After cutting the vein there are two modes of proceeding—continuing the shaft perpendicularly through the vein, or obliquely upon the vein. Which of these two plans is followed will depend in great measure upon its produce and promise, as already ascertained by the upper levels, and partly also on the means of the miner, the former plan being most expensive and requiring the longest time, although ulti mately most advantageous, while the latter, though a cheaper and quicker mode of exploring the vein, since it renders cross-cuts unneces sary, and is itself continually proving one portion of it, 1.9 not well adapted for the application of pumps and machinery,—an evil which may not at first be very sensibly felt,but which increase, proportionally with the depth of the mine and the quantity of water and stuff which require to be drawn from it.
Supposing the shaft to proceed perpendicularly after cutting the vein, on reaching the depth of 10 fathoms or thereabouts below the point of intersection another cross-cut will be driven to it ; but as the shaft is now on the opposite side of the vein, this cross-cut will have an opposite direction to the former ones; and as they had successively become shorter as the shaft approached the vein, they will now succes sively become longer as the shaft, proceeding perpendicularly down wards, recedes further and further from the vein. In this manner the shaft proceeds indefinitely, cross-cuts being driven at every 10 fathoms or whatever distance is most convenient,and levels extended from each upon the course of the vein, the nature and value of which are thus thoroughly explored. The continuance of these and other operations necessarily supposes that ore in some quantity has been found in the upper levels, which will have been all this time in progress, or at any rate that the indication., of future produce are sufficiently strong to encourage the miner to proceed with hie undertaking, the magnitude and expense of which will now be daily increasing, while various diffi culties will be encountered in the progress of his works, more especially the want of ventilation in those parts which are most distaut from the shaft, by which alone they can be supplied with air. It is chiefly in the ends of the levels that the evil of imperfect ventilation begins to be felt, the air hero gradually becoming close and unfit for respiration as they advance further from the shaft, especially when, from the hardness of the ground, frequent blasting is necessary. As soon as this is found to be the case a remedy of.a very simple nature is applied, which consists in sinking a small pit, termed a " " upon the vein, of course, from the upper level to the extremity of the one below it. This communication having been effected, the two levels become perfectly ventilated, each hexing a double communication with the atmosphere, by which both an ascending and descending current is produced. By thus plan it is evident that the levels may be extended for a considerable distance upon each side of the shaft, winzes being continually formed between them at convenient intervals. Besides the
purpose of ventilation, these winzes answer another um, since they make trial of the vein in the intermediate apace between two levels, and also divide it into solid rectangular masses, which may be examined all round, and thus the miner has the means of judging with tolerable certainty of the nature and value of the ores contained in each, and can extract the produce in the most expeditious and economical manner. That such is the case will at. once be evident when it is con sidered that these portions of the vein are perfectly drained and ventilated, that they may be attacked at once from as many points as may be convenient or may contain ore of sufficient value, and from this circumstance no necessity exists for breaking down the unpro ductive masses which are often found to intervene even where the vein is richest and the ore most continuous. When the vein has been properly laid open, the ore may be worked away round such unpro ductive pieces of ground, which, being left standing, will answer the purpose of supports to the rock on each side of the vein. Where the excavations are extensive such support becomes extremely necessary, and often requires the use of strong timbering.
The utility of winzes for working out the ore is indeed so great, that it is only when little or no ore has been found in a level that it will have proceeded far enough for ventilation to become very defective, before a communication of this kind has been made. When, on the contrary, the ore is found to ho tolerably continuous in driving a level, winzes arc generally sunk at intervals of 20 or 30 fathoms, their position being so regulated as to prove the richest and most promising parts of the vein, and to avoid hard and unproductive portions which do not appear worth exploring. We will suppose, however, that a continuous body of ore is met with in one of the upper levels, and that winzes have been regularly carried down to the level below it. Similar operations will then be required here, and winzes will be sunk from it to the next deeper one in the same manner, but they will generally be situated about mid-way between the former, so that each may explore the ground under the middle of the rectangle formed by the two upper winzes and the levels between which they are placed, so as effectually to explore the vein with the smallest number of excavations. The system of works by which a vein is thus laid open, although by no means so regular, is not unlike the seams formed by courses of masonry, the horizontal joints of which may be supposed to represent the levels, and the vertical one the winzes. In cases where the ore extends above the upper level in the mine, this part of the vein may be laid open by perpendicular excavations similar to winzes, but formed in the reverse manner, or by "rising" upwards instead of "sinking" downwards, as in the former cases, the height to which these " rises" are carried depending on the extent of the ore in that direction.