8 ON THE GEOLOGY OF LOWER LOUISIANA 



seen by Bartram ; his description agrees substantially with that given by the former, 

 but he mentions the bed of vegetable mould about the tops of the stumps, as distinct 

 from the clay in which the roots are buried ; he also found in the former layer a 

 variety of fruits, the same, so far as they go, as those I have collected from the 

 upper stratum No. 3. He states that "the stump stratum (No. 1) is covered with 

 a bed of clay twelve feet thick, and is followed by another bed of superimposed 

 vegetable matter four feet thick, containing logs and branches half turned into 

 lignite, and erect stumps, among which there are none of the large cypress, as in 

 the lower bed. Among the logs, the Water Oak was recognizable, and a pine 

 with a great deal of bark" (doubtless P. glabra Walt.) " and the strobiles of P'lnm 

 imda. . . . Above the upper layer of erect stumps are various beds of clay, 

 with two thin layers of vegetable matter intercalated ; and above the whole, more 

 than twenty feet of sand, the lower part of which included siliceous pebbles derived 

 from some ancient rocks, and containing the marks of Encrinites and Corals." 



At the present time, the clay bed of statum No. 1, is in no place less than twenty- 

 five feet in thickness, and at several points it extends thirty feet. Moreover, it 

 appears that Dr. Carpenter found stumps, in situ, in the upper stratum. No. 3, of 

 my section, where I have vainly sought for them; where he observed no cypress, I 

 saw an abundance of it, as well as of the trees of the higher swamps mentioned by 

 him. But the nature of the stratum as now observable at the upper landing (see 

 above) shows that it has in part been formed as a swamp deposit, the non-occur- 

 rence of stumps in which would be a matter of local accident. 



Lyell, in 1846, found the stump stratum, No. 1, twelve feet under water. He 

 distinctly describes, however, strata Nos. 2, 3, and 4, and mentions the occurrence 

 of fossil trees in No. 3, but not of stumps. 



The variability of the latter stratum, as now exhibited in the three miles of north 

 and south exposure, and recorded in the successive observations as equally existing 

 in an east and west direction, is interesting as a proof of the exact analogy of the 

 present state of things, with that existing at that distant period. The variable 

 thickness of the stratum, the alternation of sandbar and drift-wood deposits with 

 those derived from swamps partly high, partly low, and others of fine silt free from, 

 or superimposed upon, vegetable mould, the result of quiet overflow — all this is what 

 any deep canal now dug across the Mississippi Bottom would exhibit. 



Not so the lower stump stratum and superincumbent clay bed. Both in thick- 

 ness and nature of materials, these vary but slightly, whether in a vertical or hori- 

 zontal direction; not only here, but elsewhere in the level belt bordering the Gulf 

 coast. They testify to the wide-spread prevalence, at the time of their deposition, 

 of quiet, shallow fresh-water lagoons and swamps of various degrees of elevation, 

 through which, perhaps, at that time the continental waters found an outlet with- 

 out a definite channel to represent the Mississippi lliver of to-day. 



THE LOWER MISSISSIPPI. 



From Natchez do^vn to New Orleans blue clay is frequently seen at low water level, 

 forming the base of the river banlts, and sometimes reaching to within a.few feet 



