taff.]  COAL   WORK    IN    INDIAN    TERRITORY.  383 
nary  reports"  were  made  upon  the  coal  deposits  and  their  develop- 
ment. The  present  report  will  present  the  economic  results  of  work 
since  1902,  together  with  a  brief  review  of  the  results  of  previous 
surveys. 
GENERAL  STATEMENT. 
The  coal  beds  of  the  Choctaw  Nation  thin  out  and  become  of  no 
economic  importance  within  a  few  miles  north  of  Arkansas  and 
Canadian  rivers.  The  coals  in  the  Creek  and  Cherokee  nations  occur 
much  higher  in  the  geologic  section  than  the  coals  farther  south. 
These  beds  thin  out  southward  and  are  not  known  south  of  Cana- 
dian River.  For  these  reasons  and  for  convenience  of  description 
the  coal  field  is  divided  into  two  parts,  and  the  maps  are  drawn 
accordingly,  the  division  line  being  marked  by  parallel  of  latitude 
35°  80'.  The  southern  part,  which  includes  the  Choctaw  Nation,  will 
be  referred  to  as  the  Choctaw  coal  field  and  the  northern  part  will  be 
known  as  the  Cherokee- Creek  field. 
CHOCTAW  COAL  FIELD. 
STRATIGRAPHY. 
The  rocks  in  this  coal  field  consist  of  sandstone,  shale,  and  coal, 
with  occasional  thin  limestone  formations  in  the  western  and  north- 
ern part.  The  shale  succeeds  sandstone  and  the  sandstone  follows 
upon  shale  repeatedly,  with  many  coal  beds  interspersed,  until  there 
is  a  thickness  of  many  thousand  feet. 
The  maximum  thickness  of  the  exposed  Coal  Measures  in  the  south- 
ern part  of  the  field,  south  of  Arkansas  River,  is  estimated  to  be 
not  less  than  17,000  feet,  The  strata,  however,  between  the  lowest  and 
highest  workable  coal  beds,  it  is  believed,  will  not  exceed  7,000  feet  in 
thickness.  On  the  north  side  of  the  Arkansas  Valley  the  thickness 
of  the  exposed  part  of  the  section  is  found  to  be  reduced  by  nearly 
6,000  feet.  From  the  base  of  the  Coal  Measures  up  to  the  lowest  pro- 
ductive coal  the  thickness  does  not  exceed  1,200  feet,  which  in  the 
south  side  of  the  field  is  represented  by  approximately  8,000  feet. 
On  going  northward  from  the  Arkansas  Valley  on  the  east  side  of  the 
field  it  is  seen  that  the  higher  formations  become  thinner  and  more 
shaly,  while  the  lower  ones  overlap  on  the  Mississippian  strata,  at 
the  same  time  becoming  less  sandy,  so  that  when  the  northern  end 
"Geology  of  the  McAlester  and  Lehigh  coal  fields,  Indian  Territory:  Nineteenth  Ann. 
Kept.,  pt.  3,  1899,  pp.  429-593.  Eastern  Choctaw  coal  field,  Endian  Territory:  Twenty- 
first  Ann.  Kept.,  pt.  2,  1900,  pp.  203-311.  The  Southwestern  coal  field:  Twenty-third 
Ann.  Kept.,  pt,  :',.  1902,  pp.  373-413.  Coalgate  folio,  Mo.  74.  Atoka  folio,  No.  TO.  De- 
scription of  unleased  segregated  coal  lands  of  the  McAlester,  Wilburton-Stigler,  Ilowe- 
Poteau,  McCurtain-Massey,  and  Lehigh-Ardmore  districts:  Circulars  1,  2,  3,  4,  and  5, 
respectively,  Department  of  the  Interior,  1904. 
