for a distance of several fathoms, then from the upper part of tunnels or even drifts that have already been driven, other drifts are driven again and again until that part of the vein is reached which does not yield metal. The timbering of these openings is done as follows: stulls are set at intervals into hitches in the hanging and footwall, and upon them smooth poles are laid continuously; and that they may be able to bear the weight, the stulls are generally a foot and a half thick. After the ore has been taken out and the mining of the vein is being done elsewhere, the rock then broken, especially if it cannot be taken away without great difficulty, is thrown into these openings among the timber, and the carriers of the ore are saved toil, and the owners save half the expense. This then, generally speaking, is the method by which everything relating to the timbering of shafts, tunnels, and drifts is carried out.
All that I have hitherto written is in part peculiar to venae profundae, and in part common to all kinds of veins; of what follows, part is specially applicable to venae dilatatae, part to venae cumulatae. But first I will describe how venae dilatatae should be mined. Where torrents, rivers, or streams have by inundations washed away part of the slope of a mountain or a hill, and have disclosed a vena dilatata, a tunnel should be driven first straight and narrow, and then wider, for nearly all the vein should be hewn away; and when this tunnel has been driven further, a shaft which supplies air should be sunk in the mountain or hill, and through it from time to time the ore, earth, and rock can be drawn up at less expense than if they be drawn out through the very great length of the tunnel; and even in those places to which the tunnel does not yet reach, miners dig shafts in order to open a vena dilatata which they conjecture must lie beneath the soil. In this way, when the upper layers are removed, they dig through rock sometimes of one kind and colour, sometimes of one kind but different colours, sometimes of different kinds but of one colour, and, lastly, of different kinds and different colours. The thickness of rock, both of each single stratum and of all combined, is uncertain, for the whole of the strata are in some places twenty fathoms deep, in others more than fifty; individual strata are in some places half a foot thick; in others, one, two, or more feet; in others, one, two, three, or more fathoms. For example, in those districts which lie at the foot of the Harz mountains, there are many different coloured strata, covering a copper vena dilatata.
When the soil has been stripped, first of all is disclosed a stratum which is red, but of a dull shade and of a thickness of twenty, thirty, or five and thirty fathoms. Then there is another stratum, also red, but of a light shade, which has usually a thickness of about two fathoms. Beneath this is a stratum of ash-coloured clay nearly a fathom thick, which, although it is not metalliferous, is reckoned a vein. Then follows a third stratum, which is ashy, and about three fathoms thick. Beneath this lies a vein of ashes to the thickness of five fathoms, and these ashes are mixed with rock of the same colour. Joined to the last, and underneath, comes a stratum, the fourth in number, dark in colour and a foot thick. Under this comes the fifth stratum, of a pale or yellowish colour, two feet thick; under-
