REPORT OF THE SECRETARY. 11 



sissippi, mainly with a view to ascertain the geological age and mode of 

 occurrence of the rock-salt deposit of Petite Anse. In the absence of 

 definite data concerning the general geology of Louisiana, his observa- 

 tions on the formations of the coast (an abstract of which was published 

 in the American Journal of Science, January, 1869) demonstrated, so 

 far as the salt deposit was concerned, only the fact that in point of age 

 it was anterior to the drift. The impulse thus given to geological re- 

 search in Louisiana, however, soon led to further explorations. By sub- 

 scription, and a special appropriation obtained from the commissioners 

 of immigration of the State, the New Orleans Academy of Sciences 

 raised a fund for the purpose of enabling Professor Hilgard to make a 

 general geological reconnaissance of Louisiana, which was executed in 

 May and June, 1869. This enabled him to communicate to the American 

 Association for the Advancement of Science, at its Salem meeting, a 

 general sketch of the geology of Louisiana. Almost simultaneously 

 with the organization of Professor Hilgard's second exploration, steps 

 were taken by the faculty of the University of Louisiana to secure legisla- 

 tive aid for a geological and physical survey of the State. The latter is 

 now in progress, and the second annual report on the work will soon be 

 published. 



As regards the rock-salt deposit, Professor Hilgard's observations in 

 Northern Louisiana point to the conclusion that it -is but one of a series 

 of cretaceous outliers, traversing the State in a northwest and south- 

 east direction, and indicating the existence of an ancient ridge which 

 must have exerted an important influence upon the physical conforma- 

 tion of the Lower Mississippi Valley. The remarkable gypsum and 

 sulphur deposits of Calcasieu are likewise, in his opinion, referable to 

 the same age. Professor Hilgard has nearly completed a final memoir 

 on the geology of the Petite Anse region for publication by the Insti- 

 tution ; the results of his simultaneous exploration of the Lower Mis- 

 sissippi and delta having been communicated to the American Associ- 

 tion at the Troy meeting, and subsequently presented to the American 

 Journal of Science. 



Dr. Horatio 0. Wood, of Philadelphia, having completed an elaborate 

 work on the fresh-water algse, principally of microscopic forms, pre- 

 sented it to the American Philosophical Society and also to the Academy 

 of Natural Sciences of Philadelphia, but the expense of publication pre- 

 vented either of these societies from undertaking it. It was therefore 

 offered to this Institution, and after a critical examination has been 

 accepted for publication. As a systematic description of the fresh- 

 water algoe of North America it will form a complement to the great 

 works on the marine algse, by Dr. Harvey, published some years ago 

 by the Smithsonian Institution. It will be copiously illustrated by 

 drawings, made principally under the microscope and will serve to illus- 

 trate an obscure department of botany, as well as to furnish the means 

 by which investigators of minute microscopic organisms may make the 



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