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BOOK V.

are arranged on two different systems ; for either the square ends of thetimbers, which reach from the hangingwall to the footwall, are fixed into corres-ponding square holes in the timbers which lie along the hanging or footwall,or the upper part of the end of one and the lower part of the end of the otherare cut out and one laid on the other. The great weight of these joinedtimbers is sustained by stout beams placed at intervals, which are deeply setinto hitches in the footwall and hangingwall, but are inclined. In order thatthese joined timbers may remain stationary, wooden wedges or poles cutfrom trees are driven in between the timbers and the vein and the hangingwall and the footwall; and the space which remains empty is filled with loosedirt. If the hanging and footwall rock is sometimes hard and sometimes soft,and the vein likewise, solid joined timbers are not used, but timbers areplaced at intervals ; and where the rock is soft and the vein crumbling,carpenters put in lagging between them and the wall rocks, and behind thesethey fill with loose dirt; by this means they fill up the void.

When a very deep shaft, whether vertical or inclined, is supported byjoined timbers, then, since they are sometimes of bad material and a fall isthreatened, for the sake of greater firmness three or four pairs of strong endposts are placed between these, one pair on the hangingwall side, the otheron the footwall side. To prevent them from falling out of position and tomake them firm and substantial, they are supported by frequent end plates,and in order that these may be more securely fixed they are mortised intothe posts. Further, in whatever way the shaft may be timbered, dividersare placed upon the wall plates, and to these is fixed lagging, and thismarks off and separates the ladder-way from the remaining part of the shaft.If a vertical shaft is a very deep one, planks are laid upon the timbers by theside of the ladders and fixed on to the timbers, in order that the men who aregoing up or down may sit or stand upon them and rest when they are tired.To prevent danger to the shovellers from rocks which, after being drawn upfrom so deep a shaft fall down again, a little above the bottom of the shaftsmall rough sticks are placed close together on the timbers, in such a way asto cover the whole space of the shaft except the ladder-way. A hole,however, is left in this structure near the footwall, which is kept open so thatthere may be one opening to the shaft from the bottom, that the bucketsfull of the materials which have been dug out may be drawn from theshaft through it by machines, and may be returned to the same place againempty ; and so the shovellers and other workmen, as it were hiding beneaththis structure, remain perfectly safe in the shaft.

In mines on one vein there are driven one, two, or sometimes threeor more tunnels, always one above the other. If the vein is solid andhard, and likewise the hanging and footwall rock, no part of the tunnelneeds support, beyond that which is required at the mouth, because at thatspot there is not yet solid rock ; if the vein is soft, and the hanging andfootwall rock are likewise soft, the tunnel requires frequent strong timbering,which is provided in the following way. First, two dressed posts are erectedand set into the tunnel floor, which is dug out a little ; these are of medium