which the tin itself is made, and a material they dig up resembling litharge; of iron, iron rust. Gold and copper are equally indicated by chrysocolla and azure; silver and lead, by the lead. But, though miners rightly call bismuth “the roof of silver,” and though copper pyrites is the common parent of vitriol and melanteria, still these sometimes have their own peculiar minerals, just as have orpiment and stibium.
Now, just as certain vein materials give miners a favourable indication, so also do the rocks through which the canales of the veins wind their way, for sand discovered in a mine is reckoned among the good indications, especially if it is very fine. In the same way schist, when it is of a bluish or blackish colour, and also limestone, of whatever colour it may be, is a good sign for a silver vein. There is a rock of another kind that is a good sign; in it are scattered tiny black stones from which tin is smelted; especially when the whole space between the veins is composed of this kind of rock. Very often indeed, this good kind of rock in conjunction with valuable stringers contains within its folds the canales of mineral bearing veins: if it descends vertically into the earth, the benefit belongs to that mine in which it is seen first of all; if inclined, it benefits the other neighbouring mines[1]. As a result the miner who is not ignorant of geometry can calculate from the other mines the depth at which the canales of a vein bearing rich metal will wind its way through the rock into his mine. So much for these matters.
I now come to the mode of working, which is varied and complex, for in some places they dig crumbling ore, in others hard ore, in others a harder ore, and in others the hardest kind of ore. In the same way, in some places the hangingwall rock is soft and fragile, in others hard, in others harder, and in still others of the hardest sort. I call that ore “crumbling” which is composed of earth, and of soft solidified juices; that ore “hard” which is composed of metallic minerals and moderately hard stones, such as for the most part are those which easily melt in a fire of the first and second orders, like lead and similar materials. I call that ore “harder” when with those I have already mentioned are combined various sorts of quartz, or stones which easily melt in fire of the third degree, or pyrites, or cadmia, or very hard marble. I call that ore hardest, which is composed throughout the whole vein of these hard stones and compounds. The hanging or footwalls of a vein are hard, when composed of rock in which there are few stringers or seams; harder, in which they are fewer; hardest, in which they are fewest or none at all. When these are absent, the rock is quite devoid of water which softens it. But the hardest rock of the hanging or footwall, however, is seldom as hard as the harder class of ore.
Miners dig out crumbling ore with the pick alone. When the metal has not yet shown itself, they do not discriminate between the hangingwall and the veins; when it has once been found, they work with the utmost care. For first of all they tear away the hangingwall rock separately from the vein, afterward with a pick they dislodge the crumbling vein from the footwall
- ↑ Presumably the ore-body dips into a neighbouring property.
