Finally, the third group, the Pelasgians, reached Greece by means of the islands of that part of the Mediterranean. It still remains uncertain whether an earlier migration still had peopled Europe with Palæolithic man, who, on this theory, would belong also to the Mediterranean race, or whether the immigrant African race displaced some earlier unrelated population. In any case, it is tolerably certain that the first peopling of Europe on any considerable scale was the result of this immigration of Mediterranean man. He doubtless first established himself on the margin of the great sea, and there became thoroughly suited to his environment. Later he spread northwards, being no doubt especially attracted by the relatively mild climate of the west, by what has been called the "winter gulf of warmth" which extends over north-western Europe. Whatever was the cause of his northward trend, however, Mediterranean man does not appear to have been left long in undisturbed possession of his acquired territory. In Scotland, in the Clyde valley, which is typical of many other parts of Europe, round barrows or cairns are found side by side with the long ones. These are of later origin, as is shown by the nature of the pottery, by the occurrence of ornaments, and especially by the presence of bronze weapons--a great advance upon stone. The skeletons in these cairns mostly show marks of fire, suggesting that cremation was practised, and the skulls are those of a round-headed race. "Round barrows mean round skulls" is a second anthropological maxim for Britain. These barrows are the first traces of the second great European race, called Alpine, Celtic, Eurasiatic, or Celto-Slavic by different anthropologists. The members of this race are of medium height, but are more stoutly built than Mediterranean man. Though generally resembling him in the coloration of hair and eyes, they are lighter in tint, the hair tending to be chestnut-coloured, and the eyes hazel grey, instead of both being very dark as in the former race. The nose, though variable, is in living types usually rather broad, and the special feature is of course the round head and broad face. As one of the names given indicates, this race is supposed by most anthropologists to have been of Asiatic origin. Where the two sets of barrows occur there are indications that the incoming race greatly influenced the culture of the old. The use of bronze must have given its members an enormous advantage in the struggle for existence, and they seem to have imposed their customs, burial and other, and apparently also their language, on the older race.