430  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
mass  of  overlying  sandstone  and  shale.  The  coal  in  this  district 
varies  greatly  in  thickness  and  purity,  but  there  is  a  large  area  in 
which  it  is  5  feet  thick  or  more,  and  in  places  it  reaches  a  thickness 
of  over  7  feet.  In  adjoining  areas  its  thickness  rapidly  diminishes 
and  the  coal  becomes  extremely  impure,  in  greater  part  giving  place 
to  dark  carbonaceous  shale.  The  principal  basin  of  purer,  thicker 
coal  forms  an  oval  area  trending  northeast  and  southwest,  its  axis 
passing  through  Cambria.  To  the  northeast  the  coal  has  been 
entirely  eroded  away  by  Salt  Creek,  and,  although  some  Lakota 
sandstone  remains  on  the  high  ridges  east  of  the  valley  of  that 
stream,  it  appears  not  to  be  underlain  by  coal.  To  the  southwest 
the  coal,  lying  from  250  to  325  feet  below  the  surface  of  the  table, 
dips  gently  downward  until,  at  the  Mount  Zion  ranch,  an  abrupt 
increase  in  dip  carries  it  farther  below  the  surface.  In  the  canyon 
a  few  rods  southwest  of  Mount  Zion  ranch  the  following  section  was 
measured  : 
Section  near  Mount  Zion  ranch,  Wyoming. 
Feet. 
Bony  coal i 
Hard  sandstone 3 
Good  coal 4 
Sandstone  with  coaly  streaks $  to  1£ 
Coal 2 
This  section  is  150  feet  below  the  top  of  the  plateau.  The  over- 
lying formations  are  sandstone  and  conglomerate.  Underneath  there 
are  40  feet  of  very  light-colored  massive  sandstone,  in  part  cross- 
bedded,  lying  on  Morrison  shale.  A  mile  northeast  of  this  locality 
two  shafts  were  sunk  in  which  the  coal  wras  found  at  depths  of  312 
and  324  feet,  exhibiting  a  thickness  of  from  5^  to  (H  feet.  In  the 
mines  the  thickness  of  the  coal  averages  from  6  to  7  feet  over  a  wide 
area. 
There  are  three  mines — the  Jumbo,  lying  east  of  Cambria;  Ante- 
lope No.  1,  between  Cambria  and  Camp  Canyon;  and  Antelope  No. 
2,  between  Camp  Canyon  and  Grant  Canyon.  The  two  Antelope 
mines  are  connected  by  a  continuous  main  gallery  leading  out  to  a 
breaker  on  the  Avest  side  of  the  valley  at  Cambria,  while  the  Jumbo 
mine  is  worked  from  the  main  drift  opening  on  the  east  side  of  that 
valley.  The  dip  is  gentle  to  the  southwest,  so  that  the  drainage  of  the 
mines  is  easily  effected,  the  workings  being  50  to  60  feet  above  the 
valleys. 
Section  in  Camp  Canyon,  Wyoming. 
Feet. 
Coal 6 
Shale  and  bone : 1£ 
Coal 6 
