In order to protect his crops from the fierce onslaught of wind-borne sand the native is compelled to erect fences and barricades along the northern boundaries of his fields. These serve his purpose for the time being, the sand which would otherwise have cut and beaten down the growing crops being deposited on either side of the fence, where the velocity of the wind is checked. The arrested sand accumulates with increasing rapidity as the size of the obstruction becomes greater, a veritable dune, constituting a really efficient protection to the cultivated lands, being formed over the site of the original small and insignificant hedge. Unfortunately, this sand continues to collect, and although the cultivator may have satisfactorily insured himself against the frequent damage caused to his crops by their exposure to wind-driven sand, he is now confronted with the still more serious prospect of having his lands overwhelmed by the ever-increasing dunes, which have grown to considerable proportions as the result of his efforts to protect himself. Fortunately for the occupiers of these outlying settlements, the progress of such dunes, formed more or less artificially on the northerly sides of the cultivated tracts, is not at the same rate as that of isolated dunes moving across the open desert plain. Owing to the presence of a certain amount of moisture in the superficial layers of the ground in the neighbourhood of the wells and the cultivated lands, plants of various kinds are enabled to thrive, with the result that the dunes become to some extent ‘fixed’ by wild vegetation. The most valuable plant in this connection is the tamarisk, which by means of immensely long roots continues to thrive and keep its head above growing dunes with remarkable facility. To a certain extent, moreover, the moisture from the soil itself rises by capillarity into the base of the sand, and assists the vegetation in binding it into a compact mass, which is not liable to movement in the same degree as dry sand. The rate of progress of such dunes may therefore be reduced to a considerable extent, but the movement can never be altogether stopped. As we have seen in the case of the hamlet of Meheriq, the sand eventually gets the upper hand, blotting out the arable lands, burying the palm-groves, and forcing man to abandon his habitations.