GLENROCK    COAL   FIELD,    WYOMING.  157 
position  of  geologic  boundaries  could  not  be  determined,  and  lines 
on  the  map  referring  to  bed  rock  are  broken  because  of  this  uncer- 
tainty. 
The  mesa  and  high-terrace  gravel  deposits  are  usually  less  than  25 
feet  thick,  but  in  the  process  of  erosion  the  gravel  is  let  down  as  a 
mantle  on  the  sides  of  the  mesas.  Many  hills  that  are  largely  com- 
posed of  coal-bearing  rock  appear  to  be  solid  gravel  because  of  this 
mantle. 
THE   COAL. 
HISTORY  OF  DEVELOPMENT. 
The  oldest  mines  in  the  field  are  at  Glenrock  and  near  Douglas. 
They  were  opened  about  1883.  The  Inez  mine  was  opened  in  1888 
by  Governor  J.  D.  Richards  and  Messrs.  Chamberlain  and  Vosbergh. 
The  Big  Muddy  mine  was  opened  by  Messrs.  Tracey  and  Veitch  in 
1900.  Coal  declaratory  statements  have  been  filed  on  many  tracts 
of  land,  and  some  have  been  taken  up  in  other  ways  because  of  their 
coal-producing  possibilities.  Much  of  this  was  done  in  1887,  when 
the  railroad  was  first  put  in  operation .  At  that  time  many  new  mines 
were  opened  and  coal  mining  received  a  great  impetus,  but  most  of 
the  beds  were  found  to  be  too  thin  or  too  poor  to  be  worked  with 
profit,  and  as  a  result  final  proof  was  not  made  on  many  of  the  tracts, 
and  they  reverted  to  the  public  domain.  The  only  productive  mines 
at  present  are  the  Glenrock  and  the  Big  Muddy. 
COAL  BEDS  OF  THE  MONTANA  FORMATION. 
Workable  coal  beds  occur  in  members  Nos.  4  and  7  of  the  section 
on  page  154.  The  coal  is  of  fair  quality  compared  with  other  Wyo- 
ming coals,  but  the  beds  are  generally  too  thin  to  be  worked  with 
profit.     The  greatest  thickness  observed  was  scarcely  4  feet. 
The  coal  in  member  No.  4  is  worked  7  to  10  miles  southeast  of  Cas- 
per, on  and  near  Nicholaysen's  ranch.  The  workings  consist  of  a 
dozen  or  more  drifts,  some  of  which  have  been  driven  100  feet  into 
the  hillsides.  The  coal  has  been  stripped  where  it  outcrops  at  Weber's 
ranch,  southwest  of  Big  Muddy,  and  a  little  is  obtained  from  the  out- 
crop in  the  north  bank  of  the  river,  3  miles  east  of  Casper,  but  it  is 
not  worked  elsewhere  in  the  field.  The  thickness  of  the  coa]  beds  of 
this  lower  zone  ranges  from  2  to  4  feet. 
The  uppermost  coal  beds  of  the  Montana  formation  occur  in  the 
resistant  white  sandstone  (No.  7),  which  is  exposed  in  many  places; 
consequently  the  coal  is  comparatively  easy  to  locate.  In  Tps.  34, 
35,  and  36  N.,  Rs.  79  and  SO  W.,  there  is  n  long  and  almost  continu- 
ous outcrop  of  the  sandstone,  bid  the  full  thickness  i~>  not  exposed  in 
any  one  place.  In  many  localities  the  coal  associated  with  the  sand- 
stone is  not  visible,  but  il  is  probable  that  one  or  more  coal  beds  2  to 
