As springs are classified those water sources where water issues naturally from the rocks, either above or near ground level, without the aid of artificial excavation. As will be seen on looking through the list of water sources on pp. 244 to 250, springs are less common than wells and rock basins, but some of the best known water sources, such as those of Abraq, Abu Saafa, Abu Hodeid, and Meneiga, belong to this class. The Arabic word for spring is _Ain_, but the Bedouin seldom use this word, calling springs and wells alike _Bir_, which properly signifies a well. Small springs are called _Megal_ by the Ababda, and _Megwel_ by the Bisharin tribes. Springs may occur in any kind of rock, but the rock must be either of a porous nature or must contain fissures. Thus the springs of Abu Saafa and Abraq occur in sandstone, which is itself porous and permits the passage of water through the body of the rock, while the springs of Meneiga occur in a crushed serpentine, which, though not itself a porous rock, is full of fissures and crush-planes, and thus is capable of holding and giving passage to underground waters. It is in consequence of the non-porosity and the comparative fewness of fissures in granitic rocks that springs are seldom seen to issue from rocks of this class. The collecting areas of the Eastern Desert springs are mostly in the immediate neighbourhood of the springs themselves. Thus, for instance, the springs of Abu Saafa and Abraq are fed by the rainfall on the great sandstone plateaux which surround them, while those of Meneiga are supplied by the rainfall on the mountain mass of Gebel Gerf. In consequence of the fact that the waters do not travel very far underground before they issue from the springs, the water is generally cool. The yield of the springs is usually small, rarely exceeding ten litres a minute from any individual spring, but it is wonderfully constant; the rocks of the collecting area form a huge reservoir which only parts slowly with its water contents, and thus springs may go on yielding supplies when, after a succession of three or four nearly rainless years, many of the wells and rock basins are quite dry. As a rule, spring waters are very clear and potable. The purest are those which pass through siliceous rocks such as sandstone; where the rocks are rich in lime and magnesia, as serpentines and gabbros, the salt-content of the spring may be fairly considerable, but there is no known spring in this part of Egypt of which the water is so salt as to be disagreable to the taste.[114] It is their constancy combined with the purity of their water that makes the springs the most highly prized of desert water sources.