﻿Ouachita 
  Mountain 
  System 
  in 
  Indian 
  Territory. 
  119 
  

  

  structure 
  of 
  diabase 
  in 
  a 
  very 
  marked 
  degree." 
  The 
  dikes 
  

   run 
  west 
  20° 
  S. 
  and 
  are 
  seen 
  at 
  the 
  crossing 
  of 
  Mill 
  Creek 
  

   road 
  and 
  Pennington 
  Creek. 
  

  

  The 
  northern 
  margin 
  of 
  the 
  granite 
  area 
  is 
  overlaid 
  by 
  hard 
  

   metamorphosed, 
  sub-horizontal 
  Silurian 
  limestone 
  of 
  the 
  same 
  

   cherty 
  and 
  flaggy 
  lithologic 
  aspect 
  as 
  the 
  Upper 
  Potsdam 
  

   rocks 
  of 
  Burnet 
  County, 
  Texas, 
  but 
  I 
  could 
  find 
  no 
  fossils. 
  

   Carboniferous 
  rocks 
  cover 
  its 
  eastern 
  point 
  at 
  Boggy 
  station. 
  

   Its 
  southern 
  border 
  was 
  the 
  sea-shore 
  of 
  the 
  ancient 
  Trinity 
  

   and 
  other 
  Mesozoic 
  and 
  Cenozoic 
  seas 
  and 
  is 
  buried 
  beneath 
  

   the 
  Trinity 
  sands. 
  The 
  western 
  border 
  is 
  covered 
  by 
  Silurian 
  

   and 
  Carboniferous 
  rocks. 
  * 
  I 
  saw 
  no 
  evidence 
  that 
  this 
  granite 
  

   was 
  of 
  later 
  age 
  than 
  the 
  oldest 
  of 
  the 
  Paleozoic 
  rocks 
  which 
  

   rest 
  upon 
  it. 
  

  

  2c. 
  The 
  Arbuckle 
  Folds 
  — 
  West 
  of 
  the 
  Washita 
  Kiver 
  the 
  

   mountains 
  again 
  present 
  a 
  new 
  and 
  entirely 
  different 
  aspect. 
  

   An 
  elongated 
  mass 
  of 
  low 
  rounded 
  barren 
  limestone 
  folds 
  

   stands 
  about 
  500 
  feet 
  above 
  the 
  plain 
  and 
  extends 
  east 
  and 
  

   west, 
  between 
  Wild 
  Horse 
  Creek 
  and 
  the 
  Washita 
  River 
  for 
  

   about 
  forty 
  miles, 
  forming 
  an 
  almost 
  impassable 
  barrier 
  for 
  

   wagon 
  travel. 
  They 
  are 
  composed 
  of 
  folds 
  of 
  hard 
  Silurian 
  

   limestones. 
  The 
  trend 
  of 
  the 
  mountains 
  — 
  north 
  of 
  west 
  — 
  

   corresponds 
  with 
  strike 
  of 
  the 
  folds, 
  but 
  is 
  opposite 
  in 
  direc- 
  

   tion 
  to 
  the 
  prevalent 
  trend 
  of 
  the 
  Choctaw- 
  Arkansas 
  division. 
  

   These 
  folds 
  are 
  the 
  "hard, 
  persistent 
  core 
  of 
  the 
  structure, 
  the 
  

   softer 
  and 
  exterior 
  Carboniferous 
  layers 
  having 
  been 
  eroded 
  to 
  

   the 
  level 
  of 
  the 
  Ardmore 
  prairies. 
  (See 
  figures.) 
  

  

  West 
  of 
  Duncan 
  the 
  limestone 
  hills 
  are 
  buried 
  beneath 
  the 
  

   red 
  beds 
  for 
  twenty 
  miles, 
  but 
  again 
  appear 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  Fort 
  Sill 
  forming 
  a 
  low 
  ridge 
  north 
  of 
  and 
  parallel 
  to 
  

   the 
  Wichita 
  Mountains, 
  as 
  is 
  explained 
  later. 
  

  

  The 
  Arbuckle 
  Mountains 
  constitute 
  a 
  great 
  and 
  wonderful 
  

   development 
  of 
  the 
  Silurian 
  system, 
  although 
  this 
  has 
  not 
  been 
  

   hitherto 
  appreciated, 
  and 
  afford 
  a 
  superb 
  example 
  of 
  folded 
  

   structure. 
  This 
  folding 
  is 
  beautifully 
  shown 
  in 
  the 
  valley 
  of 
  

   the 
  Washita 
  which 
  has 
  cut 
  a 
  deep 
  and 
  tortuous 
  water 
  gap 
  

   through 
  these 
  mountains 
  where, 
  unobscured 
  by 
  forest 
  growth, 
  

   fold 
  after 
  fold 
  of 
  the 
  stratified 
  limestones 
  and 
  shales 
  appear 
  

   in 
  startling 
  boldness. 
  Several 
  journeys 
  through 
  this 
  gap 
  only 
  

   increased 
  the 
  appreciation 
  of 
  the 
  greatness 
  of 
  the 
  task 
  of 
  

   thoroughly 
  delineating 
  the 
  section, 
  the 
  complexity 
  of 
  which 
  

   may 
  be 
  inferred 
  from 
  the 
  accompanying 
  figures. 
  

  

  Twenty 
  miles 
  south 
  of 
  the 
  Arbuckle 
  ridges 
  proper, 
  and 
  

   separated 
  from 
  it 
  by 
  a 
  valley 
  based 
  upon 
  Carboniferous 
  shales 
  

   and 
  sands, 
  near 
  the 
  crossing 
  of 
  Hickory 
  Creek 
  and 
  the 
  Santa 
  

  

  * 
  The 
  only 
  previous 
  mention 
  of 
  this 
  important 
  granite 
  area 
  of 
  which 
  I 
  am 
  

   aware 
  was 
  made 
  by 
  Dr. 
  R. 
  H. 
  Loughridge 
  in 
  the 
  10th 
  Census 
  Report 
  on 
  Cotton 
  

   Production. 
  

  

  