248         CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,    1907,   PART   TT. 
and  as  a  rule  somewhat  conglomeratic.  The  pebbles  of  the  con- 
glomerate are  small  and  usually  chert,  although  near  the  Union 
Pacific  Railroad  fragments  of  Carboniferous  limestone  and  Creta- 
ceous shale  were  observed  by  E.  E.  Smith.0  Smith  found  that  in  the 
area  north  of  the  railroad  this  conglomeratic  sandstone  is  underlain 
by  a  mass  of  beds  about  800  feet  thick  composed  of  alternating  layers 
of  shale  and  rusty-brown  conglomeratic  sandstone,  the  latter  decreas- 
ing in  number,  thickness,  and  conglomeratic  character  toward  the 
bottom.  For  several  miles  south  of  the  railroad  there  are  no  satis- 
factory exposures  to  show  the  southward  extent  of  these  beds.  In 
the  southern  portion  of  the  area  the  heavy  sandstone  is  separated  by 
3  to  100  feet  of  dark  shale  from  a  thin  bed  of  rather  coarse,  highly 
quartzose  conglomerate  with  chert  pebbles  held  in  a  matrix  of  coarse 
chert  and  crystalline  quartz.  In  some  places  a  second  conglomerate 
is  separated  by  about  100  feet  of  shale  from  the  first.  The  coal  beds 
of  this  member  are  the  most  extensively  prospected  in  the  area,  the 
Muddy  Bridge  and  Dixon  Cut-off  openings  and  a  number  of  smaller 
prospects  being  on  these  beds. 
Overlying  the  basal  member  is  a  member  consisting  of  clay  shale 
and  sandy  clay,  with  a  small,  extremely  variable  amount  of  soft 
sandstone,  either  massive  or  thin  bedded.  In  the  most  northerly 
exposures,  which  occur  about  midway  between  Coal  Bank  and 
Chicken  springs,  the  clay  is  white  and  the  sandstone  gray,  whereas 
farther  south  the  color  of  the  rocks  is  gray,  brown,  and,  near  the 
river,  almost  black.  In  some  places  toward  the  south  the  beds  con- 
tain large  quantities  of  cherty  conglomerate;  in  other  places  this 
conglomerate  is  confined  to  the  top  or  to  the  top  and  bottom,  and 
elsewhere  it  is  absent.     This  member  contains  no  coal  beds. 
Gray  and  brown  sandstones  with  interbedded  gray,  brown,  and 
drab  shales  and  numerous  coal  beds  compose  the  next  member.  The 
coal  beds  have  not  been  prospected,  although  very  prominently 
exposed  at  Coal  Bank  Spring  and  along  the  ridge  west  of  Fillmore 
Creek. 
The  division  between  the  uppermost  or  fourth  member  and  the  one 
underlying  it  is  based  on  a  conglomerate  which  Smith  a  observed  in 
the  north  end  of  the  Great  Divide  Basin  and  traced  southward  to 
Fillmore,  finding  evidence  of  unconformity.  The  conglomerate  was 
observed  for  about  4  miles  south  of  the  Union  Pacific  Railroad, 
showing  distinct  unconformity;  but  beyond  that  point  it  is  com- 
pletely obscured  by  gravel  and  other  covering.  Lithologically  the 
beds  above  the  conglomerate  resemble  those  immediately  below,  con- 
sisting of  interstratified  gray  and  brown  sandstones  and  brown,  drab, 
and  black  shales,  with  many  beds  of  impure  coal,  and  near  the  top 
a  peculiar  brown  shale  weathering  greenish. 
a  See  table,  pp.  224-225. 
