72  CONTBIBUTIONS   TO   ECONOMIC    GEOLOGY,  1907,   PART  IT. 
Its  irregularity  and  lenticular  form,  however,  render  it  of  so  little 
value  that  practically  the  next  important  coal  above  the  Bull  Moun- 
tain coals  is  the  Strait  coal  (D  coal,  PL  IV).  This  bed  averages  200 
feet  above  the  lower  Bull  Mountain  coal  and  always  outcrops  near  the 
base  of  the  steep  slopes  of  the  Bull  Mountain  mesas.  Hence  the  out- 
crop of  the  Strait  coal  as  shown  on  the  map  outlines  the  extent  and 
shape  of  the  mesas.  The  outcrop  of  the  Strait  coal  lies  within  T.  6  N., 
R.  27  E.;  except  where  the  northern  group  of  mesas  extends  beyond 
the  northwest  corner  of  that  township.  A  massive  sandstone  30  to  40 
feet  thick  usually  overlies  this  coal  and  forms  a  prominent  protruding- 
ledge  or  bench  along  the  bluffs.  The  Musselshell  road,  where  it 
crosses  the  divide  between  Fattig  and  Dorrity  creeks,  passes  through 
a  notch  in  this  sandstone  and  the  underlying  coal  bed,  which  is 
exposed  on  either  side  of  the  road.  In  the  southernmost  mesa  this  bed 
generally  measures  2  feet  or  less  in  thickness,  though  at  some  points, 
especially  in  the  southern  half  of  the  mesa,  it  is  nearly  3  feet  thick. 
Toward  the  northern  mesas  the  thickness  is  less,  and  at  their  base  the 
coal  is  generally  only  a  few* inches  thick.  The  coal  around  the 
northern  mesas  of  the  Bull  Mountains  is  not  deemed  sufficiently 
important  to  be  represented  on  the  map.  An  average  section  of  the 
Strait  coal  is  given  below: 
Section  of  Strait  coal  bed  in  sec.  32,  T.  6  N.,  R.  27  E. 
Ft.  in. 
Coal 5 
Shale 1 
Coal 1     6 
Shale 1     6 
Coal 1     G 
5 
The  lower  parting  indicated  in  this  section  increases  eastward  from 
this  point  to  a  thickness  of  5,  8,  and  even  15  feet. 
Above  the  massive  sandstone  which  overlies  the  Strait  coal  occurs 
a  series  of  coals,  the  most  important  of  which  are  the  Red  Butte, 
Fattig,  and  Summit  beds  (C,  B,  and  A  coals,  PL  IV).  These  lie  35  or 
40  feet  apart,  the  lowest  one  being  65  feet  above  the  Strait  coal.  All 
three,  consequently,  have  the  same  general  extent  as  the  Strait  coal, 
and  follow  the  tops  of  the  main  mesas  which  form  the  Bull  Mountains. 
One  of  the  thinner  coal  beds  intermediate  between  the  Red  Butte  and 
Strait  coals  presents  a  thickness  of  nearly  3  feet  in  sec.  32,  T.  7  N., 
R.  27  E.,  but  this  is  probably  a  local  development,  as  such  dimensions 
were  not  observed  elsewliere.  The  three  coal  beds  named  above  do 
not  exceed  3  feet  in  thickness  so  far  as  known.  The  lowest  or  Red 
Butte  bed  is  not  well  exposed,  owing  to  the  heavy  talus  fringing  the 
steep  bluffs  of  the  mountains.  Where  exposed  it  measures  generally 
2  feet  or  less,  and  rarely  exceeds  that  figure.  The  Fattig  coal  is  com- 
monly thicker  than  the  Red  Butte  bed,  measuring  between  2  and  3 
