This definition is wider than what is popularly known as mining, for it includes not only underground excavations but also open workings; at the same time it excludes underground workings which are simply used for passages, such as railway tunnels and sewers, and galleries for military purposes. We must remark also that the word “mine,” or its equivalent in other languages, varies in signification in different countries on account of legal enactments or decisions which define it. Thus, in France and Belgium, the workings for mineral are classified by the law of 1810, according to the nature of the substance wrought, into mines, minières, et carrières. In the United Kingdom, on the contrary, it is the nature of the excavation which decides the question for certain legislative purposes, and the term mine is restricted to workings which are carried on underground by artificial light. The consequence is that what is merely an underground stone quarry in France becomes a true mine in England, whilst the open workings for iron ore, such as exist in Northamptonshire, would be true mines under the French law. It is necessary, therefore, in an article on mining, to go beyond the English legal definition of a mine, and include the methods of working minerals in excavations open to daylight as well as in those which are purely subterranean. Furthermore, as it is customary for the miner to cleanse his ore to a greater or less extent before selling it to the smelter, we shall treat, under the head of mining, those processes which a·re commonly known as the dressing or mechanical preparation of ores; and, finally, a few remarks will be made concerning legislation affecting mines in the United Kingdom, accidents in mines, and the production of the useful minerals in various parts of the globe.

The subject therefore will be dealt with as follows :—

1. Manner in which the useful minerals occur in the earth’s crust, viz., tabular deposits and masses; faults or dislocations.

2. Prospecting, or search for mineral.

3. Boring with rods and ropes; diamond drill.

4. Breaking ground; tools employed; blasting by various methods; machine drills; driving levels and sinking shafts.

5. Principles of employment of mining labour.

6. Means of securing excavations by timber or masonry.

7. Exploitation, or the working away of strata or veins.

8. Carriage or transport of minerals through underground roads.

9. Winding, or raising in the shafts, with the machinery and apparatus required.

10. Drainage of mines, adit-levels, pumps, pumping engines.

11. Ventilation and lighting of mines.

12. Means of descending into and ascending from mines.

13. Dressing or mechanical preparation of minerals.

14. Recent legislation affecting mines in the United Kingdom.

15. Accidents in mines.

16. Useful minerals produced in various parts of the globe.

1. Manner in which the Useful Minerals Occur.— The repositories of the useful minerals may be classified according to their shape as (A) tabular deposits, and (B) masses.

A. Tabular Deposits.— These are deposits which have a more or less flattened or sheet-like form. They may be divided, according to their origin, into (1) beds or strata, and (2) mineral veins or lodes.

(1) Beds.— Geology teaches us that a large proportion of the rocks met with at the surface of the earth consist of substances arranged in distinct layers, owing to the fact that these rocks have been formed at the bottom of seas, lakes, or rivers by the gradual deposition of sediment, by precipitation from solutions, and by the growth or accumulation of animal and vegetable organisms. If any one of these layers consists of a useful mineral, or contains enough to make it valuable, we say that we have a deposit in the form of a bed, stratum, or seam. Of course the most important of all bedded or stratified deposits is coal, but, in addition, we have beds of anthracite, lignite, iron ore, especially in the Oolitic rocks, cupriferous shale, lead-bearing sandstone, silver-bearing sandstone, diamond-, gold-, and tin-bearing gravels, to say nothing of sulphur, rock-salt, clays, various kinds of stone, such as limestone and gypsum, oil-shale, alum-shale, and slate.

The characteristic feature of a bed is that it is a member of a series of stratified rocks; the layer above it is called the roof of the deposit, and the one below it is the floor. Its thickness is the distance from the roof to the floor at right angles to the planes of stratification; its dip is the inclination downwards measured from the horizontal; its strike is the direction of a horizontal line drawn in the middle plane.

The thickness of beds that are worked varies within very wide limits. Whilst the thickness of certain workable beds of coal is only 1 foot, and that of the Mansfeld cupriferous shale only 10 to 20 inches, we find on the other hand one of the beds of lead-bearing sandstone at Mechernich no less than 85 feet thick, and beds of slate far exceeding that thickness. It must not be supposed, however, that the thickness of a bed necessarily remains uniform. Occasionally this is the case over a very large area; but frequently the thickness varies, and the bed may dwindle away gradually, or increase in size, or become divided into two owing to the appearance of a parting of valueless rock. Fig. 1 shows beds of shale, limestone, iron ore, and sandstone. Any one of these beds may be valuable enough to be worked.

(2) Mineral Veins or Lodes. —Veins or lodes are tabular or sheet-like deposits of mineral which have been formed since the rocks by which they are surrounded; they differ, therefore, by their subsequent origin from beds, which, as just stated, are of contemporaneous origin with the enclosing rocks (although of course cases occur in which the deposit is lying unconformably upon very much older strata, or is covered unconformably by very much younger strata). It is necessary to explain that the term “vein” in this definition is used in a more restricted sense than is sometimes customary among miners, who speak of veins of coal, clay-ironstone, and slate, which geologically are true beds. They see a band of valuable mineral or rock, and, careless of its origin, call it metaphorically a vein or seam. On the other hand, the definition is broader than that which prevails among some geologists, who would confine the term vein to deposits occupying spaces formed by fissures.

The term “lode” was defined in 1877 by Mr Justice Field in the celebrated Eureka v. Richmond case as follows:—“We are of opinion, therefore, that the term, as used in the Acts of Congress, is applicable to any zone or belt of mineralized rock lying within boundaries clearly separating it from the neighbouring rocks.” This interpretation seems suitable for the peculiar mining tenure of the United States, where the discoverer of a vein or lode can obtain a mining claim of 500 yards in length along the lode. It protects the prospector, whose object is to obtain a secure title, the mode of origin of the deposit being a matter of small importance to him so long as it is worth working. In many cases also it would be impossible to decide upon the mode of origin until workings had progressed considerably, and even then there would be room for disputes.

No doubt a very large number of mineral veins are simply the contents of fissures; others are bands of rock impregnated with ore adjacent to fissures or planes of separation; others, again, have been formed by the more or less complete replacement of the constituents of the original rock by particles of ore.

Veins may occur in igneous or in sedimentary rocks, and in the latter they frequently cut across the planes of stratification.

Like a bed, a vein has its dip and strike; but, as the dip of veins is generally great, the inclination is usually measured from the vertical, and is then spoken of as the τ<,nderlie or hade. The bounding planes of a vein are called the walls or cheeks, and they are frequently smooth and striated, showing that one side must have slid against the other. The upper wall is known as the hanging wall, the lower one aS the foot wall. The width of a vein is measured at right angles to the walls.

A typical example of a fissure-vein is shown in fig. 2, representing a lead lode in slate at Wheal Mary Ann mine in Cornwall.

It is evident that a fissure in the surrounding slate has here been filled up by the successive deposition of bands of mineral on both sides.

A large proportion of the contents of a lode may consist of fragments of the walls that have fallen into the original fissure, and these are often tightly cemented together by minerals that have been introduced subsequently. The horizontal section of part of the Comstock lode (Plate IV.) shows much “country” rock enclosed within the walls.

Where a lode consists of rock impregnated with ore, the mineralized. part may fade away gradually into the surrounding rock (country) without there being any distinct wall, as shown in fig. 3, which is an illustration taken from the Great Flat Lode near Redruth in Cornwall.

The celebrated Ruby Hill deposit in the Eureka district, Nevada, is a mineralized zone of dolomitic limestone varying in width from a few inches to 450 feet, and having a mean width of 250 feet. It contains numerous irregular ore-bodies, which consist mainly of highly ferruginous carbonate of lead, rich in silver and gold. This mineralized limestone band, long called a lode by miners, has been determined by the decision just mentioned to be a lode in the eyes of the law.

Veins often continue for a great distance along their strike. The Van lode in Montgomeryshire is known for a length of 9 miles, whilst the Great Quartz Vein in California has been traced for a distance of no less than 80 miles. Veins are of less uniform productiveness than beds, and are rarely worth working throughout. Rich portions alternate with poor or worthless portions. The rich parts have received various names according to the forms they assume: fig. 4 represents a longitudinal section along the strike (course) of a lode, and the stippled parts are ore-bodies; B, B, B are bunches; A is a large bunch or course of ore ; when an ore-body forms a sort of continuous column we have a shoot, and ore-bodies which on being excavated leave chimney-like openings are called pipes (fig. 4, C). In the United States the Spanish word bonanza, literally meaning “fair weather” or “prosperity,” is frequently used for a rich body of ore.

The richness of veins is dependent in many cases upon the nature of the adjacent rock (country), upon the underlie, and upon the strike, variations in any one of these three elements being often sufficient to cause a decided change of productiveness.

Various theories have been formed concerning the origin of mineral veins. Some geologists suppose that the minerals now constituting the veinshave been dissolved out of the adjacent rocks and re-deposited in the vein cavity; others, on the contrary, believe that the ores have been brought up from great depths by mineral springs. In all probability both theories are correct, some lodes having been formed by the former process and some by the latter; and, furthermore, other lodes appear to owe their origin to a gradual substitution of valuable minerals in the place of some of the constituents of a worthless rock. One of the most important contributions to the science of ore-deposits of late years has been the discovery by Professor F. Sandberger of small quantities of silver, lead, copper, nickel, cobalt, bismuth, arsenic, antimony, and tin in silicates, such as oUvine, augite, hornblende, and mica, which are constituents of igneous rocks. He therefore regards these rocks as the sources ιrom which lodes have derived their riches.

B. Masses.— These are deposits of mineral, often of J irregular shapes, which cannot be distinctly recognized as beds or veins. Such, for instance, are the red haematite deposits of the Ulverston district (fig. 5) and the brown haematite deposits (churns) of the Forest of Dean, which occupy irregular cavities in the Mountain Limestone. These may have been formed by the percolation of water bringing down iron in solution from overlying Triassic rocks. Other examples of masses are the calamine deposits of Altenberg (fig. 6), Sardinia, and Lombardy, the iron ore deposits in Missouri, such as Iron Mountain and Pilot Knob, the huge upright “necks” or “pipes” of diamantiferous rock in South

Africa, and the granite decomposed in situ worked for china clay in Cornwall.

Under this head also are included by most authors the so-called “stockworks” or “reticulated masses,” names applied to masses of sedimentary or igneous rock which are penetrated by so many little mineral veins as to make the whole worth excavating.

It must be understood that we cannot expect nature to make distinct lines of demarcation between the different kinds of deposits. Though we may be able to see clearly that a seam of coal is contemporaneous with the enclosing rocks, and that a vein intersecting beds of shale and sandstone was formed subsequently, cases frequently occur where the origin of the mineral is uncertain. For example, we have the lead-bearing sandstone of Mechernich and the silver-bearing sandstone of Utah. The grains of sand are of sedimentary origin; but opinions differ as to whether the lead and silver respectively were deposited with the sand or were introduced subsequently by solutions percolating through the beds. In the case of the well-known bed of Cleveland ironstone, Dr Sorby considers that the iron was “derived partly from mechanical deposition and partly from subsequent chemical replacement of the originally deposited carbonate of lime.” Furthermore, a bed may be so folded and contracted as to lose its original sheet-like form in places and assume the shape of an irregular mass. This may happen even with a coal seam.

All kinds of deposits are subject not only to irregularities of origin dependent upon their mode of formation but also to dislocations or shiftings known as faults, heaves, or throws.

We will take the case of a bed (fig. 7). AB is a seam λvhich ends off suddenly at B, whilst the continuation is found at a lower level at CD. The bed was evidently once continuous; but a fracture took place along the line XY followed by a displacement. As a rule the portion of rock on the hanging-wall side of a fault appears to have slid downwards, but occasionally this is not so, and we have a reversed fault (fig. 8). It is very evident, in some cases, that the motion took place, not along the line of greatest dip, but in a dia gonal direction, causing a displacement sideways as well as downwards. Nevertheless, where beds or veins are not horizontal, a mere shift along the line of dip is sufficient to cause an apparent heave sideways. This will be understood from fig. 9. Let AB and CD represent two portions of a lode dislocated by the fault EF. The point B' corresponded originally with B, and the dislocation was caused by a simple sliding of B ’ along the line of dip BB'.

An instance of the complication caused by a succession of faults is shown in fig. 10.

2. Prospecting, or Search for Mineral.— The object of the prospector is to discover valuable deposits of mineral. This search is beset with many difficulties: the outcrops of mineral deposits are frequently hidden by soil; the nature of the deposit itself is generally entirely changed near the surface; and, in addition to this, the explorer may have to pursue his work in trackless forests far away from any settlements.

The prospector seeks for natural sections of the rocks, such as occur in cliffs or in river valleys and their tributary gullies and gorges; he examines the materials constituting the river-beds, often digging up and washing portions in a pan, in order to ascertain whether they contain traces of the heavy ores or metals. If, while prospecting in a valley, he discovers stones that have the appearance of having once belonged to veins, he endeavours to trace them to their source, and is perhaps rewarded by finding similar fragments, but less water-worn, as he goes up the stream; further on he may come upon large blocks of veinstuff lying about, and finally find the vein itself laid bare in a gorge, or at the bottom of a brook, or possibly projecting above the soil in the form of huge crags of quartz. Thus at the Great Western quicksilver mine in California the outcrop of the vein appears as a dike over 100 feet wide, and having precipitous sides in places 75 feet high. Loose pieces of veinstuff found lying about are known in Cornwall as shoad-stones, and shoading is the term given to the process of tracking them to the parent lode.

The upper portion of a deposit is frequently much altered by atmospheric agencies, and bears little resemblance to the undecomposed bed or vein which will eventually be met with at a greater or lesser depth. The principal difference consists in the change of sulphides into oxides or oxidized compounds. Thus iron pyrites, which is such a common constituent of mineral veins, is converted into hydrated oxide of iron, and a vein originally consisting largely of iron pyrites and quartz now becomes a cindery mixture of quartz and ochre, known in Cornwall as gossan. This gossan, or iron hat, may often furnish important indications concerning the nature of the lode itself, because such minerals as pyromorphite or cerussite point to the existence of galena, whilst melaconite, cuprite, malachite, and azurite are the forerunners of chalcopyrite or copper glance. The gossan itself may contain a sufficient quantity of valuable ores to be worth working.

The seams containing native sulphur in Sicily often show no trace of that element immediately at the surface, as the sulphur-bearing limestone weathers into a soft white granular or pulverulent variety of gypsum, called briscale by the miners, and considered by them as affording important indications concerning the bed itself.

Other signs of mineral deposits are given by springs and by certain plants dependent upon the deposit or its associated minerals for part of their nourishment. The appearance of the so-called lode-lights may be explained by the production of phosphoretted hydrogen from the action of organic matter and water upon phosphates, which are so common in the upper parts of mineral veins; and one hears also of differences in the appearance of the vegetation along the line of the deposit, of places where snow will not lie in winter, and of vapours hanging over the ground. Though some writers refuse to put any value upon these indications, they should not be entirely overlooked, because the outcrop of a lode, of different nature and texture to the surrounding rocks, and which is generally a channel for water, may readily cause the phenomena just mentioned. Where the surface is cultivated and the natural springs are tapped by adit-levels or other mine-workings, these appearances cannot be looked for to any great extent. With one special mineral, magnetic iron, the position of the deposit may be traced out with some degree of accuracy with a dipping needle; this is used in Sweden.

After having acquired an idea of the position of a vein or seam by some of the surface indications just mentioned, it is necessary, before attacking it by shafts or levels, to obtain more certain data concerning it. In the case of mineral veins, trenches are dug at right angles to the supposed strike; and, when the upper part of the deposit has been cut in several places, its general course and dip can be determined sufficiently for the purpose of arranging the future workings. These trenches are called “costean pits”; in some cases, instead of a trench, a pit is sunk a short distance and a little tunnel driven out.

Where the mineral to be wrought occurs as a bed or mass, the process of boring is resorted to, and indeed this method is also applied in the case of veins, especially in the United States. Boring is a work of such importance that it deserves to be treated under a separate heading.

3. Boring with Rods and Ropes—Diamond Drills.— The object of boring is to reach a deposit by a small hole and ascertain its nature, its depth from the surface, thickness, dip, and strike. Bore-holes are also used for obtaining water, brine, and petroleum, which either rise to the surface or have to be pumped up from a certain depth, and finally for tapping water in old workings or for...