of the Walnut Hills, §c., Mississippi. 213 
earth, in which no shells oceur. No gravel is mixed with either of 
these strata, but calcareous concretions abound in the lower stra- 
tum of loam with shells. I am indebted to the polite attention 
of Dr. E. H. Bryan, who resides near the Jackson rail road, nine 
miles east of Vicksburg, for an opportunity to make some inter- 
esting explorations in his vicinity. We visited one of the nu- 
merous horseshoe lakes formed by the rivers’ deserting old chan- 
-nels and seeking a new course. We passed through a tract of 
alluvial land still subject to be overflowed, and in one of the riv- 
ulets collected two species of Cyclas which are not seen in the 
fossiliferous loam. The land shells, on the contrary, are precise- 
ly of such species as abound in it, and occur plentifully under logs 
and dead leaves in the woods, where they must be subject to be 
killed by freshets and buried under the deposit left by-the retiring’ 
Waters. Almost as soon as the freshet subsides, another genera- 
tion of these shells exists here, and thus as the deposition goes 
on, the land shells are distributed throughout the alluvium to a 
great depth precisely as they are in the fossiliferous loam of the 
hills. In the rivulets the Cyclas exists, and is carried out by 
floods and distributed among the land shells, but they are rare in 
comparison with the latter both in the fossil and recent state. In 
_ the numerous cut-offs or lakes Unios and Paludinas abound, and 
these are represented in the ancient deposit by the beds of similar 
shells, all of existing species, which occur in patches everywhere 
throughout this singular region. They always occur in a black 
soil, evidently once the bed of lakes, and entirely different in 
and consistence from the loam containing land shells, and 
they are always at a much lower level than the top of the latter 
deposit. One of these beds of the fossil Unio we observed near Big 
Black river, which though much below the surface of the hills 
of fossiliferous loam, is yet at an elevation of about fifty feet 
above the river when the water is moderately high. Among 
these shells I noticed Unio cicatricosus and Paludina ponderosa. 
In the bluff near Vicksburg and on Dr. Smith’s plantation north- 
east of the town, Unio quadrulus, Raf., was the most common 
Species observed. The identity of the fossiliferous loam with 
the alluvium of the Mississippi, is confirmed by a singular phe- 
Nomenon in the nearly perpendicular banks formed by cutting 
through hills on the line of the Jackson railroad. Dr. Bryan 
called my attention to the willow and cottonwood trees, which 
_ Steonp Senizs, Vol. II, No. 5.—Sept., 1846. 
* 
