Nomadism in actionclimate by the artificial factor of a world-religion. The congestion of Yemen, therefore, becoming extreme, found its only relief in the east, by forcing the weaker aggregations of its border down and down the slopes of the hills along the Widian, the half-waste district of the great water-bearing valleys of Bisha, Dawasir, Ranya and Taraba, which ran out towards the deserts of Nejd. These weaker clans had continually to exchange good springs and fertile palms for poorer springs and scantier palms, till at last they reached an area where a proper agricultural life became impossible. They then began to eke out their precarious husbandry by breeding sheep and camels, and in time came to depend more and more on these herds for their living.

Finally, under a last impulse from the straining population behind them, the border people, (now almost wholly pastoral), were flung out of the furthest crazy oasis into the untrodden wilderness as nomads. This process, to be watched to-day with individual families and tribes to whose marches an exact name and date might be put, must have been going on since the first day of full settlement of Yemen. The Widian below Mecca and Taif are crowded with the memories and place-names of half a hundred tribes which have gone from there, and may be found to-day in Nejd, in Jebel Shammar, in the Hamad, even on the frontiers of Syria and Mesopotamia. There was the source of migration, the factory of nomads, the springing of the gulf-stream of desert wanderers.

For the people of the desert were as little static as the people of the hills. The economic life of the desert was based on the supply of camels, which were best bred on the rigorous upland pastures with their strong nutritive thorns. By this industry the Bedouins lived; and it in turn moulded their life, apportioned the tribal areas, and kept the clans revolving through their rote of spring, summer and winter pasturages, as the herds cropped the scanty growths of each in turn. The camel markets in Syria, Mesopotamia, and Egypt determined the population which the deserts could support, and regulated strictly their standard of living. So the desert likewise over-peopled itself upon occasion; and then there were heavings and thrustings of the crowded tribes as they elbowed themselves by natural courses towards the light. They might not go south towards

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