94  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1907,   PART   II. 
at  Red  Lodge,  in  the  Rock  Creek  valley,  along  which  a  railroad  found 
a  natural  route.  This  railroad  was  barred  from  entry  into  the  Bear 
Creek  area  by  the  high  divide  east  of  Rock  Creek  and  by  the  relative 
depression  of  Bear  Creek.  Previous  to  the  entry  of  the  other  railroad 
into  the  Bear  Creek  district  development  was  very  slow,  for  to  deliver 
coal  to  the  railroad  at  Red  Lodge  it  was  necessary  to  haul  it  by  teams 
over  the  divide  above  described,  which  materially  increased  the  cost 
of  production.  This  difficulty  has  recently  been  overcome  by  the  con- 
struction of  the  Yellowstone  Park  Railroad,  which  enters  the  Bear 
Creek  area  from  the  east.  Reverse  conditions  are  now  to  be  met, 
however,  in  the  delivery  of  mine  timber  from  Red  Lodge  to  the  Bear 
Creek  district. 
GEOLOGY. 
STRATIGRAPHY. 
The  sedimentary  rocks  outcropping  in  the  Red  Lodge  coal  field  con- 
sist mainly  of  sandstone  and  shale  of  the  Fort  Union  formation,  which 
are  cut  in  a  few  places  by  igneous  intrusions  and  are  covered  in  the 
valleys  by  alluvium  and  on  some  of  the  interstream  areas  by  gravel. 
The  sandstone  and  shale  of  this  formation  comprise  a  mass  of  rocks 
8,500  feet  thick,  in  which  carbonaceous  shale  and  coal  beds  are  inter- 
calated at  various  horizons.  Workable  coal  beds,  however,  are  con- 
fined to  a  zone  above  the  middle  of  the  section.  For  the  sake  of 
convenience,  therefore,  in  the  following  discussion  the  formation  is 
divided  into  three  parts,  depending  on  the  presence  or  absence  of 
workable  coal  beds:  (1)  A  lower  barren  member  5,700  feet  thick,  the 
lower  part  of  which  is  not  exposed  in  the  field  discussed  in  this  report, 
but  outcrops  to  the  northeast  in  the  region  between  Bear  Creek  and 
Bridger;  (2)  a  middle  productive  member  825  feet  thick;  and  (3) 
an  upper  barren  member  1,975  feet  thick. 
The  lowest  member  is  composed  mostly  of  yellowish  sandstone  and 
shale.  Beginning  1*,650  feet  above  the  bottom  of  the  formation  is  a 
group  of  beds  1,000  feet  thick,  composed  of  varicolored  sandy  shale 
with  a  few  beds  of  soft  yellowish  sandstone,  numerous  beds  of  car- 
bonaceous shale,  and  in  the  upper  part  a  few  coal  beds,  one  of  which 
contains  18  to  24  inches  of  coal.  Above  this  group  carbonaceous 
shale  and  coal  beds  occur  at  diminishing  intervals  as  the  productive 
member  is  approached,  but  none  of  these  beds  is  of  workable  thick- 
ness, and  they  are  therefore  not  given  special  consideration  in  this 
report. 
In  the  middle  productive  member  of  the  formation  the  sandstone 
and  shale  resemble  the  sandstone  and  shale  of  the  lower  member  and 
do  not  seem  to  indicate  any  essential  difference  in  conditions  of  depo- 
