Ore reef

“ Since 1898, however, deep and yet deeper depths have been explored, especially in following the richer reefs, and always with the similar result of meeting with the same, or a superior, grade of ore contents peculiar to the higher sections of the particular reef, so that the inference is strengthened to certainty that profitable exploitation is only limited to the ultimate depth at which modern mining can be carried on. The problem, therefore, is one for the engineers ”

“ The claim subsequently known as the Progress was originally worked by the Oriental Company, which was formed in 1876, and, like its neighbour, the Globe Company, worked some large low-grade ore-bodies without success. In 1881 it purchased the battery of the Union Company, and did a certain amount of crushing, but in 1886 it went into liquidation, only a short time before the discovery of the east-and-west reef in the Globe ground, and the mine and plant were sold to Mr. ”

“ An instance occurred recently where one was wheeled against our grating after occupying a safe position for many years. Those that take up positions in the boat tracks are of course assailed at the earliest opportunity, an operation which generally entails a bit of submarine mining on our part. The reef consists of hard, red sandstone, arranged in irregular layers, with a dip of 15 degrees towards the south-east and extends in a north-easterly and south-westerly direction, having an area of about 500 yards by 100 yards considered dangerous to shipping. ”

“ High, precipitous, perpendicular, level, and dotted with farm-houses, this singular bit of land stretches several miles out southward to sea, bordered with a rocky beach, and tapered off into the wide ocean with Duxbury Reef—a dangerous rocky reef, curving down to the southward and almost always white with foam, save when the sea is calm, and then the great lazy green waves eddy noiselessly over the half-hidden rocks, or slip like oil over the dreadful dangers which they hide. ”

“ The waste from the land keeps the sea shallow offshore and constantly renews the sand reef. The energy of the waves is consumed in handling shore drift, and no energy is left for an effective attack upon the land. Indeed, with an excessive amount of waste brought down by streams the land may be built out and encroach temporarily upon the sea; and not until long denudation has lowered the land, and thus decreased the amount of waste from it, may the waves be able to cut through the sand reef and thus the coast reach maturity. ”

“ Where the channel is narrow, the agency, which on unprotected coasts is most productive of sediment, namely the force of the breakers, is here entirely excluded, and the reef being breached in the front of the main valleys, much of the finer mud from the rivers must be transported into the open sea. As a current is formed by the water thrown over the edge of atoll-formed reefs, which carries sediment with it through the deep-water breaches, the same thing probably takes place in barrier-reefs, and this would greatly aid in preventing the lagoon-channel from being filled up. ”

“ The ring-shaped reef, or atoll, is broken in one or more places, generally on the leeward side, and built up higher on the windward side. The reason for such omissions and buildings is obvious when we remember that the coral animal cannot move from its fixed position to seek food, but must depend upon the waves to bring it within reach. The water dashing up against the reef on the windward side brings an abundance of food, while the slight movement of the waves on the leeward side brings but little food. ”

“ No theory worthy of notice has been advanced to account for those barrier-reefs, which encircle islands of moderate dimensions. The great reef which fronts the coast of Australia has been supposed, but without any special facts, to rest on the edge of a submarine precipice, extending parallel to the shore. The origin of the third class or of fringing-reefs presents, I believe, scarcely any difficulty, and is simply consequent on the polypifers not growing up from great depths, and their not flourishing close to gently shelving beaches where the water is often turbid. ”

“ About a mile more or less off shore, there is as a rule a rocky reef, on which the breakers may be seen to dash violently in many places, the depth above the reef being in several places, 1, 11⁄2 and even 2 fathom, so that pinnaces and boats may get over it for the purpose of landing, there being deeper water close inshore, but all of it with a rocky, sharp coral-bottom, so that it is difficult to land there, and much harder still to keep a pinnace at anchor with a drag ”

“ Then, as the Crust of the Earth gradually subsides, the water encroaches on the land, and forms a channel between it and the reef. Meanwhile the Zoophytes are at work, and the coral rock is growing upward as the foundation on which it rests is sinking downward: each year it is higher from the bed of the sea, and yet no nearer to the surface of the waters. And when at length the channel, which is ever growing wider and wider, has reached a certain limit, the Fringing Reef becomes a Barrier Reef, or if it encompasses an island, an Encircling Reef. ”

“ The engineers propose, by a jetty from the south beach to a group of rocks forming the south side of the middle channel, to extend the narrow deep channel inside, and the consequent force of concentrated tidal and river water, up to the rocky reef itself. They judge that the tidal force is ample to scour away clean all the sand deposited both in and outside the reef. ”

“ The 'Father of the African Mines,' dating from 1878, lies on the northern third of the celebrated Tákwá ridge, and its concession embraces an area of 1000 x 2000 fathoms. The rich auriferous reef is the backbone of a long narrow line of hill whose diameter ranges between 1,000 feet to 600 where it is pinched. The lode strikes to the north-north-east with a dip of 47o west. The angle of underlay, I may remark, greatly varies in these Gold Coast reefs; some are nearly vertical (82o) , others are moderately inclined (20o to 50o) , and others run almost flat. ”

“ At one time I thought it convenient thus to restrict the term, but as these reefs are similar in structure, and in position relatively to the land, to those, which, like a wall with a deep moat within, encircle many smaller islands, I have classed them together. The reef, also, on the west coast of New Caledonia, circling round the extremities of the island, is an intermediate form between a small encircling reef and the Australian barrier, which stretches for a thousand miles in nearly a straight line. ”

“ As we went on, the reef-belt still accompanied us; turning as we turned, and thundering its distant bass upon the ear, like the unbroken roar of a cataract. Dashing forever against their coral rampart, the breakers looked, in the distance, like a line of rearing white chargers, reined in, tossing their white manes, and bridling with foam.
These great natural breakwaters are admirably designed for the protection of the land. Nearly all the Society Islands are defended by them. ”

“ At New Caledonia (Plate II, Fig. 5.) the barrier-reefs extend for 150 miles on each side of the submarine prolongation of the island; and at their northern extremity they appear broken up and converted into a vast atoll-formed reef, supporting a few low coral-islets: we may imagine that we here see the effects of subsidence actually in progress, the water always encroaching on the northern end of the island, towards which the mountains slope down, and the reefs steadily building up their massive fabrics in the lines of their ancient growth. ”

“ LOUISIADE.—The dangerous reefs which front and surround the western, southern, and northern coasts of this so-called peninsula and archipelago, seem evidently to belong to the barrier class. The land is lofty, with a low fringe on the coast; the reefs are distant, and the sea outside them profoundly deep. Nearly all that is known of this group is derived from the labours of D’Entrecasteaux and Bougainville: the latter has represented one continuous reef ninety miles long, parallel to the shore, and in places as much as ten miles from it ”

“ In very many instances, however, atolls and barrier reefs may be explained without subsidence. Thus a barrier reef may be formed by the seaward growth of a fringing reef upon the talus of its sea face. In Figure 162 f is a fringing reef whose outer wall rises from about one hundred and fifty feet, the lower limit of the reef-building species. At the foot of this submarine cliff a talus of fallen blocks t accumulates, and as it reaches the zone of coral growth becomes the foundation on which the reef is steadily extended seaward. ”

“ But there is a third kind of reef, of very common occurrence in the Pacific and Indian Oceans, which goes by the name of "atoll." This is, to all intents and purposes, an encircling reef, without anything to encircle; or, in other words, without an island in the middle of its lagoon. The atoll has exactly the appearance of a vast, irregularly oval, or circular, breakwater, enclosing smooth water in its midst. The depth of the water in the lagoon rarely exceeds twenty or thirty fathoms, but, outside the reef, it deepens with great rapidity to two hundred or three hundred fathoms. ”

“ These reefs, however, vary in construction; some are called encircling reefs, when they appear at a distance from the shore, and a lagoon intervenes; others are called fringing reefs, which are joined to the land, and extend out from it without any lagoon. Others are denominated lagoon islands, when the reef itself, raised above the surface of the ocean, forms the land generally in a circular shape, and surrounds a lake or lagoon, which has sometimes a passage to the sea, and at others is completely closed. ”

“ Small as are these tiny workmen, each and every one does his bit and, speck by speck, adds his minute contribution to the growing mass of coral until entire islands are surrounded by extensive reefs. Tahiti, for example, is surrounded by a barrier reef which is really an immense wall. The large barrier reef on the northeast coast of Australia extends in a continuous line for 1,000 miles, and varies from 10 to 90 miles in breadth. ”

“ Here, as in Whitsunday Island, the whole of that part of the reef which is visible is converted into land. This is a circumstance of rare occurrence; more usually a snow-white line of great breakers, with here and there an islet crowned by cocoa-nut trees, separates the smooth waters of the lagoon-like channel from the waves of the open sea. The barrier-reefs of Australia and of New Caledonia, owing to their enormous dimensions, have excited much attention: in structure and form they resemble those encircling many of the smaller islands in the Pacific Ocean. ”

“ These ever-growing reefs would surround the whole coast were it not for the fresh water that oozes out from the land and prevents the coral from growing at certain points, thus keeping open narrow passages through the reef, or wider stretches along the coast free from rocks. These basins form good anchorages for small craft, as the swell of the open sea cannot cross the reef; only the entrances are often crooked and hard to find. ”

“ As far as the actual reef is concerned, there is no essential difference between it and that forming a barrier or an atoll: it is, however, generally of less width, and consequently few islets have been formed on it. From the corals growing more vigorously on the outside, and from the noxious effect of the sediment washed inwards, the outer edge of the reef is the highest part, and between it and the land there is generally a shallow sandy channel a few feet in depth. ”

“ Of all the wonderful animal structures in the world the Great Barrier Reef of Australia is the most remarkable. It consists of a chain of coral islands and reefs parallel to the east coast of Queensland. This great reef is about twelve hundred miles long, and the distance from the mainland to its outer border is from ten to more than one hundred miles. It is far enough off the coast to leave a wide channel between the reef and the shore. ”

“ A citizen told me a curious thing about those mines. With all my experience of mining I had never heard of anything of the sort before. The main gold reef runs about north and south—of course—for that is the custom of a rich gold reef. At Ballarat its course is between walls of slate. Now the citizen told me that throughout a stretch of twelve miles along the reef, the reef is crossed at intervals by a straight black streak of a carbonaceous nature—a streak in the slate; a streak no thicker than a pencil—and that wherever it crosses the reef you will certainly find gold at the junction. ”

“ Submerged and dead reefs.—In the second section of the first chapter, I have shown that there are in the neighbourhood of atolls, some deeply submerged banks, with level surfaces; that there are others, less deeply but yet wholly submerged, having all the characters of perfect atolls, but consisting merely of dead coral-rock; that there are barrier-reefs and atolls with merely a portion of their reef, generally on the leeward side, submerged ”

“ In latitude 31 degrees 47 minutes 50 seconds, and at the distance of two miles and a quarter from the shore, is a dangerous reef, on which the sea constantly breaks; it was named by Lieutenant Oxley, who discovered it, the MERMAID'S REEF; it is about a quarter of a mile in extent, and bears South 85 degrees East from the South Brother; a small detached portion of the reef is separated from the principal rock, within which there appeared to be a narrow navigable channel. A quarter of a mile without the latter we found sixteen fathoms water. ”