It may be stated with certainty that the Pliocene period of geology affords no trace of human remains or implements; and the same may I think be affirmed of the period of glaciation and subsidence which constitutes the earlier Post-pliocene. With the rise of the land out of the Glacial sea indications of man are believed to appear, along with remains of several mammalian species now his contemporaries. Archæology and geology thus meet somewhere in the pre-historic period of the former, and in the Post-glacial of the latter. Wherever, therefore, human history extends farthest back, and geological formations of the most modern periods exist and have been explored, we may expect best to define their junctions. Unfortunately it happens that our information on these points is still very incomplete and locally limited. In many extensive regions, like America and Australia, while the geological record is somewhat complete, the historic record extends back at most a few centuries, and the pre-historic monuments are of uncertain date. In other countries, as in Western Asia and Egypt, where the historic record extends very far back, the geology is less perfectly known. At the present moment, therefore, the main battle-field of these controversies is in Western Europe, where, though history scarce extends farther back then the time of the Roman Republic, the geologic record is very complete, and has been explored with some thoroughness. It is obvious, however, that we thus have to face the question at a point where the pre-historic gap is necessarily very wide.