﻿Ouachita 
  Mountain 
  System 
  in 
  Indian 
  Territory. 
  115 
  

  

  prairies 
  occupy 
  the 
  more 
  compact 
  clays 
  of 
  the 
  valley. 
  Even 
  

   where 
  the 
  vertical 
  outcrops 
  have 
  been 
  eroded 
  to 
  a 
  level 
  plain, 
  

   the 
  alternations 
  of 
  sandstones 
  and 
  clays 
  can 
  often 
  be 
  traced 
  for 
  

   miles 
  by 
  the 
  timber 
  which 
  follows 
  the 
  sandstone 
  outcrops 
  in 
  

   narrow 
  ribbon-like 
  parallel 
  belts. 
  (See 
  fig. 
  2.) 
  

  

  The 
  northern 
  half 
  of 
  this 
  area 
  contains 
  coal 
  strata 
  whose 
  

   extent 
  and 
  known 
  occurrence 
  are 
  indicated 
  ou 
  the 
  map. 
  An 
  

   admirable 
  paper 
  upon 
  the 
  structure 
  of 
  these 
  coal 
  beds 
  has 
  been 
  

   published 
  by 
  Mr. 
  H. 
  M. 
  Chance.* 
  Mr. 
  Arthur 
  Winslowf 
  has 
  

   equally 
  well 
  defined 
  them 
  in 
  Arkansas. 
  Mr. 
  J. 
  T. 
  Munson 
  

   of 
  Denison, 
  Texas, 
  has 
  much 
  unpublished 
  information 
  con- 
  

   cerning 
  the 
  formation 
  of 
  this 
  region, 
  and 
  to 
  him 
  the 
  writer 
  is 
  

   indebted 
  for 
  his 
  invaluable 
  assistance 
  and 
  data. 
  

  

  The 
  coal 
  fields, 
  for 
  which 
  the 
  name 
  Fort 
  Smith-McAllister 
  

   area 
  is 
  most 
  appropriate, 
  are 
  of 
  great 
  commercial 
  importance, 
  

   for 
  they 
  are 
  the 
  chief 
  source 
  of 
  fuel 
  supply 
  for 
  the 
  Arkansas- 
  

   Texas 
  region. 
  These 
  extend 
  along 
  the 
  northern 
  border 
  of 
  the 
  

   mountains 
  and 
  are 
  terminated 
  on 
  the 
  southwest 
  by 
  the 
  Silurian 
  

   and 
  granite 
  field 
  of 
  the 
  Tishomingo 
  district 
  which 
  are 
  an 
  

   apparent 
  barrier 
  between 
  this 
  and 
  the 
  Texas-Ardmore 
  coal 
  

  

  GzrboTu/erouLS 
  ? 
  ? 
  L 
  HeUZerberg 
  ? 
  

  

  o 
  Scale 
  of 
  mites 
  

  

  Section 
  north 
  and 
  south 
  through 
  Woodford, 
  showing 
  structure 
  of 
  Prairie 
  and 
  

   Mountain. 
  Continuation 
  of 
  fig. 
  1. 
  

  

  field, 
  the 
  fuel 
  of 
  which 
  is 
  of 
  an 
  entirely 
  different 
  character 
  and 
  

   should 
  not 
  be 
  confused 
  with 
  it 
  J 
  geographically, 
  structurally, 
  

   or 
  economically. 
  

  

  Mr. 
  Chance 
  has 
  published 
  a 
  section 
  of 
  the 
  rocks 
  of 
  the 
  

   eastern 
  division. 
  He 
  estimates 
  at 
  least 
  8500 
  feet 
  of 
  coal- 
  

   bearing 
  strata, 
  but 
  the 
  total 
  thickness 
  of 
  the 
  Carboniferous 
  and 
  

   Permo-Carboniferous, 
  as 
  seen 
  in 
  the 
  folds 
  near 
  Ardmore, 
  is 
  

   greater 
  by 
  the 
  addition 
  of 
  the 
  uppermost 
  or 
  Permo-Carbonif- 
  

   erous 
  which 
  here 
  has 
  a 
  thickness 
  of 
  several 
  thousand 
  feet. 
  

  

  The 
  most 
  marked 
  feature 
  of 
  these 
  mountains 
  is 
  the 
  ex- 
  

   cessive, 
  compressed 
  and 
  vertical 
  folding 
  which 
  the 
  whole 
  

   region 
  has 
  undergone, 
  and 
  the 
  displacement 
  of 
  these 
  folds 
  by 
  

   a 
  lateral 
  dislocation 
  which 
  has 
  squeezed 
  them 
  into 
  S-shaped 
  

   flexures. 
  So 
  excessive 
  is 
  this 
  folding 
  that 
  every 
  stratum 
  in 
  

  

  * 
  Geology 
  of 
  the 
  Choctaw 
  Coal 
  Fields 
  by 
  H. 
  M. 
  Chance. 
  Transactions 
  Ameri- 
  

   can 
  Institute 
  of 
  Mining 
  Engineers, 
  Feb., 
  1890. 
  

  

  f 
  Arkansas 
  Geological 
  Survey, 
  Report 
  for 
  1888, 
  vol. 
  iii. 
  

  

  X 
  The 
  writer 
  is 
  inclined 
  to 
  believe 
  that 
  the 
  greater 
  excess 
  of 
  ash 
  in 
  the 
  coals 
  of 
  

   the 
  more 
  horizontal 
  Texas 
  region 
  is 
  due 
  to 
  the 
  calcium 
  carbonate 
  and 
  other 
  im- 
  

   purities 
  deposited 
  in 
  the 
  joints 
  during 
  their 
  long 
  submergence 
  beneath 
  the 
  Creta- 
  

   ceous 
  seas, 
  while 
  the 
  McAllister 
  coals 
  have 
  remained 
  above 
  water. 
  

  

  