ROCK    SPRINGS    COAL   FIELD,    WYOMING.  261 
dome  in  the  vicinity  of  Baxter  Station  these  may  lie  near  enough  to 
the  surface  to  be  mined  some  day,  but  at  present  no  borings  have 
penetrated  deep  enough  to  reveal  them,  and  information  is  lacking 
regarding  their  depth  and  existence.  In  this  field  the  Mesaverde 
consists  of  four  distinct  members,  two  of  which  are  coal  bearing.  The 
lowest  member,  as  well  as  the  beds  underlying,  consists  chiefly  of 
sandstone,  shaly  sandstone,  and  shale,  all  of  which  are  barren  of  coal 
and  show  no  indications  of  bituminous  matter.  The  two  coal-bearing 
members  of  the  Mesaverde  are  separated  from  each  other  by  a  mas- 
sive white  sandstone,  approximately  800  feet  thick.  The  lower 
group  of  coal  beds  is  known  as  the  Rock  Springs  coal  group,  and  the 
other  as  the  Almond  coal  group.  The  Almond  coal  group  is  overlain 
by  noncoal-bearing  shale  which  corresponds  to  the  Lewis  shale  in 
other  parts  of  the  Rocky  Mountain  region. 
Rock  Springs  coal  group. — The  Rock  Springs  coal  group  is  the  most 
important  and  the  one  containing  the  highest  grade  of  coal  in  this 
area.  Its  basal  portion  consists  of  heavy,  ridge-making,  coal-bearing 
sandstones  and  the  remainder  of  brown,  yellow,  and  white  sandstones, 
shale,  clay,  and  interbedded  coal.  The  group  is  prolificaHy  coal  bear- 
ing throughout  and  contains  at  least  twelve  coal  beds  ranging  from  2 
to  10  feet  in  thickness  and  many  other  beds  less  than  2  feet  thick. 
These  beds  occur  somewhat  regularly  throughout  the  group  and  are 
fairly  persistent  along  the  strike.  They  have  been  prospected  all  the 
way  from  Rock  Springs  to  Superior.  Very  little  prospecting  has  been 
done  south  of  Superior.  In  this  locality  the  coal  beds  are  somewhat 
thinner,  and  the  number  of  the  beds  is  not  so  great  as  it  is  between 
Superior  and  Rock  Springs.  The  coal  is,  however,  of  high  grade,  and 
additional  mines  are  certain  to  be  opened  in  the  near  future.  Mines 
are  in  operation  on  beds  of  this  group  at  Rock  Springs  and  Superior, 
upper  beds  being  worked  at  both  places,  and  at  Gunn  the  coal  beds 
near  the  base  of  the  group  are  being  opened.  New  mines  were 
to  be  opened  last  season  north  of  Rock  Springs  along  Killpecker 
Valley  and  at  Gunn  camp,  northwest  of  Baxter,  but  owing  to  the 
money  stringency  work  was  greatly  delayed  and  some  of  it  tem- 
porarily abandoned.  In  Rock  Springs  all  the  mines  now  in  operation, 
with  the  exception  of  mine  No.  1  of  the  Union  Pacific  Coal  Company, 
are  working  the  No.  7  bed.  No.  1  mine  is  working  the  No.  1  bed, 
which  is  strut igraphically  higher  than  No.  7.  The  area  under- 
lain by  the  Rock  Springs  coal  was  mapped  in  detail,  and  the 
locations  of  mines,  prospect  pits,  and  coal  crops  were  determined 
by  means  of  stadia.  The  locations  of  the  outcrops  of  the  more 
important  coal  beds  and  of  the  mines  and  prospect  pits  and  tunnels 
are  shown  on  PL  NY. 
