Advancing south-eastwards by the plain, some _calcareous_ rocks are passed, and afterwards a line of _sandstone_,[19] with limestone over it, running parallel to, and nearly equidistant between the _two primitive_ ridges. _Wadi-el-Enned_ succeeds to the eastward, where a beautifully clear rivulet is found; but its water is too bad for the use of animals, being chiefly serviceable for the nourishment of numerous date palms. This spot lies at the foot of some _limestone_ hills of the _cretaceous_ series that join the eastern _granitic_ ridge. Footnote 19: Mr J. Wilkinson (_ibid_, Note, p. 41), says, "Judging from the angle of its dip, it formerly rose _over_ the lower, or eastern primitive range, from which, however, it is now separated by a valley, or bed of a torrent." Next, on the south, comes _Gebel Kuffra_, where the water is so _salt_ as only to be drunk by camels. _Gebel Dochan_, (smoke)--the "Mons Porphyrites" of the ancients--rising about eleven miles more southward, and in the same line with the supposed site of _Myos Hormus_, Myos Hormos, the "mouse harbour," is too distant from our proposed limits, to receive a full description in the present Memoir. I will only remark that at Mount _Dochan_, there exist some interesting ruins, and "those vast _quarries_, from which Rome took so many superb pieces of _porphyry_, to adorn her baths and porticoes."[20] On its southern side, Mr J. Wilkinson adds, "we met with some _Breccia Verde_; and of other kinds of _Breccia_ we had observed great quantities and varieties at Dochan." The sea-shore, about Myos Hormus, is bare and deserted; to the west, at some distance from the harbour, the _granitic_ chain extends; on the east, between it and the sea, a low ridge of _limestone_ hills, which unites with the primitive rocks on the north, comes down towards the shore. "And, in the distance, on the north, is seen the mountain _El Zeit_, so called from the quantity of _petroleum_ found there; whence project two small headlands, forming two gulfs, at the entrance of which are many long _sandbanks_. May not this be the '_mons Eos_' of Pliny?"[21] Footnote 20: _Ibid_, p. 42.--Pliny writes of the _quarries_, "quantis libet molibus cædendis sufficiunt _Lapidicinæ_." Lib. 36, cap. 7. They produced _red porphyry_ of a most beautiful, close-grained kind; so Pliny says, "_rubet porphyrites_ in eadem OEgypto." Footnote 21: Ibid., p. 51. This _Gebel Zeit_, or "Mount of Oil," runs out into a promontory on one side of the Strait of Jubal; at its foot a copious supply of _Petroleum_, or rock oil, is obtained. It is about as liquid as turpentine, of a black or dark-brown colour, and is collected by the Greek Christians of Tur, who take it there and sell it, for rheumatism and for healing sores. The Arabs call it _Zeit-el-Gebel_--"oil of the mountain."