From this position also, the white terrace of Jebel Usdum—“the salt mountain” where the Crusaders wrongly placed Sodom—is seen projecting from the sides of the loftier limestone terraces of the Judæan hills. Towards the east, similar terraces of whitish alluvial deposits are seen clinging to the sides of the Moabite hills, or running far up the deep glens which penetrate the sides of the great table-land. In these terraces, the upper surfaces of which reach a level of about 600 feet above the waters of the Salt Sea, we behold but the remnants of an ancient sea-bed, which must originally have stretched from side to side.
Eight hundred feet higher than these terraces there are others composed of marl, gravel, and silt, through which the ravines of existing streams have been cut; and this indicates that the level of the Salt Sea stood at one time 100 feet higher than the waters of the Mediterranean stand now.
Origin of the saltness of the Dead Sea.—It has been generally recognised that the waters of lakes which have no outlet ultimately become more or less saline. Of these the most important in the old world are the Caspian, the Sea of Aral, Lakes Balkash, Van, Urumiah, and, lastly, the Dead Sea, or as it was originally called, “the Salt Sea.” “The Caspian,” says Professor Hull, “owing to its great extent and other causes, is but slightly saline; but that with which we have here to deal is the most saline of all. It is probable that the water of the ocean itself has become salt owing to the same cause which has produced saltness in the inland lakes, as it may be regarded as a mass of water without an outlet. The cause of the saltness in such lakes I now proceed to explain.
“It has been found that the waters of rivers contain, besides matter which is in a state of mechanical suspension, carbonates of lime and magnesia, and saline ingredients in a state of solution; and as those lakes which have an outlet, such as the Sea of Galilee, part with their waters and saline ingredients as fast as they receive them, the waters of such lakes remain fresh. It is otherwise, however, with regard to lakes which have no outlet. In such cases the water is evaporated as fast as it is received; and as the vapour is in a condition of purity, the saline ingredients remain behind. Thus the waters of such a lake tend constantly to increase in saltness, until a state of saturation is attained, when the excess of salt is precipitated, and forms beds at the bottom of the lake. The contrast presented by the waters of the Sea of Galilee on the one hand, and those of the Dead Sea on the other, though both are fed by the same river, is a striking illustration of the effects resulting from opposite physical conditions. In the former case, the waters are fresh, and abound in fishes and molluscs; in the latter, they are so intensely salt that all animal life is absent.
“The increase of saltness in the waters of the Dead Sea has probably been very slow, and dates back from its earliest condition, when its waters stretched for a distance of about 200 miles from north to south....
“The excessive salinity of the waters of the Dead Sea will be recognised from a comparison with those of the Atlantic Ocean. Thus, while the waters of the ocean give six pounds of salt, &c., in a hundred pounds of water, those of the Dead Sea give 24·57 pounds in the same quantity; but in both cases the degree of salinity varies with the depth, the waters at the surface being less saline than those near the bottom....
“As to the depth of the waters:—The floor of the Dead Sea has been sounded on two occasions: first, by the Expedition under Lieutenant Lynch in 1848, and secondly, by that under the Duc de Luynes. In the former case the maximum depth was found to be 1278 feet; in the latter 1217 feet, being close approximations to each other. We may therefore affirm that the floor of the lake descends to nearly as great a depth below its surface as the surface itself below the level of the Mediterranean Sea.
“The section given by Lynch indicates that the place of greatest depth lies much nearer the Moabite than the Judæan shore, and the descent from the base of the Moabite escarpment below Jebel Attarus and between the outlets of the Wâdies Mojeb and Zerka Maïn, is very steep indeed. The deepest part of the trough seems to lie in a direction running north and south, at a distance of about 2 miles from the eastern bank; and while the ascent towards this bank is rapid, that towards the Judæan shore on the west is comparatively gentle. The line of this deep trough seems exactly to coincide with that of the great Jordan Valley fault. From the bottom of the deeper part, the sounding line brought up specimens of crystals of salt (sodium-chloride), and it can scarcely be doubted that a bed of this mineral, together with gypsum, is in course of formation over the central portions of the Dead Sea.”
[Authorities and Sources:—“Memoirs of the Survey: Geology”, Dr E. Hull. Smith’s “Dict. of Bible.” “Tent Work in Palestine.” By Major Conder, R.E.]