I. C. Russell—The Jordan-Arabah and the Dead Sea. 389 
basin, near the Sea of Galilee, about 175 miles to the north of the 
locality mentioned above, other lake beds have been observed at 
about the same level. These observations, and others of a similar 
nature which might be cited, show very clearly that the Dead Sea 
basin was once occupied by a freshwater lake, whose bottom at 
certain localities was 1400 feet higher than the present surface of 
the Dead Sea, or at about the level of the Mediterranean. 
The surface of this lake during its greatest expansion must neces- 
sarily have been at a higher elevation than the deposits accumulated 
on its bottom, but unless the beach observed by Hull in the Wady 
Arabah, of which mention has already been made, indicates the 
level of the ancient lake during the time the lacustrine sediments 
were deposited, we have no observations of shore records that can 
be correlated with the formation of the higher sedimentary deposits. 
Providing no change has taken place in the depth of the Jordan- 
Arabah depression since this great freshwater lake deposited its 
high-level marls, it must at one time have been about 2700 feet 
deep. Its length from north to south probably exceeded 200 miles, 
its average width being from eight to nine miles. Its full extent 
cannot be definitely known, however, until its shore records have 
been studied and their extent accurately mapped. Its depth is also 
uncertain, and has possibly been considerably overestimated, as will 
appear on the following page. 
The existence of calcareous tufa on the terraces of the Jordan and 
in the lower portions of the lateral gorges opening into The Ghor, 
as observed by Johnson and Lartet, show that calcium carbonate was 
~ among the first precipitates thrown down by the waters of the ancient 
lake. The presence of freshwater shells in these tufas is to be ex- 
pected, as such deposits may be formed from the waters of lakes that 
are essentially fresh. Future observers should also look for alterna- 
tions of various varieties of tufa, for the reason that varying deposits 
of this character record changes in the chemistry or perhaps varia- 
* tions in the temperature, of the water from which they are precipi- 
tated. 
Near the southern border of the Dead Sea, at a locality called 
Jebel Usdum, or Salt Mountain, there is a well-marked terrace, the 
surface of which has an elevation of about 600 feet above the Dead 
Sea, and corresponds with the level of the escarpment previously men- 
tioned farther to the south. It is also represented on the east side of 
the valley, as well as near the mouth of the Jordan. The detached 
portions of this terrace, which is the most pronounced of any in the 
basin, mark the boundaries of the profound gorge known as The 
Ghor. The escarpment at Jebel Usdum exposes the edges of horizon- 
tal strata and owes its precipitous character to the removal of the 
eastern portion of the deposit. In this respect it corresponds with 
the escarpment at the south end of The Ghor. The lower portion of 
the cliff at Jebel Usdum consists of a layer of rock salt from 30 to 50 
feet thick, resting on beds of gravel, shales and laminated sandstone.’ 
Above the stratum of salt are some 400 feet of evenly-bedded 
1 Mount Seir, Sinai, and Western Palestine, p. 131. 
