to conclude that, because it paid to work a mine some centuries ago, the same ore will yield a greater profit or even be worth working nowadays. The change in the value of the precious metals, and the change in the remuneration of the labourer, must be duly weighed before a decision can be arrived at.

It is important to ascertain why the old mines were abandoned. If no good reason, such as a sudden inrush of water, or the breaking out of a great war, for instance, can be assigned for the stoppage, it is usually safe to assume that no great riches have been left in sight; statements to the contrary must be very carefully sifted.

Minerals that were at one time worthless or even regarded as obnoxious, such as nickel and cobalt ores, or zinc blende, become valuable by the discovery of new or improved processes of manufacture or smelting. An instance of this kind has occurred quite lately. Some forty years ago the outcrops of beds of impure carbonate of manganese in North Wales were worked for the black oxides, the gozzans, in fact, which had been produced by the weathering of the deposit near the surface. The undecomposed carbonate was at that time of no value and was carefully separated by cobbing and rejected; and the workings had to be abandoned when the black oxide diminished in quantity at a shallow depth, and was replaced by unweathered ore. Owing to the use of ferromanganese in making steel, the carbonate can now be utilised, and the ore is regularly mined and sent to the blast furnaces to be smelted with iron ore.

On the other hand the discovery of a new process may be the means of cansing a mine to be unprofitable. The discovery by Weldon of a method of regenerating the oxide of manganese used in making bleaching powder, seriously affected manganese mining by lessening the demand for the ore.

Old mine plans, reports, and deeds should be consulted when available; and information should be sought from official geological surveys and mining records when they exist, as they do in this country. A prospector told me a few years ago that he missed securing some manganese properties in North Wales, from not being aware that a government geological map of the district had been published, showing some of the outcrops of the manganiferous bed.

Slag heaps afford indirect evidence of mining, and like old rubbish-heaps may occasionally be worth smelting. The most notable instance of late years has been the profitable treatment of such heaps at Laurium, in Greece.

Ruined cities, or other indications of a country having been more thickly populated, are sometimes adduced as proofs of its mineral wealth. Where it is possible to show, from remains found in the towns or encampments, that the inhabitants were engaged in mining or smelting operations, the prospector may fairly lay stress

upon evidence of this kind. It has often been supposed that some of the old entrenchments in Cornwall were made for the protection of diggers or smelters of alluvial tin ore; and after the careful explorations of Mr. Theodore Bent at Zimbabwe, in Mashonaland, most persons will be disposed to agree with him that this old city and its fellows owed their existence to gold mining.

Names of Places.-Local names may sometimes supply information, either by denoting some natural feature connected with the deposit, or by recording in some way the existence of mine workings. They will be found in all languages, and I need only give a few instances. "Cae Coch," near Trefriw, in Carnarvonshire, means the "red field," from the chalybeate springs, which are due to the existence of a bed of iron pyrites now being worked. "Graig Goch" or "red rock," a name which is not uncommon for mines in Wales, denotes no doubt that the vein was discovered by a red ferruginous outcrop, and so does the name " Fron Goch " or "red breast." Red Mountain, near Birmingham, Alabama, owes its name to the outcrop of an important bed of iron ore. “Glasdir,” meaning "blue ground," is the name of a copper mine in North Wales. I cannot help suspecting that the locality was so called in consequence of the blue colour given to rocks or stones by coppery minerals derived from chalcopyrite near the surface. Balmynhir" or the "diggings at the long stone," denotes workings for tin in the neighbourhood of a "menhir " or erect stone in Cornwall. Sometimes the substance is named, as in the words Tincroft, Stahlberg (steel mountain), Porto Ferraio (iron port) in Elba, Gebel Zeit (oil mountain) on the shores of the Red Sea, Yenang-yaung (Creek of oil), the site of the petroleum wells in Burmah. The names Leadhills (Scotland), Bleiberg (Germany), and Gebel-el-Kohol (Tunis), all have the same signification, and have been given from the existence of workings for lead ore. "Al maden means "the mine," and turning from Spain to our own country, we find "Minera," near Wrexham, with a similar signification given in this case by the Romans, instead of the Moors. The Smoky Mountains, in North Carolina, were called by the Indians "Unaka," from their word "Unakeh," meaning "white," because they obtained white kaolin from them.

66

Salt is indicated by the prefix "Sal," "Salz," or its equivalent "Hall," in numerous names of places.

The German word for miner, "Bergmann"-i.e., mountain man or highlander-reminds us that the old ore-seekers were hillmen, and found their treasures among the mountains, and we constantly find the word "Berg" (mountain), or its equivalent in other languages, forming part of the names of mines or mining towns. Schneeberg, Marienberg, Freiberg, in Saxony, are instances, and of recent date we have Mount Morgan in Queens

*W. B. Phillips, "Mica Mining in North Carolina," Eng. Min. Journ., vol. xlv. (1888), p. 398.

land, and Broken Hill in New South Wales. In the list of copper mines of South Australia* I find no less than twenty-six names of mines beginning with "Mount," in addition to others containing the word "hill" or "knob."

Other names refer to mining or smelting operations. The village of Pestarena, near Monte Rosa, was evidently so called from the crushing of gold ore in the days of the Romans. "Cinderford," in the Forest of Dean, points to old heaps of iron slag, and such a name as "hammer pond," in the Weald of Kent and Sussex, likewise tells us of iron working in days gone by. But no stress should be laid upon names; they afford at most an indica. tion of the existence of a mineral, without any evidence of its value at the present day.

Divining Rod.-Belief in the divining rod, or dowsing rod, has not died out completely even in Cornwall, where one still

meets with educated persons who profess to be able to discover mineral veins by the dipping down of the forked twig when they walk across them.

Fig. 92, reduced from Agricola,† shows old German miners scarching for veins with the rod.

Dipping Needle.-In the special case of magnetic iron we have a safer guide. In Sweden a magnet, suspended so that it can dip

H. Y. L. Brown, "A Record of the Mines of South Australia." Adelaide, 189c.

+ De re Metallica, Basle, 1556, p. 28; and Brough, "Cantor Lectures on Mine Surveying," Jour. Soc. Arts, vol. xl. (1892), p. 803.

in any direction, is regularly used for tracing masses of magnetic iron ore, even when concealed by some thickness of drift or some depth of water; when the lakes are frozen over in winter, this kind of prospecting is easy.

FIG. 93.

The miner carries his compass carefully over the ground, and on approaching magnetic ore the needle dips towards it; the amount of dip increases, until at last, when standing directly over the deposit, the needle becomes vertical, and remains so as long as there is a strong mass of ore underneath it. The boundary of the deposit can thus be laid down on a map with some degree of accuracy. The modification of the Swedish dipping needle shown in Fig. 93, borrowed from Brough, has been adopted in the United States. Improved methods devised by Brooks, Thalén, and Tiberg are described by the same author.

*

Qualifications of the Prospector. -From the above observations it will be seen that the miner is greatly aided in his search by a variety of natural indications;

but in a new and unsettled country the physical difficulties of travel are often so great, that strength of body and the capability of supporting fatigue and hardships become some of the most important qualifications of the prospector. He should have

a general knowledge of geology, and understand mineralogy sufficiently to recognise all the common and valuable minerals and their ordinary associates, and to confirm his opinion by simple tests. The pick, shovel, and pan should be handled with ease, as well as the rifle and the gun. Keen and good eyesight is a sine qua non; a myopic prospector would fail to recognise natural features, and a colour-blind person would not be struck by important differences of tint.

The mode of discovering minerals by boring is a subject of so much importance that it requires a separate chapter.

A Treatise on Mine Surveying. London, 1891, p. 261.

CHAPTER III.

BORING.

Uses of bore-holes.-Methods of boring holes :-I. Boring by rotation; Auger; Diamond drills.-II. Boring by percussion with rods; Iron rods, wooden rods; Driven wells.-III. Boring by percussion with rope; American system; Mather and Platt's system. -Surveying bore-holes.

The uses of bore-holes are numerous :

I. To reach a mineral deposit by a small hole and ascertain its nature, depth from the surface, thickness, dip, and strike, with the object of working it if possible.

2. To ascertain the nature of the subjacent rocks for engineering purposes, such as their suitability for railways, canals, locks, sewers, or foundations of bridges and buildings.

3. To obtain liquids, such as ordinary water, mineral water, brine or petroleum, which either rise to the surface, or have to be pumped up from a certain depth.

4. To make absorbent wells in dry and porous strata.

5. To obtain gases, such as natural inflammable gas, carbonic acid gas, or vapours containing boric acid.

6. To drain off gas from rocks, and water or gas from mine workings. 7. To make passages for conveying power into underground workings by steam, water, wire-ropes, or electricity.

8. To put signal wires or speaking tubes into underground workings. 9. To introduce cement into unsound foundations in order to strengthen them, and also into mine-workings in order to dam back water. 10. To sink holes for lightning conductors, house-lifts, or piles.

11. To sink mine shafts.

The methods of boring holes for these purposes are:

I. By rotation.

II. By percussion, with rods.

III. By percussion, with ropes.

I. BORING BY ROTATION.-Auger.-Soft rocks, such as clay, soft shale, sandy clay, and sand can be bored by an open auger (Fig. 94), like the well-known carpenter's tool.

The mode of working consists in twisting the tool round by means of a cross-head or spanner, and lengthening it as the hole is deepened. The lengthening rods are made of wood or iron, the iron ones being 1 inch gas-pipe, with screwed pin

* Darley, "Artesian Wells," Engineering, vol. xxxix. (1885), p. 633.

H