346 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
jacent limestone) in the mud covering the middle and upper portions 
of the delta, which are found in it in abundance, mingled with fluvia- 
tile and land testacea, on its arrival at the Mediterranean, that the 
present alluvium must have been deposited, for the most part, on a 
surface previously raised above the ocean’s level, probably by subter- 
ranean forces. 
The bulging-out aspect of the present coast-lme indicates, how- 
ever, the operation of other causes in the raising and extending its 
lower portions. When we come to examine the coast-line of the 
delta, we find that the deposit brought down by the Nile forms but 
an insignificant component im its structure; and that this elevated 
fringe consists almost entirely of banks of marme sand thrown up 
generally by the conflicting currents of the river freshes and tidal 
’ wave, and of a recent marie limestone, in whose formation the Nile 
could have had no share. , 
Ancient Alexandria stood on the calcareous rock of the Libyan 
desert immediately land of modern Alexandria, which stands on 
sand-banks and a recent marine limestone, on a site over which the 
water of the great harbour formerly flowed*. The city of Foah, 
which, at the commencement of the fifteenth century, was on the 
Canopic mouth, and now more than a mile inland, Rosetta, Nicopolis, 
and Taposiris, all owe their present inland position in great measure 
to the intervention of marme sand-bankst. Over these newly thrown- 
up sands, in some low situations, the waters of the imundations either 
flow naturally or are conducted by art, and by deposition contribute 
to the fertility and to the permanent increase of land. 
The increase of soil, by the Nile, in the delta is much slower than 
in the valley of Egypt, being spread over a much greater extent; and 
it must be borne in mind that a very considerable proportion of what 
remains In suspension in the water, after passmg through the valley 
of Egypt in slow and serpentine windings, is carried off into the Me- 
diterranean. 
Rise of the Delta under the Mediterranean.—tThe rise of the 
delta from fluviatile deposition under the Mediterranean cannot be 
rapid, as will be readily conceded from what has been said already ; 
and, besides this, we must take mto consideration the effects of the 
ocean current, which flows from the Straits of Gibraltar, m carrying 
away toward the east the light mud of the Nile. We are assured of 
the little tendency of the deposit to spread westerly by the fact of the 
soundings to the westward of Rosetta being on sand, while those be- 
tween Rosetta and Damietta are on mud. The depth of the Medi- 
terranean off the delta at a short distance is about twelve fathoms ; 
it increases gradually to fifty, and then suddenly descends to 380, 
which Mr. Lyellf thinks is perhaps the original depth of the sea 
* Appendix to Denon’s Travels, English edition, vol. ii. 
+ Sir H.de la Beche has shown that the present inland position of Damietta, two 
leagues from the sea, gave rise to very exaggerated ideas of the rapid advance of 
the land, until it was found that the sites of the ancient and modern towns are not 
identical, the inhabitants of the former having removed inland, partly from fear a 
maritime invasion (Manual, Third edition, p. “70). 
t Lyell’s Elements of Geology, vol. i. pp. 441, 442. 
