The theory of human degradation to explain the existence of savages and of barbarians is no longer tenable. It came in as a corollary from the Mosaic cosmogony, and was acquiesced in from a supposed necessity which no longer exists. As a theory, it is not only incapable of explaining the existence of savages, but it is without support in the facts of human experience. The remote ancestors of the Aryan nations presumptively passed through an experience similar to that of existing barbarous and savage tribes. Though the experience of these nations embodies all the information necessary to illustrate the periods of civilization, both ancient and modern, together with a part of that in the Later period of barbarism, their anterior experience must be deduced, in the main, from the traceable connection between the elements of their existing institutions and inventions, and similar elements still preserved in those of savage and barbarous tribes. It may be remarked finally that the experience of mankind has run in nearly uniform channels; that human necessities in similar conditions have been substantially the same; and that the operations of the mental principle have been uniform in virtue of the specific identity of the brain of all the races of mankind. This, however, is but a part of the explanation of uniformity in results. The germs of the principal institutions and arts of life were developed while man was still a savage. To a very great extent the experience of the subsequent periods of barbarism and of civilization have been expended in the further development of these original conceptions. Wherever a connection can be traced on different continents between a present institution and a common germ, the derivation of the people themselves from a common original stock is implied. The discussion of these several classes of facts will be facilitated by the establishment of a certain number of Ethnical Periods; each representing a distinct condition of society, and distinguishable by a mode of life peculiar to itself. The terms “Age of _Stone_,” “of _Bronze_,” and “of _Iron_” introduced by Danish archæologists, have been extremely useful for certain purposes, and will remain so for the classification of objects of ancient art; but the progress of knowledge has rendered other and different subdivisions necessary. Stone implements were not entirely laid aside with the introduction of tools of iron, nor of those of bronze. The invention of the process of smelting iron ore created an ethnical epoch, yet we could scarcely date another from the production of bronze. Moreover, since the period of stone implements overlaps those of bronze and of iron, and since that of bronze also overlaps that of iron, they are not capable of a circumscription that would leave each independent and distinct.