The main stream of the geological evidence of the antiquity of man tends to one point, viz., _that man coexisted with the extinct animals_. There are collateral branches of proof, but this is the main channel. The remains of man and of man's works and the remains of extinct races of animals lie side by side, and claim from the geologist the same meed of antiquity. This is the burden of the book before us. We offer the reader a brief outline of this evidence. In doing so, we will follow the order of Sir Charles Lyell's work, and merely state the leading facts which geological investigations have brought to light. In the Danish islands there are deposits of peat from ten to thirty feet thick, formed in the hollows or depressions of the northern drift or bowlder formation. These beds of peat have been examined to the bottom, and they reveal the history of vegetation in those localities, and the contemporaneous history of human progress. Beginning at the top, the explorer finds the first layers to contain principally the trunks of the beech tree, along with implements and tools of wood and iron. Below these is a deposit of oak trunks, with implements mainly of bronze. Farther down still he finds the trunks of the _Pinus sylvestris_, or Scotch fir, together with implements of stone. This clearly indicates that in the lapse of centuries the pine was supplanted by the oak, and the oak by the beech, and that man advanced contemporaneously from the knowledge and use of stone implements to those of bronze and iron. Now the known fact is that in the time of the Romans, as now, the Danish isles were covered by magnificent beech forests, and that eighteen centuries have done little or nothing toward changing the character of the vegetation. How many centuries must have elapsed to enable the oak to supplant the pine, and the beech to supplant the oak, can only be vaguely conjectured. Yet the evidence is clear that man lived in those old pine forests--leaving his implements of stone behind him, as he did his tools of bronze and iron in the succeeding periods. Along the coast of Denmark, also, are found shell mounds mixed with flint knives, hatchets, etc., but never any tools of bronze or iron, showing that the rude hunters and fishers who fed on the oyster, cockle, and other mollusks, lived in the period of the Scotch fir, or, as it has been called, the 'age of stone.' In many of the Swiss lakes are found ancient piles driven into the bottom, on which were once erected huts or villages, the lacustrine abodes of man. This use of them is proved by the abundance of flint implements and fragments of rude pottery, together with bones of animals, which have been dredged up from among the piles. The implements found belong to the 'age of stone,' or the period of the Scotch fir in Denmark, and the bones of animals are all, with one exception, those of living species.