110         CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,   1907,   PART   II. 
GEOLOGY. 
STRATIGRAPHY. 
The  rocks  of  the  Lewistown  coal  field  range  in  age  from  lower  Car- 
boniferous to  Quaternary,  inclusive.  Workable  coal  in  this  region 
occurs  at  only  one  horizon,  which  is  near  the  base  of  the  Kootenai 
formation,  of  Lower  Cretaceous  age.  In  one  locality  a  thin  bed.  of 
coal  was  noted  in  the  Quadrant  formation,  the  upper  part  of  the 
Carboniferous  (?).  A  lignitic  shale  also  occurs  just  below  the  heavy 
bed  of  the  Eagle  sandstone,  the  lowest  member  of  the  Montana 
group,  but  it  is  improbable  that  either  the  Quadrant  or  the  Eagle 
formation  will  yield  coal  of  workable  thickness  anywhere  within  the 
area  described.  The  succession  of  the  rocks  and  the  relation  of  the 
principal  coal-bearing  beds  to  strata  above  and  below  are  shown  in 
the  following  generalized  section: 
Generalized  section  of  sedimentary  rocks  in  the  Lewistown  coal  field. 
Feet. 
Claggett  formation  (Upper  Cretaceous):  White  and  brown  sandstone 
in  lower  part  and  greenish,  sandy  shale  above. 
Eagle  sandstone  (Upper  Cretaceous) : 
Shale,  dark  bluish,  containing  carbonized  wood  fragments 5 
Sandstone,  soft,  yellowish,  cross-bedded,  containing  iron  con- 
cretions and  woody  fragments 53 
Sandstone,  soft,  white,  usually  without  bedding 170 
Sandstone,  white,  with  coaly  layer  at  top 10 
Colorado  shale  (Upper  Cretaceous) : 
Shale,  dark  gray  to  black,  with  a  few  thin,  sandy  members ....  720 
Sandstone,  hard,  greenish,  weathering  brown,  fine  grained,  fer- 
ruginous        3 
Shale,  dark  gray  to  black,  with  a  hard  bed  420  feet  above  base. .  675 
Sandstone,  grayish  brown,  thinly  bedded,  containing  an  abun- 
dance of  fish  scales  (supposed  Mowry) 47 
Shale,  dark  gray  to  black,  alternating  hard  and  soft  layers 890 
Sandstone  and  shale,  alternating,  brownish  in  color  throughout.     25 
Kootenai  formation  (Lower  Cretaceous): 
Shale,  maroon,  argillaceous 200 
Sandstone,  grayish,  coarse  grained,  cross-bedded 8 
Shale,  maroon,  argillaceous 60 
Sandstone,  gray,  coarse  grained,  cross-bedded 25 
Shale,  maroon,  argillaceous 72 
Sandstone,   massive,   coarse  grained  to  pebbly,   weathering  soft 
gray 50 
Coal  and  coaly  shale 10 
Shale  and  sandstone,  alternating;  the  shale  is  sandy  and  the 
sandstone  thinly  bedded 87 
Morrison  formation  (Jurassic?). 
The  above  section,  being  compiled  from  measurements  made  in 
several  places  in  the  field,  should  not  be  considered  as  a  type  of  any 
one  locality. 
