The reefs towards the sea outside the Lagoons go down very suddenly, and the soundings are generally deep, close alongside them. This is ascribed to their being built upon the tops of submarine hills and mountains, for it is believed that the polypes cannot work at very great depths. The surface of the reef is seldom quite so high as high-water-mark; but they sometimes go along an incredible distance without interruption, very near that point. The inhabitants of the group of islands called Disappointment Islands, and also of those called Duff's Islands, pay visits to each other over a bridge of coral 600 miles in length, on a great part of which their feet are close to the water, so that they look when on their journey at the time of high-water, just like troops marching on the surface of the ocean. The natives of some of the Polynesian islands have actually employed some of these wonderful little masons to build quays and piers. The way they do this, is to break off large masses of coral from any reef that may be near, and drop them down where they want to form the pier. In a short time the polypes will have stuck them together as firmly as possible. In an island called Barabora, a very fine quay has been thus constructed, where a good-sized vessel may conveniently take in or discharge its cargo. There were once coral islands where England is now, for in many counties fossil coral is found in great quantities. It is indeed most likely that there are large tracts in every part of the world, which owe their existence to the labours of polypes. This would most probably be the history of the formation of one of these tracts, if it were in the Pacific Ocean. A volcanic eruption would throw up a mountain from the bottom of the sea, the top of which might be 60 or 70 feet below the surface. As soon as the eruption had ceased, some polypes who may have left their position on a neighbouring reef, might be brought by the tide into contact with the summit, and would immediately begin to work. The race of polypes would multiply, and the building would go on year after year, till the reef reached the surface. Pieces of wood which are always drifting about in the ocean, might be washed into the Lagoon and rest upon the shore. A little soil might thus be formed in the course of years, and a cocoa-nut or some other sort of seed, which would equally well bear soaking in the salt water, might be brought from some distant land, and may take root and produce a tree. The steady trade winds would also bring some of those seeds which are provided with wings, such as thistles. Various sea birds might build their nests upon the infant land, which would thus be increased in a hundred different ways. Small animals driven out to sea on pieces of timber or trees, torn away from their original position by hurricanes, might land upon it; and after a succession of ages, man would take possession, and a populous country in time be formed.