212 T. A. Conrad on the Eocene Formation 
As near as I could ascertain, the Eocene strata rise to a level of 
sixty feet above the river when there is an ordinary freshet.. The 
limestone, nearly on a level ‘with the water, is the lowest stratum 
known, as debris and deposits from the river cover and conceal 
whatever may be ata lower level. At the plantation of Dr. 
George Smith, five miles northeast of Vicksburg, a ravine cuts 
through the Eocene strata and exposes about the same elevation 
of horizontal beds, and between them and the loam with land 
shells, is a stratum of loam with coarse gravel without a trace of 
organic remains. ‘This gravel is also visible at Vicksburg, but 
the thickness of it; or its relation to the Eocene is not oe de- . 
termined. 
The only abundant shell of the Vicksburg Bocens, common ~ 
also at Claiborne in Alabama, is Dentalium thalloides. It is prob- 
able that the deposits of the Walnut Hills were made in shoaler 
water, and nearer the shore of the Eocene ocean than those of Clai- 
borne, but it is remarkable that no species of Cerithiwm occurs, 
a genus so abundant in species in the Eocene of France, and 
which is supposed, where it abounds in a fossil state, to indicate an 
ancient estuary. 
Vicks burg Fossiliferous Loam. 
wins the Eocene of Vicksburg, Grand Gulf, Rodney and 
Natchez, there is a thick deposit of loam of uniform composition 
and appearance, which is at least fifty feet thick in many places, 
and probably much more in others ; but owing to land slides and 
the vast accumulation of debris between this loam and the Eo- 
cene, the depth of the former is uncertain, and there may be a 
distinct deposit between the two. The loam is apparently iden- 
tical in composition with the cane-brake lands of the Mississippi, 
and abounds in land shells of such species as exist plentifully in 
the alluvial flats subject to the overflow. of freshets. I have 
collected Helix thyroidus, H. ligera, H. concava, H. setosa, H. 
arborea, H. perspectiva, &c., together with Succinea ovalis and 
Helicina orbiculata. Of fiedh water shells, there is a small Cy+ 
clas and Paludina which I have not seen in the rivulets near 
Vicksburg, though two other species of Cyclas abound in one of 
these small streams. ~'The fossiliferous loam has a very undula- 
ting summit line, following the outline of the innumerable hills, 
and it is covered by six to eight feet ne Breaches kind of 
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