Prehistoric general divisions of the prehistoric period of the life of the race have been based, as was stated in Volume I. (p. 169), on the substance most successfully employed to produce a cutting edge. This has led to a classification into the Age of Stone, the Age of Bronze, and the Age of Iron, following the order in which each of these materials in turn became known and was used for the manufacture of cutting instru ments. This classification was first introduced to science by the Danish antiquaries, especially by Professor \Vorsaae, and has been generally re ceived throughout the antiquarian world. But the fact of this succession of materials was familiar to the classical writers of ancient times, and it has been pointed out that these three ages are distinctly named by the Latin poet Lucretius in his celebrated work De Natztra Rerun!, composed about 75 B. C. The passage in which he refers to this succession is as follows: "The ancient arms were the hands, nails, and teeth, stones and pieces of the branches of trees; later, the value of iron was discovered, and of bronze; but bronze was in use before iron." Although these so-called "ages" are primarily divisions with regard to time, they must not be so understood in an absolute sense. They refer quite as much to a condition of culture, of industrial development, as to periods of duration,—indeed, more so, for although the Age of Stone is always considered the most ancient, yet it is true that it exists to-dav; for example, among those tribes who have not yet come into contact with civilization and still continue to be wholly ignorant of metals. So late as ISS.1 several such tribes were discovered in the interior of Brazil by a German traveller.
Again, the development of culture in the Eastern and Western Hemi spheres has been, especially in its later phases, essentially different, and we cannot with profit introduce into 'American Archmology these distinc tions. The American tribes never discovered the industrial applications
of iron; and although they had a technical knowledge of several metals, and in single instances manufactured instruments of bronze on an exten sive scale, the principal material for producing a cutting edge remained everywhere some species of stone. For these reasons we shall treat sepa rately the Archaeology of the two hemispheres, and by such a contrast we shall be enabled the more easily to explain the marked differences in culture which existed in these two great land divisions of the globe.
course of Geologic Time.—The study of the earliest specimens of human art is intimately associated with that of the later geology of the inhabitable areas of the globe. It is only by ascertaining the characters and relative ages of the later deposits and strata, as they now exist, that we can hope to fix with any degree of accuracy the date when man first appeared in any given quarter of the globe, and in what relations the events of his subsequent career down to the era of written record took place. For this reason the archteologist must call to his aid the sciences of Geology and Palaeontology, of Zoology and Botany.
Unfortunately, these are not yet able to answer many of the questions which the archaeologist would put to them. Even the terms by which the later geologic epochs are designated are not employed with uniformity by the leading authorities on that branch. By some, the term "Tertiary Epoch" is understood to reach down to and include the present time. These say that we are now living in the Tertiary Age of the world. This view has been adopted by one of the most eminent of British archreolo gists, Professor W. Boyd Dawkins. His division of the geologic record as applied to the history of man is as follows: