﻿S. 
  Potvers—The 
  Butler 
  Salt 
  Dome. 
  133 
  

  

  center 
  of 
  the 
  prairie. 
  Cracks 
  a 
  foot 
  in 
  depth 
  and 
  half 
  a 
  

   foot 
  in 
  width 
  develop 
  on 
  the 
  lower 
  side 
  as 
  the 
  mass 
  

   moves 
  forward. 
  A 
  fraction 
  of 
  an 
  inch 
  of 
  motion 
  a 
  year 
  

   and 
  a 
  similar 
  amount 
  of 
  added 
  height 
  develop 
  in 
  the 
  

   course 
  of 
  time 
  a 
  sizable, 
  symmetrical 
  natural 
  mound 
  with 
  

   trees 
  securing 
  a 
  foothold 
  on 
  the 
  top. 
  With 
  increasing 
  

   height 
  and 
  firmness 
  caused 
  by 
  deep-rooted 
  vegetation, 
  

   together 
  with 
  the 
  forward 
  movement 
  of 
  the 
  whole, 
  the 
  

   water 
  begins 
  to 
  run 
  around 
  instead 
  of 
  into 
  the 
  mound 
  

   and 
  it 
  sometimes 
  develops 
  a 
  small 
  channel 
  which 
  isolates 
  

   the 
  mound. 
  The 
  various 
  stages 
  of 
  the 
  process 
  may 
  be 
  

   observed 
  in 
  Burton 
  Hollow. 
  5 
  

  

  Examples 
  are 
  also 
  seen 
  of 
  the 
  formation 
  of 
  somewhat 
  

   similar 
  mounds 
  by 
  simple 
  erosion 
  where 
  drainage 
  cuts 
  

   l)ack 
  on 
  each 
  side 
  of 
  and 
  finally 
  completely 
  through 
  a 
  

   ridge 
  or 
  terrace 
  three 
  feet 
  or 
  less 
  in 
  height. 
  Mounds 
  

   clearly 
  of 
  this 
  mode 
  of 
  origin 
  are 
  abundant. 
  They 
  are 
  

   also 
  abundant 
  on 
  the 
  west 
  side 
  of 
  the 
  Brooks 
  salt 
  dome 
  

   and 
  in 
  many 
  other 
  localities 
  both 
  in 
  Texas, 
  Louisiana, 
  

   and 
  Oklahoma. 
  It 
  is 
  the 
  belief 
  of 
  the 
  writer 
  that 
  the 
  

   abundant 
  mounds 
  of 
  the 
  Gulf 
  Coast, 
  concerning 
  which 
  so 
  

   much 
  has 
  been 
  written, 
  will 
  ultimately 
  be 
  proven 
  to 
  be 
  in 
  

   large 
  part 
  erosional 
  in 
  origin. 
  

  

  Surface 
  Geology. 
  

  

  Four 
  formations 
  are 
  exposed 
  in 
  the 
  vicinity 
  of 
  the 
  

   dome 
  : 
  the 
  Mount 
  Selman, 
  "Wilcox, 
  and 
  Midway 
  (?) 
  of 
  

   the 
  Eocene, 
  the 
  Navarro 
  (?) 
  of 
  the 
  Upper 
  Cretaceous. 
  

   The 
  Mount 
  Selman 
  consists 
  of 
  ferruginous 
  red 
  sand- 
  

   stones 
  interbedded 
  with 
  sands 
  and 
  some 
  clays. 
  The 
  hard 
  

   sandstones 
  which 
  cap 
  the 
  hills 
  between 
  Butler 
  and 
  the 
  

   dome 
  and 
  which 
  also 
  cap 
  Rocky 
  Mountain, 
  north 
  of 
  the 
  

   dome, 
  probably 
  belong 
  to 
  this 
  formation. 
  No 
  fossili- 
  

   ferous, 
  glauconitic 
  sandstones 
  of 
  the 
  Mount 
  Selman 
  are 
  

   exposed 
  in 
  the 
  region. 
  

  

  The 
  outer 
  rim 
  of 
  hills 
  around 
  the 
  dome 
  is 
  composed 
  of 
  

   crossbedded 
  sands 
  and 
  sandy 
  clays 
  with 
  limonite 
  part- 
  

   ings 
  and 
  thin 
  lignite 
  beds. 
  These 
  are 
  part 
  of 
  the 
  Wilcox 
  

   formation. 
  The 
  age 
  of 
  the 
  rocks 
  in 
  which 
  the 
  saline 
  

   prairie 
  has 
  been 
  eroded 
  is 
  probably 
  in 
  part 
  Wilcox, 
  in 
  

  

  5 
  The 
  formation 
  of 
  these 
  mounds 
  is 
  also 
  described 
  by 
  E. 
  G. 
  Woodruff 
  in 
  

   a 
  brief 
  description 
  of 
  the 
  dome 
  (Bull. 
  Southwestern 
  Ass. 
  Petrol. 
  Geol., 
  vol. 
  

   1, 
  p. 
  81, 
  1917). 
  

  

  