The earliest man who has left traces in Europe is he of the Palæolithic Period, or Old Stone Age, a hunter and cave-dweller without domesticated animals, whose traces are especially found in southern Europe. No traces of his presence have yet been found in Scandinavia or in Scotland, where the climatic conditions perhaps made his existence impossible. Not much is known of this early race, but it seems to have been long-headed, and was probably dark. It is no longer believed that there was a complete rupture between the culture of the Palæolithic period, with its unpolished stone implements, and that of the Neolithic age, with its polished implements, but the relations of the two remain somewhat uncertain. The remains of the Neolithic period are much more extensive and enable us to draw much more satisfactory conclusions as to racial characters. We shall describe briefly some of these Neolithic remains as they appear in Great Britain. Before doing this, however, it is necessary to say a few words about the means of recognising different races of men. The criterion most employed is that of head form, and especially what is known as the cephalic index, that is, the ratio between the breadth of the skull between the ears and its length from front to back. The ratio is expressed as a percentage, the length being taken as 100, and the breadth stated as a fraction of it. When the index rises above 80, the skull is said to be brachycephalic, or rounded; when it is below 75, the skull is long, or dolichocephalic. The Italian anthropologist, Sergi, adopts another classification of skulls, based upon the shape, but this is only a refinement of the ordinary distinction between long and round skulls. Another important character, which, like the shape of the skull, can be measured either in the living person or in the skeleton, is the height, which has some racial significance. A third character, of much importance, is the colouring of the skin, eyes and hair. This can only be inferred in the case of pre-historic peoples. Finally, the shape of the features, especially of the nose, has some racial significance.