COAL  ON   NORTHEAST  SIDE  OF  BIGHORN   BASIN,   WYO. 
167 
scraggy  pines  on  some  of  the  higher  sandstone  ridges.  Elsewhere 
there  is  no  vegetation  except  sagebrush,  prickly  pear,  greasewood, 
grasses,  and  similar  small  plants.  The  nearest  trees  suitable  for  mine 
timber  grow  on  Pryor  Mountain,  northeast  of  Bowler;  on  the  Bear- 
tooth  Mountains,  25  miles  southwest  of  the  Bridger  field;  and  on  the 
headwaters  of  No  Wood  Creek,  35  miles  southeast  of  the  Basin  field. 
GEOLOGY. 
STRATIGRAPHY. 
GENERAL    SECTION. 
The  rocks  exposed  on  the  east  side  of  the  Bighorn  Basin  embrace 
strata  of  all  ages  from  the  Carboniferous  to  the  lower  Eocene,  but  only 
the  Cretaceous  and  Tertiary  formations  need  be  considered,  as  they  are 
the  only  ones  containing  coal.  These  formations  are  shown  in  the 
accompanying  geologic  section. 
Stratigraphic  colum 
n  on  the  east  side 
of  the  Bigi 
horn  Basin,  Wyoming.  « 
Series. 
Group. 
Formation. 
Thickness 
(feet). 
Characteristics. 
Eocene  (Tertiary). 
Wasatch    forma- 
tion. 
-  Unconformity. — 
Fort   Union  for- 
mation. 
500 
Bright-colored  clays,  with  a  few  thin 
lenses  of  sandstone.  Contains  work- 
able coal  in  the  central  part  of  the 
basin. 
1,000  to 
2,000 
Dark-colored  shale  and  massive 
sandstone.  Contains  workable 
coal. 
Laramie  (?)  for- 
mation.b 
150  to  700 
Massive  sandstone  with  subordinate 
shale.    Contains  workable  coal. 
Montana. 
Bearpaw  shale. 
150 
Dark  marine  shale. 
Judith  River  for- 
mation. 
300  to  400 
Variegated  clays  and  soft  sandstone. 
Upper  Cretaceous. 
Claggett    forma- 
tion. 
400  to  500 
Massive  fresh  and  brackish  water 
sandstones  and  dark  shale.  Coal 
not  workable. 
Eagle  sandstone. 
Massive  fresh  and  hrackish  water 
i  *n  tr,  99*;  '      sandstones,  separated  by  carbon- 
iou  to  no        aceous  shale.    Contains  workable 
coal. 
Colorodo  shale. 
Unconformity. 
Cloverly. 
4,400 
Dark  shale  with  one  or  two  conspicu- 
ous sandstones,  not  divisible  in 
this  field,  though  more  than  1,500 
feet  of  the  lower  part  is  known  to 
be  equivalent  to  the  Benton  shale 
Lower  Cretace- 
ous (?). 
0  to  275 
Bright-colored  clays,  with  massive 
sandstones  at  the  top  and  bottom. 
Coal  not  workable. 
o  For  the  recognition  of  the  formations  in  the  field  the  writer  is  indebted  to  the  guidance  of  C.  A. 
Fisher.  The  subdivisions  of  the  Montana  group  are  correlated  with  similu  r  subdivisions  proposed  by 
Stanton  and  Hatcher  in  the  Judith  River  region  of  northern  Montana  (Stanton,  T.  \\  and  Matcher, 
J.  B.,  Geology  and  paleontology  of  the  Judith  River  beds;  Bull.  U.  S.  Geol.  Survey  No.  257,  1905).  I  his 
correlation  also  is  made  possible  through  the  work  of  Fisher,  who  has  traced  the  formations  southw  ara 
from  the  type  locality  into  Wyoming  (Econ.  Geology,  vol.  3,  1908,  pp.  77-99). 
£>The  evidence  is  not  sufficient  to  class  this  formation  as  undoubted  Laramie,  consequently  tiic  term 
is  used  throughout  this  report  in  a  questionable  sense. 
