_In_ closing these sketches it may seem unsatisfactory not to link the geological ages with the modern period in which we live; yet, perhaps, nothing is more complicated or encompassed with greater difficulties or uncertainties. The geologist, emerging from the study of the older monuments of the earth's history, and working with the methods of physical science, here meets face to face the archæologist and historian, who have been tracing back in the opposite direction, and with very different appliances, the stream of human history and tradition. In such circumstances conflicts may occur, or at least the two paths of inquiry may refuse to connect themselves without concessions unpleasant to the pursuers of one or both. Further, it is just at this meeting-place that the dim candle of traditional lore is almost burnt out in the hand of the antiquary, and that the geologist finds his monumental evidence becoming more scanty and less distinct. We cannot hope as yet to dispel all the shadows that haunt this obscure domain, but can at least point out some of the paths which traverse it. In attempting this, we may first classify the time involved as follows: (1) The earlier Post-pliocene period of geology may be called the _Glacial_ era. It is that of a cold climate, accompanied by glaciation and boulder deposits. (2) The later _Post-pliocene_ may be called the Post-glacial era. It is that of re-elevation of the continents and restoration of a mild temperature. It connects itself with the pre-historic period of the archæologist, inasmuch as remains of man and his works are apparently included in the same deposits which hold the bones of Post-glacial animals. (3) The _Modern_ era is that of secular human history.