204         CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,   1907,   PART   II. 
The  remaining  formations  are  thought  to  be  represented,  but  there  is 
not  sufficient  evidence  at  hand  to  identify  them  positively.  There- 
fore the  group  is  presented  in  this  report  as  Eagle  and  undifferentiated 
Montana. 
EAGLE    SANDSTONE. 
The  Eagle  sandstone  is  recognized  in  the  west  side  of  the  Bighorn 
Basin  on  stratigraphic  and  lithologic  and  not  on  paleontologic  evi- 
dence. The  fossil  plants  that  were  collected  from  this  formation  are 
either  new  or  not  sufficiently  typical  to  prove  its  age  conclusively. 
The  formation  is  rather  definitely  identified,  however,  both  by  its 
stratigraphic  position  immediately  above  known  Colorado  shale  and 
by  its  lithologic  characteristics.  In  all  essential  particulars  the  forma- 
tion resembles  the  Eagle  as  it  is  recognized  20  miles  to  the  north,  in 
the  Clark  Fork  valley.  It  consists  of  massive  sandstone  and  sandy 
shale  with  carbonaceous  and  coal  beds.  A  section  of  the  formation 
measured  on  Shoshone  River  3  miles  northeast  of  Cody  is  as  follows : 
Section  of  Eagle  sandstone  exposed  along  Shoshone  River  3  miles  northeast  of  Cody,  Wyo. 
Feet. 
Shale,  drab,  containing  a  few  iron  concretionary  layers,  also  a  12-inch 
bed  of  coal 22 
Sandstone,  gray,  massive 5 
Sandstone  and  shale  with  dark  coaly  bands,  in  alternating  layers  ....  65 
Sandstone,  gray,  massive 28 
Sandstone,  greenish,  shaly  at  base 33 
Sandstone,  gray,  massive,  concretionary,  weathering  tan 65 
218 
The  Eagle  is  usually  characterized  by  two  massive  sandstones  from 
25  to  65  feet  thick,  which  weather  into  bold  cliffs.  These  sandstones 
serve  as  guides  to  the  location  of  the  coal  horizon  which  occurs 
between  them.  Coal  of  workable  thickness  is  not  continuous,  how- 
ever, at  this  horizon,  but  varies  locally.  In  general  character  the  for- 
mation remains  fairly  constant  throughout  the  field,  except  in  the 
extreme  southern  part,  where  it  is  slightly  thicker  and  contains  a 
greater  number  of  beds,  none  of  which  is  so  massive  as  those  to  the 
north. 
UNDIFFERENTIATED    MONTANA. 
As  considered  in  this  report  the  upper  or  undifferentiated  part  of 
the  Montana  consists  of  gray  sandstone  and  dark-colored  shale  in 
alternating  layers.  It  generally  maintains  a  thickness  of  about  750 
feet  throughout  the  field  except  near  Meeteetse,  where  the  formation 
seems  to  be  much  thicker.  Fossils  collected  from  these  beds  include 
forms  similar  to  those  found  in  the  Judith  River  formation  of  Mon- 
tana. Insufficient  evidence  exists,  however,  to  differentiate  the  for- 
mations recognized  to  the  north,  hence  only  the  group  name  is  here 
applied.     The  upper  limit  of  the  group  is  drawn  on  lithologic  grounds 
