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Cii. xix.] 



BLUFFS' OF THE MISSISSIPPI. 



463 



most conspicuous of them. Above this buried forest the bluff 

 rises to a height of about 75 feet, and it affords a section of 

 beds of river-sand, including trunks of trees and pieces of 

 drift wood, and above the sand a brown clay. From the top 

 of the cliff the ground slopes to a height of 150 feet above 

 the level of the buried forest, or about 200 feet above the 

 sea. From this section we learn that there have been great 

 movements and oscillations of level since the Mississippi 

 be^an to form an alluvial plain, and to drift down timber into 

 it, and to burv under its sand and sediment ancient forests, 

 resembling those which now flourish in the swamps of its 

 plain and delta. When the trees were buried, the ground 

 was probably sinking, after which it must have been raised 

 a^ain, so as to allow the stream to cut through its old allu- 

 vium. The depth of this ancient fluviatile formation is seen 

 to be no less than 200 feet, without any signs of the bottom 

 being reached. In character it is identical with the deposit 

 called Coast-Pliocene by Prof. Hilgard (see p. 460, and a, a, 

 map, p. 448), of which, I presume, it is a continuation, but 

 no marine shells have been detected in Hudson's Bluff, like 

 those occasionally met with on the coast. 



If again we ascend the river to about sixty-five miles due 

 north of Port Hudson, or about 225 above New Orleans, we 

 observe another bluff at Natchez, on the same left bank of 

 the river, more than 200 feet in perpendicular height. The 

 lower part of this cliff consists of gravel and sand, while the 

 uppermost, sixty feet in thickness, is a mass of loam exactly 

 resembling the loess of the valley of the Rhine, without stra- 

 tification, and full of land-shells, such as Helix and Pupa, 

 together with the amphibious genus Succinea, all of species 

 now living in the same country. At a few points in the 

 lower part of this formation, I observed shells of living spe- 

 cies of Limnea, Planorbis, and Cyclas, genera which inhabit 

 ponds, and which may indicate the channel of an ancient river, 

 on the borders of which, after it had shifted its course, the 

 loess was deposited during inundations. This same loess is 

 continuous over a vast extent of country, always increasing 

 m thickness near the Mississippi. It occurs in a bluff at 

 Vicksburg, eighty miles due north of Natchez (see section, 



