562  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         I  bull.  260. 
The  extensive  deposits  of  bentonite  discovered  by  the  writer  in  the 
northern  part  of  the  Bighorn  basin  are  on  Dry  Creek  about  8  miles 
east  of  Frannie,  Wyo.  The  Benton  formation  here  consists  of  a  basal 
member  of  rusty -brown,  sandy  shales  200  feet  thick,  overlain  by  500 
feet  of  very  black  shale,  in  the  upper  part  of  which  occurs  several 
horizons  of  bentonite.  Immediately  above  these  beds  there  is  a  very 
characteristic  series,  about  150  feet  thick,  of  hard,  lighter-gray  shales 
and  sandstone  of  the  Mowrie  beds.  Next  above  occur  about  300  feet 
of  light-gray  shales,  alternating  with  sandy  beds  of  no  great  thick- 
ness. This  series  is  capped  by  60  feet  of  gray,  coarse-grained,  cross- 
bedded  sandstone,  which  in  turn  is  overlain  by  another  shaly  series.. 
200  feet  thick,  containing  concretionary  bands  and  constituting  the 
uppermost  member  of  the  Benton.  The  bentonite  occurs  in  the  black 
shales  of  the  lower  part  of  the  Graneros  shales,  a  short  distance  below 
the  Mowrie  beds,  which  here  are  well  developed.  The  deposits  have 
a  total  thickness  of  11  feet,  distributed  throughout  a  vertical  range 
of  100  feet.  The  thickest  layer  is  about  7^  feet  thick.  Below  the 
bentonite  series  beds  of  dark  shale  abound,  and  above  are  lighter 
shales,  containing  bands  of  iron  concretions.  The  material  is  a  gray., 
fine-grained,  massive  clay,  of  green  and  yellow  tints,  apparently  oi? 
good  quality  throughout.  The  thin  seams  of  gypsum  generally  asso- 
ciated with  the  clay  in  other  localities  are  present,  though  not  con- 
spicuous. These  deposits,  when  seen  at  a  distance,  appear  as  dull 
gray  bands  on  the  face  of  the  barren  slopes  of  the  Benton  shales.  The 
following  section  will  show  the  -approximate  position  of  the  differen.il 
deposits  at  this  place : 
Section  of  a  portion  of  the  Benton  formation  on  Dry  Creek. 
Feet. 
Bentonite    ^ 2 
Dark   fissile  shale 12 
Bentonite    . 1\ 
Shale    30 
Bentonite    1$ 
Shale    'SO 
Near  the  head  of  Dry  Gulch,  about  5  miles  north  of  Cowley,  Wyo. 
a  H-foot  layer  of  bentonite  is  found  near  the  top  of  the  Bentoi 
formation.  The  following  section  shows  the  materials  associate! 
with  the  bentonite : 
Section  at  head  of  Dry  Gulch. 
Feet. 
Black  shale  capped  by  brown  sandstone 6 
Bentonite   li 
Black  fissile  shale 20 
