﻿236 
  Geological 
  Survey 
  of 
  Louisiana 
  [Sect. 
  

  

  emerge 
  in 
  the 
  form 
  of 
  salt 
  springs 
  at 
  or 
  near 
  sea-level. 
  The 
  

   removal 
  of 
  the 
  salt 
  bj^ 
  water 
  would 
  form 
  caverns. 
  Dirt 
  and 
  sand 
  

   would 
  naturally 
  be 
  carried 
  by 
  the 
  water 
  into 
  these 
  caverns 
  in 
  the 
  

   salt 
  and 
  finally 
  a 
  large 
  funnel-shaped 
  opening 
  would 
  be 
  produced 
  

   on 
  the 
  surface. 
  Such 
  sink 
  holes 
  are 
  common 
  in 
  limestone 
  

   regions 
  and 
  quite 
  a 
  number 
  have 
  been 
  very 
  recently 
  produced 
  

   artificially 
  on 
  Petite 
  Anse. 
  The 
  galleries 
  and 
  rooms 
  hollowed 
  

   out 
  by 
  man 
  in 
  mining 
  the 
  salt 
  correspond 
  to 
  the 
  caverns 
  which 
  

   would 
  have 
  been 
  produced 
  by 
  water 
  if 
  the 
  salt 
  were 
  elevated 
  

   enough 
  to 
  give 
  the 
  water 
  an 
  outlet 
  above 
  sea-level. 
  Water 
  run- 
  

   ning 
  into 
  these 
  chambers 
  through 
  natural 
  crevices 
  in 
  the 
  salt 
  

   would 
  soon 
  enlarge 
  them 
  to 
  good 
  sized 
  holes 
  when 
  the 
  dirt 
  and 
  

   sand 
  and 
  gravel 
  would 
  follow 
  giving 
  rise 
  to 
  a 
  great 
  funnel-shaped 
  

   opening 
  which 
  would 
  tend 
  to 
  enlarge 
  with 
  every 
  succeeding 
  rain. 
  

   As 
  the 
  water 
  is 
  kept 
  pumped 
  out 
  of 
  the 
  mine 
  the 
  effect 
  is 
  the 
  

   same 
  as 
  if 
  the 
  salt 
  stood 
  90 
  or 
  100 
  feet 
  higher. 
  

  

  Now, 
  if 
  a 
  subsidence 
  should 
  occur, 
  the 
  chambers 
  and 
  caverns 
  

   would 
  become 
  clogged 
  with 
  sand 
  and 
  gravel 
  and 
  clay 
  because 
  of 
  

   the 
  diminished 
  velocity 
  of 
  the 
  waters. 
  The 
  material 
  washed 
  

   down 
  from 
  the 
  steep 
  sides 
  of 
  the 
  sink 
  hole 
  would 
  tend 
  to 
  fill 
  it 
  

   and 
  if 
  there 
  was 
  a 
  considerable 
  amount 
  of 
  clay 
  in 
  the 
  material 
  

   the 
  subterranean 
  outlet 
  would 
  become 
  effectually 
  stopped. 
  

   Water 
  would 
  accumulate 
  in 
  the 
  depression 
  till 
  it 
  reached 
  the 
  

   lowest 
  point 
  in 
  the 
  surrounding 
  rim 
  of 
  hills, 
  flow 
  over 
  and 
  begin 
  

   to 
  destroy 
  itself 
  by 
  cutting 
  down 
  the 
  outlet. 
  This 
  second 
  stage 
  

   is 
  shown 
  in 
  only 
  one 
  of 
  the 
  holes 
  near 
  the 
  mine 
  on 
  Petite 
  Anse, 
  

   This 
  one, 
  which 
  is 
  northeast 
  of 
  the 
  shaft, 
  has 
  become 
  clogged 
  

   with 
  clay 
  even 
  though 
  the 
  subterranean 
  channels 
  are 
  still 
  open 
  

   and 
  a 
  little 
  pond 
  has 
  formed 
  in 
  its 
  bottom. 
  

  

  Lakes 
  formed 
  outside 
  of 
  the 
  glacial 
  limits 
  by 
  the 
  irregular 
  

   filling 
  of 
  a 
  valley 
  by 
  loess, 
  where 
  the 
  latter 
  seemed 
  to 
  collect 
  in 
  the 
  

   form 
  of 
  a 
  great 
  levee 
  across 
  the 
  mouth 
  of 
  a 
  valley, 
  have 
  been 
  

   noticed 
  by 
  the 
  writer 
  in 
  southern 
  Indiana.* 
  No 
  trace 
  of 
  such 
  a 
  

   structure 
  was 
  observed 
  here, 
  and 
  further 
  the 
  lakes 
  have 
  neither 
  

   the 
  shape 
  nor 
  appearance 
  of 
  a 
  dammed 
  valley, 
  the 
  upper 
  end 
  

   being 
  commonly 
  larger 
  than 
  the 
  lower. 
  

  

  * 
  Notes 
  on 
  the 
  Ohio 
  Valley 
  in 
  Southern 
  Indiana. 
  Jour, 
  of 
  Geol. 
  vol. 
  6, 
  

   p. 
  262, 
  1898. 
  

  

  