Jacobs." Mr. O'Reilly then sent the stone to Cape Town for examination, when it turned out to be a true diamond, worth £500.*

The value of the diamonds produced annually far exceeds that of the gold of any one of our colonies.

Gold. The story told of the finding of gold in California, in 1848, is that Marshall, who was superintending a sawmill, happened to see something glittering in the mill leat. It turned out to be gold. He found more nuggets, and soon the discovery was noised abroad.

In Australia the first discoveries of gold were by chance.

The attention of Dr. Plassard was directed to the existence of gold in Venezuela from seeing some specimens in the possession of a native.

Iron.-Traces of soft hæmatite, noticed among the roots of an overturned tree, led to the discovery, in 1891, of the important Biwabikt iron mines of the Mesabi range, Minnesota.

Nickel.-The Sudbury nickel deposits were discovered in making a cutting for the Canadian and Pacific Railway, and even then it was the copper which first attracted notice.

Phosphate of Lime.-In May 1886, a geologist, M. Merle, took it into his head to analyse the sand of an apparently abandoned pit, which had been worked for centuries in order to give bricks a violet tint much esteemed in the neighbourhood. He found it contained 77.85 per cent. of phosphate of lime. This was the origin of the workings in the Upper Chalk at Beauval, in the department of the Somme.‡

The discovery of the phosphate beds of Florida§ was made in the autumn of 1889 by an orange-grower, who out of curiosity sent to a chemist a sample of the white subsoil of his grove; this turned out to contain 80 per cent. of phosphate.

Quicksilver. The Redington Quicksilver Mine,|| in California, was discovered in making a cutting for a road.

Silver.-A man made a fire to cook his food and protect himself from the cold, near the site of Catorce,¶ in Mexico, and in the morning found silver shining in the ashes. This was in 1775,

T. Reunert," Diamond Mining at the Cape," Official Handbook to the Colonial Exhibition. History, Productions, and Resources of the Cape of Good Hope. Cape Town, 1886, p. 178.

+ Winchell, Twentieth Annual Report of the Geol. and Nat. Hist. Survey of Minnesota, p. 157. Minneapolis, 1893.

Statisque de l'Industrie Minérale en France pour l'année 1886. Paris, 1888, p. 252.

§ Ledoux, "The Phosphate Beds of Florida," Eng. Min. Jour., vol. xlix. (1890), p. 176.

Becker, "Geology of the Quicksilver Deposits of the Pacific Slope," Monographs of the U.S. Geol. Survey, vol. xiii. p. 10. Washington, 1888. ¶ Chism, "The Catorce Mining District," Eng. Min. Jour., vol. xlviii, (1889), p. 340.

and three years later another man pulled up a bush to throw upon his fire, and found native silver in the roots. Mining soon began, and between 1779 and 1812 the district yielded ore worth from thirty to forty million pounds sterling. Tradition relates that the famous silver mines of Potosi, in Bolivia, were discovered in a similar manner in 1538, by the accidental displacement of a bush which had small lumps of native silver among the roots.

*

The existence of silver in the Province of Famatina, in the Argentine Republic, was made known by a pure accident. Leita and Echavarria were making a journey, in 1811, across the Andes, and during a terrible storm, took refuge in a cave, and there passed the night. In the morning they found that the stones they had put round the fire at night were white, and on further examination silver was plainly to be seen in them.

Adventitious Finds.-Search for one mineral often leads to the discovery of another. The working of veins for tin ore has revealed the presence of the decomposed granite which furnishes china clay.

The finders of the Comstock lode worked it at first for gold, being quite ignorant of the presence of rich silver ore.

In the winter of 1858-59, some prospectors washed a panful of earth from a broad-topped mound which one of them had noticed previously. This gave gold to the value of fifteen cents, a high average return. They then noticed a gopher hole in the mound, and took up the earth which had been thrown up. This they washed, with satisfactory results, and at once staked out claims. Another part of the lode was discovered by some other prospectors, who had dug a hole in order to make a little reservoir for water. They chanced to wash some of the earth, and to their surprise found it rich in gold. The upper part (back) of the lode was then worked for this metal. They threw away bits of a black rock which they found mixed with the earth and yellow sand, and when, at a depth of 3 or 4 feet, they came upon a vein of the black mineral, they had not the least idea that it was valuable. Pieces, however, were carried away by curious visitors, and one was given to Mr. Melville Attwood for assay. He discovered

that it was worth $3,000 per ton for silver and $876 for gold. The black mineral was sulphide of silver, and the yellow sand proved to be the chloride. The working of the Comstock lode for silver dates from this discovery, which was in June 1859.

There are reasons for supposing that the original discoverers of the Comstock lode were two brothers na med Grosh who had found a rich vein of silver in 1856. But one brother died from

* Hoskold, La République Argentine, p. 19.

Lord, "Comstock Mining and Miners," Monographs of the U.S. Geol. Survey, vol. iv. pp. 34-55.

Op. cit. pp. 27-31.

the effects of a slight accident, and the other soon after succumbed under the hardships he had undergone in crossing the snows of the Sierras in December 1857. The knowledge of this vein was then lost for a time.

In 1885* some natives or Spaniards took to M. Bastide specimens of what they thought was calamine from the top of Djebel Toumaï-Kebir, Department of Oran, Algeria. It turned out to be phosphate of lime.

When boring for rock salt in 1839 near Stassfurt, the Prussian Government found brine with chloride of magnesium and chloride of potassium. Later, in 1852, they sank two shafts through the beds containing these minerals, without in any way recognising their value, in order to work the rock-salt underneath. However, it was not long before this mistake was corrected, and the potassium salts soon became the main object of the mining.

The sub-wealden bore-hole near Battle, which was put down for general information concerning the underlying strata, met unexpectedly with a bed of gypsum, which is now regularly mined.

The bed of salt in the Cleveland district was discovered in 1863 by a boring made for the purpose of getting water. The total area now proved is 20 square miles; and if the approximate average thickness of the bed is taken at only 90 feet, it may be estimated to contain 115,200,000 tons of salt per square mile.‡

A bore-hole was put down in Louisiana near Lake Charles on the New Orleans-Texas Railway in search of petroleum,§ and a rich bed of sulphur-bearing rock, 100 feet (30 m.) thick, was pierced unexpectedly. Owing to the watery nature of some of the strata by which it is overlain, it has not yet been worked.

According to a statement issued by the Broken Hill Proprietary Company, Limited, the original claims of this productive silver mine were pegged off under the impression that the outcrop was that of a tin lode.

The Sulphur Bank¶ in California was originally worked for sulphur, and the fact of there being quicksilver was long unsuspected.

Instances of valuable minerals passing unrecognised are

common.

It is related that the original proprietor of the site of Mount

Statistique de l'Industrie minérale en France pour l'année 1886. Paris, 1888, p. 285.

+ Führer zum vierten allgemeinen Deutschen Bergmannstag. 1889. Halle a. d. Saale, 1889, p. xxxiii.

Marley, "On the Cleveland and South Durham Salt Industry," Trans. Fed. Inst. M. E., vol. i. (1889-90), p. 342.

§ Rivista del Servizio Minerario, 1888, p. clxxxiii.

Report and Statement of Accounts for Half-year ending November 30, 1886. Melbourne, Victoria, 1886, p. 57.

Becker, op. cit. p. 10.

Morgan gold mine used to sell some of the auriferous stone, which resembles pumice, as hearthstone for cleaning doorsteps.

Geology as a Guide to Minerals.-A knowledge of geology will often serve to guide the miner. Coal has been discovered in the south-east of England by very careful reasoning, based upon the geological structure of South Wales and Somersetshire on the west and that of Northern France and Belgium on the east.

M. Meugy,† Inspector-General of Mines, hearing of the discovery of phosphate of lime in the Lower Greensand of England, concluded that similar deposits might occur in the Cretaceous rocks of France. Search was made, and valuable deposits were found in 1852.

Geology also affords the miner aid by enabling him to identify certain horizons in stratified rocks by their fossils. The valuable bed itself may not always be fossiliferous, but definite horizons above or below it may be recognisable, and so guide the miner in his explorations.

Associated Minerals.-The existence of valuable minerals may be suspected from meeting with some of their common associates, and, even for the sake of its importance to the prospector, the subject of the paragenesis of minerals deserves careful study.

The facts are specially marked in the case of tin ore. Cassiterite is usually associated with minerals containing boron and fluorine, such as tourmaline, topaz, fluor-spar and lithia mica, and also with wolfram, chlorite, and arsenical pyrites; masses of magnetic iron ore are frequently accompanied by rocks containing garnets, hornblende, and epidote.

Zinc blende is a common hanger-on of galena, which likewise often has barytes in its train. Galena invariably contains silver, and frequently enough to enhance its value.

The associates of gold in quartz veins are various metallic sulphides, such as iron pyrites, magnetic pyrites, copper pyrites, mispickel, galena, zinc blende, stibnite, tetradymite, and bismuthine.

Salt is accompanied by gypsum and anhydrite, and frequently has its habitat in red rocks. Mottura explains this by pointing out that when sea water is evaporated, the first precipitate is oxide of iron, that gypsum crystallises out next, and later the sodic chloride.

SURFACE INDICATIONS.-The indications which guide the prospector are precisely those upon which the geological surveyor depends in making his maps, viz., form of the ground, colour, nature of the decomposed outcrop, ordinary springs, mineral springs, indicative plants, altered vegetation, burrows of animals, old workings, slag heaps, ruins, names of places and old records. W. H. Dick. A Mountain of Gold. Brisbane, 1889, p. 11. ↑ Stat. Min. France, 1886. Paris, 1888, p. 280.

Form of the Ground.—If the valuable mineral is harder or softer than the surrounding rocks, it will affect the manner in which the surface is sculptured by atmospheric agencies. Hard rocks will project in some way, soft ones will be cut into hollows. especially if they are impermeable. The outcrop of a hard bed will be denoted by a steep face or escarpment, and unyielding mineral veins project above the surface in the form of huge crags (Fig. 89). In parts of our country, these outcrops have been worked away and are no longer apparent; but lodequartz blanched by weathering may often be seen standing up several feet above the surface on the Welsh hills, and the run of some lodes can be traced for a long distance by a succession of such outcrops.

FIG. 89.

In the United States and in Australia this phenomenon is

common.

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.

Some of the silver veins of Butte, Montana, crop out, according to vom Rath, as great wall-like ridges of brown and black rock, which is quartz containing the oxides of iron and manganese; the Rainbow lode stood up 20 feet above the surface.

The Broken Hill lode at Silverton, New South Wales, was traceable for fourteen miles by the outcrop of huge black crags consisting of ferruginous quartz, brown ironstone, pyrolusite and other minerals, which in places rose to a height of 50 feet above the ground, and were 10 to 120 feet wide.

Speaking of the outcrops of gold veins of the Hodgkinson goldfield of Queensland, Mr. R. L. Jack. the government geologist, says, "they can be followed from hill top to hill top, forming at times insurmountable walls a hundred feet high; as, for example, in the peaks west of Mount Tenison Woods. In other places denudation has left their remains on hill sides or hill tops in the form of huge cubes of quartzite, from which the surrounding soft rocks have crumbled away. These cubes stand up weird and solitary, like the ' perched blocks' of Alpine and Arctic lands."

The tin lodes of San Jacinto in California are found in a country destitute of all vegetation except grass, and their black outcrops are said to be unusually distinct.§

Luther Wagoner, "The Geology of the Quicksilver Mines of California," Eng. Min. Jour., vol. xxxiv. (1882), p. 334.

Neues Jahrb. f. Miner., Geol., u. Paläontologie, 1885, p. 162.

Handbook of Queensland Geology. London, 1886, p. 27.

§ Benedict, "The San Jacinto Tin Mines," Eng. Min. Jour., vol. 1. (1890),