MINING 



305 



under operation. If the rubbish be very considerable, as is commonly the case the 

 floor planks are lost. However strongly they may be made, as they cannot be re- 

 paired, they sooner or later give way under the enormous pressure of the rubbish 

 and as all the weight is borne by the roof of the oblong gallery underneath, this must 

 be sufficiently timbered. By this ingenious plan, a great many miners may go to 

 work together upon a vein without mutual interference ; as the portions which they 

 ietach have always two faces at least free, they are consequently more easily separable, 

 tither with gunpowder or with the pick. Should the vein bo more than a yard thick' 

 or if its substance be very refractory, two miners are set upon each step, bbbb 

 indicate the quadrangular masses that are cut out successively downwards ; and 1 1 

 2 2, 3 3, forwards ; the lines of small circles are the sections of the ends of the billets 

 which support the floors. 



at 



2. To attack a mass ~y,fiff. 1454, a scaffold m, is erected in one of its terminal pits p, 

 the level of the ceiling of the gallery B E', where it terminates below. A miner 



1454 



placed on this scaffold, cuts off at the angle of this mass a parallelepiped 1, from one 

 to two yards high, by six or eight long. When ho has advanced thus far, there is 

 placed in the same pit upon another scaffold m', a second miner, who attacks the vein 

 above the roof of the first cutting, and hews down, above the parallelepiped 1, a paral 

 lelopiped of the same dimensions 1', while the first is taking out another, 2, in advanca 

 of 1. When the second miner has gone forward 6 or 8 yards, a third is placed also 

 in the same pit. <He commences the third step, while the first two miners are pushing 

 forward theirs, and so in succession. 



In this mode of working, as well as in the preceding, it is requisite to support the 

 rubbish and the walls of the vein. For the first object, a single floor, n n n, may be 

 sufficient, constructed above the lower gallery, substantial enough to bear all the 

 rubbish, as well as the miners. In certain cases, an arched roof may be substituted ; 

 and in others, several floors are laid at different heights. The sides of the vein aro 

 supported by means of pieces of wood fixed between them perpendicularly to their 

 planes. Sometimes, in the middle of the rubbish, small pits are left at regular dis- 

 tances apart, through which the workmen throw the ore coarsely picked, down into 

 the lower gallery. The rubbish occasionally forms a slope///, so high that miners 

 placed upon it can work conveniently. When the rich portions are so abundant as 

 to leave too little rubbish to make such a sloping platform, the miners plant them- 

 selves upon moveable floors, which they carry forward along with the excavations. 



These two modes of working in the step-form have peculiar advantages and dis- 

 advantages ; and each is preferred to the other, according to circumstances. 



In the descending workings, or in direct steps, Jig. 1453, the miner is placed on the 

 very mass or substance of the vein ; he works commodiously before him ; he is not 

 exposed to the splinters which may fly off from the roof ; but by this plan he is 

 obliged to employ a great deal of timber to sustain the rubbish ; and the wood is fixed 

 for ever 



In the ascending workings, or in reversed steps, fig. 1454, the miner is compelled to 

 work in the re-entering angle formed between the roof and the front wall of his ex- 

 cavation, a posture sometimes oppressive ; but the weight of the ore conspires with 

 his efforts to make it fall. He employs less timber than in the workings with direct 

 steps. The sorting of the ore is more difficult than in the descending working, because 

 the rich ore is sometimes confounded with the heap of rubbish on which it falls. 



When seams of diluvium or gravel-mud occur on one of the sides of the vein or on 

 both, they render the quarrying of the ore more easy, by affording the means of un- 

 covering the mass to be cut down, upon an additional face. 



VOL. in. X 



