310 



MINING 



cross-section of the gallery. In the two figures, a represents the rock, and b the 

 timbering ; round which there is a garniture of small spars or lathes for the purpose of 

 drainage and ventilation, with the view of promoting the durability of the wood-work. 



1464 



465 



The working of minerals by the mass is well exemplified a few leagues to the north 

 of Siegen, near Miisen (Rhenish Prussia), in a mine of iron and other metals, called 

 Stohlberg, which forms the main wealth of the country. The plan of working is 

 termed the excavation of a direct or transverse mass. It shows in its upper part the 

 danger of bad mining, and in its inferior portion, the regular workings, by whose 

 means art has eventually prevented the destruction of a precious mineral deposit. 



Fig. 1466 is a vertical section of the bed of ore, which is a direct mass of spathose 

 iron, contained in Devonian clay-slate, a, a, a, are pillars of the sparry ore 

 reserved to support the successive stages or floors, which are numbered 1, 2, 3, &c. ' 

 b, b, b, are excavations worked in the ore ; which exhibit at the present day several' 

 floors of arches, of greater or less magnitude, according to the localities. It may be 

 remarked, that where the metallic deposit forms one entire mass, rich in spathose iron 

 ore of good quality, there is generally given to the vaults a height of 3 fathoms ; 

 leaving a thickness over the roof of 2 fathoms, on account of the numerous fissures 



1466 



which pervade the mass. But where this mass is divided into three principal 

 branches, the roof of the vault has only 1J fathom of thickness, while the excava- 

 tion is 3 J fathoms high. In the . actual state of the workings, it may be estimated 

 that from all this direct mass, there is obtained no more out of every floor than 

 one-third of the mineral. Two-thirds remain as labours of reserve, which may be 

 resumed at some future day, in consequence of the regularity and the continuation 

 of the subterranean workings, e is a shaft for extraction, communicating below 

 with the gallery of efflux, k ; A is an upper gallery of drainage, which runs in 

 different directions (one only being visible in this section) over a length of 400 

 fathoms ; the lower gallery, k, runs 646 fathoms in a straight line ; m m, represents 

 the mass of sparry iron. 

 Figs. 1467, 1468, 1469, represent tho cross system of mining, which consists in 



