358 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
the  uppermost  prominent  band  of  hard  siliceous  shale.  The  oil  is  probably  derived  fr< 
the  diatoms  and  other  minute  vegetable  remains  found  in  the  underlying  shale,  and  finds 
way  into  the  sandy  layers  at  the  top  of  the  series  mainly  through  the  multitude  of  jo 
cracks  which  penetrate  both  the  shale  and  sandstone.  The  Miocene  shales  are  overl 
(probably  unconformablv,  although  having  the  same  general  dip)  by  at  least  2,000  f 
of  Pliocene  sediments,  which  in  the  Salt  Lake  field  appear  to  consist  largely  of  clayey  sh 
- 
Hill 
<u  t- 
3.      "^ 
5        8   cu  v  <G  ^ 
with  occasional  interbedded  sandy  or  gravelly  layers.  The  Pleistocene  beds  are  m 
up  of  clay,  sand,  and  gravel,  the  clay  predominating,  and  are  often  highly  impregna 
with  oil,  forming  brea. 
Great  deposits  of  this  brea  occur  in  the  immediate  vicinity  of  the  lagoon  and  north  $ 
northwest  of  it  for  a  considerable  distance.  Numerous  bones  of  extinct  Pleistocene  mi 
naals,  such  as  the  saber-toothed  tiger,  elephant,  giant  sloth,  cave  bear,  camel,  and  dog 
embedded  in  this  brea,  and  indicate  not  only  the  age  of  the  deposits  but  also  the  import 
