Popular Science Monthly/Volume 30/February 1887/The South-African Diamond-Mines
|THE SOUTH-AFRICAN DIAMOND-MINES.|
IT was a pleasant fancy of a writer in the "Cornhill Magazine," to argue for the plausibility of the fairy-story of the princess from whose pretty lips "fell diamonds, both in speaking and in singing, and even in silence," when she merely smiled. "For, consider," he says. "into what cloes the diamond blaze, when, on combustion, the spirit of the gem leaps upward home again to its parent, the sun; into what but carbonic-acid gas?—that carbon dioxide of the chemist which attends the combustion of every fire-and gas-burner, the decomposition of every vegetable, which is exhaled in every breath we breathe?" The same writer also utters the less pleasing but equally striking thought that "the chimney-sweep is covered by that which, under happier auspices, would be jewels."
The diamond is mentioned yerj anciently in literature. Jupiter, according to classical mythology, was anxious to make men forget the days he had spent among them, and finding that one man—Diamond of Crete—remembered him, turned him into a stone: not a very credible story of the origin of the gem, but men of science in the nineteenth century are not much nearer to knowing the truth on the subject. The Greeks call the stone adamas (ảẟáμaς) the indomptable or unchangeable; and from this has come down our word adamantine and, after the letters have undergone changes of a kind that are not rare in the growth of language, our name of the stone itself. But, long before the Greeks had emerged from the darkness of the mythic age, the diamond was made, among the Hebrews, the peculiar jewel of the tribe of Zebulon; and Aaron's breastplate, when he was dressed in his priestly robes, was adorned in the second of the four rows of its setting with precious stones—with an emerald, a sapphire, and a diamond; and Jeremiah, when the Greeks were just beginning to be known, rebuking the misgoings of his people, said, "The sin of Judah is written with a pen of iron, and with the point of a diamond."
But, although the ancients considered the diamond indestructible, and were capable of trying the most daring experiments with it, no specimen that is known to have belonged to them has come down to us. Some persons suppose that the Koh-i-nor is five thousand years old, as man's possession, but no one knows or can trace its history back with certainty for more than a few centuries.
The diamond has been found in widely separated parts of the world. Among these, Central India, Sumatra, Borneo, the Ural Mountains, California, Brazil, the Cape of Good Hope, and China have been named, in their several times, as principal localities, while it might be hard to enumerate all the minor sites. The Greeks said it was found in Ethiopia. The Indian mines are certainly of very high antiquity, for the stones are mentioned in the "Mahabaratta," and the Romans obtained their supplies chiefly from the mines of Jumalpoor, in Bengal. The Indian mines are scattered along the center of the peninsula, through 10° of latitude, from near the southern bank of the Ganges in latitude 25° to latitude 15° in the Madras Presidency. The most famous ones where those of Golconda, in the Nizam's territory, which were called after the city and fort of that name, where was the market to which they wero brought, although none of them were found there or in the near neighborhood. Nothing of the city is left, ar-d the mines have fallen into neglect; but when Tavernier visited the district, in 1636, he found twenty-three mines in operation, employing sixty thousand men and women, girls and boys, and producing some wonderfully large and fine stones.
The mining district between the Godavery and the Mahanadi-the Adamas River of the ancients, where, it was said, "They find diamonds in quantities"—was also visited by Tavernier in 1655. The whole population were then accustomed to explore the river-bed in the late winter, when the water was low, and there was no work in the fields, and wash the diamonds from the sand.
The only mines in India now worked are at Pannah—the Panossa of Ptolemy—in Bundelcund. These also were in their day the most important diamond-fields in the world; now they are let by the local ruler to native workers, who put on an air of deep poverty, and whose greatest trouble arises from the fear that their lord may think they are becoming prosperous, and increase his charges upon them. They excuse their listlessness by averring that the tutelary deities of the soil, being irritated by the English conquest, have deserted the mines and ceased to plant them with precious stones. The rajah, however, expects at least a minimum of revenue from his mines, for, we are told, if it falls below a fixed sum, he beheads a chief and confiscates his goods. "He is cheated all the same, but he gets an actual share of one kind or another, which, without the making of an occasional example, would doubtless be denied him." The diamond industry of this country, whence nearly all the most famous crown-jewels of Europe were derived, which was once so prolific that the very mention of the name of India still awakens in the imaginative visions of untold wealth and glittering splendor, has fallen off till it is now estimated that the whole weight of Indian diamonds exported to Europe is not greater than one hundred carats a year. It was practically extinguished by the opening up of the mines of Brazil, which were discovered in 1725, and began to send in their consignments in 1730.
The first Brazilian diamonds were found by the gold-washers in the Villa do Principe, who used the crystals for counters in playing cards. A monk, who had been in India, recognized them as diamonds, and sent some of them to Europe to be cut, and thereby advertised their existence. In 1730 the diamond-fields were declared to be royal property; and from that time on, till diamonds were found in South Africa, Diamantina, in Minas-Geraes, Matto-Grosso, and the mines of the Paraguay River, were the chief sources of the world's supply. Another diamond-field was discovered in 1843, in the province of Bahia, which soon became the center of a population of thousands of seekers, and for a time yielded rich returns.
Of other famous diamond-fields—Madame Meunier records that the Chinamen in the mountains of Chinkangling collect diamonds from the sands in the valleys by wearing slippers of straw which catch the precious stones and hold them, and then, on being burned, give them up. Diamonds in considerable quantities have been mined in Borneo, which has furnished one of the largest gems in the world, valued by the Governor of Batavia, who made the offer to the owner to be refused, at the worth of two brigs of war fully equipped and ammunitioned, plus one hundred and sixty thousand dollars. Some specimens have been found in Australia, which might have attracted more attention but for the discovery of the South-African fields, and small numbers or small crystals in nearly every other country.
The diamond-fields of South Africa are richer and more extensive than any others—so far as we know of present and have accounts of past richness—although they were only discovered less than twenty years ago. They are situated in Griqualand West, north of the Orange River, at an elevation of four thousand feet above the sea, six hundred and ten miles from Cape Town, and four hundred and eighty miles from Port Elizabeth. They might have been found long before they were, for the place was marked on a French mission-map of 1750 with the phrase Ici sont des diamants ("Here there are diamonds"), but that had long been lost sight of or disregarded. The rivers of the region had been resorted to by the natives and their ancestors for perhaps generations, for crystals with which to bore their weighting-stones, but no account seems to have been taken of that fact. Van Niekerk's children at Barkly, on the Vaal, and De Beer's at Dutoitspan, were in the habit of playing with the diamonds along with the other pretty pebbles which they found in the gravel, and no one thought the diamonds were anything more than pretty stones till one evening in March, 1867, when a trader, John O'Reilly, "out-spanned" at Mr.Niekerk's farm. "O'Reilly saw a beautiful lot of Orange River stones on the table, and examined them. 'I told Niekerk,' he says, 'they were very pretty. He showed me another lot, out of which I at once picked the first diamond. I asked him for it, and he told me I could have it, as it belonged to a Bushman boy of Daniel Jacob's. I took it at once to Hope Town, and made Mr.Chalmers, civil commissioner, aware of the discovery. I then took it on to Colesberg, and gave it to the acting civil commissioner there, for transmission to Cape Town to the high commissioner.' "Another account says that O'Reilly and Niekerk tried the stone on the window, and scratched the glass with scratches that are still there; and that on his way, O'Reilly was laughed at for believing that he had a diamond, and the stone was taken from him and thrown into the street, whence he had some difficulty in recovering it. This stone was sold to Sir Philip Wodehouse, for £500. Several other diamonds were obtained during the year, among them the famous "Star of South Africa," which was bought of a native for £400, and sold in Hope Town for more than £10,000; and now, cut, reduced from 832 carats in the rough to 462 carats, and in the jewel-case of the Countess of Dudley, is valued at £25,000. Upon the news that such a gem as this had been found, which was spread in 1869, a "rush" of diggers took place to the Orange River. It was on the Vaal, however, that they found the diamonds, and they scattered their camps for a hundred miles or so along its course, where the washings still yield more or less satisfactory returns. The importance of this district was destined to be speedily eclipsed by the discovery, in 1871, of the famous Kimberley mine—first known as the "Colesberg Kopje," or Colesberg Hill, because it was discovered by three men from Colesberg, afterward by the suggestive name of "De Beer's New Rush," and finally by its present title—and its companion mines De Beer's, Bultfontein, and Dutoitspan. These mines are situated some twenty miles south of the river-mines, in a sandy, treeless country, that contrasts most unfavorably with the green and shady valley of the Vaal, and are so placed with reference to one another that a circle three and a half miles in diameter will inclose them all.
The Kimberley mine was opened to the public on the 21st of July, 1871, the allotments being made in claims thirty-one feet square. Any one could take one or two claims, but no more, for himself, on the payment of thirty shillings a month. If the claim remained unworked for a month, it could be allotted to another applicant on the same terms. A strip of seven and a half feet on one side of each claim was reserved for roadways, of which some fourteen or fifteen, each fifteen feet wide, were provided. But as the claims were worked, forming pits of greater and greater depth, the roadways soon became unsafe and began to cave in, and they eventually had to be abandoned. But the scene while they were in operation is described by Mr.Theodore Reunert, in the "Hand-Book" of the colony, which was published in connection with the recent Indian and Colonial Exhibition, as having been most picturesque: "Hundreds of carts and wheelbarrows careering along the roads, bearing their precious freight of excavated ground clear of the mine to be sorted; down below, at all distances from the surface, a succession of rectangular ledges, representing the various working-levels of different claims, where thousands of diggers and native laborers, crowded together on the narrow working-spaces, were busy picking and shoveling the ground and filling it into the original tubs and buckets of all sorts and sizes employed for conveying it to the surface; some of these were hauled up by ropes and tackle, others carried by hand up inclined planks and staircases cut in the perpendicular walls; each man worked on his own device, without regard to his neighbor, the only general rule being that the roadways must be kept intact."
After the roadways collapsed, the problem was presented of finding a way to work the large number of successive holdings, so as to preserve free access to each, and still let no claim-holder encroach or trespass on his neighbor's ground. A system of haulage upon endless ropes stretched between the claims and the edge of the mine, was adopted as a temporary expedient; but this had to yield to the objections that the entire circumference of the mine did not afford frontage enough for the erection of a hauling-gear to each claim; and even if it had been enough, difficulties would have to be encountered in the crossing of the ropes. These difficulties were remedied by the erection of a system of stagings around the margin of the mine, having four or five stories of scaffolds, on which the endless ropes could be landed at different levels, the highest platforms communicating with the claims nearest the center of the mine. This arrangement gave way in time to "horse-whims," and then to steam-engines, the introduction of which was long delayed on account of the cost of transit over the five hundred miles from the coast, and of the uncertainty which prevailed whether the mines would hold out long enough to make the expenditure for them profitable.
The four principal diamond-mines of the Kimberley district have substantially the same formation. They are like bowls of diamond-bearing earth lying in a funnel-shaped inclosure of unknown depth. The surface of the whole country is covered with red, sandy soil, varying from a few inches to about two feet in depth; underneath this is a thin layer of calcareous tufa, never extending beyond a few feet in thickness. Both of these layers are of recent date, or even still in course of formation, and are general. Beneath them, the distinction between the mine formation proper and the outside rocks or "reef," first becomes apparent. The next general formation going down, in which the diamond-bearing funnel is hollowed out—the "reef" of the miners—is a shale, yellow, or colored from gray to pink, the "upper reef" extending to a depth of from thirty-five to fifty feet, beneath which is a black carbonaceous shale, running to from two hundred and sixty to two hundred and eighty-five feet below the red sand, where it gives place to an amygdaloid dolerite, identical with the bed-rock at the Vaal River diggings.The diamond-bearing soil is, for the first hundred feet down, soft and friable, of a yellowish color, and crumbling as soon as it is exposed to the air. At about this level, although there were variations in the depth on different claims, the character of the rock all at once changed, and it became hard and of a slate-blue color. This feature caused a panic among the miners, for they at once presumed that the bottom of the diamond-deposit had been reached. They, however, treated the matter in a business sort of way, as things are said to be done in the exchanges where speculation rages. According to the story, as told by Mr.George J.Nathan, in "Longman's Magazine," "the claim-holders determined to say nothing about their discovery, but to go at once and try to sell their claims to unsuspecting diggers. Several of them accordingly put back the diamondiferous soil to the depth of a few feet, and
Interior view of the kimberley diamond mine
sold the claims at the ruling prices, which were then, in 1872, fifty to one hundred pounds per claim. Naturally the purchasers found (as they thought) that they had been sold, and they in their turn again planted "the claims on some more of their brother-diggers," A few, however, held their claims on the chance of something turning up, and they had their reward; for, before long, "some one had cut through this hard blue rock and hauled it from the mine into the air. Here it was left for some time exposed to the rays of the sun and the dews and rains of heaven; when one day it was found to have pulverized into a kind of mixed soil, consisting of iron-stones, pieces of hard carbon, garnets, flakes of mica, quartz-crystals, iron pyrites, peridot basalt, and what was not expected, diamonds! Yes, imbedded in this compact mass were numbers of diamonds far exceeding in quantity and quality anything taken from the upper stratum of yellow soil. Diggers had only been scratching the outer skin of the great Kimberley mine." The "yellow ground" is now known to be only the blue ground, which has been changed in color and consistency by exposure to the atmosphere; and the character of the "blue" has not shown any alteration, except that it has become harder and more crystallized, at the depth of six hundred feet, to which the lowest sinkings have been extended. The rock itself is described, generally, as a hydrous magnesian conglomerate, with silica as a base; but it is added that its precise nature is still doubtful, and "a catalogue of all it contains would fill a page." In the shale on the south side of the mine a lump of coal was discovered, and within the mine itself charred-wood fossils have been found. Thin veins of calc-spar are pf frequent occurrence. Vaalite, mica, iron pyrites, and hornblende, are disseminated through the 'blue,' besides fragments and masses of shale, sandstone, and bowlders of dolerite."
The working of the mines has been seriously impeded and made vastly more expensive by the treacherous nature of the "reef," or formation of yellowish and blue shale with which its upper part is surrounded. Wherever this rock is exposed it becomes disintegrated, and is then liable to slip down at any time, like a land-slide, upon the miners working beneath it, covering up their claims and making it extremely difficult as well as dangerous to work in them; for the removal of such masses as came down soon grew to be a formidable task. In fact, the mine has not yet fully recovered from the troubles which this reef has imposed upon its workers. These most affected the claim-holders near the margin of the mine. At the same time those near the center were embarrassed by the accumulation of water in their holdings. "It soon became a recognized principle that both reef and water should be treated as common enemies, and accordingly a general rate was levied upon the whole mine to deal with them." To work more effectually with the reef-removal, the Mining Board erected costly hauling machinery on two of the corners of the mine, and sank a large vertical shaft through the reef at the northeast corner some two hundred yards back from the limit of the claim-ground. The shaft, however, was stopped as soon as the hard rock was reached at two hundred and eighty-six feet below the surface. Tramways were laid to take the place of the carts that had been used, and the capacity of all the machinery for removing material was greatly increased. Early in 1878 one quarter of the claims were covered by reef, which was hauled out at an expense of four shillings per load of sixteen cubic feet. In 1879-'80 the board expended £300,000 on the removal of reef, dibris, and water; in 1881, £200,000; and in 1882, more than £500,000, while claims were still covered, and other slips were impending. Although at the beginning of 1883 three shafts, one of them four hundred and fifty and another six hundred and fifty feet deep, had been sunk to assist the process, the removal of reef did not keep pace with the constantly recurring slips; and the board having spent £650,000 in eighteen months, and laboring under a deficit of £250,000, could not get its bills discounted. Consequently a "Black Friday" came to the mines, and the value of their shares fell by fifty, seventy-five, and ninety per cent; and holders of shares on which calls were liable to be made "would have been only too glad to have paid men to take them over, so as to free themselves from the liability which they were incurring."
The discovery of the hard rock, says Mr. Reunert in his report, practically confined the reef difficulty within manageable limits, as there is little doubt that this rock will stand without disintegrating, even when exposed to a great depth. But the experience of successive reef-slips has considerably increased the estimate of the shale to be removed to render the mine safe for working on the open or quarry principle. It was at first supposed that the reef would stand if cut back to an angle of 60° receding from the mine; then 45° was spoken of as the angle of repose; but it has now been found that an angle of 30° will be needful. The cost of removing this obstruction has been vastly increased by the failure to apply comprehensive and systematic plans in the beginning; but this failure is apologized for by saying that no one knew what the future of the mine would be, or was ready to venture at once upon so large a permanent outlay as would be required.
The area of the Kimberley mine, originally inclosed within the reef, was about eleven acres. Successive slips and removal of reef have widened the area till it is now twenty-five or thirty acres. The inclosing rocks which form the walls of the diamond-bearing "pipe" converge inward from the surface downward, so that the area of claim-ground is constantly reduced as the mine deepens; but in some of the lowest sinkings, which have gone to more than six hundred feet below the surface, the rock has been found to recede from the mine, and thus to permit the regaining of a certain area of rich ground.
The difficulties caused by the reef have been at last overcome without having first to remove the accumulation of material by the adoption of a system of shafts and tunnels which is called, after its inventor, "Jones's system." A shaft was sunk through the fallen reef within the mine by letting down a series of caissons till the solid "blue ground" was reached. A hundred feet of loose reef was thus penetrated, after which the shaft could be extended to any desired depth in the "blue," and tunnels driven in all directions, so as to continue the excavation of the mine underground. The scheme had the merit of entailing little initial outlay, while, as soon as the "blue" was reached, the work of opening up the galleries more than paid for itself in the value of the ground removed. Other shafts have been sunk outside of the mine, one being more than five hundred and twenty feet deep, and others going down to the hard rock, and connected by tunnels and cross-tunnels, so built that the cross-tunnels have a wall of hard rock on one side, while the roof and other side are solid "blue." The excavation, says the report, "is then continued by cutting down the 'blue' from the roof overhead; but instead of trucking away the 'blue' as it falls, the rails in the tunnel are taken up and the 'blue' is allowed to pack underfoot, the miners therefore being continually climbing to a higher level, while the height of the tunnel remains uniform, just enough for the miners to be 'in touch' with the roof." In order to preserve safe means of access and egress for the workers in this continually rising chamber, a couple of cross-headings are driven parallel with it, five feet high by four wide, branching out at right angles from either side of the main tunnel, and leaving a solid wall of "blue" ten feet thick between the cross-headings and the main chamber. "A number of inclined passes are then driven at a sharp angle through this wall of blue, connecting the cross-heading with the working-chamber, and where they strike the latter vertical 'pass-pits' are carried up, rising simultaneously with the chamber, and separated from it by a three-inch plank, which prevents the loose pack of blue from filling the passes. At last the overhead excavation has proceeded so far as nearly to strike the fallen reef which at present covers all the open workings in the mine. The crown of the chamber is then broken through at either end, and the loose reef allowed to enter and pack on the top of the excavated blue. A sliding-door in the planks at the bottom of the pass-pits is then opened and the excavated blue drawn off, sliding down the inclined passes into trucks in the cross-headings, which convey it through the main tunnel and shaft to the surface. As the blue is drawn off, the loose reef above it subsides and takes its place till the chamber is entirely emptied of blue and filled with reef. The sliding-doors are then closed, and the excavation of that chamber is complete." This process is repeated, with modifications in the several chambers as they are successively excavated; while in another part of the mine an opposite system of excavation is succesfully conducted. A shaft is sunk in the blue to a total depth of five hundred and twelve feet below the red soil, and two sets of workings are opened up—one at this lowest level in course of preparation, while a first level eighty feet higher is now being worked out. At each level two sets of tunnels are used, one above the other, at a vertical distance of fifty feet apart. The upper tunnels give the level at which the excavation of large chambers is begun; and these are gradually worked downward, the roof being left untouched, while the excavated ground is delivered down vertical passes to the trucks in the lower or main tunnel.
The De Beer's mine is similar in formation to the Kimberley mine, but about one fifth larger in area. The reef incasing it for a depth of one hundred feet is a yellow basalt, after which succeeds a layer of black shale, extending to a total depth of two hundred and ninety feet from the red sand, where the hard igneous rock is struck. Within the mine the diamondiferous soil is "yellow ground" to a depth of one hundred feet from the surface, after which follows an unknown depth of "blue ground." As in the Kimberley mine, the richness of the ground greatly varies in the different sections. Having the advantage of the experience of the Kimberley, this mine has been steered clear of serious difficulties from reef. But some falls of reef which took place in 1883 and 1884, and a fall of nearly half a million loads of top unpayable ground, forced the claim-holders to consider some alternative to continuous working in the open mine; and it has become apparent that the future excavations must proceed underground. Five out of the seven companies holding the mine have sunk shafts within it for the purpose of reaching the "blue ground." One company has a shaft outside of the reef-margin, with a tunnel leading into the mine at a depth of one hundred and fifty feet from the surface. Another company has sunk a shaft from the outside at an angle of thirty-five degrees from the vertical to a depth of five hundred feet from the surface, from which working-galleries open at depths of five hundred and three hundred and eighty feet. This mine, like the Kimberley, is reduced in size at the cutting in of the hard rock.
The Bultfontein mine is almost circular in shape, with a diameter of about three hundred yards. It does not present equal promise to the operator with the two mines already described, and a considerable proportion of its claims are still unworked, while others have been abandoned on account of the encroachment of a mass of shale upon them. No underground workings having been begun in it, it presents to the casual observer a better idea of the nature of the operations that have been carried on within the last ten years than any of the other three mines, and for that reason it has been chosen to furnish a model of diamond-mining for the Indian and Colonial Exhibition.The Dutoitspan mine derives its name from the "pan," or small lake, which lies between it and the Bultfontein mine. This pan is filled by surface drainage after heavy rains, and sometimes covers fifty or sixty acres, when good boating and wild-duck shooting may be had upon it, but in times of drought it is entirely dry. The water of the pan, and of another body, Blankenberg's Vley, is leased by the diggers for mining purposes. Except that it is semicircular instead of being circular or oval, the description of the Dutoitspan is very similar to that of the other mines.
The gems were extracted from the earth, at the beginning, when everything was crude and done in haste, and when water was scarce, by the method of "dry-sorting," which consisted in sifting the excavated ground through hand-sieves, and then passing the finer portions over a sorting-table. By this method as many diamonds were missed as were found, and frequently the yield from the rewashing of the earth over which the process had been performed gave better returns than were gained in the first instance. A modification of the "cradle" was then introduced, but it eventually gave way to the "Rotary Washing-Machine," which is still generally employed. It consists of an annular-shaped pan, from eight to fourteen feet in diameter, which is closed by an outer and an inner rim, of which the inner rim is about four feet in diameter, and is not so high as the outer rim. A vertical shaft rotates in the center of the open space, carrying ten arms radiating around it, each of which has half a dozen vertical knives, or teeth, set within half an inch of scraping the bottom of the pan. The diamondiferous ground, mixed with water, enters through an orifice in the outer rim of the pan, and is stirred up into a ripple by the revolving knives, whereby the lighter stuff comes to the surface and continually floats away through an orifice in the inner rim, while the heavier gravel falls to the bottom of the pan. The mud, or "tailings," which flows to waste over the inner rim, is led by a shoot to a pit, whence it is lifted by a chain and bucket elevator some twenty or thirty feet high. At the top of the elevator the buckets deliver the tailings onto suitable screens, over which the solid mud runs to waste, while the muddy water is led back by an overhead shoot to the machine to assist in forming a puddle of sufficient consistency to float the lighter stones in the pan, and allow only the heaviest ground to accumulate at the bottom. For the better mixing of this puddle, an inclined cylindrical screen is fixed above the level of the pan. The dry ground from the mine is tipped into the upper end of the screen, where it is met by the muddy water from the elevator and a certain amount of clear water. The large stones, of a size unlikely to include diamonds, roll out at the lower end of the cylinder, but the puddle, carrying all the smaller stones with it, passes through the wire netting of the screen and down a shoot into the pan, as above described. At the end of the day's work the machine is stopped, and the contents of the pan, after they have undergone an intermediate cleaning in a cradle, or in a small gravitating machine, called a "pulsator," are emptied upon the sorting-table. The "pulsator" is also often so employed as to dispense with the "panning" process.
At the "river-diggings" (on the Vaal) the diamondiferous deposit is imbedded between bowlders and mixed with fine red sand, and sometimes with lime. The diamonds are separated by sifting the earth through a machine called a "baby"—a kind of swinging sieve, which, the coarser pebbles having been taken out by another sieve impending above it, allows the medium-sized pebbles, supposed to contain diamonds, to roll into a tub, while the finer refuse sand passes through its meshes. The contents of the tub are then gravitated, and the heavier stones are turned upon a "sorting-table," and the diamonds picked out by careful scraping. An experienced digger can tell at a glance, from the appearance of the deposit, what chance there is of "finding well" in it. He knows by sight the heavier stones that occur in diamond-bearing ground, and their presence is a sure sign of diamonds being there too. This is particularly the case with a curiously marked pebble that is streaked with a succession of parallel rings, from which it has received the descriptive name of "banddoom" (bandround). The specific gravity of the "banddoom" is almost identical with that of the diamond, and, where the former is found, experience has taught that the latter may be confidently expected. Beautiful agates are also found in this deposit, as well as quartz-crystals, jaspers, chalcedony, but few garnets, and no iron pyrites or carbon, which occur so plentifully in the Kimberley mines. An assortment of "river-stones" forms a very pretty collection, and it is conceivable enough that, prior to the opening of the diggings, diamonds should have been picked up by the natives and valued as more than ordinarily pretty pebbles. The river-digging is, however, not very profitable in the face of the large returns given by the Kimberley mines, and is now relatively of but little importance.
The whole number of claims in the four mines of Kimberley and Beaconsfield is 3,238, covering about seventy acres of diamondiferous gravel. The whole property is assessed at £5,172,975, or at the rate of £75,000 per acre, and is divided among ninety-eight holders, forty-two of whom are joint-stock companies, and the remaining fifty-six private firms and individuals. The gross capital of the joint-stock companies, which hold 2,211 claims, is returned at £7,970,490; and that of the private holders is estimated at £1,624,900, making the gross capital of the entire mines £9,595,390. The annual expenditure in labor, material, etc., is not less than two million sterling, or ten million dollars. It has been estimated, by the comparison of information from various official sources, that the gross value of diamonds exported from the Cape Colony up to the end of 1885, exclusive of such as were not reported or were illicitly taken away, amounted to £35,000,000. The total yield of diamonds from the Vaal River to date has probably exceeded £2,000,000.
In quality the Vaal River stones are rated highest, in the degree that while in the three years ending with August, 1885, the weight of those sent away from that district was only about 1⁄125, that of the entire exports their declared value was as much as 1⁄62 of the total value exported. Of the four Kimberley and Beaconsfield mines, Dutoitspan produces the finest stones, ninety per cent being perfect. Bultfontein comes next, with its beautiful white stones, weighing from a quarter of a carat to two carats. De Beer's comes next, and Kimberley last. In absolute value of production, the order is, Dutoitspan, De Beer's, Kimberley, Bultfontein. The largest diamond ever found in Griqualand West was an irregular octahedron from Dutoitspan, slightly spotted, and of yellow color, which weighed 404 carats, or nearly three ounces. The only larger stone than this known to have ever been found was a very imperfect one, discovered near Jagersfontein, which weighed about 500 carats. Another diamond, of 352 carats, has been found at Dutoitspan. The largest stone ever found at Bultfontein weighed a little more than 150 carats. The Bultfontein diamonds, while superior in color to all others except those of Jagersfontein, are of smaller average size than those of the other three mines.
All the diamonds coming from the various South-African mines are said to have a distinct personality, by means of which experts can at once recognize stones from either of the four mines, and tell from which it came, and can again distinguish those of the Kimberlev and Beaconsfield mines from those of the river-diggings, and their testimony on this point is accepted by the courts.
All the theories by which the attempt is made to account for these mines recognize them as of volcanic origin. Their form suggests at once the crater of an extinct volcano, or the tube of a geyser. When the attempted explanation goes beyond this, the range of diverging opinions is quite wide. Of these various views, we will refer only to the observation of Sir Henry Roscoe, that the most noteworthy feature of the diamond-bearing rocks of Kimberley is the discovery in the diamond-earth of a volatile crystalline hydrocarbon, soluble in ether, which seems to confirm the hypothesis that the carboniferous shales, which are penetrated by the diamond-bearing pipes, have been the source of the carbon now found in the crystalline state in this gem. The physical structure of the ash, or incombustible portion of the stone, is of a very singular character, and has hitherto not been examined. A careful study of it may possibly throw light on the important question of the mode of formation of the diamond.