MR. HORNER ON THE ALLUVIAL LAND OF EGYPT. 
109 
the rock on which they may rest had not been ascertained, I determined to make an 
etFort to have the experiment made, even to the limited extent within my means, as 
the results thus obtained might lead the way to other researches on a greater scale. 
The ground upon which I hoped to be able to form a chronometric scale by which 
the total depth of sediment reached might be measured, was the same as that on 
which the French engineers in 1800 had proceeded, viz. the accumulation of Nile 
sediment around monuments of a known age. Certain works of art of a very early 
age exist near the Nile, the approximate dates of whose erection have been esta- 
blished upon reliable evidence ; and we know also that the sediment has accumu- 
lated to a considerable height above their base. If that depth of sediment be divided 
by the number of centuries that have elapsed since the date of the erection of the 
monument, we obtain a scale of the secular increase of which the l?ase of the monu- 
ment is the zero, assuming, as we are entitled to do, that the average increase from 
century to century has been uniform within an area of some extent. If the excava- 
tion be continued below the base stone, and the sediment passed through exhibits 
similar characters as to composition with that above the base line of the monument, 
it would be fair to apply the same graduation below the zero-point of the scale as 
above it ; and, if we reached so far, we should be able to estimate the time that has 
elapsed since the first layer of sediment was deposited on the rock forming the chan- 
nel over which the water spread when it first flowed northward from its source in 
the interior of Africa; subject, however, to correction for causes that might make a 
difference in the rate of increase between earlier and later periods ; an investigation 
of which causes forms a necessary, but a very difficult part of such an inquiry. 
I submitted my project to the President and Council of the Royal Society, stating, 
that it appeared to me to be a scientific inquiry of sufficient importance to justify my 
asking for a grant from the Donation Fund under their control, for the purpose of de- 
fraying the expense of the proposed excavations. My proposal was favourably received, 
and the Council were pleased to place a liberal grant of money at my disposal. 
I have thought it advisable, before entering upon the narrative of the researches 
carried on towards the accomplishment of the object of this inquiry, to give a brief 
sketch of the physical geography of Egypt and of its geological structure ; and a 
somewhat more detailed account of the annual inundations of the Nile and of the 
sediment it deposits. 
Physical Geography and Geological Structure of Egypt *. 
Egypt is separated from Nubia by a low hilly region, fifty miles in breadth from 
north to south, which is a part of a range extending from the Red Sea in an east and 
* The principal authorities are, — Russegger, Reisen in Europa, Asien und Africa, Stuttgart, 1843 ; Broc- 
CHi, Giornale delle Osservazioni fatte ne’ Viaggi in Egitto, &c., Bassano, 1841 ; Newbold, Quarterly Journal 
of the Geological Society, Nov. 1848; and Talabot, Memoire de la Societe d’Etudes de I’lsthme de Suez, 
1846-47, — the latter not published. 
