“In a trough from 2 to 10 kilometres wide and 100 to 300 metres deep lies the Nile, meandering through a flood plain formed by yearly deposits of silt brought down from the Abyssinian table-land by the Blue Nile and the Atbara. This trough was determined in the first instance by fractures of the crust which caused a strip of country from about Edfu (lat. 25° N.) to Cairo to be depressed, leaving the plateau standing high above it, just as the Red Sea and the gulfs of Suez and Akaba were formed, probably about the same epoch. This interference with the drainage of the country doubtless produced a series of lakes in the low-lying area, while the drainage of the eastern plateau commenced to excavate the valleys which now exist as dry desert wadies, their development being in many cases far from complete, as shown by the cliffs which interrupt the slope of the valley when a harder bed of rock than usual is met with.