On the Arabian Frontier of Egypt. 29 



sons to be satisfied that the Etham branch cannot have been 

 naturally extinct in the time of Moses and the older Pharaohs. 

 If we compare the level of the bed of the river at the time of its 

 excision (which is displayed by the section)* with the height 

 of the waters of the Nile at the remote period represented 

 by the map, (which can be estimated with considerable pre- 

 cision), we shall be convinced that it must then have yielded 

 a deep and useful channel, both for navigation and irrigation, 

 along the whole inhabited region of the valley. We must 

 subtract from the height which the Nile now attains during 

 the inundation, the amount added to the river's bed, in the in- 

 terval, by the annual sedimentary depositions ; — and the nilo- 

 meter of Roda Island affords a sure index to the height gained 

 by the point of the Delta, from this cause, in a given time. 

 In an average favourable inundation, the water now rises 

 about 35 inches above the 16th cubit of the nilometer, that 

 marked such an inundation — one of 16 cubits — when the 

 column was erected and graduated. This was about A.D. 

 860.t Thence we may conclude that about a yard in 1000 

 years is the amount of rise in the bed and banks of the Nile, 

 by its depositions at Roda Island. For we are not reckoning 

 from a local measurement of the quantity of matter deposited 

 in one given spot in a given time, which is liable to the greatest 

 variations, according as the spot lies high or low with respect 

 to the adjacent lands, and according to the depth of the water ; 

 but we have a natural index susceptible of the strictest accu- 

 racy, the actual height of a water line that covers and in- 

 cludes all these possible variations, and that thus gives us a 

 natural average far more precise than any one could obtain 

 by computation. 



At the rate of a yard of increase in 1000 years, a favour- 

 able inundation of the Nile, 3500 years ago, must have been 

 lower by about 3i yards, with respect to the invariable mean 

 level of the sea, then it is at the present time at the point of 

 the Delta. The slope to the sea being less by so much, the 

 water would be unable to flow farther than Hero, except 

 during the season of inundation. 



* Section 2, — between Abbasieh and " Hero." 



t Viih Bir 0. WilUinson's Modern Kgypt and TlicboH, vol. i., pp. 270-282. 



