Chapter III: The Historical Divisions of the Pleistocene

The writer accepts the divisions of the Pleistocene which the geologists appear to have established. Formerly it was believed that North America had been subjected to a single glacial epoch; now it seems to be proved that there have occurred five such glacial epochs, or stages, and that there have intervened four interglacial stages of mild climate. The interglacial stages are italicized. The Nebraskan stage is the earliest, the Wisconsin the latest: Wisconsin, _Peorian_, Iowan, _Sangamon_, Illinoian, _Yarmouth_, Kansan, _Aftonian_, Nebraskan.

The characteristics of the various stages will be briefly discussed. The stages are not equally well understood and at present do not seem to be of equal importance in their relation to vertebrate paleontology.