taff.]  COAL   WORK    IN    INDIAN    TERRITORY.  385 
diately  above  the  group  of  sandstone  deposits,  are  also  near  together, 
and  are  known  as  the  "  McAlester  coals." 
SAVANNA.    FORMATION. 
Next  above  the  McAlester  formation  is  a  succession  of  strata,  con- 
sisting of  sandstone  and  shaly  sandstone,  in  three  groups  or  collec- 
tions of  beds,  separated  b}^  deposits  of  shales,  the  whole  making  a 
thickness  of  1,000  to  1,500  feet  south  of  the  Canadian  and  Arkansas 
rivers.  North  of  the  Canadian  the  formation  becomes  rapidly  thin- 
ner, and  is  lost  to  view  in  the  Cherokee  Nation,  18  miles  south  of  Mus- 
cogee. In  the  Choctaw  Nation  the  outcrop  of  the  formation  is  marked 
in  the  low  country  by  many  ridges  and  hills,  and  surrounding  the 
Sansbois  and  Cavanal  mountains  the  sandstone  members  make  escarp- 
ments and  benches.  In  the  Choctaw  Nation  the  Savanna  formation 
contains  two  coal  beds  of  workable  thickness,  and  a  third  is  found 
near  the  upper  sandstone  member  in  the  shale  of  the  succeeding 
formation.  This  third  coal  bed,  which  is  mined  in  the  east  end  of 
Cavanal  Mountain  and  is  known  as  the  Witteville  coal,  is  the  highest 
coal  known  to  be  of  economic  value  south  of  Canadian  River. 
A  coal  bed  having  approximately  the  same  position  in  the  rocks 
has  been  developed  for  local  purposes  in  the  southern  part  of  the 
Creek  Nation,  east  of  Checotah.  All  the  formations  which  carry 
coals,  and  as  far  as  known  those  still  higher  in  the  section  in  the 
southern  part  of  the  Indian  Territory  coal  field,  become  thin  north- 
ward and  the  sandy  portions  become  shaly.  The  rocks  which  in- 
clude the  coal  beds  in  the  central  part  of  the  Creek  Nation  and 
the  northern  Cherokee  Nation  are  far  above  the  coal-bearing  strata 
in  the  Choctaw  Nation.  They  strike  southwestward,  approaching 
Canadian  River  near  the  extreme  northwestern  part  of  the  Choctaw 
Nation. 
STRUCTURE. 
The  southeastern  part  of  the  Indian  Territory  coal  field  lies  in 
the  Arkansas  Valley,  which  is  here  a  dee})  structural  basin  between 
the  uplifts  of  the  Ouachita  Mountains  on  the  south  and  the  Ozark 
Mountains  on  the  north.  The  Ozark  region  is  a  low,  broad,  dome- 
like uplift,  and  the  rocks  at  its  southern  border  in  the  north  side  of 
the  Arkansas  Valley  are  gently  folded,  with  a  general  downward 
inclination  southward.  The  rocks  of  the  Ouachita  Mountains,  on 
the  contrary,  have  been  thrown  into  steep  folds,  overturned  toward 
the  north,  and  in  many  instances  faulted.  The  northern  border  of 
the  greatly  folded  belt  is  definitely  limited  a  few  miles  south  of  the 
outcrop  of  the  lowest  coal  in  the  field.  This  boundary  is  marked 
on  the  map  by  a  long  dashed  line.  The  overthr  listing  forces  of  the 
Bull.  200—05  m 25 
