Every fact furnished from Kansas seems to substantiate Cope’s conclusion that the _Megalonyx_ fauna of the East and the _Equus_ fauna of the West were contemporaneous and that both occurred during the period of depression; that is, during late Pleistocene time. This paragraph was quoted by Osborn in 1910 (“Age of Mammals,” p. 453), who appears to agree in part with Williston, although he expressed the opinion that some of the deposits were earlier than the others. Osborn supported the view of the existence of two faunas, that of the “_Equus_ zone” and that of the “_Megalonyx_ zone.” The former fauna was regarded as the older, but overlapping somewhat during the “mid-Pleistocene” the _Megalonyx_ fauna. He presented a catalogue of deposits belonging to his _Equus_ zone (his page 453) and another of those of the _Megalonyx_ zone (p. 467). In the latter he included deposits that he would now doubtless refer to the earliest Pleistocene, for example, the Ashley River beds. It was necessary for the geologists to come again to the rescue of the palæontologists. They established the fact that there had passed, not a single glacial stage, but a series, and that these had been separated by corresponding interglacial stages. They were able to show also that between the drift-sheets there were to be found remnants of old gravels and fossil-bearing soils. In Iowa, through the careful researches of Calvin and Shimek, numerous remains of fossil mammals were discovered in gravels lying between the earliest drift, the Nebraskan, and the second drift, the Kansan. Among these mammals were identified horses, camels, elephants (_E. columbi_, _E. imperator_), _Mylodon_, _Megalonyx_, and a large ruminant which is certainly a species of bison. This fauna, known as the Aftonian, was correlated by Calvin with that of the Sheridan beds of Nebraska (Bull. Geol. Soc. Amer., vol. XX, p. 354). The writer has had the opportunity to study this Aftonian material (Iowa Geol. Surv., vol. XXIII), and, although it is not as abundant as might be desired, he agrees with Calvin’s correlation.