Page:South African Geology - Schwarz - 1912.djvu/113

 the Jordan, the Dead Sea, and Lake Tiberias, and is finally cut off north of the last by the Alpine folds that here run eastwards into Asia. The fault scarps on either side of the rift are often stupendous; in Lake Nyasa they rise abruptly 8000 ft. above the level of the lake, and in Tanganyika, on the western side, they are 6000 to 7000 ft. high. In the Dead Sea the surface of the lake lies 1286 ft. below sea level; the Judaean hills, in the west, rise to 3281 ft.; and from here to the bottom of the lake, 2625 ft. below sea level, there is a drop of nearly 6000 ft., the throw of the fault. Volcanoes are common along the faults. The M'fumbiro Mountains, north of Lake Kivu, are volcanoes that are connected with the faulting, and they are exceedingly important, because they are of quite recent origin, and before they poured out their lavas into the rift valley the waters of Lake Tanganyika found their way into the Nile, whereas the way is now barred, and the Tanganyika drains into the Congo. It should be recalled that the volcanoes of the Drakensberg in a similar way turned the waters of the streams flowing into the Indian Ocean into the Orange River, which empties into the Atlantic. It is possible that the Drakensberg are on the southern extension of the Great Rift Valley system. So stupendous are these rift valleys in Africa that one is apt to forget that similar rift valleys exist in many other places, such as in the Great Glen that traverses Scotland from the Firth of Lome to the Moray Firth, and Loch Lochy and Loch Ness are lakes similar to the Tanganyika and Dead Sea. The upper valley of the Rhine, also, lies in a rift valley. There is good reason to believe that the canals on Mars are of this nature.

In South Africa there is a system of rifts similar in