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Rh northern limits of the Delta this cannot, however, be depended on, since the well water at these depths has proved on several occasions to be salt. The surface of the Delta is a wide alluvial plain sloping gently towards the sea, and having an altitude of 29 ft. above it at its southern extremity. Its limits east and west are determined by the higher ground of the deserts, to which the silt-laden waters of the Nile in flood time cannot reach. This silt consists largely of alumina (about 48%) and calcium carbonate (18%) with smaller quantities of silica, oxide of iron and carbon. Although the Nile water is abundantly charged with alluvium, the annual deposit by the river, except under extraordinary circumstances, is smaller than might be supposed. The mean ordinary rate of the increase of the soil of Egypt is calculated as about 4 in. in a century.

The Lakes.—The lagoons or lakes of the Delta, going from west to east, are Mareotis (Mariut), Edku, Burlus and Menzala. The land separating them from the Mediterranean is nowhere more than 10 m. wide. East of the Damietta mouth of the Nile this strip is in places not more than 200 yds. broad. All the lakes are shallow and the water in them salt or brackish. Mareotis, which bounds Alexandria on the south side, varies considerably in area according to the rise or fall of the Nile; when the Nile is low there is a wide expanse of marsh, when at its highest the lake covers about 100 sq. m. In ancient times Mareotis was navigable and was joined by various canals to the Nile. The country around was cultivated and produced the famous Mareotic wine. The canals being neglected, the lake decreased in size, though it was still of considerable area in the 15th and 16th centuries, and was then noted for the value of its fisheries. When the French army occupied Egypt in 1798, Mareotis was found to be largely a sandy plain. In April 1801 the British army besieging Alexandria cut through the land between Aboukir and the lake, admitting the waters of the sea into the ancient bed of Mareotis and laying under water a large area then in cultivation. This precedent was twice imitated, first by the Turks in 1803 and a second time by the British in 1807. Mareotis has no outlet, and the water is kept at a uniform level by means of powerful pumps which neutralize the effect of the Nile flood. A western arm has been cut off from the lake by a dyke, and in this arm a thick crust of salt is formed each year after the evaporation of the flood water. Near the shores of the lake wild flowers grow in rich profusion. Like all the Delta lakes, Mareotis abounds in wild-fowl. North-east of Mareotis was Lake Aboukir, a small sheet of water, now dry, lying S.W. of Aboukir Bay. East of this reclaimed marsh and reaching to within 4 m. of the Rosetta branch of the Nile, lies Edku, 22 m. long and in places 16 wide, with an opening, supposed to be the ancient Canopic mouth of the Nile, into Aboukir Bay. Burlus begins a little eastward of the Rosetta channel, and stretches bow-shaped for 64 m. Its greatest width is about 16 m. Adjoining it S.E. is an expanse of sandy marsh. Several canals or canalized channels enter the lake. Opposite the spot where the Bahr-mit Yezir enters is an opening into the Mediterranean. Canal and opening indicate the course of the ancient Sebennytic branch of the Nile. Burlus is noted for its water-melons, which are yellow within and come into season after those grown on the banks of the Nile.

Menzala greatly exceeds the other Delta lakes in size, covering over 780 sq. m. It extends from very near the Damietta branch of the Nile to Port Said. It receives the waters of the canalized channels which were once the Tanitic, Mendesian and Pelusiac branches. The northern shore is separated from the sea by an extremely narrow strip of land, across which, when the Mediterranean is stormy and the lake full, the waters meet. Its average length is about 40 m., and its average breadth about 15. The depth is greater than that of the other lakes, and the water is salt, though mixed with fresh. It contains a large number of islands, and the whole lake abounds in reeds of various kinds. Of the islands Tennīs (anciently Tennesus) contains ruins of the Roman period. The lake supports a considerable population of fishermen, who dwell in villages on the shore and islands and live upon the fish of the lake. The reeds are cover for waterfowl of various kinds, which the traveller sees in great numbers, and wild boars are found in the marshes to the south. The Suez Canal runs in a straight line for 20 m. along the eastern edge of the lake. That part of the lake east of where the canal was excavated is now marshy plain, and the Tanitic and Pelusiac mouths of the Nile are dry. East of Menzala is the site of Serbonis, another dried-up lake, which had the general characteristics of the Delta lagoons. In the Isthmus of Suez are Lake Timsa and the Great and Little Bitter Lakes, occupying part of the ancient bed of the Red Sea. All three were dry or marshy depressions previously to the cutting of the Suez Canal, at which time the waters of the Mediterranean and Red Sea were let into them (see ).

A chain of natron lakes (seven in number) lies in a valley in the western desert, 70 to 90 m. W.N.W. of Cairo. In the Fayum province farther south is the Birket-el-Kerun, a lake, lying below the level of the Nile, some 30 m. long and 5 wide at its broadest part. Kerun is all that is left of the Lake of Moeris, an ancient artificial sheet of water which played an important part in the irrigation schemes of the Pharaohs. The water of el-Kerun is brackish, though derived from the Nile, which has at all seasons a much higher level. It is bounded on the north by the Libyan Desert, above which rises a bold range of mountains; and it has a strange and picturesque wildness. Near the lake are several sites of ancient towns, and the temple called Kasr-Karun, dating from Roman times, distinguishes the most important of these. South-west of the Fayum is the Wadi Rayan, a large and deep depression, utilizable in modern schemes for re-creating the (q.v.).

The Desert Plateaus.—From the southern borders of Egypt to the Delta in the north, the desert plateaus extend on either side of the Nile valley. The eastern region, between the Nile and the Red Sea, varies in width from 90 to 350 m. and is known in its northern part as the Arabian Desert. The western region has no natural barrier for many hundreds of miles; it is part of the vast Sahara. On its eastern edge, a few miles west of Cairo, stand the great (q.v.) of Gizeh or Giza. North of Assuan it is called the Libyan Desert. In the north the desert plateaus are comparatively low, but from Cairo southwards they rise to 1000 and even 1500 ft. above sea-level. Formed mostly of horizontal strata of varying hardness, they present a series of terraces of minor plateaus, rising one above the other, and intersected by small ravines worn by the occasional rainstorms which burst in their neighbourhood. The weathering of this desert area is probably fairly rapid, and the agents at work are principally the rapid heating and cooling of the rocks by day and night, and the erosive action of sand-laden wind on the softer layers; these, aided by the occasional rain, are ceaselessly at work, and produce the successive plateaus, dotted with small isolated hills and cut up by valleys (wadis) which occasionally become deep ravines, thus forming the principal type of scenery of these deserts. From this it will be seen that the desert in Egypt is mainly a rock desert, where the surface is formed of disintegrated rock, the finer particles of which have been carried away by the wind; and east of the Nile this is almost exclusively the case. Here the desert meets the line of mountains which runs parallel to the Red Sea and the Gulf of Suez. In the western desert, however, those large sand accumulations which are usually associated with a desert are met with. They occur as lines of dunes formed of rounded grains of quartz, and lie in the direction of the prevalent wind, usually being of small breadth as compared with their length; but in certain areas, such as that lying S.W. and W. of the oases of Farafra and Dakhla, these lines of dunes, lying parallel to each other and about half a mile apart, cover immense areas, rendering them absolutely impassable