The general line of advance I have indicated shows, wherever we can trace it, many similarities—similarities not necessarily dependent on an ancient intercourse, but simply because primitive man felt everywhere the same wants, and satisfied them in pretty much the same manner. He felt the need of defence and attack, and everywhere a stick and a stone offered themselves as the handiest and most effective weapons; he used both wherever he was, and adapted them to like shapes. In casting about for some standard wherewith to measure the long progress from this simple beginning to the present day, antiquaries have hit upon a very excellent one—the choice of a material employed at any given epoch for obtaining a cutting edge—for manufacturing _l’instrument tranchant_. Man conquers nature as he does his enemy—by cutting her down. The world at present uses iron, or its next product steel, for that purpose; before it came into vogue many nations employed bronze; but in the earliest periods of man’s history, and to-day in some savage tribes, stone was the substance almost exclusively wrought for this purpose. These distinctions divide the progress of man into the three great periods; the Age of Iron, the Age of Bronze, and the Age of Stone. Do not make the mistake of supposing that the remains of human art reveal this sequence in every locality; I have already hinted that this is not the case. And do not make that other mistake of supposing that all three are found in chronologic sequence over the whole world. On the contrary, they are synchronous even to-day, as there are now tribes in Brazil in the Age of Stone and nations in Asia in the Age of Bronze. The word “Age” in this connection does not mean a definite period of time, but a recognized condition of art. In Western Europe, however, where these terms originated, the three Ages were chronologic. Previous to about two thousand years before the Christian era, all the nations in that region employed stone exclusively to manufacture their cutting implements; later, bronze was preferred for the same purpose; and still later, iron. I say “preferred,” for do not imagine that the implement of stone or of bronze was straightway discarded when the better material was learned. We know that stone battle-axes were used in Ireland and Germany down to the tenth century, and bronze was employed by Romans and Egyptians long after they became acquainted with iron. Each of these three Ages has various subdivisions. Those of the Age of Stone are particularly important. They are two, based upon the manner in which the stone was brought to an edge. All the specimens in geologically the oldest deposits have been brought to an edge by a process of chipping off small pieces, so as to produce a sharp line or crest on a part or the whole of the border of the stone. This artificial process leaves such peculiar traces that a practiced eye cannot confound it with any accidental chipping which natural means effect.