CHAPTER XXXIV. 



Alluvial Formations of the Mississippi, ancient and modern. Delta defined. 

 Great Extent of Wooded Swamps. Deposits of pure Vegetable Mat 

 ter. Floors of Blue Clay with Cypress Roots. Analogy to ancient Coal- 

 measures. Supposed &quot; Epoch of existing Continents.&quot; Depth of Fresh 

 water Strata in Deltas. Time required to bring down the Mud of the 

 Mississippi. New Experiments and Observations required. Great Age 

 of buried and living Cypress-trees. Older and Newer Parts of Alluvial 

 Plain. Upraised Terraces of Natchez, &c., and the Ohio, the Monuments 

 of an older Alluvial Formation. Grand Oscillation of Level. The ancient 

 Valleys inhabited by Quadrupeds now extinct. Land-shells not changed. 

 Probable Rate of Subsidence and Upheaval. Relative Age of the an 

 cient Alluvium of the Mississippi, and the Northern Drift. 



BEFORE leaving the valley of the Mississippi, I shall take this 

 opportunity to offer some general remarks on the modern delta and 

 alluvial plain of the great river, and on those fresh-water deposits 

 before described in the bluffs of Port Hudson, Natchez, Vicksburg, 

 and Memphis, which I regard as the monuments of a more an 

 cient alluvial formation, one of high antiquity, yet formed when 

 the physical geography of the country already bore a great re 

 semblance to that now existing, and when, moreover, the land 

 and waters were inhabited by the same species of terrestrial, 

 fluviatile, and lacustrine mollusca, which now inhabit this region, 

 although the land quadrupeds were almost entirely different. 



The delta of the Mississippi may be defined as that part of the 

 great alluvial slope, which lies below, or to the south of the 

 branching off of the highest arm, or that called the Atchafalaya. 

 Above this point, which is the head of the delta, the Mississippi 

 receives water from its various tributaries ; below, it gives out 

 again, through numerous arms or channels, the waters which it 

 conveys to the sea. The delta, so defined, is about 14,000 

 square miles in area, and elevated from a few inches to ten feet 

 above the level of the sea The greater part of it protrudes into 

 the Gulf of Mexico, beyond the general coast line. The level 

 plain to the north, as far as Cape Girardeau, in Missouri, above 



