The quality of galt water varies very much with the interval since rainfall and with the nature of the rocks. Sandstone galts are very pure, because of their short life and the siliceous nature of the rock. Serpentine and diorite galts contain magnesium and other salts, and as the loss by evaporation continues the water may become somewhat bitter and purgative by concentration of these saline constituents, though galts never suffer to the extent that some wells do in this respect. A galt is frequently accompanied by a small spring (_megal_ or _megwel_); the galt represents the run-off, while the spring receives the percolating water. Thus for months after a galt is empty it may in some cases be possible to obtain water in small quantity by scooping out sand-filled rock cavities close to the basin. Galts are generally named after the mountain in which they occur, though when large and well known they may have special names given to them, as in the case of the Galt el Aguz mentioned above. =Remarks on Water Transport.= As will be gathered from the map on Plate III, water supplies are seldom more than two days’ march apart in this part of Egypt. For the ordinary traveller it will therefore be usually an ample provision to carry four days’ supply; in special cases, where it is desired to camp for any purpose remote from water sources, special provision will of course have to be made. There is seldom any trouble with the Arabs about their own water, as when their supplies run short one or two camels can always be detached from a caravan to fill their skins from the nearest well, and they are always content to travel day and night for this purpose. With regard to the quantity of water to be carried, I found ten gallons per European per day to be ample, including water for cooking and for one’s personal servants. Water is best carried in rectangular galvanized iron tanks, each holding ten gallons, fitted with a good brass or wooden plug; two of these carried horizontally make a light camel load, and on the march one can add a little in the shape of tents or bedding to the load. I have tried the barrel-shaped galvanised steel tanks used by the mining companies, which hold sixteen gallons each and are easily carried vertically, a pair forming a camel load; but I have found them much more liable to damage than the smaller rectangular tanks, and do not recommend them for regular desert travel. =List of Water Sources.=