In [fig. 723.], A, B are the side walls supported upon the buttresses C and D; in [fig. 724.], E is the masonry of the wall, borne upon the arch F at the entrance to a gallery; the continuation being at G, which is sustained by a similar arch built lower.
L, is the vault arch of the roof, supported upon another vault M, which presents a double curvature, at the entrance of a gallery; at H is the continuation of the arch or vault L, which underneath is supported in like manner at the entrance of a lower gallery.
a b, c d, [fig. 723.], are small upright guide-bars or rods for one of the corves, or kibbles.
e f, g h, are similar guide-bars for the other corf.
i i, are cross-bars of wood, which support the stays of the ladders of descent.
k k, are also cross-bars by which the guide-rods are secured.
t, a corf, or extraction kibble, furnished with friction rollers; the other corf is supposed to be drawn up to a higher level, in the other vertical passage.
[Figs. 725.] [726.] represent in a vertical section the mode of timbering the galleries of the silver and lead mines at Andreasberg in the Hartz. [Fig. 725.] shows the plan viewed from above. Upon the roof of the timbering, the workman throws the waste rubbish, and in the empty space below, which is shaded black, he transports in his waggons or wheelbarrows the ores towards the mouth of the mine. [Fig. 726.] is the 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.