In the outset, it can not be assumed reasonably that this stone-age civilization, apparent in Northern and Western Europe, was _necessarily universal at that time over all the earth_. It may have been coeval with the very high civilization of Egypt and even of Babylonia, Phenicia, Etruria. We must consider that large portions of the world in those early times were unknown to each other, even as interior Africa has been unknown to the civilized world almost to this very hour. It is therefore entirely an open question――Was this stone-age civilization pre-Adamic? Was it anterior to Noah; or shall its place in the ages be found contemporaneous with the early civilized nations of known history? It is important here to premise yet further that the earth’s surface has at no very remote period experienced considerable elevations and depressions and changes of temperature. Especially there are proofs of an extraordinary period of glaciers and icebergs, by means of which huge bowlders have been transported from their ancient beds and scattered afar, and vast masses of debris, rocks ground down and pulverized, mixed with sand, gravel, and small stones, have been heaped up along the line of the glaciers and spread over their track. It is not easy to conceive the full measure of _utility_ resulting from this great ice-flood and glacier movement, in grinding the surface of the rocky strata and mixing this finely pulverized matter with decomposed vegetable elements to prepare soil for our earth’s surface. The opinion is becoming general that man was not placed upon the earth until _after_ this glacial and ice-bound age. He could not have lived here then: certainly not in portions reached by glacial action and ice floods; the earth was not ready for him till afterwards. No decisive traces of his presence at an earlier period have been found. Such traces appear shortly after. The problem of the _time_ of man’s first appearance upon the earth is for the most part one _of estimates_; and these estimates in the department of geology are comprised, at least chiefly, under these five heads: (1.) The time required for the _alluvial deposits_ underneath which his remains or implements have been found. (2.) The time required for the _growth of the peat_ under which we find man or his works. (3.) The time required for the succession of forest growths since his first appearance. (4.) The age of the animal races, extinct or living, whose remains are found associated with his. (5.) We have next and last another source of testimony which is mainly free from the uncertainties of estimate, viz. the question of commercial relations between the barbarous stone-age, bronze-age, or iron-age tribes, and the civilized nations of the early historic ages. The estimates on these several points demand distinct consideration.