As the principal level of a mine worked in this manner is always, when possible, carried at or near the bottom of the lowest productive stratum, the whole process of working may often be carried on by rises, and no necessity will exist for sinking below the main level, which answers the purposes both of drainage and extraction. When, however, other productive strata exist below this, which from the nature of the country are inaccessible by day levels, recourse must be had to sinking wines below it to explore them.
When a level has been driven a considerable distance from its month or entrance, a shaft will be required, which is usually sunk from the surface so as to come down upon it near the end. The deeper work ings are then carried on by means of this shaft, which is either con tinued perpendicularly or upon the vein, till it reaches the next productive stratum, upon which a level will be driven. By extending the day level or adit upon the course of the principal vein, and such others as may be found in its vicinity, and by sinking shafts occasionally where they may be found necessary; a mine worked in this manner may be indefinitely extended, and its workings arranged so as to be accommodated to the nature of the metalliferous deposits which may be discovered in their progress.
Although the general principles which regulate the direction• of mining operations will best be understood from thus tracing their most important modification from the beginning to a mature and systematic development, it must not be supposed that all mines are invariably worked upon the same plan, or even that the first opening of mines is a thing of very frequent occurrence. The local circum stances of mines are so exceedingly various, and the Irregularity and complexity of mineral deposits so great, that a corresponding diversity must exist in the means adapted for exploring them, and hence, although the general principles and features are the same in all, no two mines will be exactly alike, nor would the same unvarying processes be suitable for them.
Mining Tools and Processes.—The tools and processes employed by the miner in the excavation of the rock or the vein are simple, and will require only a brief notice. As his work is chiefly of two kinds, simply excavating the ground when soft, and blasting it when hard, his tools are suited to each process, the " pick " and "gad" being used for the former ; the " borer " or " jumper," and the " hammer " used to propel it, for the latter, with several minor accessories for firing the shots, when the bole has been completed to its proper depth. The pick
is a very useful tool and much employed by the miner both in working in the rock and in breaking down ore where the ground is not so hard as to require blasting. It resembles a common pickaxe, but is smaller and more convenient, the iron head being sharp and pointed at one end, and very short and hammer-shaped at the other, a form which peculiarly adapts it to underground uses. The wedge or " gad " is sometimes used in conjunction with the pick ; it is made of wrought iron, and often with curved sides. The borer or " jumper " is an iron rod or circular bar usually about two feet in length, steeled and formed into a flat sharp edge at the end ; it is driven into the rock by one man with a heavy hammer, while the other continually turns it round so as to expose the cutting edge to fresh surfaces of rock. The pulverised matter is drawn out from time to time by a tool called a " scraper," and when the hole has proceeded to a sufficient depth, and been charged with powder, an iron wire with a copper point, or, what is still better, a piece of copper wire, with a loop at the end, is intro duced, when the charge having been firmly rammed down with clay or other soft mineral substance, the wire or " needle " is withdrawn, and a train of gunpowder inserted in its place. The train is then fired by a slow match (often a piece of brown paper smeared with grease), and the miners retire till the explosion has taken place. A very ingenious contrivance for firing the charge was invented some years ago in Corn wall, by Messrs. Bickford, called the " safety fuse," which is now getting into very general use in our mining districts. The safety fuse consists of a small train of powder inserted in a water-proof cord, and being cut to the required length, regulates the time of the explosion by its known and steady rate of ignition. The use of this contrivance and the substitution of copper for iron in the " needle," have contri buted of late years to prevent the accidents arising from premature explosion, which were formerly of very common occurrence in mines.