1avoid wearing
away their clothes and injuring their left shoulders they
usually bind on themselves small wooden cradles. For this reason, this
particular class of miners, in order to use their iron tools, are obliged to bend
their necks to the left, not infrequently having them twisted. Now these
veins also sometimes divide, and where these parts re-unite, ore of a richer and
a better quality is generally found; the same thing occurs where the stringers,
of which they are not altogether devoid, join with them, or cut them crosswise,
or divide them obliquely. To prevent a mountain or hill, which has in
this way been undermined, from subsiding by its weight, either some natural
pillars and arches are left, on which the pressure rests as on a foundation, or
timbering is done for support. Moreover, the materials which are dug out
and which are devoid of metal are removed in bowls, and are thrown back,
thus once more filling the caverns.
usually bind on themselves small wooden cradles. For this reason, this
particular class of miners, in order to use their iron tools, are obliged to bend
their necks to the left, not infrequently having them twisted. Now these
veins also sometimes divide, and where these parts re-unite, ore of a richer and
a better quality is generally found; the same thing occurs where the stringers,
of which they are not altogether devoid, join with them, or cut them crosswise,
or divide them obliquely. To prevent a mountain or hill, which has in
this way been undermined, from subsiding by its weight, either some natural
pillars and arches are left, on which the pressure rests as on a foundation, or
timbering is done for support. Moreover, the materials which are dug out
and which are devoid of metal are removed in bowls, and are thrown back,
thus once more filling the caverns.
Next, as to venæ cumulatæ.
These are dug by a somewhat different
method, for when one of these shows some metal at the top of the ground,
first of all one shaft is sunk; then, if it is worth while, around this one many
shafts are sunk and tunnels are driven into the mountain. If a torrent or
spring has torn fragments of metal from such a vein, a tunnel is first driven
into the mountain or hill for the purpose of searching for the ore; then
when it is found, a vertical shaft is sunk in it. Since the whole mountain, or
more especially the whole hill, is undermined, seeing that the whole of it is
composed of ore, it is necessary to leave the natural pillars and arches, or the
place is timbered. But sometimes when a vein is very hard it is broken by
fire, whereby it happens that the soft pillars break up, or the timbers are
burnt away, and the mountain by its great weight sinks into itself, and then
the shaft buildings are swallowed up in the great subsidence. Therefore,
about a vena cumulata it is advisable to sink some shafts which are not sub
ject to this kind of ruin, through which the materials that are excavated may
be carried out, not only while the pillars and underpinnings still remain whole
and solid, but also after the supports have been destroyed by fire and have
fallen. Since ore which has thus fallen must necessarily be broken by fire,
new shafts through which the smoke can escape must be sunk in the abyss.
At those places where stringers intersect, richer ore is generally obtained
from the mine; these stringers, in the case of tin mines, sometimes have in
them black stones the size of a walnut. If such a vein is found in a plain,
as not infrequently happens in the case of iron, many shafts are sunk, because
they cannot be sunk very deep. The work is carried on by this method
because the miners cannot drive a tunnel into a level plain of this kind.
method, for when one of these shows some metal at the top of the ground,
first of all one shaft is sunk; then, if it is worth while, around this one many
shafts are sunk and tunnels are driven into the mountain. If a torrent or
spring has torn fragments of metal from such a vein, a tunnel is first driven
into the mountain or hill for the purpose of searching for the ore; then
when it is found, a vertical shaft is sunk in it. Since the whole mountain, or
more especially the whole hill, is undermined, seeing that the whole of it is
composed of ore, it is necessary to leave the natural pillars and arches, or the
place is timbered. But sometimes when a vein is very hard it is broken by
fire, whereby it happens that the soft pillars break up, or the timbers are
burnt away, and the mountain by its great weight sinks into itself, and then
the shaft buildings are swallowed up in the great subsidence. Therefore,
about a vena cumulata it is advisable to sink some shafts which are not sub
ject to this kind of ruin, through which the materials that are excavated may
be carried out, not only while the pillars and underpinnings still remain whole
and solid, but also after the supports have been destroyed by fire and have
fallen. Since ore which has thus fallen must necessarily be broken by fire,
new shafts through which the smoke can escape must be sunk in the abyss.
At those places where stringers intersect, richer ore is generally obtained
from the mine; these stringers, in the case of tin mines, sometimes have in
them black stones the size of a walnut. If such a vein is found in a plain,
as not infrequently happens in the case of iron, many shafts are sunk, because
they cannot be sunk very deep. The work is carried on by this method
because the miners cannot drive a tunnel into a level plain of this kind.
There remain the stringers in which gold alone is sometimes found,
in the vicinity of rivers and streams, or in swamps. If upon the soil being
removed, many of these are found, composed of earth somewhat baked and
burnt, as may sometimes be seen in clay pits, there is some hope that gold
may be obtained from them, especially if several join together. But the
very point of junction must be pierced, and the length and width searched
for ore, and in these places very deep shafts cannot be sunk.
in the vicinity of rivers and streams, or in swamps. If upon the soil being
removed, many of these are found, composed of earth somewhat baked and
burnt, as may sometimes be seen in clay pits, there is some hope that gold
may be obtained from them, especially if several join together. But the
very point of junction must be pierced, and the length and width searched
for ore, and in these places very deep shafts cannot be sunk.
I have completed one part of this book, and now come to the other, in
which I will deal with the art of surveying. Miners measure the solid
which I will deal with the art of surveying. Miners measure the solid
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