Sidor som bilder
PDF
ePub

the metals come, before they were melted by the heat below, or dissolved by the fluid above?

This, after all the arguments that have been employed on both sides, is the principal question; and the reasonable answer is obvious. The metals were created by Him who made the other parts of the earth; but whether they were formed at the same time, and in the veins as we see them, or whether the veins were fissures, afterwards filled with the metals; and, if so, whether they came from below, being dissolved by heat, or from above, in solution with some fluid, are questions which man, with all his curiosity, seems destined never to answer.

[merged small][graphic]

The adjoining cut represents the most common varieties of metallic veins. It is from Sir W. T. Brande's "Outlines of Geology," and is placed here to gratify the curiosity of the reader, on this mysterious subject.

With respect to the direction of different metallic veins, we have already observed, that in the same neighborhood, they commonly run parallel with each other, and are often nearly, or quite vertical, or perpendicular to the line of the horizon. But the inclination of different series of veins is found at every angle, from the perpendicular to the horizontal; and the manner in which they run among the strata is also exceedingly various. In most instances, the line of the vein is across that of the strata, but sometimes they run parallel with each other, and the veins spread out between the strata, as represented at No. 4. Sometimes, also, a vein, whose general direction is across the strata, will take a short turn between them, and then proceed on as before, as represented at 7. The branches

of the veins do not terminate as they seem to do in the figure, but commonly join themselves together again, as

seen at 2.

It must not be understood that metallic veins consist of metals, or their ores alone; on the contrary, they are mixed with greater or less proportions of stony matter. Sometimes the ore is diffused through the vein, in some manner as it would be, had the stone been porous, and dipped into a solution of the metal. In other instances, the metal lies in concretions, or crystals, entirely surrounded by the stone. An instance of this is common in the sulphurct of iron, the crystals of which appear as though they had been perfectly formed, and then dropped into the stone when in a soft state. Indeed, so mysterious are the phenomena which metallic veins exhibit, as in the present state of knowledge, to defy all hypothesis.

MINES AND MINERS.

The means of arriving at a vein, or working a mine, varied according to the nature of the rock or country which it traverses, and are dependent upon a great variety of adventitious circumstances, frequently connected with those under which the vein was discovered; which discovery is often accidental, as during the making of roads, cutting of ditches, or draining land; or sometimes it is arrived at, by the discovery of fragments, or pebbles of ore in the bed of rivers, or in alluvial soils through which streams formerly appear to have passed. Thus the ancient mode of shoding, or searching for tin, consisted in tracing certain stones containing that metal, to the vein. whence they came. Sometimes the course of a vein may be learned by the nature of the fragments and stones upon the surface, and, more especially, when it is of iron, by their ocherous tints. A knowledge too, of the substances which, in different countries, usually accompany the ore of a metal, forming what is called the ganue, or matrix, is often of much importance in these inquiries.

Sometimes the springs in the vicinity of metallic veins are so tainted, as to lead to their discovery. Of this, a singular instance occurred some years ago at Dolgetty, where the peat in the neighborhood of the vein, was so

impregnated by sulphate of copper, as to leave some of the metal in its ashes when burned. When this was ascertained, the injured vegetation guided to the vein. By the retention, therefore, of these contaminated waters, in the soil near the vein, it may become unfit for vegetation, and thus the sterility of certain patches of ground, may indicate the existence of metallic substances in the district.

It was,

(Mr. Brande, who writes the above account, has not stated what species of copper was discovered. however, undoubtedly a sulphuret, and from the decomposition of which, the sulphuric acid was produced, which uniting with the oxide of the metal, formed sulphate of copper. In the Anglesea copper-mine, considerable quantities of the metal are obtained from the natural solution of the sulphate in water. This is done by throwing in pieces of waste iron, on which the copper is precipitated.)

[ocr errors]

"There are no class of persons," continues Mr. Brande, more curiously superstitious than miners; and hence a variety of omens, connected with the interference of agents from the spiritual world, are among the items of their creed. Sometimes while under ground, they fancy they hear another pick at work, announcing the presence of a little man, or pixey-knocker, in some neighboring cavern, and the consequent vicinity of a good course of ore. Sometimes the divining rod is resorted to, as a means of finding the ore; and sometimes it is said that flames of light, dancing about a mining district, have suddenly perched upon the looked for vein; a circumstance not improbable, and perhaps referable to the power of the vein to conduct electricity."

The habits, however, of the miner, are those of indus try and perseverance, which sometimes tempt him to ex ploits that excite astonishment at his venturous hardihood "The very idea of a descent beneath the surface of the earth, has something in it of the terrible," says Mr. Phil lips, "and at which those shudder who are unacquainted with practical mining; but such is the force of habit, that any other employment rarely tempts him to forsake his own. The occasional perils of his occupation are scarcely noticed, or if noticed, are soon forgotten. He walks, often in the middle of the night, and in all weathers, two, or three, or more miles, to the mine, undresses, and puts

on his underground clothes, and with his tools, slung over his shoulder, descends to a depth of 1000 or 1200 feet, assisted by the light of a small candle, and works in the bottom of the mine six or eight hours, amidst the noise of the working of the pumps, with as much alacrity and with as little sense of danger, as he would feel amidst his ordinary occupations above ground. We should be inclined to feel pity for the wretch, who, as an atonement for his crimes, should be compelled to undergo what the Cornish miner voluntarily undertakes for a small pittance, and that even of an uncertain amount." W. Phillip's

Geol. Trans.

One of the mines in the parish of St. Just, is wrought nearly 500 feet under the sea, beyond low-water mark; and the sea, in some places, is only about eighteen feet over the back of his workings; insomuch that the miners underneath hear the break, flux, ebb, and re-flux of every wave; which, upon the beach overhead, may be said to have the run of the Atlantic ocean for many hundred leagues, and consequently are amazingly powerful and boisterous. They also hear the rumbling noise of every nodule, and fragment of a rock, which are continually rolling upon the submarine stratum; which altogether make a kind of thundering roar, which would surprise and terrify the stranger. Add to this, that several parts of the land which were richer than others, have been indiscreetly hulked, and worked within four feet of the sea, whereby, in violent stormy weather, the noise overhead has been so tremendous, that the workmen have many times deserted their labor, under the greatest fear, lest the sea should break in upon them.-Pryce's Mineralogia Cornubiensis.

In former times, when a vein of metal was discovered, it was worked to a certain depth, and then often abandoned, in consequence of the insufficiency of the pumps to carry off the water, or the expense incurred in their erection and working. In certain situations, however, it was found that this water run off at lower levels, and that in most instances it might be carried away by an underground tunnel, commencing at the foot of the hill, penetrating to the vein, and thus forming a communication with the working of the mine, and a neighboring valley. These tunnels are now called adits, and when it is resolved to try a vein, one of these underground passages,

about six feet high, and two and a half wide, is begun at the bottom of the neighboring valley, and driven up to the vein for the purpose of carrying off the water; or if a mine has an engine to raise the water from a greater depth than that of the entrance of the adit, the engine then, instead of having to lift the water to the surface, throws it off, with diminished labor, at the adit. In general, adits are nearly horizontal, for although a declivity would accelerate the drainage, it would enter the mine at a less depth. The importance of draining mines by adits has led to some gigantic undertakings of this kind. The great Cornish adit, commences in a valley above Carnon, near the sea, and branches off in its course in several di rections to about fifty mines. Most of the mines are far below the level of the adit, the water being raised into it by means of steam engines. The entire length of this adit, with its various branches, is about thirty miles. But the greatest length of any one branch from its mouth to the mine, is that of Cardrew Mine, which is about five and a half miles. The greatest depth of any part of this adit is at Wheel Hope, where it is about 400 feet deep. It empties itself into Falmouth harbor. Several great works of the same kind exist in different parts of Great Britain. The adit belonging to the Duke of Bridgewater's coal mines, is nearly thirty miles long, and navigable for small boats.

Where an adit is of any considerable length, it is obvious that the air would become stagnant in it, so that the workmen would be unable to proceed. To prevent this, and also to enable them to remove the produce of the excavation without transporting it to great distances, perpendicular openings, called shafts, are made at various intervals. From these shafts, levels, or galleries, are driven in different directions, either for exploring for new veins, or for removing the contents of those already known.— See Brande's Geology.

PHENOMENA OF SPRINGS AND WELLS.

The origin of common springs is easily understood The water which falls on the surface of the earth, penetrates its substance, until meeting with a stratum of clay

« FöregåendeFortsätt »