Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/103

 tion being confined to a few localities. Judging by the present conditions of mining economy, it may be fairly said that no such deposit could possibly be worked now unless the value of copper was to be raised to several times that of gold. On the other hand, it may be said that the ground worked away by the ancients was possibly richer than that which has been left ; but there does not appear to be much reason for such a supposition, as it is evident from the nature of the excavations that the rock has been searched with extraordinary diligence : numerous small cavities in the walls show that even the smallest nodules of ore have been removed wherever there was a chance of doing so without breaking down a quantity of dead rock. So perfectly has nearly every visible spot of ore been removed, that we were for some time in doubt as to whether the outer hollow was really an old mine and not a natural cavern.

Copper-works of Nasb. — The ores from the mine at Wady Khalig were smelted in Wady Nasb, close to the springs, as is evidenced by the mass of slags, which forms a roughly elliptical heap about 350 yards in length and 200 in breadth. The depth is very variable, and probably not more than 8 or 10 feet at the most; and over the greater part of the area the slags form only a thin covering to the rock. Upon digging into the heaps, numerous clay twyer-nozzles, with an air-passage of about 3/4 inch diameter, were found. These have evidently been formed by the accretion of the slag to the wall of the furnace in front of the blast, and in many cases have been repaired by plastering fresh clay over the former face — an operation that is seen, from some of the broken twyors, to have been repeated three or four times. In one instance the slag nose has accumulated to such an extent as almost completely to block up the passage for the blast. In nearly all cases shots of metallic copper are found included in the slag adhering to the twyers ; but not a fragment of unaltered ore, or of any kind of regulus, was found, although carefully looked for. The only building that can be regarded as having formed part of a furnace is a pair of small walled enclosures of unequal size, the larger one being about 6 feet square, and the other 2-1/2 feet square, both being walled in on three sides to a height of about 2 feet above the ground. These may possibly have been the outer walls of a hearth or low blast-furnace ; but no trace of any lining that had been subjected to the action of heat could be detected. In the smaller compartment a stone pestle, worked round, and about 1-1/2 inches in diameter, was found.

On examining the different parts of the heap, it becomes evident, from the nature of the slags themselves, that several different operations were carried on here. Thus in places the fragments are broken up small, and contain many shots of metal now mostly changed into malachite ; these are probably rich selected cinders, either from the first fusion, or perhaps from the refinery, which have been put on one side for farther treatment ; while, on the other hand, at the upper end of the heap, crusts of well-melted clean slags, from 1-1/2 to 2 inches in thickness, are spread over the ground, as though they had been allowed to flow from the furnace and solidify upon the rock