BOOK V.

117

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 andazure; silver and lead, by the lead. But, though miners rightlycall bismuth “ the roof of silver,” and though copper pyrites is the commonparent of vitriol and melanteria, still these sometimes have their ownpeculiar 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 theirway, 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 abluish or blackish colour, and also limestone, of whatever colour it may be, isa 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 whenthe whole space between the veins is composed of this kind of rock.Very often indeed, this good kind of rock in conjunction with valuablestringers contains within its folds the canales of mineral bearing veins : ifit descends vertically into the earth, the benefit belongs to that mine inwhich it is seen first of all; if inclined, it benefits the other neighbouringmines 12 . As a result the miner who is not ignorant of geometry can calculatefrom the other mines the depth at which the canales of a vein bearing richmetal will wind its way through the rock into his mine. So much for thesematters.

I now come to the mode of working, which is varied and complex, for insome places they dig crumbling ore, in others hard ore, in others a harderore, and in others the hardest kind of ore. In the same way, in some placesthe hangingwall rock is soft and fragile, in others hard, in others harder, andin still others of the hardest sort. I call that ore “ crumbling ” which is com-posed of earth, and of soft solidified juices ; that ore “ hard ” which is composedof metallic minerals and moderately hard stones, such as for the most partare those which easily melt in a fire of the first and second orders, like leadand similar materials. I call that ore “ harder ” when with those I have alreadymentioned are combined various sorts of quartz, or stones which easily meltm fire of the third degree, or pyrites, or cadmia, or very hard marble. I callthat ore hardest, which is composed throughout the whole vein of these hardstones and compounds. The hanging or footwalls of a vein are hard, whencomposed of rock in which there are few stringers or seams ; harder, inwhich 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 softensx t- But the hardest rock of the hanging or footwall, however, is seldom ashard as the harder class of ore.

Miners dig out crumbling ore with the pick alone. When the metalhas not yet shown itself, they do not discriminate between the hangingwalland 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.