14 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
into the heart of Palestine, and enabled the marine fauna of the 
former country to migrate to the latter. 
As Tertiary time went on, however, the land was still further 
elevated, and with its great lines of fracture assumed somewhat its 
present form. The district between the Dead Sea and the Gulf 
of Akaba was raised above the ocean, and, in consequence of this, 
the molluscan fauna of the Jordan system was enclosed as in a trap. 
The struggle for existence grew keener and keener; the laws of 
natural selection, and of the survival of the fittest, had the fullest 
seope for exercise. The newly formed great inland sea gradually 
dried up into three lakes—namely, the Lake of Merom, the Sea 
of Galilee, and the Dead Sea—and all three were connected by a 
river channel, that of the Jordan. The southern lake—the Dead 
Sea—became salter and salter owing to its total want of outlet, 
to the excessive evaporation, and to the nature of its subsoil; the 
Lakes of Merom and of Galilee became fresher and fresher by the 
influx of pure water from the hills.* Many of the old marine 
forms by degrees died out. The Miocene corals and crinoids 
would disappear: the less adaptable species would succumb to the 
altered conditions. The process of change in the quality of the 
water, from salt to brackish, and from brackish to fresh, would be 
so slow, however, that many of the more plastic forms of molluscan 
life were able to adapt themselves to the slowly altering environ- 
ment, and the result was the creation of a series of apparently 
totally new species. 
But a further time of trial was in store for these survivals of 
the old Miocene marine forms, The Ice Age arrived : the slopes 
of Hermon and of Lebanon were covered with snow, and probably 
glaciers ; the Jordan Valley was depressed nearly 300 feet, and 
* Nore.—Will it ever be found that increase of salinity may be used as a 
basis in calculating geological time? If the specific gravities of several of 
the salt lakes of the world (such as the Dead Sea, the Caspian, the Sea of 
Aral, the Lake of Urumia, the Great Salt Lake) were compared with that 
of the ocean, and allowance made for the respective difference in the time 
since each lake was cut off from the sea, might not the ratio thus found 
prove of service? Of course the disturbing factors would in each case be 
very great—the most stupendous being the glacial period—and special 
allowances would here and there require to be made; but with care an 
approximate result might be arrived at, and might be, in the main, 
satisfactory. 
