WYOMING.  247 
of  it  strongly  cross-bedded,  with  a  few  interbedded  gray  and  drab 
shales.  No  coal  bed  of  workable  thickness  was  found  in  this  part  of 
the  formation.  Overlying  the  basal  member  is  a  series  of  sandstone, 
shaly  sandstone,  and  shale  beds,  in  many  places  producing  a  region  of 
minor  relief  between  the  prominent  ridges  or  escarpments  formed  by 
the  upper  and  lower  members.  The  upper  third  of  the  formation 
closely  resembles  the  basal  member,  but  the  sandstones  are  some- 
what thinner  and  less  prominently  cross-bedded.  This  upper  mem- 
ber contains  a  few  thin  beds  of  good  coal  in  the  north  end  of  the  field, 
the  number  and  thickness  of  the  beds  increasing  toward  the  south. 
The  Dillon  mine,  southwest  of  Rawlins,  and  the  Robertson  opening, 
just  east  of  Sulphur,  are  on  beds  at  the  base  of  this  member. 
LEWIS    SHALE. 
The  Lewis  shale  is  dark  drab,  slightly  sandy,  somewhat  concre- 
tionary, and  highly  gypsiferous.  It  contains  a  few  thin,  soft  sand- 
stones which  increase  in  number  toward  the  north  end  of  the  field. 
It  weathers  rapidly,  producing  a  depression  between  the  ridges  of 
Mesaverde  sandstone  on  the  one  side  and  those  of  the  Laramie  on  the 
other.     It  was  not  found  to  be  coal  bearing. 
LARAMIE    FORMATION. 
In  the  north  end  of  the  field  the  Laramie  or  middle  coal  group  is 
made  up  of  interstratified  gray  and  brown  sandstones,  shaly  sand- 
stone, concretionary  sandstone,  and  brown  and  black  shales,  with  a 
number  of  beds  of  coal.  The  base  of  the  formation  as  mapped  is  a 
massive  white  sandstone,  usually  forming  an  escarpment.  Marine 
Montana  (Lewis)  fossils  were  in  places  found  as  high  as  400  feet 
above  this  sandstone.  Farther  south  the  lower  half  of  the  formation 
is  softer  and  more  sandy  until  in  the  south  end  of  the  field  it  consists 
of  yellow,  poorly  consolidated,  thin-bedded  sandstone,  with  a  few 
beds  of  resistant  sandstone  and  drab  shale.  Coal  beds  seem  to  be 
less  abundant  in  this  part  of  the  formation  toward  the  south,  although 
their  apparent  scarcity  may  be  due  to  the  fact  that  the  poorly  con- 
solidated sandstone  weathers  rapidly  and  does  not  produce  good 
outcrops.  The  upper  half  of  the  formation  continues  unchanged 
throughout  the  area.  The  coals  of  the  Laramie  formation  have  been 
very  little  prospected,  the  Nebraska  mine  southwest  of  Rawlins  being 
the  only  opening. 
UPPER    COAL    OROUP. 
The  basal  member  of  the  upper  coal  group  is  composed  of  gray  and 
brown  sandstones,  with  interbedded  gray,  brown,  and  drab  shales  and 
numerous  beds  of  coal.  The  sandstones  arc  thicker,  more  numerous, 
and  more  massive  toward  the  base,  which  is  marked  by  a  bed  that  is 
extremely  massive,  cross-bedded,  in  many  places  highly  ferruginous, 
