168         CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY, 
DESCRIPTION    OF   FORMATIONS. 
Cloverly  formation. — At  the  base  of  the  Cloverly  formation  in  its 
typical  development  on  Gypsum  Creek,  north  of  Lovell,  Wyo.,  there  is 
40  to  50  feet  of  massive  sandstone,  locally  containing  shale  partings 
and  a  thin  coal  bed.  The  coal  is  of  little  economic  importance,  though 
it  has  been  mined  at  times  for  local  use  near  Bell's  ranch  on  No  Wood 
Creek.  There  is  no  coal  in  the  Cloverly  at  any  place  within  the  ter- 
ritory studied  by  the  writer.  Overlying  the  sandstone  are  100  to  150 
feet  of  bright  variegated  clays  and  soft  sandstones,  with  concretions 
of  limestone  and  chert.  The  top  member  of  the  formation  is  a  mas- 
sive gray  sandstone  about  70  feet  thick,  overlain  by  15  feet  of  dark- 
purplish  shale.  In  all  other  places  examined  none  of  the  formation 
above  the  basal  sandstone  is  certainly  present,  and  in  most  places  the 
entire  formation  is  absent.  This  hiatus  is  due  to  an  unconformity, 
separating  the  Cloverly  formation  from  the  overlying  marine  Colorado 
shale.  The  age  of  the  Cloverly  is  believed  to  be  Lower  Cretaceous, 
probably  equivalent  to  that  of  the  Kootenai  of  northern  Montana 
and  Alberta. a 
Colorado  shale. — The  Colorado  shale  consists  of  over  4,000  feet  of 
dark  marine  shale,  with  one  or  two  conspicuous  sandstones  about  1,000 
feet  above  the  base.  The  upper  part  of  the  formation  is  probably 
synchronous  though  not  lithologically  identical  with  the  Niobrara, 
and  an  indeterminate  amount  of  the  lower  part  of  the  formation 
is  of  Benton  age.  The  Benton  fauna  ranges  through  more  than 
3,000  feet  of  the  lower  part  of  the  formation.  The  Colorado  con- 
tains some  oil  and  probably  valuable  stores  of  gas.  In  its  lower  part 
occur  thin  beds  of  pure  white  bentonite. 
Eagle  sandstone. — The  Eagle  sandstone  consists  of  two  or  three  mas- 
sive sandstones,  35  to  75  feet  thick,  separated  by  carbonaceous  shale 
with  three  beds  of  coal.  These  are  the  workable  beds  of  the  Silver  tip 
and  the  Bridger  coal  fields. 
Olaggett  formation. — Overlying  the  Eagle  is  another  partially  marine 
formation,  the  Claggett,  consisting  of  massive  yellow  and  gray  sand- 
stones with  subordinate  dark  shale.  Beds  of  coal  occur  in  the  forma- 
tion in  most  exposures,  but  they  are  thin  and  valueless. 
Judith  River  formation. — The  Judith  River  formation  is  like  the 
Cloverly  in  its  bright  coloration.  It  consists  of  variegated  green, 
white,  purple,  and  red  clays  and  soft  white  sandstone.  Fossil  wood 
and  bones  are  abundant  nearly  everywhere  in  this  formation. 
Bearpaw  shale. — The  Bearpaw  shale  consists  of  dark,  thin-bedded 
shale,  in  many  places  laminated,  with  rarely  some  thin  beds  of  sand- 
stone. The  shale  is  thought  to  be  marine,  but  no  marine  fossils  have 
been  found  south  of  the  Silvertip  anticline  on  the  Montana- Wyoming 
a  Fisher,  C.  A.,  Southern  extension  of  the  Kootenai  and  Montana  coal-bearing  formations  in  northern 
Montana:  Econ.  Geology,  vol.  3,  1908,  pp.  77-99. 
