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We learn also from the accurate levellings made by the French engineers, that the mean height of the surface of the Red Sea is 29'57 English feet above the mean height of the surface of the Mediterranean Sea near Tineh.

Between the two seas the land of the Isthmus is stated to be remarkably flat, with the exception of some scat­tered hillocks of drifted sand. For two or three miles from the Gulph, northwards, the ground is only elevated three feet above the high-water-mark of the Red Sea, and from thence it is said to decline gradually to the Mediter­ranean shore. The general character of the soil near the surface is stated to consist of a hard compact gravel, but the limit to which this kind of soil extends has not been very fully ascertained.

Proceeding north from the head of the Gulph, the direct line across the Isthmus passes for twelve miles through a valley or narrow plain, confined on either side by rising ground, beyond which the remainder of the distance lies over flat open plains, diversified only by hillocks of drifted sand, as already noticed.

Somewhat to the westward of the direct line, and at the distance of twelve miles from the Gulph of Suez, commences a remarkable series of depressions of the land, the first extending about twenty-seven miles in a north­west direction, with a width of from five to seven miles. The bottom of this hollow or trough, though from 20 to 54 feet below the high-water-mark at Suez, is nearly destitute of water, containing only a few shallow pools, at present called the Bitter Lakes; and there can be no reason for doubting that this trough constituted the bed or basin of the Lacus Amari of Pliny, through which the navigation of the antients was conducted between the Red Sea and the Nile.