In the course of these excursions, on the side of one of these narrow vales, winding among the mountains, I observed a narrow branch or inlet, towards the termination of which the rocky heights from each side closed, and formed a cavern of about nine feet deep, and five feet wide; and, considering its appearance and situation in this desolate, obscure, and mournful region, I was inspired with feelings, as on viewing the entrance to the subterraneous world, and very passage, _ad inferos_. My interpreter told me, that at some time when I had taken another path, and when the caravan was travelling about midway through the mountains, he saw a cavern in which the stones to a considerable depth were black, and that under these lay a stratum of white stones. On travelling afterwards from Fezzan to Tripoly, in continuation of the Harutsch, (as I supposed it), I myself observed ranges of basaltic hills, alternate with ranges of calcareous hills. My interpreter brought me a specimen of the white stone taken from the cave himself had seen, but I think was not happy in its selection, it consisting of a mere lump of indurated argillaceous earth, such as often adheres to limestone. In respect to the many hills, and their curious ranges and direction, the _Harutsch_ exhibits a similitude to the excrescences on the bordering mountains I refer to in a subsequent journey; it agrees too in the circumstance of single stones scattered on the surface, which, in the Harutsch, are distinguished as being only of one species or substance, peculiar to the district. There is too a further analogy in the plains formed of bare rock; and in the white quicksand covering other levels, and laying round the mountains, and up their base, though to no considerable height. Contiguous to the _Harutsch-el-assuat_, or black Harutsch, lies the white Harutsch, or _Harutsch-el-abiat_. The country denoted by this appellation is a vast plain, interspersed with mounds or isolated hills, and spreads to the mountains rising towards Fezzan. The stones covering the surface of this plain have the appearance of being glazed, and so too every other substance, and even the rocks which occasionally rise or project from the level. Among the stones are found fragments of large petrified marine animals, but mostly shells closed up and insolidated. These shells struck or thrown forcibly on others, give a shrill sound, and the fracture presents a vitreous appearance.