Besides these vertebrates, there were reported by Leidy the land snails Helix albolabris, H. alternata, and H. tridentata; also a pair of valves of the river mussel Margaratina margaritifera and a fragment of another valve. Leidy regarded these as showing that this mussel formerly lived in Delaware River; whereas in his view it no longer existed there; but specimens of it from Philadelphia are in the U. S. National Museum.

An examination of the list shows that nearly all of the species of vertebrates are yet in existence and most of these still living in that general region. Rangifer caribou lives now far to the north and Lynx canadensis has its range somewhat further north. The two indicate a colder climate, especially the reindeer. Both got into the cave probably after the glacial front had withdrawn from that vicinity. The remains of Castoroides may have been carried in there at about the same time. The type specimen of Mylohyus pennsylvanicus was found in this cave. Cope referred specimens of a peccary found in Port Kennedy Cave to the same species with doubt. Undetermined species of the genus were recognized by Barnum Brown in his collection made in the Conard fissure in northwestern Arkansas. Dr. W. J. Holland reported Mylohyus pennsylvanicus from the cave at Frankstown, Pennsylvania. The type of the genus, M. nasutus, was found in Indiana. Beyond the testimony furnished by the Crystal Hill Cave, we have no evidence that the genus Mylohyus existed after the Wisconsin stage; the possibility exists that this species got into the cave before this stage.

The specimen of Equus is still more doubtful. It consisted of two isolated first and second milk molars of a very young colt. Leidy was in doubt whether the colt belonged to the domestic horse or to an indigenous species. The specimen had been collected with no record as to the part of the cave or of the depth in the upper layer of soil where it was buried. A fragment of a jaw of a colt might easily have been carried into the cave by some carnivorous animal since the coming of the whites. A fragment of the lower jaw of a bison also was found which had in it the last molar; and this was referred by Leidy to the existing buffalo.

It can hardly be doubted that this cave was hollowed out before the Wisconsin ice period. It may have been formed during the early Pleistocene. The fact that it was filled to a depth of 14 feet, in some places, with a fine laminated clay devoid of all traces of organic beings seems to indicate that for ages it had been shut off from the outer world, and that streams charged with fine sediment were permitted to pass through it. During possibly some glacial stage preceding the Wisconsin, erosion may have opened the cave so that the horse remains, those of a bison, and of Castoroides were dragged into it. The evidence for these suppositions is slender, but so too is that for a late Wisconsin indigenous species of horse in Pennsylvania. It is probable that most of the species found in the cave belong to the late Pleistocene or even to the Recent.

Fossil vertebrates found in a cave in Bucks County require our attention.

In 1880 (Proc. Acad. Nat. Sci. Phila., 1880, p. 349), Leidy presented a list of vertebrate remains which had been lying unstudied for 40 years in the collection of the Academy. These had been found in Durham Cave, somewhere near Riegelsville, in Bucks County. It is not improbable that the cave took its name from the village of Durham, about 2 miles southwest of Riegelsville. Leidy stated that the cave appeared to have been obliterated in the quarrying of limestone. In 1889 (Ann. Rep. Geol. Surv. Pennsylvania, for 1887, pp. 18–19) Leidy published a list of the species which he had identified.

List of fossil vertebrates from Durham Cave.

This list differs in its species from Leidy’s list of 1880 only in the exclusion of the bison and the inclusion of the elk, Cervus canadensis. All the species are still in existence, most of them in that region. The presence of the reindeer, the moose, and the porcupine suggests a cooler climate than now prevails there. These animals may all have become buried in that cave during the latest times of the Wisconsin stage or even during the Recent.

We are now to study a case which furnishes us with a store of knowledge regarding the life of the Pleistocene. In 1871 there was found at Port Kennedy, Montgomery County, a cave which was worked for its fossils by Charles Wheatley and later by Dixon, Mercer, and Cope, the latter having devoted himself to the description of the vertebrates. First of all will be given a list of the species of vertebrates, mostly mammals which have been recognized in the materials found in the cave. When Cope’s names differ from those employed here they are put in parenthesis.