true relief of the land had been determined by cureful surveys. It has now been made evident that neither in historic times, nor even in the present geological epoch, did the Igharghar reach the Tunisian shotts, which are separated from each other and from the sea by two rocky sills, showing no trace of ever having been subject to the action of water. The general slope of the land is aleo opposed to such a view, being inclined not seawards, but in the opposite direction, towards the inland lakes. The salts of the shotts are of diverse composition, differing from those of sea-water, and in certain places containing more sulphate of soda than
marine salt. Nevertheless saline incrustations are found in some of these basins, especially the Shott-el-Gharsa, which yields salt of a very fine quality.
The great Algerian shott and surrounding saline depressions lie below sealevel, whence the hasty conclusion that by connecting them with the Gulf of Cabes, the Sahara itself might be converted into a vast inland sea. Recent measurements have shown that the area of the whole region lying at a lower level than the Mediterranean scarcely exceeds 8,300 miles. Hence the idea of flooding the Suhara, advocated especially by Rudaire, can never be realised in our days.
