This fact seems to be pretty certain: Had horses lived at Fish House during the deposition of the Cape May they would (as did the mastodon, Elephas primigenius, and E. columbi) quite certainly have spread out over northern New Jersey and over the grassy plains of New York and Ohio; and their remains would somewhere have been found, as are those of the other species just mentioned, in old swamp and lake deposits overlying the Wisconsin drift; but no horse remains have ever been reported from such deposits. Furthermore, in all the digging that has been done at Trenton, in deposits acknowledged by all to belong to Wisconsin times, no trace has been found of horse remains.
Near the bottom of the Fish House clay bed, just below the level of the horse remains, there is found a layer which contains river clams represented by the genera Unio and Anodonta. Ten species of Unio have been recognized and two of Anodonta. When these were first studied the beds were believed to belong to the Cretaceous. Nevertheless, the close resemblance of the shells to still living species was recognized; and to them were given names differing from those of the related existing forms by the ending oides. The species were described by Lea and Whitfield and have been restudied by Dr. H. A. Pilsbry, of the Academy of Natural Sciences, Philadelphia. The species are probably identical with forms yet living; but half of them no longer exist in the region of Delaware River. Pilsbry (Proc. Acad. Nat. Sci. Phila., 1896, pp. 567–570) stated that five of them have no longer any representatives in the Atlantic drainage south of the St. Lawrence River system. It is probable that these species had, when they lived at Fish House, spread into other rivers south of the Delaware and thus were not trapped in this river by the Wisconsin ice. It seems certain, therefore, that a longer period of time and a longer series of vicissitudes must have intervened to produce such changes in geographical distribution. According to C. T. Simpson’s work, “Descriptive Catalogue of the Naiades,” 1914, Unio (Quadrula) subrotundus now inhabits the Ohio, Cumberland, and Tennessee Rivers; U. (Lampsilis) anodontoides occupies the Mississippi River and Gulf drainage regions; while Anodonta corpulenta is found in the Upper Missouri region. The Wisconsin ice-sheet and the short period of time since its disappearance are hardly sufficient to explain this wide dispersion of species, while others have been able to retain their place in the Delaware.
Opposed to this view regarding the identity of the unios of the Fish House beds, see Ortmann (Proc. Amer. Philos. Soc., vol LII, p. 280, 1913) and Baker (Univ. Ills. Bull., XVII, p. 205, 1920). These writers contend that the species have no especial relationship to western forms. According to Baker the deposits are older than the earliest glacial stage. On the other hand, according to Dr. E. W. Berry (quoted by Baker), who has studied the plants, the beds belong to the late Pleistocene.
We have, then, these reasons for holding that the Fish House clays are of early Pleistocene age: (1) Competent geologists have determined them as belonging to the Pensauken formation, laid down at or before the time of the Kansan stage; (2) the presence of remains of horses, evidences of whose existence during or after the Wisconsin have not been produced; (3) the presence of many species of naiades, some of which yet live in that region, but the majority of which now live only in far-distant regions.
We may confidently conclude that the horse remains which were found at Swedesboro belonged likewise to the Pensauken.
In Burlington County mastodons have been found at Pemberton ( p. 64), but one can not be certain of their geological age. A reindeer has been unearthed at Vincentown (p. [64]). It seems highly probable that it lived there while the Wisconsin ice-sheet occupied the northern part of the State; but there is a possibility that it is older. In the Academy of Natural Sciences at Philadelphia are some remains of Odocoileus found at Vincentown (p. [227]).
In the vicinity of Trenton, Mercer County, scant remains of six species of Pleistocene mammals have been reported. These are Mammut americanum (p. [64]), Elephas primigenius (p. [132]), Bison bison (p. [287]), Ovibos moschatus (p. [248]), Cervus canadensis (p. [237]), and Rangifer caribou? (p. [248]). All are known to have existed elsewhere during late Pleistocene times, and three indicate a cold climate. The presence of fossil vertebrates here is of special interest because many evidences have been found of man’s occupation of the region in apparently late Pleistocene times.
At and in the vicinity of Trenton are found both Pensauken and Cape May deposits, the latter overlying the former (Salisbury and Knapp, op. cit., pp. 120, 165). The Cape May rises about 60 feet above sea-level. At various places the Pensauken protrudes through the mantle of Cape May and rises to a height of as much as 130 feet above sea-level. Its base is about 20 feet above sea-level. The materials consist of sand, gravel, and cobblestones. So far as the writer knows, no fossils have been found in the Pensauken about Trenton.
The Cape May at Trenton is held to have been laid down principally during the presence of the Wisconsin ice-sheet in the northern part of the State; and naturally it consists mostly of sands, gravels, coarse and fine, and some boulders. In the localities where excavations have been made for sand and gravel for building purposes, for sewers, and for railroads, and in search for relics of man, two principal divisions are recognized. Below are strata of clays, sands, gravels, and boulders which are believed to have been deposited by the floods of varying intensity which issued from the glacial moraine then about 60 miles above Trenton (figs. 8, 9). Over this lies a bed of what is called yellow drift, which reaches a thickness of about 3 feet. It consists mostly of fine sand, but there are many pebbles and occasionally some large boulders. It is everywhere characterized by wavy red bands. While some geologists have held the opinion that this deposit had been produced by winds, it appears to be definitely determined that it was waterlain (Wissler, Scient. Monthly, vol. II, p. 237). This “yellow drift” is overlain by about a foot of black soil which belongs to the Recent epoch and is the result of cultivation by whites. For details regarding the Trenton gravels and the yellow sands above it the reader should consult Ernest Volk’s work, “Archæology of the Delaware Valley” (Papers Peabody Mus., vol. V, 1911).
All the species mentioned above have been reported from the beds known as the Trenton gravels. A femur of a bison was found also in the yellow drift (see p. [287]).