384  C01TTRIBUTI0NS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
is  reached  hundreds  of  feet  of  rock  section  are  represented  by  thou- 
sands in  the  south  side  of  the  Arkansas  Valley. 
Besides  the  remarkable  thickness  of  the  rocks  as  a  whole  and  the 
even  texture  of  the  sandstones  in  the  southern  part  of  the  field,  there 
is  the  not  less  remarkable  extension  from  east  to  west  of  many  of  the 
sandstone  and  coal  beds.  The  Hartshorne  sandstone  and  coal  are 
examples.  This  sandstone,  not  more  than  200  feet  thick,  extends 
westward  from  the  Arkansas  State  line  completely  across  the  Choc- 
taw Nation,  a  distance  of  nearly  200  miles,  and  one  or  more  coal 
beds  are  found  everywhere  in  or  immediately  above  its  top.  North- 
ward, however,  both  the  sandstone  and  the  coal  thin  out,  so  that 
in  the  north  side  of  the  Arkansas  Valley  south  and  west  of  the  Ozark 
uplift  it  can  not  be  recognized,  and  the  coal  which  elsewhere  lies  above 
it  is  too  thin  to  be  of  value  or  does  not  occur. 
Only  the  formations  which  contain  or  are  associated  with  coal  of 
economic  value  are  shown  on  the  map.  These,  with  the  mapping  of 
the  outcrops  of  the  coal  beds  and  the  conventional  signs  indicating 
structure,  will  make  sufficiently  clear  the  occurrence  of  the  coal. 
m'alester  formation. 
The  McAlester  formation  consists  chiefly  of  shale.  A  group  of 
several  sandstone  beds  interstratified  with  shale  occurs  near  the 
center  of  the  formation.  These  sandstones,  however,  are  not  dis- 
tinctive in  the  southwestern  part  of  the  field.  Eastward  from  the 
Missouri,  Kansas  and  Texas  Railroad  they  are  more  clearly  defined, 
cropping  out  in  ridges  and  capping  flat-topped  hills,  which  are 
surrounded  by  the  valleys  and  plains  developed  on  the  shales.  These 
sandstone  beds  vai^y  in  thickness  locally,  but,  as  a  whole,  are  per- 
sistent from  the  vicinity  of  Krebs  eastward  to  the  Arkansas  line. 
North  of  Cavanal  and  Sansbois  mountains,  where  a  number  of 
upward  folds  bring  them  to  the  surface,  the  sandstone  beds  are  seen 
to  be  much  thicker.  The  ridges  south  of  Bokoshe,  north  and  south 
of  McCurtain,  south  and  east  of  Stigler,  and  on  each  side  of  the 
Canadian  River  near  its  mouth  are  made  by  these  sandstones.  Each 
of  the  shaly  members  above  and  below  the  group  of  sandstones  is  700 
to  800  feet  thick,  and  the  sandstone  beds,  with  included  shales, 
approximate  500  feet  in  thickness,  making  nearly  2,000  feet  in  all 
for  the  thickness  of  the  formation.  The  McAlester  formation  can 
not  be  defined  north  of  Arkansas  River,  since  the  boundary  for- 
mations of  sandstone  above  and  below  thin  out  and  can  not  be 
traced.  The  McAlester  formation  contains  four  coal  beds,  which  are 
being  extensively  developed,  besides  others  reported  to  be  locally 
workable.  The  two  lowest  are  near  together  and  near  the  base,  and 
are  known  as  the  "  Hartshorne  coals."    The  upper  ones  occur  inline- 
