1for
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.
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-
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-