Page:Africa by Élisée Reclus, Volume 1.djvu/97

 it yielded from your to year, from century to century, to the incessant action of the stream. The whole delta thus becomes displaced from south to north, according as the river beds are raised and the mouths extended seawards by the accumulation of alluvial deposits. At present the Batn-el-Bagara fork is over 12 miles from Cairo, following the windings of the island-studded stream, and has consequently been displaced at the annual rate of about 24 feet. Analogous changes have taken place throughout the whole of the delta, where the current has eaten its banks now to the right, now to the left, where simple channels have become broad watercourses, while copious streams have disappeared or shifted their beds.

Under the influence of the mystic ideas prevalent regarding the value of numbers, the old writers unanimously agreed to reckon seven chief branches in the delta, all the others being regarded as "false mouths." At the same time the normal direction of the streams required for irrigation purposes was carefully maintained during peaceful epochs by incessant dredging, embankments, and works of canalisation. It is now, however, no longer possible to trace the course of the seven ancient branches, which, left to themselves, resumed their erratic tendencies, shifting their beds with every fresh inundation. But there is a general agreement regarding their main direction, and many doubtful points of the hydrology of the Nile as described by Herodotus and Strabo have been cleared up by the naturalists of the French expedition to Egypt at the close of the last century.

At present two main branches only are enumerated, and these are indicated on the convex curve of the seaboard by two points formed by the tongues of alluvial land advancing continually seawards. They are the Rashid or Rosetta branch, identified with the Bolbitinis of the ancients, and that of Damietta, which formerly bore the names of Phatnetica and Bucolica. The Rosetta branch, some 14 miles the shorter of the two, but flowing in a bed from 30 to 50 inches lower, carries o£E the largest quantity of water, leaving not more than four-ninths to that of Damietta and the intermediate Menufieh channel, Nevertheless the Damietta River, thanks to its greater elevation, is much more available for irrigation purposes. The two branches, diverging like the radii of a circle, flow respectively north-west and north-east, advancing at their mouths some 5 miles beyond the normal coast-line. But, like all rivers falling into the Mediterranean, both are half closed by mud and sandbanks, barring the passage to large vessels. The western or Rosetta River has two channels from 7 to 8 feet deep, while that of Damietta, being less open, has a depth of scarcely 65 inches at its entrance. At high water, when there is a discharge of 470,000 cubic feet per second, the bar is reduced not more than 4 or 5 inches, its elevation depending more on the action