Until the close of the stone age the movements of people had been by means of gradual drifting. During the palæolithic age, when the population supported itself by hunting, the people wandered over considerable areas in search of game, and the inhabitants of different regions frequently met and mingled with one another. As the forest conditions arose during the close of the Magdalenian period these wanderings were restricted in scope, and with the gradual introduction of domesticated animals and the practice of agriculture during the neolithic age, more settled communities arose. Thus the different types mixed less with one another, and the communities became more specialised, both in type and culture, as their wanderings diminished. A new method of intermixture was, however, soon to arise, as the practice of commerce developed. It is possible that even during the palæolithic age, tribes who lived in a region where flint or other suitable material was abundant, or who had become skilled in the fashioning of some advanced type of implement, sometimes bartered their spare products for other commodities. Such operations, if they did exist, must have been very limited in extent, and confined to bartering between neighbouring tribes. During the neolithic age this simple principle of exchange continued, though it was probably more frequent, since communities had a narrower range, and some must have been living in regions where suitable raw material was scarce or non-existent. Some well favoured regions also had begun to develop regular commerce. The inhabitants of the island of Santorin, the ancient Melos, had before metal was known organised an export trade in obsidian goods, for they held a monopoly of that excellent volcanic glass in the Ægean region[78]. It seems likely, too, that the people of the Lipari islands traded in the same material with south Italy, Sicily and Malta.[79] Some of the natives of the French department of Indre-et-Loire, finding themselves possessed of great quantities of beautiful honey-coloured flint in the neighbourhood of Le Grand-Pressigny, exported implements, both finished and in the rough, to many distant places in France,[80] and the same is probably true of the dwellers on Pen-maen-mawr, if we may judge from the extensive remains of their industry recently discovered at Graig Llwyd.[81] The industry of Le Grand-Pressigny seems, however, like the obsidian trade in the Mediterranean, to belong to the closing phases of the neolithic age, while the Graig Llwyd factory may well date from the bronze age.