Both these were superseded, perhaps in historic times, by a people having a knowledge of the properties and use of Iron. Hence their epoch came to be distinguished by the name of that metal. There seems no doubt but that the people of the Stone age were generally, if not exclusively, of that great family which we now know as the Turanian. The race who introduced bronze seem to have been the ancestors of the Celtic races who afterwards peopled so large a portion of Europe. The Aryans were those who introduced the use of iron, and with it dominated over and expelled the older races. If any prehistoric traces of the Semitic races are to be found, they must be looked for in Western Asia or in Africa; they certainly had no settlements in Europe. Further researches may perhaps at some future time enable us to fix approximative dates to these various migrations. At present we know that men using flint implements lived in the valleys of the Garonne and Dordogne when the climate of the south of France was as cold as that of Lapland, or perhaps Greenland; when the reindeer was their principal domestic animal, and the larger animals of the country belonged to species many of which had ceased to inhabit those regions before the dawn of history. On the other hand, we may assert with certainty that the climate of Egypt has not varied since the age of the Pyramid builders; and there is nothing in the history of either Greece or Italy that would lead us to believe that any remarkable alteration in the climate of these countries has taken place in historic times. These questions, however, hardly come within the scope of the present work. The men of the Stone age have left nothing which can be styled architecture, unless we include in that term the rude tumuli of earth with which they covered the remains of their dead. It is also extremely uncertain if we can identify any building of stone as belonging certainly to the age of Bronze. All the rude cromlechs, dolmens, menhirs, &c., which usher in the early dawn of civilisation in Europe, belong, it is true to the earlier races, but seem to have been erected by them at a time when the Aryan races had taught them the use of iron, and they had learnt to appreciate the value of stone as a monumental record. This, however, was at a period long subsequent to the use of iron in Egypt and the East, and long after architecture had attained maturity; and its history became easily and distinctly legible in the Valley of the Nile.[18]