RED   LODGE    COAL   FIELD,    MONTANA.  95 
sition,  but  the  carbonaceous  shale  and  workable  coal  beds  inter- 
calated with  the  other  rocks  serve  to  distinguish  the  member.  As 
indicated  above,  the  coal  beds  of  the  middle  member  do  not  begin 
abruptly,  but  are  presaged  in  the  lower  member  by  thin  beds  of 
coal.  At  the  upper  limit  of  the  middle  member,  however,  there  is 
a  sharp  transition  from  the  productive  measures  to  the  barren 
beds  above. 
The  coal  beds  were  apparently  deposited  in  basins  which  are 
believed  to  have  been  shallower  toward  the  southwest,  because  all 
the  coals  thin  in  that  direction  or  merge  into  carbonaceous  shale, 
whereas  to  the  northwest  the  beds  thicken  to  the  western  limit  of  the 
field.  The  present  survey  was  not  sufficiently  extended  to  locate  the 
western  boundary  of  the  basins  in  which  the  coal  was  laid  down,  but 
the  indications  are  that  the  thickest  deposits  are  at  Red  Lodge,  or 
possibly  a  short  distance  farther  west.  A  section  of  the  productive 
member  of  the  Fort  Union  formation  as  it  is  exposed  on  the  east  side 
of  Rock  Creek  at  Red  Lodge  is  given  below. 
Section  of  coal-bearing  beds  exposed  in  east  bluff  of  Rock  Creek  at  Red  Lodge,  Mont.a 
Ft.     in. 
Shale,  yellowish,  with  layers  of  tan  sandstone 22               rf 
Shale,  carbonaceous 5 
Shale  alternating  with  layers  of  yellowish  sandstone 43 
Shale,  carbonaceous,  with  a  few  thin  layers  of  coal 4 
Coal  (bed  No.  1),  not  well  exposed 7-f- 
Shale,  carbonaceous 4-6 
Sandstone,  tan,  and  shale,  in  alternating  layers 25 
Shale,  bluish,  with  thin  layers  of  rusty  sandstone 35 
Sandstone,  gray,  with  a  few  thin  shale  partings 70 
Shale,  drab,  with  unio  shells 1     6 
Coal  (bed  No.  1J) 5 
Shale,  carbonaceous 8 
Sandstone,  yellowish 2 
Shale,  sandy 17 
Sandstone,  yellowish,  shaly 6 
Sandstone,  yellow,  massive 18 
Shale,  bluish,  with  carbonaceous  material  at  base 8 
Coal  (bed  No.  2),  with  several  thin  shaly  partings 4     7 
Shale,  sandy,  alternating  with  thin  layers  of  sandstone 25 
Sandstone,  gray,  shaly  at  top 12 
Shale,  sandy,  alternating  with  layers  of  sandstone 16 
Coal  (bed  No.  3),  unexposed;  thickness  in  mine 10 
Coal,  in  thin  layers,  alternating  with  thick  layers  of  carbo- 
naceous shale 12 
a  This  section  was  measured  along  the  bluff  east  of  Rock  Creek  by  J.  E.  Carman.  The  thick- 
nesses of  many  of  the  members  disagree  with  those  given  in  the  section  on  page  181  of  Hull.  U.  S. 
Geol.  Survey  No.  316.  Mr.  Darton  informs  the  writer  that  the  latter  section  was  furnished  him  by 
Mr.  Pettigrew,  manager  of  the  Northwestern  Improvement  Company's  mine.  As  the  coal  beds  vary 
in  thickness  from  place  to  place,  measurements  taken  at  different  points  do  not  agree,  and  the 
difference  in  the  thickness  of  the  coal  beds  in  the  two  sections  may  be  thus  explained. 
