WYOMING.  155 
consequently  the  most  conspicuous  part  of  the  whole  section.  At 
many  places  it  forms  a  large,  low,  pine-covered  hogback.  One  very 
^  )od  exposure  is  located  in  sec.  16,  T.  33  N.,  R.  78  W.,  6  or  7  miles 
southeast  of  Casper.  This  sandstone  contains  one  or  two  beds  of  coal, 
and  its  outcrop  agrees  approximately  with  that  of  coal  bed  A,  which 
crosses  sec.  16,  as  shown  on  the  map. 
In  going  from  the  resistant  white  sandstone  (No.  7)  in  the  direction 
of  the  dip,  one  usually  crosses  a  broad,  shallow  depression  which  is 
underlain  by  shale  (No.  8)  and  comes  to  an  outcrop  of  brown  sand- 
stone '(No.  9).  In  some  places  the  latter  forms  a  hogback  several 
miles  long,  for  example,  6  or  8  miles  southeast  of  Glenrock.  Its 
weathered  surface  is  everywhere  much  smoother  than  exposed  parts 
of  No.  3. 
The  upper  boundary  of  the  brown  sandstone  is  usually  indistinct, 
as  the  brown  grades  into  the  white  of  the  succeeding  member  (No.  10). 
This  and  the  remaining  members  of  the  Montana  are  not  resistant,  and 
few  outcrops  are  visible. 
The  exact  upper  boundary  of  the  Montana  was  hard  to  determine 
in  the  field  because  the  strata  known  to  be  of  this  age  are  overlain  by  a 
nonf  ossilif erous  sandstone  which  is  much  like  the  beds  below  and  which 
in  turn  is  overlain  by  the  Fort  Union  (?).  No  distinct  stratigraphic 
break  was  found,  although  in  one  or  two  places  there  are  slight  indi- 
cations of  such  a  break  at  the  base  of  this  sandstone,  and  on  the  map 
the  boundary  between  the  formations  is  drawn  at  tins  horizon.  It 
may,  however,  possibly  be  as  much  as  400  feet  stratigraphically,  or 
one-fourth  to  one-half  mile  on  the  surface,  from  its  true  position. 
Parts  of  the  Montana  formation  contain  many  shells  and  other  ani- 
mal remains,  but  there  are  very  few  fossil  leaves.  In  this  respect  the 
Montana  is  different  from  the  succeeding  coal-bearing  formation, 
which  has  many  leaf  imprints  and  almost  no  shells. 
The  upper  two-thirds  of  the  Montana  may  be  equivalent  to  the 
Mesaverde  of  Colorado  and  southern  Wyoming,  but  exact  correlation 
is  not  possible  at  the  present  time. 
FORT    UNION  (?)    FORMATION. 
At  or  immediately  above  the  top  of  the  Montana  formation  there  is 
about  400  feet  of  massive  white  or  buff  sandstone  (mentioned  above), 
with  several  coal  beds  and  some  shale.  No  fossils  were  found  in  it. 
This  member  and  the  accompanying  coal  beds  may  be  Montana,  Lar- 
amie, or  Fort  Union.  In  this  paper  they  are  provisionally  regarded 
as  Fort  Union. 
The  Fort  Union  (?)  as  a  whole  resembles  the  Montana,  but  it  is  even 
more  irregularly  bedded.  There  are  very  few  zones  winch  can  be 
recognized  wherever  seen,  and  the  formation  is  much  thicker  than  the 
Montana.     It  may  be  separated  into  three  members  —a  lower  one  of 
