This vein, which may be of great length and puissance, I took the liberty of calling the "Filon Husayn," from the prince who had so greatly favoured the Expedition. Here we had hit upon the Negros,[EN#25] or coloured quartzose formations of Mexico, in which silver appears as a sulphure; and we may expect to find the Colorado, or argillaceous, that produces the noble metal in the forms of chlorure, bromure, and iodure. The former appears everywhere in Midian, but our specimens are all superficial, taken à ciel ouvert. To ascertain the real value and the extent of the deposits required exposure of the veins at a horizon far lower than our means and appliances allowed us to reach. If the rock prove argentiferous I should hope to strike virgin silver in the capillary or aborescent shape below. Above it, as on the summit of the Jebel el-Abyaz, and generally in the "Marú" hills and hillocks of North Midian, the dull white quartz is comparatively barren; showing specks of copper; crystals of pyrites, the "crow-gold" of the old English miner, and dark dots of various metals which still await analysis. Thus, I would divide the metalliferous quartzes of this North-Midianite region into two chief kinds: those stained green and light blue, whose chief metallic element is copper, with its derivatives; and the iridescent Negro, which may shelter the Colorado. In South Midian the varieties of quartz are incomparably more numerous, and almost every march shows a new colour or constitution. About the Jebel el-Abyaz, as in many mining countries, water is a serious difficulty. The principal deposit lies some three miles east of the camping ground in a Nakb or gorge, El-Asaybah, offsetting from the great Fiumara, "El-Simákh;" and apparently it is only a rain-pool. Throughout Midian, I may say, men still fetch water out of the rock. M. Philipin, whilst pottering about this place, saw two Beden (ibex) with their young, which suggests a permanent supply of drink.[EN#26] However that may be, Norton's Abyssinian pumps, for which I had vainly applied at Cairo, would doubtless discover the prime necessary in the Wadys, many of the latter being still damp and muddy. Moreover, the crible continue à grilles filtrantes, the invention of MM. Huet and Geyler, introduced, we are told, into the mechanical treatment of metals, a principle which greatly economizes fluid. Founded upon the fact that sands of nearly the same size, but of different densities, when mixed in liquid and subjected to rapid vertical oscillation, range themselves by order of weight, the heavier sinking and not allowing passage to lighter matter, the new sieve offers the advantages of a single and simple instrument, with increased facility for treating poor "dirt." Finally, as I shall show, the country is prepared by nature to receive a tramway; and the distance to the sea does not exceed fourteen miles, liberally computed.[EN#27]