306 MINING 



Should the vein be very narrow, it is necessary to remove a portion of the sterile 

 rock which encloses it, in order to give the work a sufficient width to enable the miner 

 to advance. If, in this case, the vein be quite distinct from the rock, the labour may 

 be facilitated, as well as the separation of the ore, by disengaging the vein, on one of 

 its faces through a certain extent, the rock being attacked separately. This operation 

 is called stripping the vein. When it is thus uncovered, a shot of gunpowder is suffi- 

 cient to detach a great mass of it, unmixed with sterile stones. 



By the methods now described, only those parallelepipeds are cut out, either in 

 whole or in part, which present indications of richness adequate to yield a prospect of 

 benefit. In other cases, it is enough to follow out the threads of ore which occur, by 

 workings made in their direction. 



The miner, in searching within the crust of the earth for the riches which it con- 

 ceals, is exposed to many dangers. The rocks amidst which he digs are seldom or 

 never entire, but are almost always traversed by clefts in various directions, so that 

 impending fragments threaten to fall and crush him at every instant. He is even 

 obliged at times to cut through rotten friable rocks or alluvial loams. Fresh atmo- 

 spheric air follows him with difficulty in the narrow channels which he lays open 

 before him ; and the waters which circulate in the subterranean seams and fissures 

 filter incessantly into his excavation, and tend to fill it. Let us now take a view of 

 the means he employs to escape from these three classes of dangers. 



1. Of the timbering of excavations. The excavations of mines are divisible into 

 three principal species : shafts, galleries, and chambers. When the width of these ex- 

 cavations is inconsiderable, as is commonly the case with shafts and galleries, their 

 sides can sometimes stand upright of themselves ; but more frequently they require to 

 be propped or stayed by billets of wood, or by walls built with bricks or stones ; or 

 even by stuffing the space with rubbish. These three kinds of support are called 

 timbering, walling, and. fitting up. 



Timbering is most used. It varies in form for the three species of excavations, 

 according to the solidity of the walls which it is destined to sustain. 



In a gallery, for example, it may be sufficient to support merely the roof, by means 

 of joists placed across, bearing at their two ends in the rock ; or the roof and the tow 

 walls by means of an upper joist, s, fig. 1455, which is then called a cap or cornice beam, 

 resting on two lateral upright posts or stanchions, a b, 

 1455 to which a slight inclination towards each other is 



given, so that they approach a little at the top, and rest 

 entirely upon the floor. At times, only one of the walls 

 and the roof need support. This case is of frequent 

 occurrence in pipe veins. Pillars are then set up only 

 on one side, and on the other the joists rest in holes of 

 the rock. It may happen that the floor of the gallery 

 shall not be sufficiently firm to afford a sure foundation 

 to the standards ; and it may be necessary to make 

 them rest on a horizontal piece called the sole. This is 

 timbering with complete frames. The upright posts 

 are usually set directly on the sole ; but the extremi- 

 ties of the cap or ceiling, and the upper ends of the 

 ^^, standards, are mortised in such a manner that these 

 cannot come nearer, whereby the cap shall possess its 

 whole force of resistance. In friable and shivery rocks 

 there is put behind these beams, both upon the ceiling and the sides, facing boards, 

 which are planks placed horizontally, or spars of cleft wood, set so close together as 

 to leave no interval. They are called fascines in French. In ordinary ground, the 

 miner puts up these planks in proportion as he goes forwards ; but in a loose soil, such 

 as sand or gravel, ho must mount them a little in advance. He then drives into the 

 mass behind the wooden framework thick but sharp-pointed planks or stakes, and 

 which, in fact, form the sides of the cavity, which he proceeds to excavate. Their one 

 extremity is thus supported by the earth in which it is thrust, and their other end by 

 the last framing. Whenever the miner gets sufficiently on, he sustains the walls by 

 a new frame. The size of the timber, as well as the distance between the frames or 

 stanchions, depends on the degree of pressure to be resisted. 



When a gallery is to serve at once for several distinct purposes, a greater height is 

 given to it ; and a flooring is laid on it at a certain level. If, for example, a gallery 

 is to be employed, both for the transport of the ores and the discharge of the waters, 

 a floor, e e,fig. 1454 is constructed above the bottom, over which the carriages aro 

 wheeled, and under which the waters are discharged. 



The timbering of shafts varies in form, as well as that of galleries, according totho 

 nature and the locality of the ground which they traverse, and the purposes which 





