Page:Mount Seir, Sinai and Western Palestine.djvu/218

180 in which places the limestone of the Tih (Cretaceo-nummulitic) is faulted against the old porphyritic and metamorphic rocks, as illustrated by the section across the Arabah Valley, given in a previous page (p. 77).

There are numerous parallel and branching faults along the Arabah Valley, but there is one leading fracture running along the base of the Edomite Mountains, to which the others are of secondary importtance; this may be called "the Great Jordan Valley fault." The relations of the rocks in The Gh6r and Jordan Valley have already been shown by Lartet, Tristram, Wilson, and others, to indicate the presence of a large fault corresponding with the line of this remarkable depression, and the author considers the fracture he has observed in the Arabah Valley to be continuous with that of the Jordan.

(d) The ancient rocks which form the floor either of the Desert, or Nubian, Sandstone formations, consist of granite, gneiss, porphyries, and more rarely of metamorphic schists—together with volcanic rocks, consisting of agglomerates, tuffs, and beds of felspathic trap. The author is disposed to concur with Dr. Lartet in considering the gneissose and granitoid rocks to be of Archaean (or Laurentian) age, as they are probably representative of those of Assouan in Upper Egypt, which Prof. Sir J. W. Dawson has recently identified with those of this age. The granites and porphyries are traversed by innumerable dykes of porphyry and diorite both throughout the Sinaitic mountains and those of Edom and Moab; and the author considers it probable that the volcanic rocks which are largely represented along the bases of Mount Hor, and of Jebel es Somrah near Es Safieh, are contemporaneous with these dykes. As far as the author was able to observe, none of these dykes penetrate the Desert or Nubian Sandstones, and, if so, they may be considered of pre-Carboniferous age. The upper surface of the ancient rocks was originally extremely uneven, having been worn and denuded into ridges and hollows, previous to the deposition of the Desert Sandstone; over this irregular floor the sandstone strata were deposited.

4. The occurrence of terraces of marl, gravel, and silt, through which the ravines of existing streams have been cut at an elevation (according to aneroid determination) of about 100 feet above the level of the Mediterranean, was taken to show that the level of the Salt Sea (Bahr Lut) at