TRANSACTIONS OF SECTION D. 1067 
cussed and illustrated, especially by Canon Tristram’ and Professor L. Lortet,? 
from which it has been determined that nearly one-half of the species are peculiar 
to the lake and its tributaries; while of the rest only one—namely, Blenniws lupulus— 
belongs to the ordinary Mediterranean fauna; two others—namely, Chromis Niloticus 
and Clarias macracanthus—are found in the Nile; seven other species occur in the 
rivers of South-western Asia; and ten more are found in other parts of Syria. 
Tristram considers that this assemblage points to a close affinity of the fauna of the 
Jordanic basin with that of the rivers of Tropical Africa (8thiopian) ; but what 
most strikes the observer is perhaps the number of species special to Jordanic waters, 
sixteen out of a total of thirty-six species being peculiar. This view seems to be 
borne out also by an analysis of the molluscous forms, which are for the most part 
also peculiar, for no less than sixteen species of Unio are special to Jordanic waters.* 
Assuming that the forms which are common to Jordanic and other waters have 
been distributed in a manner similar to that by which we have to account for the 
distribution of lacustrine forms in other parts of the world, we have yet to account 
for the presence of the forms which are special and peculiar. 
This leads to a consideration of the manner in which the Jordanic basin was first 
formed and afterwards modified; and without entering here into this wide question, 
which I have endeavoured to deal with in the memoir above referred to, I may be 
allowed to summarise my conclusions somewhat as follows :— 
In the first place, it must be recollected that as the whole region on both sides 
of the Jordanic valley was originally overspread by strata of the Eocene period 
(known as the Nummulitic Limestone), this region formed the floor of the ocean 
down to the close of the Eocene period ; the only possible lands in the district may 
have been those of the crystalline rocks of the Sinaitic group of mountains. 
The Geological period which succeeded, that of the Miocene, was that in which 
land first appeared in the Palestine area. The bed of the sea was locally elevated 
into dry land, but at the same time most of the leading physical features by which 
that land is now diversified were traced out and finally determined. Chief 
amongst these was the line of the great Jordan-Arabah depression—marked out 
by a line of fault or displacement of the strata, ranging from the slopes of the 
Lebanon on the north to the Gulf of Akabah on the south. It seems to me probable 
that as the land on either side of this depression was being elevated, the displace- 
ment of the strata on either side of the great fault was also proceeding, and the 
floor of the sea was subsiding along the line of the Jordan valley. An inland lake 
of considerable extent was thus formed, whose waters were first derived from those 
of the ocean itself,in which were enclosed the fishes and mollusks and other forms 
which inhabited these waters themselves. There are good grounds for believing 
that once the lake was enclosed and shut off from the outer sea by a barrier of land, 
it was never again physically connected with the outer sea. ‘he saddle of the 
Arabah valley, rising some 600 feet above the highest limit to which the waters of 
the old Jordanic lake ever ascended, would have proved an effectual barrier towards 
the south. Towards the west the barrier would have been much more elevated. 
Hence the living forms in the waters of the inland salt lake became isolated from 
those of the ocean, and had either to adapt themselves to their new conditions or 
to die out. 
We may suppose that the first to disappear would be the corals, crinoids, and 
starfishes. On the other hand, fishes, mollusks, and crustaceans, having greater 
powers of adaptation, would in many cases survive. Meanwhile the law of 
‘descent with modification ’ would now come into operation, and we may suppose 
that throughout the Miocene and Pliocene periods the process of modification in 
form, colour, and habit gradually proceeded. ‘The fittest forms would survive, and 
1 «Fauna and Flora of Palestine,’ preface, p. xii, Wem. Palestine Survey (1884). 
2 Poissons et Reptiles du Lac de Tibériade, Archives du Musée d Histoire 
Vatwrelle de Lyon, tome iii. (1883). 
8 Tristram, ibid. p. 178. The mollusks have been also recently described by M. 
A. Locard, Malacologie du Lac de Tibériade (1883). 
4 See Mount Seir, Sinai, and Western Palestine, pp. 95 and 99, &e. 
