=Geological History.= The great gorge of the Jordan and Dead Sea valley is the most striking natural phenomenon in Palestine. No place on the face of the earth has had a more dramatic geological history. As has already been noted (p. 14), this great rift which runs from northern Syria to the Red Sea was probably formed in the latter part of the Pliocene Age. At the northern end of the Dead Sea its bed reaches a depth of nearly one-half a mile beneath the ocean level. It is thus by far the deepest depression on the face of the earth. During the Pluvial period this huge rift was filled with water, making a large inland sea, fully two hundred miles long, with its surface nearly one hundred feet above the ocean level. Apparently the higher land to the south of the present Dead Sea cut off the ocean, so that at the first it was a fresh-water lake. During the Interglacial period, possibly in part as the result of volcanic changes, it fell to a level of not more than three hundred feet above the present surface of the Dead Sea. It was during this period and the ice age that followed that the deposits were made on the side of the valley, which have given it its present terraced form. =Evidences of Volcanic Action.= From the Pluvial period to the present the valley has been the scene of frequent volcanic disturbances. The water, sinking through the great rifts and subterranean passages, and being transformed by the heat into steam, forced up great masses of lava, which may be traced at many points on the heights both to the east and to the west of the Jordan valley. Earthquakes, many of them severe, are still common in this volcanic region. That of 1837 destroyed the city of Safed, killing one thousand of its inhabitants. In recent years severe shocks were felt in June, 1896, January, 1900, March and December, 1903. Many copious, hot, mineral springs still bear testimony to the presence of volcanic forces. Those near Tiberias, on the eastern side of the Sea of Galilee and in the Wady Zerka Ma'in, east of the Dead Sea, have a temperature of about 144°, while the waters of El-Hammeh in the Yarmuk Valley vary in temperature from about 93° to 110.° These springs are strongly impregnated with mineral salts and it is from these and similar sources that the salts have come that make the waters of the Dead Sea what they are to-day, heavy and far more saline than the ocean itself. =Natural Divisions.= The Jordan and Dead Sea valley falls into four natural divisions: (1) the upper Jordan, from Mount Hermon to the Sea of Galilee, (2) the Sea of Galilee, (3) the lower Jordan, and (4) the Dead Sea. At its northernmost point rises Mount Hermon, called by the natives Jebel es-Sheik, that is, Mountain of the White-haired.