LEWTSTOWN    COAL    FIELD,    MONTANA.  113 
the  Judith  Mountains,  although  there  is  another  similar  area  in 
T.  17  N.,  R.  19  E.  These  domes  are  believed  to  be  small  laccoliths, 
and  are  probably  related  in  some  way  with  the  main  igneous  mass 
of  the  Judith  uplift.  As  they  are  in  an  area  of  workable  coal  they 
are  of  considerable  importance,  viewed  from  the  standpoint  of  the 
coal  miner.  All  the  domes  are  cut  across  by  streams  and  the  coal 
bed  is  thus  exposed  near  the  periphery.  Although  %  several  square 
miles  of  coal  have  been  removed  by  the  dissection  of  these  minor 
uplifts,  yet  the  domes  are  a  beneficial  factor  in  mining,  as  they  bring 
the  coal  into  a  favorable  attitude  for  working. 
THE   COAL. 
DISTRIBUTION. 
Although  coal-bearing  rocks  of  the  Kootenai  formation  outcrop 
over  a  large  part  of  the  Lewistown  field,  and  in  general  underlie  the 
entire  region,  the  coal  is  not  continuous  throughout  the  area.  A 
feature  noted  in  the  Great  Falls  field  to  the  west  is  that  the  coal 
occurs  in  limited  districts  with  unproductive  areas  between,  and  it 
was  seen  early  in  the  season  that  the  Kootenai  coal  has  the  same 
habit  t )  the  east.  For  convenience  the  several  coal  areas  of  the 
Lewistown  field  will  be  discussed  as  separate  units — termed  the  Sage 
Creek,  Buffalo  Creek,  Rock  Creek,  Warm  Spring  Creek,  and  McDonald 
Creek  districts.  The  location  and  approximate  extent  of  these 
districts  are  shown  in  PI.  VII. 
DESCRIPTION   OF  COAL  DISTRICTS. 
SAGE    CREEK    DISTRICT. 
General  conditions.- — The  Sage  Creek  district  has  been  described 
in  a  previous  report a  as  lying  mainly  in  Tps.  15  and  16  N.,  Rs.  11 
and  12  E.,  but  including  portions  of  Tps.  15  and  16  N.,  R.  13  E.  The 
latter  two  townships  were  inch*  the  area  investigated  the  last 
season,  and  hence  are  mapped  /rt;  *  the  Lewistown  field, 
though  coal  does  not  show  in  o.  op:  '  hin  them,  and  even  on 
their  extreme  western  edge  it  prob*.  /  Ik  fc  least  500  feet  beneath 
the  surface.  At  this  locality  the  beds  dip*  to  t\e  east  at  a  moderately 
low  angle,  so  that  within  a  short  distance  the  coal  passes  beyond  a 
depth  at  which  it  can  be  mined  economically  under  present  conditions. 
Although  it  is  not  probable  that  the  coal  mined  near  Utica,  in  sec.  24, 
T.  14  N.,  R.  13  E.,  is  properly  to  be  considered  as  belonging  in 
the  Sage  Creek  district,  it  is  tentatively  included  as  such.  The 
extent  of  this  portion  of  the  district  is  limited  to  only  a  square  mile  or 
so  northwest  of  Utica,  for  to  the  south  the  coal  thins  rapidly,  and 
to  the  east  it  is  carried  to  great  depths  by  dips  in  that  direction. 
a  Fisher,  C  A.,  The  Great  Falls  coal  field,  Montana:  Bull.  U.  S.  Geol.  Survey  No.  316, 1907.  pp.  161-173. 
71497— Bull.  341—09 8 
