The appearance of water on the sandy and gravelly deserts is very frequent, and is generally so well defined, that it would be difficult to distinguish it from a river, were it possible that both could be seen at the same time. It is called Shrab شراب by the Arabs, who often amused themselves by calling to us that water was in sight, until we became accustomed to the appearance. Of this curious phenomenon so much has been said by various writers, that any attempt at description on my part would be unnecessary. The looming of objects when the sun is at its greatest strength, is very striking; as from the vapour which rises, they are, at a slight distance, much obscured. I have frequently, in riding along, been delighted at observing in the distance, a tree which appeared sufficiently large to shade me from the sun, and to allow of my reposing under it, until the camels came up; and have often quickened my pace in consequence, until, on a near approach, it has proved to be nothing more than a bush, which did not throw a shade sufficient even to shelter one of my hands. Sand hills deceive still more, always appearing very distant when the sun is on them; and it has often happened, that I have been startled by seeing a man or camel rise close to me, on the top of one of the apparently distant hills. The excessive dryness of the Desert is in some places very extraordinary, particularly to the southward of the Soudah mountains, where, in going to as well as coming from Fezzan, I observed that our clothes, and the tails of our horses, emitted electric sparks. Water is not to be found by digging in all parts of the Desert; but is more particularly difficult to find in the Sereer, or gravel, which generally lies over sand stone. In two instances I have seen remains of pits which had been dug to one hundred feet without coming to water. The wells which are on the Desert are generally found in Wadeys or in the sandy country; and in all those I have seen, the water was salt and putrid, but the putrescence diminished after a quantity had been drawn. Some wells have only a sufficiency for the supply of five or six horses at once, and are a long time before they again fill. These wells which were so scantily supplied, I observed, were always in a soft clayey rock; but those which kept themselves tolerably full, were in a yellow clay. The depths vary from 6 or 8 feet to 70 or 80. In almost every part of the stony desert, small piles of stones are frequently discovered, which are erected by travellers as marks to direct them across the country, or in the event of their missing their route, to assist them again to find it. These little heaps are called Aālum علم, or “teachers;” and some become so remarkable, as to acquire other names, and to be favourite resting-places for Kafflés. * * * * *