112  CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,   1907,   PART   II. 
Little  Belt  and  Big  Snowy  anticlines  extend  somewhat  past  each  other 
and  are  connected  across  Judith  Gap  by  a  sharply  folded  anticline 
with  curving  axis. 
In  contrast  with  the  ranges  above  described  the  Judith  and  Moc- 
casin mountains  present  quite  different  structural  features,  being 
laccolithic  in  type.  Erosion  has  removed  the  softer  Mesozoic  strata 
from  these  uplifts,  exposing  Paleozoic  or  igneous  rocks,  and  as  a 
result  the  coal-bearing  rocks  encircle  them,  the  continuity  of  the 
coal  outcrop  being  broken  here  and  there  by  irregular  igneous  masses. 
MINOR    FEATURES. 
Folds. — In  addition  to  the  large  folds  of  the  Little  Belt  and  Big 
Snowy  ranges,  numerous  smaller  folds  are  developed  in  their  vicin- 
ity, one  of  which  is  cut  through  by  Saager  Canyon.  Near  Judith 
Gap  there  has  been  considerable  folding,  the  convolutions  usually 
not  influencing  the  topography  to  any  great  extent.  In  the  district 
southeast  of  Lewistown  minor  folds  also  occur. 
Faults. — Ten  faults  of  considerable  magnitude  were  noted  in  the 
field.  The  most  disturbed  district  is  between  the  forks  of  Big  Spring 
Creek  in  T.  14  N.,  R.  19  E.,  where  a  block  fault  about  6  miles  long, 
trending  northeast-southwest,  ends  suddenly  in  sec.  3  in  an  anticline 
with  its  axis  at  right  angles  to  the  line  of  fault.  To  the  west  the 
faults  run  together  near  the  southern  limits  of  the  field  in  sec.  36, 
T.  14  N.,  R.  18  E.  The  block  is  about  half  a  mile  wide.  A  third 
fault  also  ends  near  the  anticline  above  mentioned  and  extends 
northeastward  to  sec.  23,  T.  15  N.,  R.  19  E.  Several  faults  occur  in 
the  vicinity  of  the  Moccasin  Mountains,  and  one  of  considerable 
length  crosses  Deer  Creek  inT.  17  N.,  R.  19  E.  A  rather  unusual 
fault  occurs  near  the  south  end  of  the  Judith  Mountains,  and  is 
known  as  the  Kelly  Hill  fault.3  It  is  about  2  miles  long,  is  curving, 
with  the  convexity  toward  the  north,  and  has  a  maximum  displace- 
ment of  nearly  1,000  feet.  T  1+.  scarp,  of  Madison  limestone,  is 
a  prominent  feature  &?°Wi  the  Lewistown-Giltedge  stage 
road.  Only  one  faulc  *  he  ast  type  was  encountered  in  the 
field.  It  occurs  in  sec.  T.  N.,  R.  13  E.,  is  about  2  miles  in 
length,  trends  almost  ^ast  and  west,  and  to  the  east  is  finally  lost  in 
the  Saager  Canyon  anticline.  A  rather  peculiar  feature  in  connec- 
tion with  the  faults  described  is  that  in  almost  every  one  the  displace- 
ment Is  about  300  feet.  None  of  these  faults  affect  areas  of  work- 
able coal,  although  in  certain  localities  minor  displacements  have 
been  encountered  in  underground  workings. 
Domes. — In  the  eastern  part  of  the  field  domes  are  of  common 
occurrence.     The  locality  of  most  pronounced  doming  is  south  of 
«Weed,  W.  H.,  and  Pirsson,  L.  V.,  Geology  and  mineral  resources  of  the  Judith  Mountains  of 
Montana:  Eighteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3, 1898,  p  499. 
