72 NORTH-WEST AFRICA. in;]^ velocity amid tlie animalculoB swarming on the surface of the lake. By means of fine nets the larva is captured, together with other larvae which prey ou it, and the fucus on which it feeds. The whole is then kneaded into a sort of paste, which has a flavour resembling that of shrimps " a little gamy." The mess is mostly used as a sauce or relish with other aliments. The plateau of dunes is abruptly terminated southwards by the depression of the Wady Lajjil, which runs mainly in the direction from west- south-west to east- north-east for a total distance of nearly 300 miles between the deserts separating Rl)at from Fezzan, and those stretching towards the AVhite Ilaruj. But the depressions in this wady are occupied by oases for a space of not more than 120 miles altogether, with a mean breadth of about 5 miles. Towards its source in the west, the Wady Lajal has an elevation of 2,000 feet above sca-lovcl, falling to 1,300 at the point where it merges in the eastern deserts. The most striking contrast is presented by the opposite banks of the wady, those on the north side consisting of gently rounded sandy heights, while on the south rise abrupt cliffs, a continuation of the partly Devonian Arasak range, which commands the entrance of the valley. Near the centre two corresponding sandy and rocky headlands projecting towards each other divide the depression into two sections, respectively known from their geographical position as the Wady-el- Gharbi and "Wady-esh-Sherki. The latter, or " eastern " wady, which is the largest, is connected eastwards with the palm-groves of Sebha, beyond which it is interruj)to(l by the desert, reappearing again in the small oases of Temenhint, Semnu, and Zighen. The position of these oases seems to indicate the existence of a former tributary between the AVadies Lajal and Esh-Shiati ; but the whole valley is now obstructed by sands. Like that of other depressions in Fezzan, the soil of the Wady Lajal is formed of hci>ilia — that is, a very light humus saturated with salt and swollen by the com- bined action of heat and the underground waters. Saline eflBorescences in many places develop a central zone skirted on either side by cultivated tracts at the foot of the cliffs and sandhills. In the Wady Lajal the mean depth of the water is about 12 feet ; hence it is unnecessary to irrigate the palms, which derive sufficient moisture through their roots. But the water required for the cereals and vege- tables is obtained from the wells, into which is plunged an apparatus made of date- wood, looking at a distance like shears for masting of ships, or the cranes mounted on the wharves of seaport towns. Notwithstanding the statement of Rohlfs to the contrary, there appear to exist in Fezzan the so-called fogarats, or systems of irrigation wells, one of which was visited by M. Duveyrier on the slope of the southern cliffs of the wady, not far from Jerma. The Murzuk hamada, which separates the Wady Lajal from the depression specially known as the Ilofra, or " Ditch," forms an extensive plateau almost uniformly level, except on its northern verge, partly skirted by the abrupt Amsak range, and at a few other points furrowed by crevasses either occupied by oases or at least containing artificial wells. Such is the Godva oasis, traversed by most of the caravans between Murzuk and Tripolitana. Narrowing towards it^ western
