' Riley 
mine,  is  a  small  prospect  in  a  gulch  separating  a  small  outlier  from  the 
main  body,  in  the  NE.  \  sec.  14,  T.  46  N.,  R.  99  W.  The  bed  contains 
7  feet  8  inches  of  coal  in  two  benches.  A  section  of  the  coal  is  shown 
by  No.  47,  PL  XI.  It  is  a  subbituminous  coal  similar  to  that  in  Dickie 
mine  No.  1.  The  bed  at  this  prospect  seems  to  be  a  local  thickening 
of  the  upper  bench.  One-fourth  of  a  mile  to  the  west  the  bed  is  too 
thin  to  work,  and  at  an  equal  distance  along  the  strike  to  the  south  it 
has  a  diminished  thickness  and  contains  so  many  partings  that  it  is 
not  min able. 
Prospecting. — All  the  coal  beds  in  the  Grass  Creek  field  have  been 
traced  out  by  prospectors  and  opened  at  short  intervals,  and  the 
limits  of  workable  deposits  have  been  determined.  In  the  Mayfleld 
syncline  erosion  has  cut  away  the  coal  beds  from  the  shallow  trough 
until. only  remnants  are  left.  Where  the  beds  are  uneroded,  however, 
there  seems  to  be  sufficient  capping  to  have  prevented  the  alteration 
of  the  coals  by  atmospheric  agencies.  The  syncline  is  cut  trans- 
versely by  Grass  Creek,  leaving  a  coal-bearing  portion  on  either  side. 
The  coal  occurs  in  three  beds  near  the  base  of  the  Fort  Union  forma- 
tion. One  of  the  beds  has  a  maximum  thickness  of  32  feet,  the  second 
of  15  feet,  and  the  third  of  6  feet.  Sections  of  these  beds  are  shown 
in  Nos.  49  to  55,  inclusive,  PL  XI,  and  an  analysis  of  coal  from  the 
first  bed  is  given  on  page  217.  The  coal  is  moderately  hard,  burns 
well,  seems  to  stand  exposure  to  the  air,  and  as  a  domestic  coal  is 
highly  satisfactory.  To  the  unaided  eye  the  coal  is  free  from  pyrite, 
but  under  a  lens  small  irregular  particles  are  visible.  The  area  of  the 
field  is  not  great,  but  owing  to  the  thickness  of  the  beds  it  contains  a 
large  tonnage.  The  Mayfield  district  has  been  extensively  pros- 
pected, but  is  wholly  undeveloped,  because  there  is  no  accessible 
market  for  the  product. 
On  the  north  of  the  Grass  Creek  anticline  there  are  opportunities 
for  small  mines.  The  beds  have  a  workable  thickness  and  a  favorable 
dip.  To  their  detriment,  however,  most  of  the  exposures  are  high  on 
the  face  of  a  steep  escarpment,  where  it  is  difficult  to  construct  and 
maintain  roads. 
