314 



MINING 



1474 



5. Clay, usually red, containing veins of white gypsum, and fine crystals of selenite. 



6. Massive gypsum of recent formation. 



7. Fetid limestone, compact and blackish grey, 

 or cellular and yellowish grey. 



8. Pulverulent limestone, with solid fragments 

 interspersed. 



9. Compact marl-limestone, or Zechstein, which 

 changes from a brownish colour above to a 

 blackish schist below, as it comes nearer the 

 cupreous schist, which seems to form a part of it. 



10. Cupreous schist (Kupersckiefer), of which 

 the bottom portion, from 4 to 6 inches thick, is 

 that selected for metallurgic operations. Be- 

 neath it is found the usual wall or bed of sand- 

 stone. A vein of cobalt ore, a, which is rich 

 only in the greyish-white sandstone (weisse 

 Licgende), traverses and deranges the beds 

 wherever it comes. 



Of working Mines by Fire. The celebrated mine worked since the 10th century in 

 the moiiHtaia called Rammelsberg, in the Hartz, to the south of Goslar, presents a 

 stratified mass of ores, among the beds of the rock which constitute that mountain. 

 The mineral deposit is situated in the earth like an enormous inverted wedge, so that 

 its thickness (power), inconsiderable near the surface of the ground, increases as it 

 descends. At about 100 yards from its outcrop, reckoning in the direction of the 

 slope of the deposit, it is divided into two portions or branches, which are separated 

 from each other, throughout the whole known depth, by a mass of very hard clay- 

 slate, which passes into flinty slate. The substances composing the workable mass 

 are copper and iron pyrites, with sulphuret of lead (galena), accompanied by quartz, 

 carbonate of lime, compact sulphate of baryta, and sometimes grey copper ore, sul- 

 phuret of zinc, and arsenical pyrites. The ores of lead and copper contain silver and 

 gold, but in small proportion, particularly as to the last. 



A mine so ancient as that of Kammelsberg, and which was formerly divided among 

 several adventurous companies, cannot fail to present a great many shafts and exca- 

 vations; but, out of the 15 pits, only two are employed for the present workings, 

 namely, those marked A B and E F in fig. 1475, by which the whole extraction and 



1475 



drainage are executed. The general system of exploitation by fire, as practised in 

 this mine, consists of the following operations : 



1. An advance is made towards the deposits of ore, successively at different levels, 

 by transverse galleries, which proceed from the shaft of extraction, and terminate at 

 the walls of the stratiform mass. 



2. There are formed in the level to be worked Large vaults in the heart of the ore, 

 by means of fire, as we shall presently describe. 



3. The floor of these vaults is raised up by means of terraces, formed from the 

 rubbish in proportion as the roof is scooped out. 



4. The ores detached by the fire from their bed are picked and gathered ; some- 

 times the larger blocks are blasted with gunpowder. 



5. Lastly, the ores thus obtained are wheeled towards the shaft of extraction, and 

 turned out to the day. 



Let us now see how the excavation by fire is practised ; and, in that view, let us 



