256 UPKAISED TERRACES [CHAP. XXXIV. 



founded on rings of growth in buried trees ; for we 

 may then add the years deduced from stumps buried 

 in the modern parts of the delta, to those proved by 

 the structure of trees included in mud of earlier date. 



After considering the age and origin of the modern 

 deposits of the Mississippi and its tributaries, we 

 have still to carry back our thoughts to the era of 

 the freshwater strata seen in the bluffs which bound 

 the great valley. These, in their southern termi 

 nation, have evidently formed an ancient coast-line, 

 beyond which the modern delta has been pushed for 

 ward into the sea. Let a, b (fig. 10.) represent the 

 alluvial plain of the Mississippi, bounded on its 

 eastern side at Vicksburg, as before described, by 

 the bluffs d, at the foot of which are seen the Eo 

 cene strata,/, the upper part of the bluff being com 

 posed of shelly loam, or loess, of freshwater origin, 

 d, e (No. 2.). 



At Memphis, Port Hudson, and many other 

 places, loam of the same age as No. 2., rising from 50 

 to 200 feet above the level of the sea, constitutes the 

 entire bluffs, forming a table-land like that repre 

 sented at d, c. Similar deposits, , c (fig. 10.), recur 

 in Louisiana, on the western side of the great valley ; 

 but they are not, I am informed, denuded so as to 

 present a steep bluff at a. They rest equally on 

 Eocene strata, /(No. 3.) 



From what has been said of the species of shells 

 contained in the loam, d, e, at Natchez, and in other 

 localities, from the remains also of associated ter 

 restrial animals, and from the buried trees of Port 

 Hudson, we have inferred that these deposits (No. 2.), 



