In the last book I have explained the methods of delimiting the meers
along each kind of vein, and the duties of mine officials. In this
book[1] I will in like manner explain the principles of underground
mining and the art of surveying. First then, I will proceed to deal with
those matters which pertain to the former heading, since both the
subject and methodical arrangement require it. And so I will describe
first of all the digging of shafts, tunnels, and drifts on _venae
profundae_; next I will discuss the good indications shown by
_canales_[2], by the materials which are dug out, and by the rocks; then
I will speak of the tools by which veins and rocks are broken down and
excavated; the method by which fire shatters the hard veins; and
further, of the machines with which water is drawn from the shafts and
air is forced into deep shafts and long tunnels, for digging is impeded
by the inrush of the former or the failure of the latter; next I will
deal with the two kinds of shafts, and with the making of them and of
tunnels; and finally, I will describe the method of mining _venae
dilatatae_, _venae cumulatae_, and stringers.
Now when a miner discovers a _vena profunda_ he begins sinking a shaft
and above it sets up a windlass, and builds a shed over the shaft to
prevent the rain from falling in, lest the men who turn the windlass be
numbed by the cold or troubled by the rain. The windlass men also place
their barrows in it, and the miners store their iron tools and other
implements therein. Next to the shaft-house another house is built,
where the mine foreman and the other workmen dwell, and in which are
stored the ore and other things which are dug out. Although some persons
build only one house, yet because sometimes boys and other living things
fall into the shafts, most miners deliberately place one house apart
from the other, or at least separate them by a wall.
[Illustration 103 (Shafts): Three vertical shafts, of which the first,
A, does not reach the tunnel; the second, B, reaches the tunnel; to the
third, C, the tunnel has not yet been driven. D--Tunnel.]
[Illustration 104 (Shafts): Three inclined shafts, of which A does not
yet reach the tunnel; B reaches the tunnel; to the third, C, the tunnel
has not yet been driven. D--Tunnel.]
Now a shaft is dug, usually two fathoms long, two-thirds of a fathom
wide, and thirteen fathoms deep; but for the purpose of connecting with
a tunnel which has already been driven in a hill, a shaft may be sunk to
a depth of only eight fathoms, at other times to fourteen, more or
less[3]. A shaft may be made vertical or inclined, according as the vein
which the miners follow in the course of digging is vertical or
inclined. A tunnel is a subterranean ditch driven lengthwise, and is
nearly twice as high as it is broad, and wide enough that workmen and
others may be able to pass and carry their loads. It is usually one and
a quarter fathoms high, while its width is about three and
three-quarters feet. Usually two workmen are required to drive it, one
of whom digs out the upper and the other the lower part, and the one
goes forward, while the other follows closely after. Each sits upon
small boards fixed securely from the footwall to the hangingwall, or if
the vein is a soft one, sometimes on a wedge-shaped plank fixed on to
the vein itself. Miners sink more inclined shafts than vertical, and
some of each kind do not reach to tunnels, while some connect with them.
But as for some shafts, though they have already been sunk to the
required depth, the tunnel which is to pierce the mountain may not yet
have been driven far enough to connect with them.
[Illustration 105 (Shafts): A--Shaft. B, C--Drift. D--Another shaft.
E--Tunnel. F--Mouth of tunnel.]
It is advantageous if a shaft connects with a tunnel, for then the
miners and other workmen carry on more easily the work they have
undertaken; but if the shaft is not so deep, it is usual to drift from
one or both sides of it. From these openings the owner or foreman
becomes acquainted with the veins and stringers that unite with the
principal vein, or cut across it, or divide it obliquely; however, my
discourse is now concerned mainly with _vena profunda_, but most of all
with the metallic material which it contains. Excavations of this kind
were called by the Greeks [Greek: kryptai] for, extending along after
the manner of a tunnel, they are entirely hidden within the ground.
This kind of an opening, however, differs from a tunnel in that it is
dark throughout its length, whereas a tunnel has a mouth open to
daylight.
I have spoken of shafts, tunnels, and drifts. I will now speak of the
indications given by the _canales_, by the materials which are dug out,
and by the rocks. These indications, as also many others which I will
explain, are to a great extent identical in _venae dilatatae_ and _venae
cumulatae_ with _venae profundae_.
When a stringer junctions with a main vein and causes a swelling, a
shaft should be sunk at the junction. But when we find the stringer
intersecting the main vein crosswise or obliquely, if it descends
vertically down to the depths of the earth, a second shaft should be
sunk to the point where the stringer cuts the main vein; but if the
stringer cuts it obliquely the shaft should be two or three fathoms
back, in order that the junction may be pierced lower down. At such
junctions lies the best hope of finding the ore for the sake of which we
explore the ground, and if ore has already been found, it is usually
found in much greater abundance at that spot. Again, if several
stringers descend into the earth, the miner, in order to pierce through
the point of contact, should sink the shaft in the midst of these
stringers, or else calculate on the most prominent one.
Since an inclined vein often lies near a vertical vein, it is advisable
to sink a shaft at the spot where a stringer or cross-vein cuts them
both; or where a _vena dilatata_ or a stringer _dilatata_ passes
through, for minerals are usually found there. In the same way we have a
good prospect of finding metal at the point where an inclined vein joins
a vertical one; this is why miners cross-cut the hangingwall or footwall
of a main vein, and in these openings seek for a vein which may junction
with the principal vein a few fathoms below. Nay, further, these same
miners, if no stringer or cross-vein intersects the main vein so that
they can follow it in their workings, even cross-cut through the solid
rock of the hangingwall or footwall. These cross-cuts are likewise
called "[Greek: kryptai]," whether the beginning of the opening which
has to be undertaken is made from a tunnel or from a drift. Miners have
some hope when only a cross vein cuts a main vein. Further, if a vein
which cuts the main vein obliquely does not appear anywhere beyond it,
it is advisable to dig into that side of the main vein toward which the
oblique vein inclines, whether the right or left side, that we may
ascertain if the main vein has absorbed it; if after cross-cutting six
fathoms it is not found, it is advisable to dig on the other side of the
main vein, that we may know for certain whether it has carried it
forward. The owners of a main vein can often dig no less profitably on
that side where the vein which cuts the main vein again appears, than
where it first cuts it; the owners of the intersecting vein, when that
is found again, recover their title, which had in a measure been lost.
The common miners look favourably upon the stringers which come from the
north and join the main vein; on the other hand, they look unfavourably
upon those which come from the south, and say that these do much harm to
the main vein, while the former improve it. But I think that miners
should not neglect either of them: as I showed in Book III, experience
does not confirm those who hold this opinion about veins, so now again
I could furnish examples of each kind of stringers rejected by the
common miners which have proved good, but I know this could be of little
or no benefit to posterity.
If the miners find no stringers or veins in the hangingwall or footwall
of the main vein, and if they do not find much ore, it is not worth
while to undertake the labour of sinking another shaft. Nor ought a
shaft to be sunk where a vein is divided into two or three parts, unless
the indications are satisfactory that those parts may be united and
joined together a little later. Further, it is a bad indication for a
vein rich in mineral to bend and turn hither and thither, for unless it
goes down again into the ground vertically or inclined, as it first
began, it produces no more metal; and even though it does go down again,
it often continues barren. Stringers which in their outcrops bear
metals, often disappoint miners, no metal being found in depth. Further,
inverted seams in the rocks are counted among the bad indications.
The miners hew out the whole of solid veins when they show clear
evidence of being of good quality; similarly they hew out the drusy[4]
veins, especially if the cavities are plainly seen to have formerly
borne metal, or if the cavities are few and small. They do not dig
barren veins through which water flows, if there are no metallic
particles showing; occasionally, however, they dig even barren veins
which are free from water, because of the pyrites which is devoid of all
metal, or because of a fine black soft substance which is like wool.
They dig stringers which are rich in metal, or sometimes, for the
purpose of searching for the vein, those that are devoid of ore which
lie near the hangingwall or footwall of the main vein. This then,
generally speaking, is the mode of dealing with stringers and veins.
Let us now consider the metallic material which is found in the
_canales_ of _venae profundae_, _venae dilatatae_, and _venae
cumulatae_, being in all these either cohesive and continuous, or
scattered and dispersed among them, or swelling out in bellying shapes,
or found in veins or stringers which originate from the main vein and
ramify like branches; but these latter veins and stringers are very
short, for after a little space they do not appear again. If we come
across a small quantity of metallic material it is an indication; but if
a large quantity, it is not an "indication," but the very thing for
which we explore the earth. As soon as a miner who searches for veins
discovers pure metal or minerals, or rich metallic material, or a great
abundance of material which is poor in metal, let him sink a shaft on
the spot without any delay. If the material appears more abundant or of
better quality on the one side, he will incline his digging in that
direction.
Gold, silver, copper, and quicksilver are often found native[5]; less
often iron and bismuth; almost never tin and lead. Nevertheless
tin-stone is not far removed from the pure white tin which is melted out
of them, and galena, from which lead is obtained, differs little from
that metal itself.
Now we may classify gold ores. Next after native gold, we come to the
_rudis_[6], of yellowish green, yellow, purple, black, or outside red
and inside gold colour. These must be reckoned as the richest ores,
because the gold exceeds the stone or earth in weight. Next come all
gold ores of which each one hundred _librae_ contains more than three
_unciae_ of gold[7]; for although but a small proportion of gold is
found in the earth or stone, yet it equals in value other metals of
greater weight.[8] All other gold ores are considered poor, because the
earth or stone too far outweighs the gold. A vein which contains a
larger proportion of silver than of gold is rarely found to be a rich
one. Earth, whether it be dry or wet, rarely abounds in gold; but in dry
earth there is more often found a greater quantity of gold, especially
if it has the appearance of having been melted in a furnace, and if it
is not lacking in scales resembling mica. The solidified juices, azure,
chrysocolla, orpiment, and realgar, also frequently contain gold.
Likewise native or _rudis_ gold is found sometimes in large, and
sometimes in small quantities in quartz, schist, marble, and also in
stone which easily melts in fire of the second degree, and which is
sometimes so porous that it seems completely decomposed. Lastly, gold is
found in pyrites, though rarely in large quantities.
When considering silver ores other than native silver, those ores are
classified as rich, of which each one hundred _librae_ contains more
than three _librae_ of silver. This quality comprises _rudis_ silver,
whether silver glance or ruby silver, or whether white, or black, or
grey, or purple, or yellow, or liver-coloured, or any other. Sometimes
quartz, schist, or marble is of this quality also, if much native or
_rudis_ silver adheres to it. But that ore is considered of poor quality
if three _librae_ of silver at the utmost are found in each one hundred
_librae_ of it[9]. Silver ore usually contains a greater quantity than
this, because Nature bestows quantity in place of quality; such ore is
mixed with all kinds of earth and stone compounds, except the various
kinds of _rudis_ silver; especially with pyrites, _cadmia metallica
fossilis_, galena, _stibium_, and others.
As regards other kinds of metal, although some rich ores are found,
still, unless the veins contain a large quantity of ore, it is very
rarely worth while to dig them. The Indians and some other races do
search for gems in veins hidden deep in the earth, but more often they
are noticed from their clearness, or rather their brilliancy, when
metals are mined. When they outcrop, we follow veins of marble by mining
in the same way as is done with rock or building-stones when we come
upon them. But gems, properly so called, though they sometimes have
veins of their own, are still for the most part found in mines and rock
quarries, as the lodestone in iron mines, the emery in silver mines, the
_lapis judaicus_, _trochites_, and the like in stone quarries where the
diggers, at the bidding of the owners, usually collect them from the
seams in the rocks.[10] Nor does the miner neglect the digging of
"extraordinary earths,"[11] whether they are found in gold mines,
silver mines, or other mines; nor do other miners neglect them if they
are found in stone quarries, or in their own veins; their value is
usually indicated by their taste. Nor, lastly, does the miner fail to
give attention to the solidified juices which are found in metallic
veins, as well as in their own veins, from which he collects and gathers
them. But I will say no more on these matters, because I have explained
more fully all the metals and mineral substances in the books "_De
Natura Fossilium_."
But I will return to the indications. If we come upon earth which is
like lute, in which there are particles of any sort of metal, native or
_rudis_, the best possible indication of a vein is given to miners, for
the metallic material from which the particles have become detached is
necessarily close by. But if this kind of earth is found absolutely
devoid of all metallic material, but fatty, and of white, green, blue,
and similar colours, they must not abandon the work that has been
started. Miners have other indications in the veins and stringers, which
I have described already, and in the rocks, about which I will speak a
little later. If the miner comes across other dry earths which contain
native or _rudis_ metal, that is a good indication; if he comes across
yellow, red, black, or some other "extraordinary" earth, though it is
devoid of mineral, it is not a bad indication. Chrysocolla, or azure, or
verdigris, or orpiment, or realgar, when they are found, are counted
among the good indications. Further, where underground springs throw up
metal we ought to continue the digging we have begun, for this points to
the particles having been detached from the main mass like a fragment
from a body. In the same way the thin scales of any metal adhering to
stone or rock are counted among the good indications. Next, if the veins
which are composed partly of quartz, partly of clayey or dry earth,
descend one and all into the depths of the earth together, with their
stringers, there is good hope of metal being found; but if the stringers
afterward do not appear, or little metallic material is met with, the
digging should not be given up until there is nothing remaining. Dark or
black or horn or liver-coloured quartz is usually a good sign; white is
sometimes good, sometimes no sign at all. But calc-spar, showing itself
in a _vena profunda_, if it disappears a little lower down is not a good
indication; for it did not belong to the vein proper, but to some
stringer. Those kinds of stone which easily melt in fire, especially if
they are translucent (fluorspar?), must be counted among the medium
indications, for if other good indications are present they are good,
but if no good indications are present, they give no useful
significance. In the same way we ought to form our judgment with regard
to gems. Veins which at the hangingwall and footwall have horn-coloured
quartz or marble, but in the middle clayey earth, give some hope;
likewise those give hope in which the hangingwall or footwall shows
iron-rust coloured earth, and in the middle greasy and sticky earth;
also there is hope for those which have at the hanging or footwall that
kind of earth which we call "soldiers' earth," and in the middle black
earth or earth which looks as if burnt. The special indication of gold
is orpiment; of silver is bismuth and _stibium_; of copper is verdigris,
_melanteria_, _sory_, _chalcitis_, _misy_, and vitriol; of tin is the
large pure black stones of 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[12].
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 into a dish placed underneath to prevent any of the metal from
falling to the ground. They break a hard vein loose from the footwall by
blows with a hammer upon the first kind of iron tool[13], all of which
are designated by appropriate names, and with the same tools they hew
away the hard hangingwall rock. They hew out the hangingwall rock in
advance more frequently, the rock of the footwall more rarely; and
indeed, when the rock of the footwall resists iron tools, the rock of
the hangingwall certainly cannot be broken unless it is allowable to
shatter it by fire. With regard to the harder veins which are tractable
to iron tools, and likewise with regard to the harder and hardest kind
of hangingwall rock, they generally attack them with more powerful iron
tools, in fact, with the fourth kind of iron tool, which are called by
their appropriate names; but if these are not ready to hand, they use
two or three iron tools of the first kind together. As for the hardest
kind of metal-bearing vein, which in a measure resists iron tools, if
the owners of the neighbouring mines give them permission, they break it
with fires. But if these owners refuse them permission, then first of
all they hew out the rock of the hangingwall, or of the footwall if it
be less hard; then they place timbers set in hitches in the hanging or
footwall, a little above the vein, and from the front and upper part,
where the vein is seen to be seamed with small cracks, they drive into
one of the little cracks one of the iron tools which I have mentioned;
then in each fracture they place four thin iron blocks, and in order to
hold them more firmly, if necessary, they place as many thin iron plates
back to back; next they place thinner iron plates between each two iron
blocks, and strike and drive them by turns with hammers, whereby the
vein rings with a shrill sound; and the moment when it begins to be
detached from the hangingwall or footwall rock, a tearing sound is
heard. As soon as this grows distinct the miners hastily flee away; then
a great crash is heard as the vein is broken and torn, and falls down.
By this method they throw down a portion of a vein weighing a hundred
pounds more or less. But if the miners by any other method hew the
hardest kind of vein which is rich in metal, there remain certain
cone-shaped portions which can be cut out afterward only with
difficulty. As for this knob of hard ore, if it is devoid of metal, or
if they are not allowed to apply fire to it, they proceed round it by
digging to the right or left, because it cannot be broken into by iron
wedges without great expense. Meantime, while the workmen are carrying
out the task they have undertaken, the depths of the earth often resound
with sweet singing, whereby they lighten a toil which is of the severest
kind and full of the greatest dangers.
As I have just said, fire shatters the hardest rocks, but the method of
its application is not simple[14]. For if a vein held in the rocks
cannot be hewn out because of the hardness or other difficulty, and the
drift or tunnel is low, a heap of dried logs is placed against the rock
and fired; if the drift or tunnel is high, two heaps are necessary, of
which one is placed above the other, and both burn until the fire has
consumed them. This force does not generally soften a large portion of
the vein, but only some of the surface. When the rock in the hanging or
footwall can be worked by the iron tools and the vein is so hard that it
is not tractable to the same tools, then the walls are hollowed out; if
this be in the end of the drift or tunnel or above or below, the vein is
then broken by fire, but not by the same method; for if the hollow is
wide, as many logs are piled into it as possible, but if narrow, only a
few. By the one method the greater fire separates the vein more
completely from the footwall or sometimes from the hangingwall, and by
the other, the smaller fire breaks away less of the vein from the rock,
because in that case the fire is confined and kept in check by portions
of the rock which surround the wood held in such a narrow excavation.
Further, if the excavation is low, only one pile of logs is placed in
it, if high, there are two, one placed above the other, by which plan
the lower bundle being kindled sets alight the upper one; and the fire
being driven by the draught into the vein, separates it from the rock
which, however hard it may be, often becomes so softened as to be the
most easily breakable of all. Applying this principle, Hannibal, the
Carthaginian General, imitating the Spanish miners, overcame the
hardness of the Alps by the use of vinegar and fire. Even if a vein is a
very wide one, as tin veins usually are, miners excavate into the small
streaks, and into those hollows they put dry wood and place amongst them
at frequent intervals sticks, all sides of which are shaved down
fan-shaped, which easily take light, and when once they have taken fire
communicate it to the other bundles of wood, which easily ignite.
[Illustration 120 (Fire-setting): A--Kindled logs. B--Sticks shaved down
fan-shaped. C--Tunnel.]
While the heated veins and rock are giving forth a foetid vapour and the
shafts or tunnels are emitting fumes, the miners and other workmen do
not go down in the mines lest the stench affect their health or actually
kill them, as I will explain in greater detail when I come to speak of
the evils which affect miners. The _Bergmeister_, in order to prevent
workmen from being suffocated, gives no one permission to break veins or
rock by fire in shafts or tunnels where it is possible for the poisonous
vapour and smoke to permeate the veins or stringers and pass through
into the neighbouring mines, which have no hard veins or rock. As for
that part of a vein or the surface of the rock which the fire has
separated from the remaining mass, if it is overhead, the miners
dislodge it with a crowbar, or if it still has some degree of hardness,
they thrust a smaller crowbar into the cracks and so break it down, but
if it is on the sides they break it with hammers. Thus broken off, the
rock tumbles down; or if it still remains, they break it off with picks.
Rock and earth on the one hand, and metal and ore on the other, are
filled into buckets separately and drawn up to the open air or to the
nearest tunnel. If the shaft is not deep, the buckets are drawn up by a
machine turned by men; if it is deep, they are drawn by machines turned
by horses.
It often happens that a rush of water or sometimes stagnant air hinders
the mining; for this reason miners pay the greatest attention to these
matters, just as much as to digging, or they should do so. The water of
the veins and stringers and especially of vacant workings, must be
drained out through the shafts and tunnels. Air, indeed, becomes
stagnant both in tunnels and in shafts; in a deep shaft, if it be by
itself, this occurs if it is neither reached by a tunnel nor connected
by a drift with another shaft; this occurs in a tunnel if it has been
driven too far into a mountain and no shaft has yet been sunk deep
enough to meet it; in neither case can the air move or circulate. For
this reason the vapours become heavy and resemble mist, and they smell
of mouldiness, like a vault or some underground chamber which has been
completely closed for many years. This suffices to prevent miners from
continuing their work for long in these places, even if the mine is full
of silver or gold, or if they do continue, they cannot breathe freely
and they have headaches; this more often happens if they work in these
places in great numbers, and bring many lamps, which then supply them
with a feeble light, because the foul air from both lamps and men make
the vapours still more heavy.
A small quantity of water is drawn from the shafts by machines of
different kinds which men turn or work. If so great a quantity has
flowed into one shaft as greatly to impede mining, another shaft is sunk
some fathoms distant from the first, and thus in one of them work and
labour are carried on without hindrance, and the water is drained into
the other, which is sunk lower than the level of the water in the first
one; then by these machines or by those worked by horses, the water is
drawn up into the drain and flows out of the shaft-house or the mouth of
the nearest tunnel. But when into the shaft of one mine, which is sunk
more deeply, there flows all the water of all the neighbouring mines,
not only from that vein in which the shaft is sunk, but also from other
veins, then it becomes necessary for a large sump to be made to collect
the water; from this sump the water is drained by machines which draw it
through pipes, or by ox-hides, about which I will say more in the next
book. The water which pours into the tunnels from the veins and
stringers and seams in the rocks is carried away in the drains.
Air is driven into the extremities of deep shafts and long tunnels by
powerful blowing machines, as I will explain in the following book,
which will deal with these machines also. The outer air flows
spontaneously into the caverns of the earth, and when it can pass
through them comes out again. This, however, comes about in different
ways, for in spring and summer it flows into the deeper shafts,
traverses the tunnels or drifts, and finds its way out of the shallower
shafts; similarly at the same season it pours into the lowest tunnel
and, meeting a shaft in its course, turns aside to a higher tunnel and
passes out therefrom; but in autumn and winter, on the other hand, it
enters the upper tunnel or shaft and comes out at the deeper ones. This
change in the flow of air currents occurs in temperate regions at the
beginning of spring and the end of autumn, but in cold regions at the
end of spring and the beginning of autumn. But at each period, before
the air regularly assumes its own accustomed course, generally for a
space of fourteen days it undergoes frequent variations, now blowing
into an upper shaft or tunnel, now into a lower one. But enough of this,
let us now proceed to what remains.
There are two kinds of shafts, one of the depth already described, of
which kind there are usually several in one mine; especially if the mine
is entered by a tunnel and is metal-bearing. For when the first tunnel
is connected with the first shaft, two new shafts are sunk; or if the
inrush of water hinders sinking, sometimes three are sunk; so that one
may take the place of a sump and the work of sinking which has been
begun may be continued by means of the remaining two shafts; the same is
done in the case of the second tunnel and the third, or even the fourth,
if so many are driven into a mountain. The second kind of shaft is very
deep, sometimes as much as sixty, eighty, or one hundred fathoms. These
shafts continue vertically toward the depths of the earth, and by means
of a hauling-rope the broken rock and metalliferous ores are drawn out
of the mine; for which reason miners call them vertical shafts. Over
these shafts are erected machines by which water is extracted; when they
are above ground the machines are usually worked by horses, but when
they are in tunnels, other kinds are used which are turned by
water-power. Such are the shafts which are sunk when a vein is rich in
metal.
Now shafts, of whatever kind they may be, are supported in various ways.
If the vein is hard, and also the hanging and footwall rock, the shaft
does not require much timbering, but timbers are placed at intervals,
one end of each of which is fixed in a hitch cut into the rock of the
hangingwall and the other fixed into a hitch cut in the footwall. To
these timbers are fixed small timbers along the footwall, to which are
fastened the lagging and ladders. The lagging is also fixed to the
timbers, both to those which screen off the shaft on the ends from the
vein, and to those which screen off the rest of the shaft from that part
in which the ladders are placed. The lagging on the sides of the shaft
confine the vein, so as to prevent fragments of it which have become
loosened by water from dropping into the shaft and terrifying, or
injuring, or knocking off the miners and other workmen who are going up
or down the ladders from one part of the mine to another. For the same
reason, the lagging between the ladders and the haulage-way on the other
hand, confine and shut off from the ladders the fragments of rock which
fall from the buckets or baskets while they are being drawn up;
moreover, they make the arduous and difficult descent and ascent to
appear less terrible, and in fact to be less dangerous.
[Illustration 123 (Timbering Shafts): A--Wall plates. B--Dividers.
C--Long end posts. D--End plates.]
If a vein is soft and the rock of the hanging and footwalls is weak, a
closer structure is necessary; for this purpose timbers are joined
together, in rectangular shapes and placed one after the other without a
break. These are arranged on two different systems; for either the
square ends of the timbers, which reach from the hangingwall to the
footwall, are fixed into corresponding square holes in the timbers which
lie along the hanging or footwall, or the upper part of the end of one
and the lower part of the end of the other are cut out and one laid on
the other. The great weight of these joined timbers is sustained by
stout beams placed at intervals, which are deeply set into hitches in
the footwall and hangingwall, but are inclined. In order that these
joined timbers may remain stationary, wooden wedges or poles cut from
trees are driven in between the timbers and the vein and the hangingwall
and the footwall; and the space which remains empty is filled with loose
dirt. If the hanging and footwall rock is sometimes hard and sometimes
soft, and the vein likewise, solid joined timbers are not used, but
timbers are placed at intervals; and where the rock is soft and the vein
crumbling, carpenters put in lagging between them and the wall rocks,
and behind these they fill with loose dirt; by this means they fill up
the void.
When a very deep shaft, whether vertical or inclined, is supported by
joined timbers, then, since they are sometimes of bad material and a
fall is threatened, for the sake of greater firmness three or four pairs
of strong end posts are placed between these, one pair on the
hangingwall side, the other on the footwall side. To prevent them from
falling out of position and to make them firm and substantial, they are
supported by frequent end plates, and in order that these may be more
securely fixed they are mortised into the posts. Further, in whatever
way the shaft may be timbered, dividers are placed upon the wall plates,
and to these is fixed lagging, and this marks off and separates the
ladder-way from the remaining part of the shaft. If a vertical shaft is
a very deep one, planks are laid upon the timbers by the side of the
ladders and fixed on to the timbers, in order that the men who are going
up or down may sit or stand upon them and rest when they are tired. To
prevent danger to the shovellers from rocks which, after being drawn up
from so deep a shaft fall down again, a little above the bottom of the
shaft small rough sticks are placed close together on the timbers, in
such a way as to cover the whole space of the shaft except the
ladder-way. A hole, however, is left in this structure near the
footwall, which is kept open so that there may be one opening to the
shaft from the bottom, that the buckets full of the materials which have
been dug out may be drawn from the shaft through it by machines, and may
be returned to the same place again empty; and so the shovellers and
other workmen, as it were hiding beneath this structure, remain
perfectly safe in the shaft.
[Illustration 125 (Timbering Tunnels): A--Posts. B--Caps. C--Sills.
D--Doors. E--Lagging. F--Drains.]
In mines on one vein there are driven one, two, or sometimes three or
more tunnels, always one above the other. If the vein is solid and hard,
and likewise the hanging and footwall rock, no part of the tunnel needs
support, beyond that which is required at the mouth, because at that
spot there is not yet solid rock; if the vein is soft, and the hanging
and footwall rock are likewise soft, the tunnel requires frequent strong
timbering, which is provided in the following way. First, two dressed
posts are erected and set into the tunnel floor, which is dug out a
little; these are of medium thickness, and high enough that their ends,
which are cut square, almost touch the top of the tunnel; then upon them
is placed a smaller dressed cap, which is mortised into the heads of the
posts; at the bottom, other small timbers, whose ends are similarly
squared, are mortised into the posts. At each interval of one and a half
fathoms, one of these sets is erected; each one of these the miners call
a "little doorway," because it opens a certain amount of passage way;
and indeed, when necessity requires it, doors are fixed to the timbers
of each little doorway so that it can be closed. Then lagging of planks
or of poles is placed upon the caps lengthwise, so as to reach from one
set of timbers to another, and is laid along the sides, in case some
portion of the body of the mountain may fall, and by its bulk impede
passage or crush persons coming in or out. Moreover, to make the timbers
remain stationary, wooden pegs are driven between them and the sides of
the tunnel. Lastly, if rock or earth are carried out in wheelbarrows,
planks joined together are laid upon the sills; if the rock is hauled
out in trucks, then two timbers three-quarters of a foot thick and wide
are laid on the sills, and, where they join, these are usually hollowed
out so that in the hollow, as in a road, the iron pin of the truck may
be pushed along; indeed, because of this pin in the groove, the truck
does not leave the worn track to the left or right. Beneath the sills
are the drains through which the water flows away.
Miners timber drifts in the same way as tunnels. These do not, however,
require sill-pieces, or drains; for the broken rock is not hauled very
far, nor does the water have far to flow. If the vein above is
metal-bearing, as it sometimes is 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; underneath
which is the sixth stratum, likewise dark, but rough and three feet
thick. Afterward occurs the seventh stratum, likewise of dark colour,
but still darker than the last, and two feet thick. This is followed by
an eighth stratum, ashy, rough, and a foot thick. This kind, as also the
others, is sometimes distinguished by stringers of the stone which
easily melts in fire of the second order. Beneath this is another ashy
rock, light in weight, and five feet thick. Next to this comes a lighter
ash-coloured one, a foot thick; beneath this lies the eleventh stratum,
which is dark and very much like the seventh, and two feet thick. Below
the last is a twelfth stratum of a whitish colour and soft, also two
feet thick; the weight of this rests on a thirteenth stratum, ashy and
one foot thick, whose weight is in turn supported by a fourteenth
stratum, which is blackish and half a foot thick. There follows this,
another stratum of black colour, likewise half a foot thick, which is
again followed by a sixteenth stratum still blacker in colour, whose
thickness is also the same. Beneath this, and last of all, lies the
cupriferous stratum, black coloured and schistose, in which there
sometimes glitter scales of gold-coloured pyrites in the very thin
sheets, which, as I said elsewhere, often take the forms of various
living things.[15]
The miners mine out a _vena dilatata_ laterally and longitudinally by
driving a low tunnel in it, and if the nature of the work and place
permit, they sink also a shaft in order to discover whether there is a
second vein beneath the first one; for sometimes beneath it there are
two, three, or more similar metal-bearing veins, and these are excavated
in the same way laterally and longitudinally. They generally mine _venae
dilatatae_ lying down; and to avoid 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.
Next, as to _venae cumulatae_. 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 subject 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.
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
mass of the mountains in order that the owners may lay out their plans,
and that their workmen may not encroach on other people's possessions.
The surveyor either measures the interval not yet wholly dug through,
which lies between the mouth of a tunnel and a shaft to be sunk to that
depth, or between the mouth of a shaft and the tunnel to be driven to
that spot which lies under the shaft, or between both, if the tunnel is
neither so long as to reach to the shaft, nor the shaft so deep as to
reach to the tunnel; and thus on both sides work is still to be done. Or
in some cases, within the tunnels and drifts, are to be fixed the
boundaries of the meers, just as the _Bergmeister_ has determined the
boundaries of the same meers above ground.[16]
Each method of surveying depends on the measuring of triangles. A small
triangle should be laid out, and from it calculations must be made
regarding a larger one. Most particular care must be taken that we do
not deviate at all from a correct measuring; for if, at the beginning,
we are drawn by carelessness into a slight error, this at the end will
produce great errors. Now these triangles are of many shapes, since
shafts differ among themselves and are not all sunk by one and the same
method into the depths of the earth, nor do the slopes of all mountains
come down to the valley or plain in the same manner. For if a shaft is
vertical, there is a triangle with a right angle, which the Greeks call
[Greek: orthogonion] and this, according to the inequalities of the
mountain slope, has either two equal sides or three unequal sides. The
Greeks call the former [Greek: trigonon isoskeles] the latter [Greek:
skalenon] for a right angle triangle cannot have three equal sides. If a
shaft is inclined and sunk in the same vein in which the tunnel is
driven, a triangle is likewise made with a right angle, and this again,
according to the various inequalities of the mountain slope, has either
two equal or three unequal sides. But if a shaft is inclined and is sunk
in one vein, and a tunnel is driven in another vein, then a triangle
comes into existence which has either an obtuse angle or all acute
angles. The former the Greeks call [Greek: amblygonion], the latter
[Greek: oxygonion]. That triangle which has an obtuse angle cannot have
three equal sides, but in accordance with the different mountain slopes
has either two equal sides or three unequal sides. That triangle which
has all acute angles in accordance with the different mountain slopes
has either three equal sides, which the Greeks call [Greek: trigonon
isopleuron] or two equal sides or three unequal sides.
The surveyor, as I said, employs his art when the owners of the mines
desire to know how many fathoms of the intervening ground require to be
dug; when a tunnel is being driven toward a shaft and does not yet reach
it; or when the shaft has not yet been sunk to the depth of the bottom
of the tunnel which is under it; or when neither the tunnel reaches to
that point, nor has the shaft been sunk to it. It is of importance that
miners should know how many fathoms remain from the tunnel to the shaft,
or from the shaft to the tunnel, in order to calculate the expenditure;
and in order that the owners of a metal-bearing mine may hasten the
sinking of a shaft and the excavation of the metal, before the tunnel
reaches that point and the tunnel owners excavate part of the metal by
any right of their own; and on the other hand, it is important that the
owners of a tunnel may similarly hasten their driving before a shaft can
be sunk to the depth of a tunnel, so that they may excavate the metal to
which they will have a right.
[Illustration 131 (Surveying): A--Upright forked posts. B--Pole over the
posts. C--Shaft. D--First cord. E--Weight of first cord. F--Second cord.
G--Same fixed ground. H--Head of first cord. I--Mouth of tunnel.
K--Third cord. L--Weight of third cord. M--First side minor triangle.
N--Second side minor triangle. O--Third side minor triangle. P--The
minor triangle.]
The surveyor, first of all, if the beams of the shaft-house do not give
him the opportunity, sets a pair of forked posts by the sides of the
shaft in such a manner that a pole may be laid across them. Next, from
the pole he lets down into the shaft a cord with a weight attached to
it. Then he stretches a second cord, attached to the upper end of the
first cord, right down along the slope of the mountain to the bottom of
the mouth of the tunnel, and fixes it to the ground. Next, from the same
pole not far from the first cord, he lets down a third cord, similarly
weighted, so that it may intersect the second cord, which descends
obliquely. Then, starting from that point where the third cord cuts the
second cord which descends obliquely to the mouth of the tunnel, he
measures the second cord upward to where it reaches the end of the
first cord, and makes a note of this first side of the minor
triangle[17]. Afterward, starting again from that point where the third
cord intersects the second cord, he measures the straight space which
lies between that point and the opposite point on the first cord, and in
that way forms the minor triangle, and he notes this second side of the
minor triangle in the same way as before. Then, if it is necessary, from
the angle formed by the first cord and the second side of the minor
triangle, he measures upward to the end of the first cord and also makes
a note of this third side of the minor triangle. The third side of the
minor triangle, if the shaft is vertical or inclined and is sunk on the
same vein in which the tunnel is driven, will necessarily be the same
length as the third cord above the point where it intersects the second
cord; and so, as often as the first side of the minor triangle is
contained in the length of the whole cord which descends obliquely, so
many times the length of the second side of the minor triangle indicates
the distance between the mouth of the tunnel and the point to which the
shaft must be sunk; and similarly, so many times the length of the third
side of the minor triangle gives the distance between the mouth of the
shaft and the bottom of the tunnel.
When there is a level bench on the mountain slope, the surveyor first
measures across this with a measuring-rod; then at the edges of this
bench he sets up forked posts, and applies the principle of the triangle
to the two sloping parts of the mountain; and to the fathoms which are
the length of that part of the tunnel determined by the triangles, he
adds the number of fathoms which are the width of the bench. But if
sometimes the mountain side stands up, so that a cord cannot run down
from the shaft to the mouth of the tunnel, or, on the other hand, cannot
run up from the mouth of the tunnel to the shaft, and, therefore, one
cannot connect them in a straight line, the surveyor, in order to fix an
accurate triangle, measures the mountain; and going downward he
substitutes for the first part of the cord a pole one fathom long, and
for the second part a pole half a fathom long. Going upward, on the
contrary, for the first part of the cord he substitutes a pole half a
fathom long, and for the next part, one a whole fathom long; then where
he requires to fix his triangle he adds a straight line to these angles.
[Illustration 133 (Surveying Triangle): A triangle having a right angle
and two equal sides.]
To make this system of measuring clear and more explicit, I will proceed
by describing each separate kind of triangle. When a shaft is vertical
or inclined, and is sunk in the same vein on which the tunnel is driven,
there is created, as I said, a triangle containing a right angle. Now if
the minor triangle has the two sides equal, which, in accordance with
the numbering used by surveyors, are the second and third sides, then
the second and third sides of the major triangle will be equal; and so
also the intervening distances will be equal which lie between the mouth
of the tunnel and the bottom of the shaft, and which lie between the
mouth of the shaft and the bottom of the tunnel. For example, if the
first side of the minor triangle is seven feet long and the second and
likewise the third sides are five feet, and the length shown by the
cord for the side of the major triangle is 101 times seven feet, that is
117 fathoms and five feet, then the intervening space, of course,
whether the whole of it has been already driven through or has yet to be
driven, will be one hundred times five feet, which makes eighty-three
fathoms and two feet. Anyone with this example of proportions will be
able to construct the major and minor triangles in the same way as I
have done, if there be the necessary upright posts and cross-beams. When
a shaft is vertical the triangle is absolutely upright; when it is
inclined and is sunk on the same vein in which the tunnel is driven, it
is inclined toward one side. Therefore, if a tunnel has been driven into
the mountain for sixty fathoms, there remains a space of ground to be
penetrated twenty-three fathoms and two feet long; for five feet of the
second side of the major triangle, which lies above the mouth of the
shaft and corresponds with the first side of the minor triangle, must
not be added. Therefore, if the shaft has been sunk in the middle of the
head meer, a tunnel sixty fathoms long will reach to the boundary of the
meer only when the tunnel has been extended a further two fathoms and
two feet; but if the shaft is located in the middle of an ordinary meer,
then the boundary will be reached when the tunnel has been driven a
further length of nine fathoms and two feet. Since a tunnel, for every
one hundred fathoms of length, rises in grade one fathom, or at all
events, ought to rise as it proceeds toward the shaft, one more fathom
must always be taken from the depth allowed to the shaft, and one added
to the length allowed to the tunnel. Proportionately, because a tunnel
fifty fathoms long is raised half a fathom, this amount must be taken
from the depth of the shaft and added to the length of the tunnel. In
the same way if a tunnel is one hundred or fifty fathoms shorter or
longer, the same proportion also must be taken from the depth of the one
and added to the length of the other. For this reason, in the case
mentioned above, half a fathom and a little more must be added to the
distance to be driven through, so that there remain twenty-three
fathoms, five feet, two palms, one and a half digits and a fifth of a
digit; that is, if even the minutest proportions are carried out; and
surveyors do not neglect these without good cause. Similarly, if the
shaft is seventy fathoms deep, in order that it may reach to the bottom
of the tunnel, it still must be sunk a further depth of thirteen fathoms
and two feet, or rather twelve fathoms and a half, one foot, two digits,
and four-fifths of half a digit. And in this instance five feet must be
deducted from the reckoning, because these five feet complete the third
side of the minor triangle, which is above the mouth of the shaft, and
from its depth there must be deducted half a fathom, two palms, one and
a half digits and the fifth part of half a digit. But if the tunnel has
been driven to a point where it is under the shaft, then to reach the
roof of the tunnel the shaft must still be sunk a depth of eleven
fathoms, two and a half feet, one palm, two digits, and four-fifths of
half a digit.
[Illustration 134 (Surveying Triangle): A triangle having a right angle
and three unequal sides.]
If a minor triangle is produced of the kind having three unequal sides,
then the sides of the greater triangle cannot be equal; that is, if the
first side of the minor triangle is eight feet long, the second six feet
long, and the third five feet long, and the cord along the side of the
greater triangle, not to go too far from the example just given, is one
hundred and one times eight feet, that is, one hundred and thirty-four
fathoms and four feet, the distance which lies between the mouth of the
tunnel and the bottom of the shaft will occupy one hundred times six
feet in length, that is, one hundred fathoms. The distance between the
mouth of the shaft and the bottom of the tunnel is one hundred times
five feet, that is, eighty-three fathoms and two feet. And so, if the
tunnel is eighty-five fathoms long, the remainder to be driven into the
mountain is fifteen fathoms long, and here, too, a correction in
measurement must be taken from the depth of the shaft and added to the
length of the tunnel; what this is precisely, I will pursue no further,
since everyone having a small knowledge of arithmetic can work it out.
If the shaft is sixty-seven fathoms deep, in order that it may reach the
bottom of the tunnel, the further distance required to be sunk amounts
to sixteen fathoms and two feet.
[Illustration 135a (Surveying Triangle): Triangle having an obtuse angle
and two equal sides.]
The surveyor employs this same method in measuring the mountain, whether
the shaft and tunnel are on one and the same vein, whether the vein is
vertical or inclined, or whether the shaft is on the principal vein and
the tunnel on a transverse vein descending vertically to the depths of
the earth; in the latter case the excavation is to be made where the
transverse vein cuts the vertical vein. If the principal vein descends
on an incline and the cross-vein descends vertically, then a minor
triangle is created having one obtuse angle or all three angles acute.
If the minor triangle has one angle obtuse and the two sides which are
the second and third are equal, then the second and third sides of the
major triangle will be equal, so that if the first side of the minor
triangle is nine feet, the second, and likewise the third, will be five
feet. Then the first side of the major triangle will be one hundred and
one times nine feet, or one hundred and fifty-one and one-half fathoms,
and each of the other sides of the major triangle will be one hundred
times five feet, that is, eighty-three fathoms and two feet. But when
the first shaft is inclined, generally speaking, it is not deep; but
there are usually several, all inclined, and one always following the
other. Therefore, if a tunnel is seventy-seven fathoms long, it will
reach to the middle of the bottom of a shaft when six fathoms and two
feet further have been sunk. But if all such inclined shafts are
seventy-six fathoms deep, in order that the last one may reach the
bottom of the tunnel, a depth of seven fathoms and two feet remains to
be sunk.
[Illustration 135b (Surveying Triangle): Triangle having an obtuse angle
and three unequal sides.]
If a minor triangle is made which has an obtuse angle and three unequal
sides, then again the sides of the large triangle cannot be equal. For
example, if the first side of the minor triangle is six feet long, the
second three feet, and the third four feet, and the cord along the side
of the greater triangle one hundred and one times six feet, that is, one
hundred and one fathoms, the distance between the mouth of the tunnel
and the bottom of the last shaft will be a length one hundred times
three feet, or fifty fathoms; but the depth that lies between the mouth
of the first shaft and the bottom of the tunnel is one hundred times
four feet, or sixty-six fathoms and four feet. Therefore, if a tunnel is
forty-four fathoms long, the remaining distance to be driven is six
fathoms. If the shafts are fifty-eight fathoms deep, the newest will
touch the bottom of the tunnel when eight fathoms and four feet have
been sunk.
[Illustration 136a (Surveying Triangle): A triangle having all its
angles acute and its three sides equal.]
If a minor triangle is produced which has all its angles acute and its
three sides equal, then necessarily the second and third sides of the
minor triangle will be equal, and likewise the sides of the major
triangle frequently referred to will be equal. Thus if each side of the
minor triangle is six feet long, and the cord measurement for the side
of the major triangle is one hundred and one times six feet, that is,
one hundred and one fathoms, then both the distances to be dug will be
one hundred fathoms. And thus if the tunnel is ninety fathoms long, it
will reach the middle of the bottom of the last shaft when ten fathoms
further have been driven. If the shafts are ninety-five fathoms deep,
the last will reach the bottom of the tunnel when it is sunk a further
depth of five fathoms.
[Illustration 136b (Surveying Triangle): Triangle having all its angles
acute and two sides equal, A, B, unequal side C.]
If a triangle is made which has all its angles acute, but only two sides
equal, namely, the first and third, then the second and third sides are
not equal; therefore the distances to be dug cannot be equal. For
example, if the first side of the minor triangle is six feet long, and
the second is four feet, and the third is six feet, and the cord
measurement for the side of the major triangle is one hundred and one
times six feet, that is, one hundred and one fathoms, then the distance
between the mouth of the tunnel and the bottom of the last shaft will be
sixty-six fathoms and four feet. But the distance from the mouth of the
first shaft to the bottom of the tunnel is one hundred fathoms. So if
the tunnel is sixty fathoms long, the remaining distance to be driven
into the mountain is six fathoms and four feet. If the shaft is
ninety-seven fathoms deep, the last one will reach the bottom of the
tunnel when a further depth of three fathoms has been sunk.
[Illustration 137 (Surveying Triangle): A triangle having all its angles
acute and its three sides unequal.]
If a minor triangle is produced which has all its angles acute, but its
three sides unequal, then again the distances to be dug cannot be equal.
For example, if the first side of the minor triangle is seven feet long,
the second side is four feet, and the third side is six feet, and the
cord measurement for the side of the major triangle is one hundred and
one times seven feet or one hundred and seventeen fathoms and four feet,
the distance between the mouth of the tunnel and the bottom of the last
shaft will be four hundred feet or sixty-six fathoms, and the depth
between the mouth of the first shaft and the bottom of the tunnel will
be one hundred fathoms. Therefore, if a tunnel is fifty fathoms long, it
will reach the middle of the bottom of the newest shaft when it has been
driven sixteen fathoms and four feet further. But if the shafts are then
ninety-two fathoms deep, the last shaft will reach the bottom of the
tunnel when it has been sunk a further eight fathoms.
This is the method of the surveyor in measuring the mountain, if the
principal vein descends inclined into the depths of the earth or the
transverse vein is vertical. But if they are both inclined, the surveyor
uses the same method, or he measures the slope of the mountain
separately from the slope of the shaft. Next, if a transverse vein in
which a tunnel is driven does not cut the principal vein in that spot
where the shaft is sunk, then it is necessary for the starting point of
the survey to be in the other shaft in which the transverse vein cuts
the principal vein. But if there be no shaft on that spot where the
outcrop of the transverse vein cuts the outcrop of the principal vein,
then the surface of the ground which lies between the shafts must be
measured, or that between the shaft and the place where the outcrop of
the one vein intersects the outcrop of the other.
[Illustration 138 (Hemicycle): A--Waxed semicircle of the hemicycle.
B--Semicircular lines. C--Straight lines. D--Line measuring the half.
E--Line measuring the whole. F--Tongue.]
[Illustration 138A (Surveying Rods): A--Lines of the rod which separate
minor spaces. B--Lines of the rod which separate major spaces.]