Thus prehistoric times have themselves become history. The historical account of every single region has henceforth to begin with the description of the oldest antiquities of the soil that tell of man’s habitation, in order thereby to obtain the chronological connection with the evolution of the history of mankind generally. That is the palæontological method of historical research. [Sidenote: Landmarks of Early Culture] The palæontology of man has proved the Stone Age to be a general primary stage of culture for the whole human race. All further general progress in culture was affected by the discovery of the art of metal-working--the extraction of the metals from their ores and the casting and forging of them. The later and latest eras of culture are the Metal Ages, as opposed to the Stone Ages. It is not the use of metal in itself, but the above-mentioned metallurgical arts, that form the criterion of the advance of culture beyond the bounds of the Stone Age. Where, as in some parts of America, native copper was found in abundance, this red malleable mineral could probably be worked in the same way as stone, without any further progress necessarily developing therefrom. The same may apply to meteor-iron, which is said to have been used for arrows, together with stone points, by American tribes who were otherwise in the age of stone and but poorly civilised. [Illustration: From stone to metallic form Growth of the stop-ridge Growth of the wings THE TRANSITION FROM STONE TO IRON This series of diagrams, reproduced from specimens in the British Museum, by permission of the Trustees, shows how the stone axehead was used as the model for the metal axe or celt, and how that in turn was modified as workers gained experience in the use of the metal ] In civilised lands it is chiefly metal casting and the forging of the heated metal which have made it possible to produce better weapons and tools and more valuable ornaments. The worked metals are first copper, then the alloy of copper and tin that bears the name of classical bronze, and to these are soon added gold and--especially in districts rich in the metal, as in Spain--silver. Later on the extraction of iron from its ores and the forging of that metal are discovered. According to this course of metallurgical progress the first metal period is distinguished as the Bronze Period, which is begun by a Copper Period lasting more or less long in different places. The second or later metal period is the Iron Period, in which we are living at the present day. In the course of time, by gradually displacing bronze and copper from the rank of metals worked for weapons and tools, this Iron Age has developed to its present stage.