UNWRITTEN HISTORY. 3 2 9 



months until the autumnal equinox, by which time the level of its sur- 

 face at Assouan is usually forty feet, at Thebes thirty-six feet, at Cairo 

 twenty-four or twenty-five feet, and at Rosetta four feet higher than 

 it is in May ; and, before reaching the delta, it flows at the rate of 

 three or four miles an hour. 



Under these circumstances, the river overflows its banks on all 

 sides. "When it does so, the movement of the water is retarded or 

 even arrested, and the suspended solid matters sooner or later fall to 

 the bottom, and form a thin layer of sandy mud. When the Nile 

 waters spread out over the great surface of the delta, the retardation 

 is of course very mai-ked. The coarse sediment is soon deposited, 

 and only the very finest particles remain in suspension at the outflow 

 into the Mediterranean. As the sun goes southward, his action on the 

 Abyssinian snows diminishes, the dry season sets in over the catch- 

 ment basin of the White Nile, and the water-supply of the Nile di- 

 minishes to its minimum. Hence, after the autumnal equinox, the 

 Nile begins to fall and its flow to slacken, as rapidly as it rose. By 

 the middle of November, it is half-way back to its summer level, and 

 it continues to fall until the following May. In the dry air of Nubia 

 and of Egypt, evaporation is incredibly rapid, and the Nile falls a prey 

 to the sun. As the old Egyptian myth has it, Osiris is dismembered 

 by Typhon. 



Relatively to the bulk of water, the amount of solid matter trans- 

 ported annually by the Nile must be far less than that which is car- 

 ried down by the rapid streams of mountainous countries in temper- 

 ate climates such, for example, as the upper Rhone. We have no 

 very satisfactory estimate of what that amount may be, but I am dis- 

 posed to think that the ordinary computation, according to which the 

 average deposit over the delta amounts to not more than a layer one- 

 twentieth of an inch thick annually, is, at any rate, not under the 

 mark. 



But this is a very interesting question, for it is obvious that, if we 

 may assume that the deposit of the Nile has taken jflace uniformly at 

 a known rate, it becomes possible, given the thickness of the alluvial 

 deposit in the delta, to calculate the minimum time occupied in its 

 formation. The borings made under the direction of the late Mr. 

 Leonard Horner in the upper part of the delta, and those subsequently 

 conducted by Figari Bey, favor the conclusion that the natural loose 

 soil which fills the flat basin of the delta nowhere exceeds sixty feet 

 in depth. Assuming it to have this thickness in any spot, it follows 

 that, at one twentieth of an inch of deposit per annum, it must have 

 taken at least fourteen thousand four hundred years to accumulate to 

 that thickness at that place. And if so, Herodotus seems, at first, to 

 have made a wonderfully good guess, when he said that the Arabian 

 Gulf and, by implication, that of the delta, might have been filled up 

 in " twenty thousand years, or even half the time." 



