312 



MINING 



1470 



/, galleries, by means of which the workmen may turn round the mass e, in order 

 to form in the roof, t, an excavation in the direction of the deposit. 



g, rubbish behind the mass e. 



h h, two shafts leading from the first story, E F, to the upper stories of the work- 

 ings, as already stated. 



m, the wall, and t the roof, of the mineral-bed. 



In the second story, nV, the gallery of prolongation, T', Jigs. 1467, 1469, 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 fg. 1469 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 maybe 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 minor, 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. Some- 

 times, 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 work- 

 ings 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 accu- 

 mulate in a short time, at little cost. 



Fig. 1470 represents a section of the celebrated lead mines of Bleiberg 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. 



e, is the metalliferous valley, 

 running from east to west, be- 

 tween the two parallel valleys of 

 the Gail and the Drave, but at a 

 level considerably above the waters 

 of these rivers. 



/, g, is the direction of a great 

 many vertical beds of metalliferous 

 limestone. 



On considering the direction and 

 dip of the marly schist and metal- 

 liferous limestone, in the space w w, 

 to the west of the line 1, , it 

 would appear that a great portion of this system of mountains has suffered a slip 

 between 1, 5, and a parallel one towards the east; whereby, probably, that vertical 

 position of the strata has been produced which exists through a considerable extent. 

 The metalliferous limestone is covered to a certain thickness with a marly schist, and 

 other more recent rocks. It is in this sohist that the ' fire-marble,' known under the 

 name of the 1/umachella of Bleiberg, is quarried. This appears to be of Liassic age. 



The galena occurs at the bottom of this rock in flattened masses, or blocks of a con- 

 siderable volume, which are not separated from the rest of the calcareous beds by any 

 seam. It is accompanied by zinc ore (calamine), especially in the upper parts of the 

 mountain. 



Several of the workable masses are indicated by r, r 3 ; each presents itself as a 

 solid analogous to a very elongated ellipse, whose axis dips, not according to the 

 inclination of the surrounding rock, but to an oblique or intermediate line between 

 this inclination and the direction of the beds of limestone ; as shown by r w, r' /. 



The faults, called kluft (rent), at Bleiberg are visible on the surface of the ground. 

 Experienced miners have remarked that the rich masses occur more frequently in the 

 direction of these faults than elsewhere. 



It is in general by galleries cut horizontally in the body of the mountain, and at 

 different levels, sg, sf, that the miner advances towards the masses of ore r, r*. 

 Many of these galleries are 500 fathoms long before they roach a workable mass. 

 The several galleries are placed in communication by a few shafts, such as t ; but few 

 of these are sunk deeper than the level of the valley, e. 



The total length of the mines of Bleiberg is about 10,000 yards, parallel to the 

 valley e ; in which space there are 500 concessions granted by the Government to 



