126         CONTRIBUTIONS    TO    ECONOMIC   GEOLOGY,    1907,   PART   II. 
Broad  stretches  of  flat,  gravel-covered  benches  and  gently  sloping 
table-lands  make  a  large  part  of  the  country  contiguous  to  the  valley 
of  Little  Goose  Creek,  and  between  Little  Goose  Creek  and  Tongue 
River. 
The  valleys  of  Goose  and  Little  Goose  «creeks  and  Tongue  River  are 
floored  with  a  thick  deposit  of  gravel,  sand,  and  silt,  and  are  wide 
and  flat. 
DRAINAGE. 
Tongue  River  and  Little  Goose,  Goose,  and  Clear  creeks  are  the 
only  streams  within  the  mapped  area  that  have  a  continuous  flow. 
These  streams  afford  an  abundant  supply  of  excellent  water.  Their 
sources  are  toward  the  crests  of  the  Bighorn  Mountains,  where  snow 
lies  during  a  large  part  of  the  year  and  where  rainfall  is  more  abundant 
than  in  the  plains  country  surrounding  the  mountains.  All  the  other 
valleys  have  intermittent  streams  that  are  dependent  on  the  scanty 
rainfall  of  the  plains  region. 
FOREST   CONDITIONS  AND   TIMBER   SUPPLY. 
The  Sheridan  district  has  no  forests.  The  few  trees  in  the  valleys 
consist  of  cottonwood,  ash,  etc.,  that  are  found  in  scattering  growths 
near  the  streams.  Pine  and  cedar  grow  here  and  there  on  the  more 
stony  uplands.  More  rarely  scrub  oaks  are  found  in  protected  gulches 
near  the  heads  of  the  valleys.  The  Bighorn  National  Forest,  a  few 
miles  west  of  the  mapped  area,  will  afford  ample  timber  supply  for  all 
needs  of  mining.  Timber  for  mines,  railroads,  and  other  purposes  is 
floated  down  Tongue  River  to  the  railroad  near  Ranchester. 
GEOLOGY. 
STRATIGRAPHY. 
GENERAL   OUTLINE. 
It  is  proposed  to  discuss  here  only  the  rock  formations  that  contain 
the  coal,  together  with  the  formation  that  lies  in  contact  below  and 
the  surflcial  gravels  and  alluvium  above,  that  have,  or  seem  to  have, 
economic  bearing  on  the  development  of  the  coal  resources.  The  sur- 
flcial deposits  are  the  only  formations  in  this  district  that  overlie  the 
coal-bearing  rocks.  The  formations  that  lie  below  the  coal-bearing 
strata  require  further  field  study  for  better  age  classification.  Two 
or  more  of  these  lower  formations  crop  out  across  the  southwestern 
part  of  T.  55  N.,  R.  85  W.  All  the  remaining  part  of  the  Sheridan 
field  as  mapped  contains  coal-bearing  strata,  except  in  the  areas  of 
surface  gravel  and  alluvium.  The  geology  of  the  coal-bearing  rocks 
has  been  briefly  discussed  by  Darton.a 
a  Darton,  N.  H.,  Geology  of  the  Bighorn  Mountains:  Prof.  Paper  U.  S.  Geol.  Survey  No.  51, 1906;  also 
Bald  Mountain-Dayton  folio  (No.  141),  Geologic  Atlas  U.  S.,  U.  S.  Geol.  Survey,  1906. 
