Practically the men of the prehistoric ages in Europe had not the use of metals (though our quasi-historical records go back to a less remote time in many parts of Europe than they do in Greece, Assyria, and Egypt). The prehistoric peoples are spoken of as the men of the Stone Age, because they used stone, chiefly flint, as many savage races do to-day, as the material from which they fabricated by means of deftly struck blows all sorts of implements. Undoubtedly they also, by aid of stone knives, saws and planes, made weapons and other implements of wood and of the horns, bones, and teeth of animals. But these latter substances are perishable, and have only been preserved from decay under special circumstances, such as their inclusion in the deposits on the floors of caverns. The Stone Age is itself readily and obviously divisible into two periods. The latter is a comparatively very short and recent period, when great skill in chipping flints and other stones was attained, and the implements so shaped were often rubbed on large stones of very hard material (siliceous grit), so as to polish their surfaces. This is the "Neolithic," or later Stone, period, and extends back in Europe certainly to 7000 B.C., and probably a few thousand years further. Passing further back than this, we leave what are called "recent" deposits, and come to those associated with great changes of the earth's surface. We enter upon "geological" time, and vastly changed climatic and geographical conditions. We are in the older Stone period, called the "Palæolithic period." It is not really comparable to the "Neolithic," since it comprises many successive ages of man, and, although called the "Palæolithic" or "ancient Stone" period, has no unity, but, whilst readily divisible into several sub-periods or epochs of comparatively late date, stretches back into immense geologic antiquity indicated by flint implements of special and diverse types, which are found in definitely ascertained geologic horizons.