386  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  2G0. 
mountain  region  continue  northward  into  the  southern  part  of  the 
coal  field,  crumpling  the  rocks  into  many  gently  curving  and  lap- 
ping folds.  The  upward  folds  are,  as  a  rule,  steeper  than  the  syn- 
clines  or  basins,  and  in  a  few  instances  are  broken  and  faulted  near 
their  axes.  The  basins  are,  as  a  rule,  broad,  and  the  wider  ones  are 
occupied  by  the  higher  hills  and  mountains,  such  as  Poteau,  Sugar 
Loaf,  Cavanal,  and  Sansbois  mountains.  North  ward  toward  the  cen- 
ter of  the  field  the  folding  gradually  declines  until,  near  Canadian 
River,  the  rocks  clip  at  low  angles  toAvard  the  northwest  and  so  con- 
tinue across  the  field.  Farther  northward  and  west  of  the  Ozark 
uplift  the  rocks  incline  at  an  equally  low  grade  toward  the  west. 
A  number  of  anticlinal  folds  in  the  southern  part  of  the  field  bring 
the  coal  beds  up  in  many  curving  outcrops,  giving  large  areas  of 
available  coal.  In  places  near  the  southern  boundary  of  the  field 
the  coal  is  steeply  upturned  and  can  not  be  exploited  far  from  the 
outcrop,  while  at  numerous  other  localities 
shallow  basins  and  stretches  of  low-dipping  rocks. 
DESCRIPTION    OF    COAL    BEDS. 
Extent  and  character. — There  are  six  beds  of  coal  having  workable 
thickness  south  of  Canadian  River.  Besides  these  coal  beds  are  oth- 
ers that  are  too  thin  or  too  poor  to  warrant  exploitation.  Many  of 
these  thinner  beds  have  been  located  while  prospecting  for  thicker 
coals  and  have  been  found  in  places  of  sufficient  thickness  to  be  mined 
profitably  for  local  consumption.  The  outcrops  of  the  known  work- 
able beds  have  been  traced  throughout  their  occurrence  in  the  field, 
and  Avhere  prospecting  and  mining  have  been  sufficiently  extended  t(| 
assure  the  thickness  and  quality,  they  are  marked  on  the  map  in  heavy 
solid  lines.  Where  there  is  question  as  to  their  thickness  or  extent 
the  location  of  outcrop  is  indicated  by  short  dash  lines. 
Hartshorne  coal. — The  Hartshorne  coal  occurs  in  large  areas  and 
is  known  to  be  more  persistent  in  thickness  than  any  other  bed.  It 
is  the  lowest  known  bed  in  the  field.  Its  thickness  and  quality  are 
known  at  short  intervals  along  the  larger  part  of  its  outcrop  and 
at  numerous  localities  for  many  hundred  feet  beneath  the  sur- 
face in  mines.  Through  a  large  part  of  the  field  in  the  south  side 
there  are  two  beds,  known  as  the  upper  and  lower  Hartshorne  coals, 
separated  by  about  50  feet  of  sandstone  and  shale.  The  upper  bed 
is  found  to  be  more  variable  in  thickness  than  the  lower,  but  the 
quality  of  each  is  practically  the  same.  The  record  of  analyses  of 
the  two  coals  is  shown  in  the  following  table: 
