blue color, attached to the rocks by a broad expansion of its base. In the figure, the fleshy substance is removed at the extremities to exhibit the stony axis. It is seldom found more than a foot in length, and is well known, being used for various ornamental purposes, and is obtained by dredging in various parts of the Mediterranean and Eastern seas. Another species of red coral, the organ-pipe, or tubipora, is shown in the above wood-cut, this derives its name from its tubular appearance, being composed of parallel tubes united by lateral plates or transverse partitions placed at regular distances. The polypi of this coral are of a beautiful green color. This species occurs on the coast of New South Wales, and in the islands of the Molucca group, in hemispherical masses of from one to two feet in circumference, which first appear as small specks, adhering to the rock, these gradually increase, and the tubes shoot forth like little rays; other tubes spring from the transverse plates, finally constituting a uniform tubular mass, the surface being covered with a green fleshy substance, beset with stellar animalcules. The geographical distribution of corals is very extended. The Pacific, throughout a space comprehended between the 30th parallel of latitude on each side of the equator is very productive, and also the Persian and Arabian Gulfs. They are very abundant APPEARANCE OF LIVING CORALS. 285 in the Indian ocean and some parts of the Atlantic. Many species of this genus are found along our Atlantic coast and on the shores of England. Some species seem to prefer the more exposed situations, flourishing in the greatest profusion, on rocks and plants which the tide every day leaves bare; the larger polyparia however, are seldom found in places exposed to violent currents; they flourish in the submarine grottoes and hollows of the rock, where they shoot out their delicately branching forms studded with zoophytes of most brilliant colors. Others attach themselves to the flexible branches of the sea plants, encasing them in a living tomb, and are thus fitted to enjoy the powerful action of the surges; the pliant branches bending to and fro, with the movements of the waters. Others form immoveable rocks, and slowly increase, until at last an island is elevated above the waters. The distribution of corals, like that of plants, varies with the climate. In the colder northern latitudes, a few sponges, and sertulariæ alone are found, but in the warmer, equatorial regions, within the tropics, they attain a luxuriance and beauty, a grandeur and importance well worthy our attention. Here, in an ocean of uniform temperature, they elevate those immense reefs which eventually become the habitations of men, and even gardens producing rich tropical fruits and flowers. These minute beings, myriads upon myriads, here exercise their empire, sometimes, in the sheltered places, or still lagoons, shooting forth the most delicate branches, and in others, where the surges beat upon them, growing firm and solid as the rock on which they are based. The appearance of the living corals in the water is described as most enchanting. The whole bed of the Red Sea is absolutely a forest of sea-plants and corals, presenting the appearance of a submarine garden of the most exquisite verdure, resembling in splendor and gorgeous coloring the most celebrated parterres of the East. Ehrenberg, the distinguished German naturalist, so well known by his admirable investigations of infusoriæ, was so struck with the view of the living corals in the Red Sea, that he exclaimed with enthusiasm "Where is the paradise of flowers that can rival in beauty these living wonders of the ocean?" Some M* have compared their appearance to beds of tulips or dahlias; and, in truth, the large fungiæ, with their crimson disks, and purple and yellow tentacula, bear no slight resemblance to the latter. The tender branches of the corals furnish food to some species of fish, which graze upon them in whole shoals, both within the lagoons in the quiet waters, and among the breakers on the outside of the reef. Nothing can be imagined more beautiful than the scene presented in the tropical climates, especially where the shore consists of alternate beds of sand, and masses of rock. "Groves of coral are seen expanding their variously colored clumps, some rigid and immovable, and others waving gracefully their flexile branches; shells of every form and hue, glide slowly among the stones, or cling to the coral boughs likę fruit; crabs and other marine animals, pursue their prey in the crannies of the rock, and sea-plants spread their limber fronds, in gay and guady irregularity, while the most beautiful fishes are on every side sporting around." VITAL CAUSES OF CHANGE. 287 CHAPTER XI. Coral Islands. "I saw the living pile ascend, The mausoleum of its architects, Still dying upwards as their labors closed; J. Montgomery. HAVING in the preceding chapter given a brief description of some of the more common varieties of corals, we shall now consider more fully the agency of these wonderful animals in the formation of rocks. It has been generally considered that the zoophytes cannot live in water of very great depths, and that therefore their structures are based upon submarine mountains. This view has been confirmed by the observations of Ehrenberg, and more recently by the careful soundings of Captain Fitz Roy, of the Royal English Navy. At a depth of ten fathoms the prepared tallow invariably came up marked with the impressions of the living corals, and as clean as if it had been dropped on a carpet of turf; at a greater depth the impressions were less numerous, and the adhering particles of sand much more frequent, until at a mean depth of twenty-five fathoms it was evident that the bottom consisted of a smooth sandy layer. We may conclude therefore that the reef building corals, do not usually flourish much below this depth. The formation of the coral islets is somewhat analagous to the growth of a tree which has been headed. The zoophyte cannot endure even a short exposure to the sun's rays in the air, their growth upwards is therefore checked as soon as the surface of the water is reached. They spread out laterally however, not unlike the top of a tree. The appearance and formation of coral islands has been described very minutely by a great number of distinguished natural ists, and various theories have been proposed to explain the observed phenomena. We have devoted some little attention to this part of our subject, and are best satisfied with the explanation given by Mr. Chas. Darwin, in a paper read before the Geological Society in May 1837, and which we will explain presentlyEverywhere in the Pacific and Indian Oceans, within the tropics, may be seen coral banks in their various stages of progress; soine covered with light soil, and the habitations of man. Most of the reefs which raise themselves above the waters are of a circular form, enclosing a basin of still water, called a lagoon, which connects by means of one or two channels with the sea. In the interior of the island, the more delicate and smaller kinds of zoophytes live, while the stronger and hardier species, fitted to endure the beating of the surf, flourish on the outer margin of the isle. When the reef rises so high that it is left uncovered at low water, the corals cease to increase, the animals die, and the branches become somewhat decomposed. limestone are thrown up by the waves, with shells, and broken fragments of crustacean animals, seeds are floated by the waves towards the new formed island, and thrown upon its shores; and trunks of trees, drifted thousands of miles, find a lodgment upon it, bringing with them small animals, as insects and lizards. Bushes and trees, spring up, and the sea-birds nestle there, and finally at a later period, it becomes the habitation of man. The reefs of coral, consist not only of the corals, and their broken fragments, but masses of compact limestone, and imbedded shells are of frequent occurrence. The limestone is found sometimes in the uppermost or newest parts of the reef, and is formed by chemical decomposition, the carbonate of lime being supplied from the decomposition of corals and testacea. Fragments of coral We have already alluded to the geographical distribution of corals, we may however, form some idea of the immense extent of the coral reefs when we learn that, off the coast of Malabar, in the Indian Ocean, there is a chain of coral islands of over 480 miles in length, called the Maldiva Group. On the coast of New Holland, is an unbroken reef-350 miles in length, and between that and the island of New Guinea is a coral formation which |