In 1898, Dr. B. Shimek visited Natchez and studied especially the loess (Amer. Geologist, vol. XXX, pp. 279–298, with plates X-XVI). He estimated the thickness of the loess as not exceeding 30 feet. He collected from this loess more than 4,600 shells of mollusks; and these proved to belong to 39 species or well-recognized subspecies. These species are all terrestrial in habit and all are now found living either on the hills in the immediate vicinity or in similar situations in other parts of the South. Shimek came to the conclusion that the loess of that region had been deposited by the action of the winds. He was unable to find any “brown loam” above the loess, the presence of which other authors had affirmed.
Shimek found no traces of mammalian bones in the loess and was inclined to doubt that they occur there. He does not appear to have visited the locality from which most of the bones were reported.
Chamberlin and Salisbury, in 1906 (Geology, vol. III, p. 386, fig. 513), discussed briefly the geological situation at Natchez. The Natchez formation (evidently including the Port Hudson) has a thickness of about 200 feet and is made up of materials derived mostly from the so-called Lafayette, on which it there rests unconformably. In this Natchez formation are also crystalline pebbles and calcareous clays assignable to wash from the glacial regions. Between this Natchez formation and the overlying loess a marked interval is indicated. The authors are inclined to assign the Natchez deposits to the earliest part of the Pleistocene, viz, to the Aftonian and the drift epoch preceding the Aftonian. Since the time when the Natchez formation was deposited the great trench of the Mississippi Valley, about 60 miles wide, has been excavated.
Already on page [391] has been given the list of fossil mammals which Leidy made out for the State geologist of Mississippi, B. L. C. Wailles. A revision of this is here presented, with the addition of Castoroides ohioensis.
- Megalonyx jeffersonii (p. [40]).
- M. dissimilis (p. [41]).
- Mylodon harlani (p. [41]).
- Ereptodon priscus (p. [41]).
- Equus complicatus (p. [200]).
- E. leidyi (p. [200]).
- Tapirus haysii (p. [208]).
- T. terrestris (p. [208]).
- Odocoileus virginianus (p. [233]).
- Symbos cavifrons (p. [254]).
- Bison latifrons? (p. [265]).
- Mammut americanum (p. [125]).
- Elephas columbi? (p. [180]).
- Castoroides ohioensis (p. [280]).
- Ursus americanus.
- U. amplidens.
- Felis atrox.
According to Lyell (Amer. Jour. Sci., vol. III, 1847, p. 268), Megatherium and Castoroides had been found in the bluffs at Natchez.
From this list of mammals it is possible perhaps to reach some conclusion regarding the geological age of the deposits containing them. In case we accept without reserve the species, 16 in number, as determined, only 3, Tapirus terrestris, Odocoileus virginianus, and Ursus americanus, are yet living, leaving about 81 per cent of the whole as being extinct, and what was called Tapirus terrestris was probably an extinct form. This alone makes it probable that the time of their existence was early in the Pleistocene. All three of the supposed existing species may, however, prove to belong to extinct species closely related to those whose names they yet bear.
Certain species may be left out of consideration because of paucity of specimens and our consequent lack of knowledge of them. These are Megalonyx dissimilis, Ereptodon priscus, and Ursus amplidens.
In case the high percentage of extinct species is not recognized as being decisive, we may consider the assemblage from another point of view. Certain species of the list appear to have existed throughout the Pleistocene, at least from the time of the first interglacial stage. These are Megalonyx jeffersonii, Mammut americanum, Elephas columbi, and Castoroides ohioensis, and their presence indicates only a Pleistocene time. Others of the list are not known to have existed after the time of the last Wisconsin drift-sheet, and may be supposed to have become extinct before that time. These are Mylodon harlani, Equus complicatus, Equus leidyi, Tapirus haysii, and Bison latifrons. All of these quite certainly existed until after the Illinoian drift period, probably into the Sangamon interglacial, except apparently Equus leidyi.
The list contains no species of primitive mastodons belonging to the genus Gomphotherium, no species of Hipparion, no camels; and Elephas imperator appears to be missing. There is, therefore, no necessity for believing that the mammal-bearing deposits at Natchez are as old as the Sheridan, or Aftonian stage, but the ancient forms mentioned may at any time turn up there or elsewhere in the immediate region.