390 TI. C. Russell—The Jordan-Arabah and the Dead Sea. 
calcareous marls, with gypsum. H.C. Hart, the only observer who 
has ascended Jebel Usdum, reports that the salt appears to cease at 
about 100 or 150 feet, and that the remainder of the elevation is com- 
posed of white powdery marl.1 These observations apparently leave 
no doubt that this deposit, as concluded by Hull, was formed dur- 
ing a previous stage in the history of the Dead Sea, and that it is 
synchronous with the lacustrine beds exposed in the escarpment south 
of the Dead Sea, in the Lisan (the peninsula at the south-east border 
of the Dead Sea) and in the Jordan valley. 
It is evident, therefore, that the stratum in question records a period 
of long duration, during which the water of the lake was a saturated 
brine, from which sodium sulphate and sodium chloride were pre- 
cipitated. The marls and clays resting on the saliferous strata show 
that the lake subsequently became less salt, and at the same time 
rose to a higher level. It follows from this that the strata of salt 
and gypsum must have been deposited during a period of concentra- 
tion intervening between two high water stages. In order to prove 
or disprove this inference, search should be made in other portions 
of the basin for lacustrine beds belonging to two high water stages, 
separated by beds of gravel and other debris indicative of a period 
of low water. An unconformity between the upper and lower lake 
beds due to the erosion of the lower member during an intervening 
period of desiccation should also be looked for. The record of a 
period of low water is perhaps indicated in a section of lacustrine 
deposits exposed on the east side of the Dead Sea, which has been 
described and figured by Lartet,? but this observation is not sufficiently 
definite to enable one who has not visited the locality to make a full 
interpretation of its meaning. 
As the Dead Sea now has a maximum depth of 1278 feet, and the 
surface of the terrace at Jebel Usdum is 600 feet above its surface, 
it follows, providing there has been no orographic change, that the 
ancient lake after the deposition of the salt bed must have been more 
than 1900 feet deep and greatly expanded beyond its present limits. 
The concentration of so great a body of highly saline water to less 
than two-thirds its original volume, as would have been the case had 
its contraction to the present limits of the Dead Sea been the result 
of increased evaporation simply, would have produced such a vast 
precipitation of sodium chloride and other salts that one would expect 
to find abundant records of the occurrence, had it taken place. The 
absence of such deposits is negative evidence which apparently 
indicated that the entire sea was never sufficiently saturated to pre- 
cipitate saline matter, or else that an important change has been 
made in the depth of its basin since the salt bed at Jebel Usdum was 
deposited. 
Two other hypotheses present themselves in this connection, each 
of which seems worthy of attention. 
1 The strata composing the cliffs at Jebel Usdum, however, are considered by 
Lartet as being of even older date than the origin of the Dead Sea basin. 
2 Expedition géologique de la Mer Morte, Paris, 1877, pp. 175-176, pl. 3, fig. 3; 
also in Kssai sur la géologie de la Palestine, Paris, 1869, p. 240. 
