If, as above seen, the study of human origins is largely a geological problem, the investigation of the later developments, during the Metal Ages and prehistoric times, belongs mainly to the field of Archaeology. Hence it is that for the light which has in recent years been thrown upon the obscure interval between the Stone Ages and the strictly historic epoch, that is to say, the period when in his continuous upward development man gradually exchanged stone for the more serviceable metals, we are indebted chiefly to the pioneer labours of such men as Worsaae, Steenstrup, Forchhammer, Schliemann, Sayce, Layard, Lepsius, Mariette, Maspero, Montelius, Brugsch, Petrie, Peters, Haynes, Sir J. Evans, Sir A. J. Evans and many others, all archaeologists first, and anthropologists only in the second instance. From the researches of these investigators it is now clear that copper, bronze, and iron were successively in use in Europe in the order named, so that the current expressions, "Copper," "Bronze," and "Iron" Ages remain still justified. But it also appears that overlappings, already beginning in late Neolithic times, were everywhere so frequent that in many localities it is quite impossible to draw any well-marked dividing lines between the successive metal periods. That iron came last, a fact already known by vague tradition to the ancients[66], is beyond doubt, and it is no less certain that bronze of various types intervened between copper and iron. But much obscurity still surrounds the question of copper, which occurs in so many graves of Neolithic and Bronze times, that this metal has even been denied an independent position in the sequence. But we shall not be surprised that confusion should prevail on this point, if we reflect that the metals, unlike stone, came to remain. Once introduced they were soon found to be indispensable to civilised man, so that in a sense the "Metal Ages" still survive, and must last to the end of time. Hence it was natural that copper should be found in prehistoric graves associated, first with polished stone implements, and then with bronze and iron, just as, since the arrival of the English in Australia, spoons, clay pipes, penknives, pannikins, and the like, are now found mingled with stone objects in the graves of the aborigines. But that there was a true Copper Age[67] prior to that of Bronze, though possibly of not very long duration, except of course in the New World[68], has been placed beyond reasonable doubt by recent investigations. Considerable attention was devoted to the subject by J. H. Gladstone, who finds that copper was worked by the Egyptians in the Sinaitic Peninsula, that is, in the famous mines of the Wadi Maghara, from the fourth to the eighteenth dynasty, perhaps from 3000 to 1580 B.C.[69] During that epoch tools were made of pure copper in Egypt and Syria, and by the Amorites in Palestine, often on the model of their stone prototypes[70].