The Five Niles

Egypt, wrote the Greek historian Herodotus, is the gift of the Nile. He was right; Egypt--or at least its most populous and fertile area--was formed by the rich silt washed down from the East African highlands by the waters of the Nile. But which Nile? According to Egypt's leading geologist, Rushdi Said, 55, the present-day Nile is a relative newcomer to Egypt, having been around for only 30,000 years. Before that, he says, at least four different Niles had flowed through--and then disappeared from--the river basin.

Said, who heads the Geological Survey of Egypt and holds a seat in the Egyptian Parliament, bases his theory on evidence he found while doing test borings for the Aswan High Dam in 1961. In some of his core samples, Said was puzzled to find a layer of alluvial (deposited by running water) sediment at a depth of 450 ft., well below the level of the modern Mediterranean Sea. Convinced that such deposits could not have been left by today's Nile, Said began looking into the possibility that they were traces of an earlier river.

Said's study took him along both banks of the Nile and deep into the deserts. He studied the magnetism of rocks to determine when they had been formed, used radioactive dating methods to determine the age of soil samples and fossils and checked other geological records, such as sea-floor samples from the Mediterranean. As a result of his research, Said has traced the history of the Nile back better than 5 million years, and identified at least five different rivers that flowed during that interval. They are;

> The Eonile, or original Nile, coursed through Egypt between 5.58 and 5.4 million years ago. Rising near Egypt's present southern frontier and fed by heavy rains, this prehistoric river cut a deep channel as it dropped to the Mediterranean, which was dry at that time and closed off at its western, or Gibraltar end. When Gibraltar opened up once more, possibly as a result of earthquakes, water from the Atlantic poured into the Mediterranean, flooding as far into Egypt as Aswan and covering the entire Nile Valley. For 2 million years the valley was a gulf of the Mediterranean. When the encroaching sea retreated, it left behind a layer of salt deposits and marine fossils for Said and fellow geologists to find.

>The Paleonile, or second Nile, followed, emerging around 3.3 million years ago. The biggest and longest-lived of the five rivers, the Paleonile probably rose in the western Sudan after a prolonged rainy period, filling the Nile Valley with silt that eventually pushed the Mediterranean back out of Egypt. Then, around 1.8 million years ago, a 1-million-year drought dried up the Paleonile, gave birth to the Sahara and turned much of Egypt into a desert that Said says must have resembled the arid "Empty Quarter" of Saudi Arabia.

> The Protonile, the third of the great rivers to flow through Egypt, came to life some 700,000 years ago during a brief rainy period, then died quickly when the rains stopped.

> The Prenile, river No. 4, appeared 620,000 years ago. Fed by rains in the highlands of Ethiopia and the western Sudan, the river flowed for nearly half a million years before vanishing during another period of aridity.

> The Neonile, or present river, emerged a mere 30,000 years ago. Fed, like its predecessor, from rains on the East African plateau, the river is the only major source of water in a virtually rainless country. Before the High Dam was built, the river dropped substantially during the winter and rose to flood levels during the summer.

Said believes that the behavior of the fifth Nile led to many of the accomplishments of Egyptian civilization. Man made his appearance in the Nile Valley toward the end of the period between the death of the Prenile and the birth of its successor, and had to adapt to the river in order to survive. He rose to the challenge superbly. The ancient Egyptians developed geometry so that they could mark out landholdings and lay out irrigation ditches; they invented a practical calendar to keep track of the seasons, and created a government to coordinate their attempts to cope with the forces of nature.

Now the Nile again seems to be in the process of change. Its delta is eroding (it has receded some seven miles since 1878). The erosion has been accelerated by the Aswan High Dam, which holds back silt that was once deposited in the valley and the delta. Free of silt, the river below the dam is flowing more swiftly and eating away its bed.

In 20 years, Said believes, the river banks may begin to collapse unless measures are taken to shore them up.

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