In addition to the general presumptions furnished by geological science, another and more precise indication of the existence of metal liferous deposits is afforded by finding pebbles or fragments of ore on or near the surface, generally either in the hods of streams or mixed up with superficial detritus. These scattered fragments, the result of alluvial action upon the outcrop of mineral velum or other deposits, may often be traced to particular spots, and thus the position of the deposits from which they originated may be established. In the north of England they-are termed "ahead stone.," and this mode of dis covering veins is called " shoading." Should the exact situation of the vein whose existence has been ascertained in this or any other manner not be observable, it may be ascertained by opening trenches in the alluvial moil deep enough to exrose the solid rock, their direction being at right angles to that in which analogy or the position of other veins in the neighbourhood would render it probable that the vein or veins in question might lie. This mode of finding veins is provincially ter med in Cornwall "col/teeming." The object of discovery may be still more effectually attained, but at a greater expense, by excavating a nearly horizontal 'merge termed a " level," "drift," or "adit," front the bottom of the nearest valley, carrying it through the solid rock in the direction before mentioned, so as to intersect or" cut" any mineral deposit which may exist in the ground through which it passes. This last plan is however seldom adopted, unless it is previously well ascer tained that mineral veins do actually exist there, as it is too slow and too expensive to be undertaken upon uncertain grounds. Discoveries are sometimes made also by driving on the course of veins which occur in cliffs or are exposed in the sides of brooks; trials of this kind fall within the compass of working miners or persons of very small capital, and in some instances form the first step in opening mines which ulti mately become of great importance.
Although the manner in which mineral deposits may be and some times are originally discovered has been thus detailed, it must not be supposed that the process is one of very frequent occurrence. The principal mineral districts in this and most other countries have been known and explored for ages, and by far the greater part of our mineral produce is extracted from deposits which have long been worked, the principal new discoveries being either made upon untried portions of known veins, or simply by excavating passages or "cross cuts " from mines now working, in a direction transverse to that of the vein upon which they are wrought, so as to prove the adjoining ground.
Financial arrangements, d.c.—When however a new vein or mineral deposit has been by any process discovered, if the indications of metallic produce are such as to render it desirable to work it, the most usual step, after obtaining the consent of the proprietor, is the formation of a company for this pm-pose. For although mines are sometimes worked by individuals, experience has shown that a company is best adapted for carrying on mining operations, the amount of capital required being large and uncertain, and the risk great, while a long period may elapse before adequate returns are made. Hence, not only in England, but in most other countries, the system of working mines by companies has been adopted, being found decidedly advantageous. Certain stipu lations are then entered into between the company and the proprietor of the land in which the vein or deposit is situated, or, should the mineral right not belong to him, with the person who does possess it.
The principal tenns of this agreement are to determine the extent of ground within which operations may be carried on, and to stipulate the proportion of the gross mineral produce or its equivalent in money which the owner is to receive free of all expense in raising and making it marketable. It often includes also compensation for damage done to the surface, and other considerations of less importance which are determined by the custom of the neighbourhood and other circum stances.
Before commencing operations, it is necessary to ascertain with some correctnelle (if it should not be previously known) the bearing or direction of the vein, and also its dip or " underlie," which may be done by sinking a few shallow pita upon it. These circumstances being known, there are two ',telltale by which the vein may be explored, either by Kinking upon its course from the surface, or by forming a horizontal passage to intersect it, commenced front some neighbouring valley or the lowest point on the surface which may be conveniently situated for the purpose; or both these modes may be carried on together If do/amble. As, however, the practieability of forming a level or edit to prove the vein at a sufficient depth and within mode rate limits as to time and expense must entirely depend on local circumstances, the former method, as being most expeditious, is generally resorted to, and is effected in the following manner.
Early Progress of the dl orks.—A spot determined either by e.otive fleece or by some promising indication Is/selected as the site of a shaft, which is frequently sunk in an incline/1 direction upon the course of the vein, or if intended to be perpendicular it is commenced upon that side towards which the vein inclines or underlies,and at such a distance from Its " beck" or outcrop as to come down upon it at a given depth, say 10, 20, or 30 fathoms. This depth is regulated by the means of the parties to prosecute the trial, and the depth at which analogy may lead them to suppose that ore in any quantity may ho found, the superficial parts of veins being usually quite unproductive.
On cutting the vein the shaft is for a time suspended, and two hori zontal passages, often termed "galleries," but by the miner "levels," are excavated or " driven " upon the vein in both directions. These passages are usually about six feet in height and three or four in breadth, and rather smaller above than below. They are the principal means of exploring the contents of veins, and are made larger or smaller according to their richness or poverty, their width, and the nature of the inclosing rock. Should the shaft be intended to cut the vein at any considerable depth, it may be desirable to explore it above thepoint of intersection, end this is done by driving a short transverse level or "cross-cut " to it, and driving two levels from the place where the "cross-out" meets it, as before described. Should the depth of the shaft before reaching the vein be very considerable, two or three of these cross-cuts will be driven first, and levels extended from them. The perpendicular distance of the levels from each other is regulated both by custom and local circumstances, but is usually about 10 fathoms, that interval having been found most convenient for the objects of the miner.