Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/94

 longer dependent upon the salt and bitter waters of Ain Mousa and a group of similar springs in the valley of the isthmus, which formerly supplied it, but receives good fresh water from the Nile by means of the so-called sweet-water canal — a work probably of greater importance and significance to the wellbeing of the country and of the transit-trade than the more pretentious, but still unfinished, maritime canal, from which such great results are expected by its spirited promoters.

Moses's Wells to Wady Amara. — From Ain Mousa to the southward for about 25 or 30 miles the desert presents the same general features as those last described, a gently swelling or terraced plain of sands and gravel, several miles broad, occupying the whole of the tract between the sea and the rise of the hills. The ground is covered with stunted bushy plants, affording a tolerable amount of feed for the camels during the spring time, and as long as any water from the winter rains remains in the pools formed on the damp retentive ground, where the gypseous shales and clays are close to the surface ; but later, or during the summer and autumn months, the whole becomes parched up and horribly barren and desolate. Sand-scored stones are abundant everywhere. Their prevalence is to be accounted for by the ceaseless activity of the sand-drift, as, even when the air is apparently calm and still, there will generally be enough wind moving to set the sand in motion on the ground and a few inches above it. As a rule, the hardest rocks are the best polished, — this being more especially the case with quartz, jasper, carnelian, and similar siliceous substances ; while the limestones, in addition to being polished, are furrowed and scored in every direction, and their surfaces studded with numberless small reticulating grooves, resembling the hill-shading on a topographical map. Occasionally masses or portions of crystals of calcite are found, which, under the same influence, have been etched in a manner in many respects similar to that produced by the action of a liquid solvent ; and the crystals show a tendency to decrement along the principal directions of cleavage. Many of the limestone-pebbles are also blackened in a peculiar manner, probably by some cryptogamic or other low form of vegetable life.

The plain of the desert is broken through by the numerous channels which convey the water of the main valleys to the sea ; but these are so small and slightly marked that they might easily be overlooked by travellers passing through the country in the summer time, when the upper watercourses are quite dry, only the recently dried and partially cracked muddy, surfaces in places showing signs of where the last water had been licked up by the fiery atmosphere of the desert. In the winter time, however, a sudden heavy rainfall in the hills occasionally sends such a flood of water rolling down that the whole plain in; the neighbourhood of the Wady is turned for the time into a lake ; and, according to the statements of the Arabs, camel-trains have occasionally been delayed for many days, until the flood has subsided ; and men have actually been drowned when suddenly overtaken by the waters in the low ground. The wormwood-