LITTLE    SNAKE   RIVER    COAL   FIELD,    WYOMING.  249 
Regarding  the  age  of  the  upper  coal  group,  the  paleontologic  evi- 
dence, principally  botanical,  from  the  three  lower  members,  con- 
flicts, pointing  partly  to  the  "Upper  Laramie,"  as  it  is  known  in  east- 
central  Carbon  County,  and  partly  to  the  Fort  Union,  with  most  of 
the  evidence  favoring  the  latter;  but  the  position  and  lithologic 
character  of  the  beds  very  strongly  suggest  the  former.  Paleontologic 
evidence  determines  the  uppermost  member  to  be  almost  certainly 
basal  Wasatch. 
UPPER    WASATCH    AND    LATER    TERTIARY    BEDS. 
Unconformably  overlying  the  upper  coal  group  is  a  succession  of 
brilliant  red  and  white,  somewhat  sandy  clays,  with  a  few  gray  and 
brown  shales  and  soft  sandstones,  the  latter  in  places  finely  con- 
glomeratic. Higher  in  the  beds  the  red  coloring  is  less  prominent, 
appearing  here  and  there  in  isolated  patches  which  decrease  in  num- 
ber and  size  until  the  beds  are  entirely  composed  of  white,  gray, 
brown,  and  drab  shales,  clay,  and  unconsolidated  sand,  with  a  few 
gray  and  brown  sandstones.  Although  brilliant  red  is  the  ordinary 
and  prominent  color,  the  roughly  bedded  clays  at  the  base  are  in 
places  purple,  green,  drab,  and  yellow.  Along  Little  Snake  River 
the  clays  are  gray  and  white,  with  the  usual  number  of  gray  and 
brown  sandstones,  which  here,  as  elsewhere  in  the  field,  are  in  places 
finely  conglomeratic.  Near  the  river  the  basal  member  seems  to  be 
a  whitish  or  yellowish  sandstone,  highly  calcareous  in  places  and 
generally  conglomeratic,  and  is  difficult  to  distinguish  in  isolated 
exposures  from  the  sandstones  of  any  of  the  three  coal  groups. 
Near  the  Union  Pacific  Railroad  these  beds  overlie  the  uppermost 
member  of  the  upper  coal  group.  To  the  south  they  successively  over- 
lap the  underlying  beds  to  the  middle  of  the  clay-shale  member  of  the 
upper  coal  group,  and  along  Little  Snake  River  they  swing  abruptly 
eastward,  covering  everything  down  to  the  Mesaverde  formation. 
The  basal  portion  of  this  group  of  beds  is  upper  Wasatch,  probably 
corresponding  in  position  to  the  Knight  formation0  of  Uinta  County; 
the  overlying  rocks  belong  in  the  Green  River  and  Bridger  formations. 
STRUCTURE. 
Between  Rawlins  and  Lake  Valley  a  shallow  syncline  separates 
the  Rawlins  dome  from  the  north  end  of  the  Sierra  Madre  uplift,  and 
connects  I  lie  Mesaverde  coal  beds  of  the  Little  Snake  River  held 
with  those  of  the  Kindt  Basin.6  Outside  of  this  small  part  near 
Rawlins  the  structure  of  the  area  is  extremely  simple,  the  formations 
dipping  regularly  to  the  west,  forming  i\\c  eastern  limb  of  the  great 
oVeatch,  A.  C,  Geography  and  geology  of  n  portion  of  southwestern  Wyoming:  Prof.  Paper  U.  S. 
Geol.  Survey  No.  56,  1907,  |>i>.  92-96. 
&Veatch,  A..  C,  Coal  fields  of . east-central  Carbon  County,  Wyo.:  Bull.  U.  S.  Geol.  Survey  No.  316. 
1907,  p.  250. 
