The region covered by the Nile's overflow is the flood plain of this river. On this plain the Pyramids, the Sphinx, and other famous monuments of Egypt stand. The statue of Rameses II. built 3,000 years ago, has its base buried nine feet deep in the rich soil made of Nile sediment. A well dug in this region goes through forty feet of this soil before striking the underlying sand. How many years ago did the first Nile overflow take place? We may begin our calculation by finding out the average yearly deposit. It is a slow process that accumulates but nine feet in 3,000 years. If you were in Egypt when the Nile went back into its banks, you would see that the scum it leaves in a single overflow adds not a great deal to the thickness of the soil. Possibly floods have varied in their deposits from year to year, so that any calculation of the time it took to build that forty feet of surface soil must be but a rough estimate. This much we know: it has been an uninterrupted process which has taken place within the present geological epoch, "the Age of Man." Not all the rich sediment the Nile brings down is left on the level flood plain along its course. A vast quantity is dumped at the river's mouth, where the tides of the Mediterranean check the river's current. Thus the great delta is formed. The broad river splits into many mouths that spread out like a fan and build higher and broader each year the mud-banks between the streams. Upper Egypt consists of river swamps. Lower Egypt, from Cairo to the sea, is the delta built by the river itself on sea bottom. From the head of the delta, where the river commences to divide, to the sea, is an area of 10,000 square miles made out of material contributed by upper Egypt, and built by the river. Layer upon layer, it is constantly forming, but most rapidly during the season of floods. Coming closer home, let us look at the map of the Mississippi Valley. Begin as far north as St. Louis. For the rest of its course the Mississippi River flows through a widening plain of swamp land, flooded in rainy seasons. Through this swampy flood plain the river meanders; its current, heavily loaded with sediment, swings from one side to the other of the channel, building up here, wearing away there, and straightening its course when the curves become so sharp that their sides meet. Then the current breaks through the thin wall, and a bayou of still water is left behind. Below Baton Rouge the Mississippi breaks into many mouths, that spread and carry the water of the great river into the Gulf of Mexico. The Nile delta is triangular, like delta, [Greek: D], the fourth letter of the Greek alphabet; but the Mississippi's delta is very irregular. The main mouth of the river flows fifty miles out into the Gulf between mud-banks, narrow and low. At the tip it branches into several streams.