242 ALLUVIAL FORMATIONS. [CHAP. XXXIV. 



CHAP. XXXIV. 



Alluvial Formations of the Mississippi, ancient and modern. 

 Delta defined. Great Extent of Wooded Swamps. 

 Deposits of pure Vegetable Matter. 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, fyc., 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 Kate of Subsidence and Up 

 heaval. Relative Age of the ancient Alluvium of the Missis 

 sippi, 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 freshwater deposits before described in 

 the bluffs of Port Hudson, Natchez, Yicksburg, and 

 Memphis, which I regard as the monuments of a 

 more ancient alluvial formation, one of high antiquity, 

 yet formed when the physical geography of the 

 country already bore a great resemblance to that 

 now existing, and when, moreover, the land and 

 waters were inhabited by the same species of terres 

 trial, fluviatile, and lacustrine mollusca, which now in- 



