subterranean levels are being thus extended, the shafts are again to be
continued downwards, until the depth of twenty fathoms, or one hundred
and twenty feet, has been attained. A second and lower set of levels are
then pushed out beneath and parallel to the first named. At the depth of
thirty fathoms, a third and still lower set of levels will extend
beneath and parallel to the second. This work of sinking vertical
shafts, and excavating horizontal levels to connect them, belongs to
what is denominated the "construction of the mine", and it is only after
this has been completed that the work of mining proper can be said to
begin.

The removal of the ore, as conducted from the levels by which access to
it has thus been gained, may be carried on either by "direct" or by
"inverted grades,"--that is, either by breaking it up from underneath,
or down from overhead, in each of the levels which have now been
described,--or, as it is more commonly called in mining language, by
"understoping" or by "overstoping." When the breadth of the lode is
equal to that of the level, it is perhaps not very material which plan
be adopted. But when, as at Oldham, Montague, or Tangier, the lodes are
only of moderate-width, and much barren rock, however soft and yielding,
has, of necessity, to be removed along with the ore, so as to give a
free passage for the miner through the whole extent of the drifts, we
shall easily understand that the working by inverted grades, or
"overstoping," is the only proper or feasible method. In this case, the
blasts being all made from the roof, or "back," as it is called, of the
drift, the barren or "dead" rock containing no gold is left on the floor
of the drift, and there is then only the labor and expense of bringing
the valuable quartz itself, a much less amount in bulk, to the surface
of the ground. The accumulating mass of the dead rock underfoot, will
then be constantly raising the floor of the drift, and as constantly