g, rubbish behind the mass e.
k k, two shafts leading from the first story E F, to the upper stories of the workings, as already stated.
m, the wall, and t the roof of the mineral bed.
In the second story E′ F′, the gallery of prolongation F′, [figs. 728.] and [730.], is not entirely perforated; but it is further advanced than that of the third story, which, in its turn, is more than the gallery of the fourth.
From this arrangement there is produced upon [fig. 730.] the general aspect of a working by reversed steps.
Whenever the workings of the cuts c in the first story are finished, those of the second, a′ a′, may be begun in the second; and thus by mounting from story to story, the whole deposit of ore may be taken out and replaced with rubbish. One great advantage of this method is, that nothing is lost; but it is not the only one. The facilities offered by the system of cross workings for disposing of the rubbish, most frequently a nuisance to the miner, and expensive to get rid of, the solidity which it procures by the banking up, the consequent economy of timbering, and saving of expense in the excavation of the rock, reckoning from the second story, are so many important circumstances which recommend this mode of mining. Sometimes, indeed, rubbish may be wanted to fill up, but this may always be procured by a few accessory perforations; it being easy to establish in the vicinity of the workings a vast excavation in the form of a vault, or kind of subterraneous quarry, which may be allowed to fall in with proper precautions, and where rubbish will thus accumulate in a short time, at little cost.
[Fig. 731.] represents a section of the celebrated lead mines of Bleyberg in Carinthia, not far from Villach.
b, c, is the ridge of the mountains of compact limestone, in whose bosom the workings are carried on.