﻿234 
  Geological 
  Survey 
  of 
  Louisiana 
  [Sect. 
  

  

  diflSculty 
  then, 
  on 
  account 
  of 
  the 
  dissoluble 
  nature 
  of 
  the 
  salt, 
  

  

  was 
  to 
  make 
  a 
  water 
  tight 
  joint 
  between 
  the 
  tubing 
  and 
  the 
  salt. 
  

  

  As 
  soon 
  as 
  this 
  is 
  accomplished 
  the 
  intention 
  is 
  to 
  erect 
  the 
  

  

  shaft 
  house 
  and 
  build 
  a 
  switch 
  from 
  theCypremort 
  branch 
  of 
  the 
  

  

  Southern 
  Pacific. 
  

  

  Geology 
  

  

  Surface 
  geology. 
  — 
  L,ike 
  C6te 
  Blanche 
  nearly 
  the 
  whole 
  of 
  the 
  

   island 
  is 
  covered 
  with 
  a 
  brownish 
  yellow 
  soil. 
  In 
  places, 
  notably 
  

   in 
  the 
  deep 
  gorges 
  along 
  the 
  Devil's 
  Backbone 
  and 
  indeed 
  in 
  

   nearW 
  all 
  hollows 
  going 
  into 
  Lake 
  valley 
  the 
  upper 
  stratum 
  of 
  

   clay 
  has 
  been 
  cut 
  through 
  exposing 
  the 
  underlying 
  sands, 
  and 
  

   sometimes 
  gravel. 
  East 
  of 
  the 
  larger 
  lake 
  is 
  a 
  sandpit 
  which 
  

   furnishes 
  sand 
  for 
  the 
  surrounding 
  country. 
  Springs 
  are 
  com- 
  

   mon 
  on 
  the 
  Northern 
  slopes 
  of 
  the 
  island. 
  

  

  The 
  wells. 
  — 
  The 
  twenty-eight 
  well 
  sections 
  (shown 
  on 
  Plates 
  

   27 
  and 
  28) 
  show 
  very 
  little 
  variety 
  in 
  the 
  subterranean 
  

   structure 
  of 
  the 
  island. 
  There 
  is 
  commonly 
  a 
  surface 
  layer 
  of 
  

   clay 
  from 
  a 
  few 
  inches 
  to 
  30 
  or 
  40 
  feet 
  thick 
  and 
  then 
  sand 
  and 
  

   gravel 
  down 
  to 
  the 
  salt. 
  In 
  two 
  wells 
  No. 
  9 
  and 
  No. 
  17 
  layers 
  

   of 
  lignite, 
  five 
  feet 
  thick 
  in 
  the 
  first 
  and 
  three 
  feet 
  in 
  the 
  second, 
  

   were 
  struck 
  just 
  above 
  the 
  salt. 
  In 
  many 
  of 
  the 
  wells 
  the 
  

   hydrostatic 
  pressure 
  is 
  sufficient 
  to 
  force 
  the 
  water 
  almost 
  to 
  the 
  

   surface 
  and 
  in 
  well 
  No. 
  6 
  it 
  is 
  sufficient 
  to 
  lift 
  the 
  water 
  above 
  

   the 
  top 
  of 
  the 
  pipe 
  and 
  form 
  a 
  flowing 
  well. 
  

  

  The 
  shape 
  and 
  position 
  of 
  the 
  salt 
  mass. 
  — 
  The 
  salt 
  on 
  Grande 
  

   Cote 
  forms 
  an 
  elongate 
  dome, 
  longest 
  along 
  its 
  north 
  and 
  south 
  

   diameter 
  (Plate 
  29). 
  It 
  occupies 
  the 
  western 
  side 
  of 
  the 
  island 
  

   and 
  appears 
  to 
  extend 
  a 
  little 
  west 
  of 
  the 
  main 
  ridge. 
  No 
  borings 
  

   have 
  been 
  made 
  along 
  the 
  ridge 
  so 
  that 
  we 
  can 
  not 
  positively 
  say 
  

   that 
  the 
  salt 
  does 
  not 
  extend 
  in 
  that 
  direction. 
  Well 
  No. 
  2 
  did 
  

   not 
  find 
  salt 
  at 
  212 
  feet 
  but 
  no 
  borings 
  have 
  been 
  made 
  between 
  

   it 
  and 
  No. 
  9. 
  Whether 
  the 
  dome 
  shape 
  of 
  the 
  salt, 
  well 
  shown 
  

   by 
  Plate 
  29 
  and 
  the 
  cross-sections 
  of 
  the 
  island 
  Plate 
  30, 
  really 
  

   indicate 
  a 
  dome 
  or 
  whether 
  its 
  present 
  shape 
  is 
  due 
  to 
  the 
  

   erosion 
  of 
  the 
  edge 
  of 
  an 
  upturned 
  fault 
  block 
  or 
  to 
  the 
  erosion 
  

   undisturbed 
  material, 
  could 
  not 
  be 
  determined 
  in 
  any 
  direct 
  man- 
  

   ner. 
  All 
  data 
  collected 
  would 
  however 
  tend 
  to 
  disprove 
  the 
  last 
  

   supposition. 
  The 
  shaft, 
  at 
  the 
  time 
  of 
  the 
  writer's 
  visit, 
  had 
  not 
  

  

  