But none of these remains bear the slightest trace of a system of signs for the transmission of ideas or recollections; there is nothing which suggests writing; and, more significant still, there is a complete absence of metal. All this is evidence that the remains in question belong to a very remote antiquity, to a period much nearer the primitive barbarism than to the civilization of Egypt and Chaldæa, to say nothing of that of Greece and Rome. The comparative method, which has done so much for natural science, has also taken these remains in hand, has attempted to classify them and to gain from them some notion of the life led by the early human families which manufactured them. These arms, tools, and instruments which have been recovered from the soil of the old and cultivated nations of Europe, have been carefully compared with similar objects still in use by the savage races which people the far corners of the world. These comparisons have enabled us to decide the former use of each of the objects discovered. By collating the observations of the various travellers who have visited the savage races in question, we have been enabled to form for ourselves a probably truthful picture, so far as it goes, of the life and social habits of those primitive Europeans who made use of similar tools and weapons. And that is not all. The general character of those early periods being established, further examination brought to light the local differences which prevailed then as now. Thus the proneness to plastic imitation seems to have been peculiar to a few tribes--although traces of this taste are found elsewhere, it is nowhere so marked as among those primitive cave-dwellers of Perigord whom Christy and Edouard Lartet have so patiently studied. By dint of careful classification and comparison, we have been enabled to follow the march of progress through those countless centuries whose number will never be known to us, whose total would, perhaps, oppress our imaginations if we knew it; we have been enabled to discover the slow steps by which mankind raised itself from the earliest, almost shapeless, flint axe, found with the bones of the mammoth in the quaternary alluvial deposits, to the rich and varied equipment of "lacustrian civilization," as it has sometimes been called. In this unlimited field, of which one side at least must ever be lost in unfathomable obscurity, the main divisions have been traced; the stone age has been defined and divided into the _palæolithic_ and _neolithic_ epochs; the age of bronze followed, and then came the iron age. With the appearance of the former metal the tribes of northern and central Europe established a connection with the civilized races which surrounded the Mediterranean, and with iron we are in the full classic period.