392 JI. C. Russell—The Jordan-Arabah and the Dead Sea. 
waters of the lake were again concentrated, and the present condi- 
tion of the basin resulted. These changes must have been accom- 
panied by many minor oscillations of humidity, and consequently 
by many changes of lake level; which were accompanied in turn 
by many variations in the character of the precipitates thrown down 
from the lake waters. 
A deepening of the central depression in the manner postulated 
would not only lower the lake surface without forming saline deposits, 
but would enable its waves to erode the surrounding shores and form 
cliffs in the previously formed sedimentary beds, like those at Jebel 
Usdum and ed Debbeb. The lowering of the Dead Sea would also 
allow the inflowing streams to cut terraced channels through the 
previously formed lacustrine sediments, its effect being in this respect 
essentially the same as the lowering of the lake surface by evapora- 
tion. 
The effect of a movement along the Dead Sea fault of the nature 
we have suggested, on the history and condition of the Sea itself, 
renders the study of this displacement of unusual interest. In this 
connection it is desirable not only to have observations on fault 
scarps in lacustrine marls and clays and in alluvial deposits if such 
exist, but we desire also accurate measurement of the elevation of the 
principal terraces and beaches on the borders of the Dead Sea 
and in the Jordan valley. Three lines of level run from the Dead 
Sea surface up the borders of its basin on both the east and the west, 
to beyond the highest of the ancient lake records, and so located as to 
cross the best-defined terraces, besides two or three cross-sections of 
the Jordan valley showing the elevation of the terraces there exist- 
ing, would give sufficient data both in reference to east and west and 
north and south axes, for determining if recent orographic movement 
has taken place in the Dead Sea basin or not. The lines of level sug- 
gested could be connected with the soundings of the Dead Sea, and 
thus give accurate profiles of the basin. 
Certain writers have considered that the Jordan-Arabah depression 
was formed in Tertiary times beneath the ocean, and that when the 
land rose, the basin was occupied by ocean water. So far as we are 
aware, no evidence of sediments containing marine fossils has been 
found in the basin. It has been argued in this connection, also, that 
the fauna of the Sea of Galilee must have been derived from the 
ocean, being entrapped in the valley at the time of the emergence of 
the land. 
That the fauna of the Dead Sea basin is specialized, and differs 
from the faunas of neighbouring drainage areas, is not a fact peculiar 
in itself. On the contrary, an insular fauna is to be looked for in 
any basin that has been cut off from oceanic drainage for a long 
period. 
It seems to the writer that there are sufficient facts to indicate 
that the Jordan drainage was once connected with other river 
systems, but has been isolated sufficiently long for its fauna to 
undergo an independent development, and thus become differentiated 
from the life of neighbouring rivers. Space however will not admit 
