126 



Dr. John Bacon, Jr., informed the Society that he had 

 recently made a microscopic examination of sand from the 

 desert of Zahara, taken from specimens in the Society's 

 cabinet. 



He had found it to consist, in a great part, of siliceous grains, 

 with a few Polythalamia intermixed. These are mostly frag- 

 ments. He had been able to identify only one species, viz., 

 Textularia glohulosa. He intended to give the subject further 

 attention. 



Dr. A. Binney exhibited a collection of fossils, and other 

 geological specimens, from the strata of the bluffs at Natchez, 

 on the Mississippi River. 



Dr. B. remarked that the flat alluvial borders of the lower 

 Mississippi are interrupted, in several places, by elevated cliffs, 

 generally on one side of the river only, at the foot of which the 

 channel flows, undermining and breaking them down from time 

 to time, and thus exposing a natural section of their strata. 

 These elevations are known as bluffs. The bluff on the eastern 

 side of the Mississippi, at Natchez, is about two hundred and 

 fifty feet above the low-water level of the river. It is made up 

 of nearly parallel strata of calcareous loams, clays, sands and 

 gravel, which contain in the different layers, besides inorganic 

 substances, great numbers of terrestrial, and some fluviatile, shells, 

 remains of mammalia, and numerous water-worn, agatized 

 pebbles, imbedding corals, madrepores, encrinites, and marine 

 shells. Agatized wood and lignites arc also found. No detailed 

 description of the bluff formation has yet been published ; but 

 in the limited notices which have been given it appears to have 

 been taken for granted to be wholly the result of diluvial action, and 

 to form a part of the extensive and as yet not fully understood 

 deposits, known as diluvium or drift. 



An incomplete scries of specimens from the different strata, 

 collected at Natchez, by Mr. John Bartlctt, had afforded Dr. B. 

 an opportunity of examining the fossil land shells, and of com- 

 paring them with existing species ; and the result of this examina- 

 tion he proceeded to lay before the Society. He ventured at the 

 same time, but with much hesitation, owing to his want of famili- 



