MINE SURVEYING.
In the following instructions on mine surveying we confine ourselves to such rules and examples as apply to coal-mining in particular, but which may, nevertheless, be used in all Mining operations. The simple change of name from seam to lode, or from gangway to level, in the phraseology, is about all the difference. In fact, most of our examples are from Budge's Practical Miner's Guide, which was written principally for the Cornish copper and tin miners. We have simply changed the phraseology in some cases to adapt the rules to coal-mining.
We think the tables, rules, and examples given will be found to cover all the require ments of mining superintendents. When difficult and delicate surveys on important occasions are demanded, a professional engineer of mines may be consulted; but there are few cases in mining experience which the simple rules and examples we give will not embrace.
In order to form good and careful habits, and make correct surveys, some uniform system should be followed and strictly persisted in. We do not wish to prescribe an unalterable form or order in commencing and conducting a survey, but give what we consider a good one: those who find better systems may use them; but we would recom mend earnestly that they should not be liable to lead to error, or be open to mistakes and confusion.
In conducting under-ground surveys, when they are intricate, and embrace numerous tunnels, cross-cuts, inclines, or diverging levels, it is important that these should not become confused with the main traverse. If those branches are surveyed as the main line advances, they should always be numbered as distinct lines, and if noted in the order in which they occur, should always be carefully marked and numbered, so that not only the writer, but any other practical man may read and understand them.
We may also recommend all new beginners—and perhaps the rule applies to the pro fessional also—to let the sight or vane fixed at 360° always take the lead, and the sur veyor's eye placed at the opposite vane, or end of the compass or theodolite, except when taking back observations. The remarks in connection with the converting table on page 495 will explain this more clearly.
In horizontal surveying, let two drafts be made from every station, which will ex pedite the work, as the surveyor will only have to wait for the settling of the needle once, instead of twice by the other method.