ON THE 



GEOLOGY OF LOWEll LOUISIANA, 



SALT DEPOSIT ON PETITE ANSE ISLAND. 



The discovery, in May, 1862, of a deposit of rock-salt on the coast of Louisiana, 

 was a fact so unexpected to geologists, that, at any other time, a detailed investi- 

 gation of the circumstances of its occurrence would quickly have followed its first 

 announcement. Under the circumstances then existing, such great practical 

 importance attached to it, that the Confederate government promptly caused 

 official examinations to be made. This, however, was of an exclusively practical 

 character, and resulted in the establishment of a system of exploitation which, 

 while perhaps necessary at the time in order to supply without delay the pressing 

 want of salt in the blockaded section, was illy calculated to endure for any great 

 length of time, or to give information as to the extent or geological character of 

 the deposit. For a considerable time these mines, together with the brine wells 

 of Northwestern Louisiana, supplied the whole of the Southwest ; until, in April, 

 1863. on the taking of the island of Petite Anse by the Federal forces, the works 

 were destroyed. 



Information gathered during the war from soldiers residing in the region had 

 satisfied me that the hypothesis of the volcanic origin of the island, set forth by 

 Mr. Thomassy in I860,' was unfounded. An analysis of a specimen of the salt 

 which I obtained in 1863, showed its only impurity to consist of 0.120 per cent, 

 of gypsum. 



The first scientific investigation of the salt region, which has come to public 

 knowledge, was made by Prof. Richard Owen, in November, 1865.^ He ascertained 

 the sedimentary character of the deposits forming the island, attributing tlicir 

 formation, however, to "the combined action of the winds and waves of the ocean." 

 The rock-salt mass he conceives to have been formed by saline inundations caused 

 by storm tides. 



In summer, 1866, I received an invitation from Prof. Henry to undertake a 

 geological examination of the Louisiana salt region, the travelling expenses to be 

 defrayed by the Smithsonian Institution. "While most anxious to avail myself of 

 this opportunity of extending my knowledge of the geology of the Gulf coast, want 

 of time, as well as the epidemic prevailing in the region, compelled me to defer the 

 excursion until November, 18(57. 



' Geologic pratique dc lu liOuisiane, 1860, p. 77. 



= Proc. Acad. St. Louis, II. 250; Amer. Journ Science, July, 1860, p. 120. 



1 April, 1872. ( 1 ) 



