Page:Philosophical Transactions - Volume 145.djvu/135

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119
MR. HORNER ON THE ALLUVIAL LAND OF EGYPT.

descendu de 11/2 à 2 pieds, et partout il dégrade les bords à tel point, qu'on voit a chaque moment une série d'avalanches du plus beau terroir noir imaginable:" and on the following day he says, "Nous sommes arrivés a Girgeh, une des villes de la haute Egypte, qui était trois fois plus grande il y a quelques années qu'aujourdhui, mais un courant du Nil qui s'est determiné centre la colline friable sur laquelle elle est bâtie, en enlève des quartiers entiers de tems à autre. Une portion des maisons et une mosquée, dont la moitié est déjà tombées dans le Nil, ressemblent aux gravures du Diable Boiteux, seulement que ces débris ne sont pas habités." The sediment of one year is also carried back into the river the following year from another cause:—" Pendant trois ou quatre. mois de l'année, la surface de l'Egypte, dénuée de végétation, sèche et pondreuse, est balayée par des vents violents, qui soulèvent dans les airs la poussière du sol, en laissant précipiter une partie dans le fleuve, qui l'entraine à la mer, et en dispersent une autre partie dans les déserts, ou l'accumulent sur d'autres portions de l'Egypte[1]." At a distance from the river, especially in those parts which are in the vicinity of valleys or gorges, in the lateral ranges of hills, blown sand from the desert is often mixed with the mud of the river that is spread upon the land.

In all calculations, therefore, as to the secular increase of the deposit, by measurements of its depth, we must take into our consideration whether the pits or the borings have been made in places least liable to these irregularities; whether the solid matter held in suspension may not have been augmnented by portions of former deposits washed or falling into the stream; and whether the mud deposited by the river has had no intermixture of blown sand.

The following observation of the traveller Rüppel is a remarkable indication of an accumulation of the Nile sediment in the Faiûm, at a distance of about twenty-five miles from the left bank of the river:—"I had a desire to visit Lake Mœris and its islands, and quitted Medina in a north-east direction, travelling over very fertile plains. In the neighbourhood of a large village called Fedimin, we passed the dried-up bed of a very deep canal, in the side of which I saw, to my great surprise, horizontal beds of the mud of the Nile, having a depth of sixty feet[2]."

 

THE RECENT RESEARCHES.

The first step which I had to take in this inquiry was to decide upon the situation in which the proposed vertical shafts should be sunk. As the neighbourhood of Cairo might afford great facilities for prosecuting the work, as the standing obelisk of Heliopolis is one of the most ancient of the existing monuments, and as the time of its erection has been made out on very reliable grounds, I chose that spot.

Having obtained an introduction to A. C. Harris, Esq., of Alexandria, well known by his active and long continued researches in Egyptian antiquities, I requested him

  1. De la Constitution physique de 1'Egypte, Hist. Nat. ii. 493.
  2. Letter in Baron de Zach's Correspondance Astronomique, vol. vii. p. 245.