﻿2i6 
  Geological 
  Survey 
  of 
  Louisiana 
  [Sect. 
  

  

  three 
  central 
  islands. 
  The 
  results 
  of 
  his 
  investigations 
  are 
  

   embodied 
  in 
  a 
  number 
  of 
  articles.* 
  

  

  Before 
  his 
  reconnaissance 
  of 
  western 
  and 
  northwestern 
  Louisi- 
  

   ana 
  in 
  May 
  and 
  June, 
  1869, 
  he 
  considered 
  the 
  rock 
  salt 
  as 
  having 
  

   been 
  formed 
  by 
  evaporation 
  in 
  a 
  lagoon 
  or 
  series 
  of 
  lagoons 
  and 
  

   as 
  resting 
  in 
  a 
  bed 
  of 
  marine 
  clay 
  similar 
  to 
  that 
  found 
  at 
  New 
  

   Orleans 
  and 
  Bayou 
  Sale 
  (since 
  correlated 
  with 
  the 
  Port 
  Hudson) 
  

   and 
  of 
  similar 
  early 
  Quaternary 
  age, 
  anterior 
  to 
  the 
  Orange 
  

   Sand. 
  During 
  the 
  Orange 
  Sand 
  and 
  Port 
  Hudson 
  deposition 
  

   the 
  western 
  part 
  of 
  the 
  Mississippi 
  valley 
  was 
  filled 
  to 
  a 
  height 
  

   equal 
  to 
  if 
  not 
  exceeding 
  that 
  of 
  the 
  highest 
  hills 
  of 
  the 
  

   islands 
  and 
  in 
  the 
  subsequent 
  erosion 
  of 
  the 
  valley 
  by 
  the 
  Mis- 
  

   sissippi 
  river 
  these 
  islands 
  were 
  formed 
  by 
  the 
  accidents 
  of 
  

   differential 
  erosion. 
  J 
  

  

  In 
  November, 
  1869, 
  Hilgard 
  first 
  advanced 
  the 
  theory 
  of 
  the 
  

   " 
  back-bone 
  " 
  of 
  Louisiana. 
  This 
  theory 
  he 
  re-affirms 
  in 
  his 
  

  

  *Preliminar}'^ 
  Report 
  of 
  a 
  Geological 
  Reconnaissance 
  of 
  Louisiana 
  

   New 
  Orleans, 
  1869. 
  

  

  De 
  Bow's 
  Review, 
  vol. 
  37-38, 
  pp. 
  754-768. 
  

  

  Geology 
  of 
  Lower 
  Louisiana 
  and 
  the 
  Rock 
  Salt 
  Deposits 
  of 
  Petite 
  

  

  Anse. 
  Am. 
  Jour. 
  Sci., 
  2d 
  series, 
  vol. 
  47, 
  pp. 
  77-88, 
  1869. 
  

  

  Am. 
  Assn. 
  Adv. 
  Sci., 
  Proc, 
  vol. 
  17, 
  pp. 
  327-340, 
  1869. 
  

  

  Abstract, 
  Neues 
  Jahrbuch, 
  1S73. 
  pp. 
  553-554, 
  1874. 
  

  

  On 
  the 
  Geological 
  History 
  of 
  the 
  Gulf 
  of 
  Mexico. 
  

  

  Am. 
  Jour. 
  Sci., 
  3d 
  series, 
  vol. 
  2, 
  p. 
  393, 
  1871. 
  

  

  Am. 
  Assn. 
  Adv. 
  Sci., 
  Proc, 
  vol. 
  20, 
  1871. 
  

  

  La. 
  State 
  Univ., 
  Report 
  of 
  Supt. 
  for 
  1871, 
  pp. 
  207-222, 
  New 
  Orleans, 
  

  

  1872. 
  

  

  Am. 
  Nat., 
  vol. 
  5, 
  pp. 
  514-518, 
  1871. 
  

  

  (Remarks 
  on 
  the 
  Age 
  of 
  the 
  Rock 
  Salt 
  of 
  Petite 
  Anse.) 
  

  

  Am. 
  Nat., 
  vol. 
  5, 
  pp. 
  523-524, 
  1871. 
  

   On 
  the 
  Geology 
  of 
  Lower 
  Louisiana 
  and 
  the 
  Rock 
  Salt 
  Deposits 
  of 
  Petite 
  

   Anse 
  Island. 
  

   Smith. 
  Contr., 
  vol. 
  23, 
  separate 
  No. 
  248, 
  Washington, 
  1872. 
  

   The 
  Salines 
  of 
  Louisiana. 
  

  

  Mineral 
  Resources 
  of 
  the 
  U. 
  S. 
  for 
  1882, 
  pp. 
  558-565, 
  Wash., 
  1883. 
  

   Physi 
  co-geographical 
  and 
  agricultural 
  features 
  of 
  the 
  State 
  of 
  Louisiana. 
  

   Tenth 
  Census 
  U. 
  S., 
  vol. 
  5, 
  p. 
  112. 
  

   f 
  On 
  the 
  Geology 
  of 
  Lower 
  Louisiana 
  and 
  the 
  Rock 
  Salt 
  of 
  Petite 
  Anse 
  

   by 
  Eugene 
  W. 
  Hilgard, 
  Am. 
  Jour. 
  Sci., 
  2d 
  series, 
  vol. 
  47, 
  p. 
  84, 
  1869. 
  

   tibid, 
  p. 
  88. 
  

  

  