And yet this minute being, which belongs to the very lowest class of animals, not only makes the branching masses of coral that look like great stone forests under the water, but they also build immense walls, and piles of rocks, sometimes hundreds of miles in extent. The coral is made from a lime-like substance within the animal, which soon becomes very hard, and also from their lime-like bodies after they die. Coral reefs are found only in the warm regions of the globe, for the little workmen cannot endure the cold of the northern ocean. They cannot live in the air, and so they never work above the surface of the water. Of the branching coral there are three kinds; white, red, and pink. The white is the most porous and the least valuable, and the pink is the rarest, and most costly. These animals are called polyps, or polypi. In some parts of the ocean there are islands that were formed by them. That is, the coral builders commenced the business by gradually piling up in the wave a mass of coral. This they began upon some sand bar far down in the ocean, and they kept at work until they got a rocky wall up to the surface of the water; and then they could go no farther. These walls are generally circular. When the rocky coral walls reach the surface, the waves rush over them constantly, carrying with them sand, and broken fragments of corals. Some of these are left on the rocks, until, finally, they are piled up so high that the waves cannot roll over them. Thus is formed a singular-looking island, consisting of a circle of rock, with a pond of still water in the centre. This little lake is called a lagoon. Sand is strewn by the waves over the rocky reef, and rolled down into the lake, which it fills up, and, after a long time the soil becomes of sufficient depth to support coarse grasses, and sea plants. These die, and enrich the soil; and the winds, bringing from other shores the seeds of palm trees, and various plants, scatter them over the island, which is soon crowned with verdure and flowers. THE GREAT EASTERN. The Great Eastern is the largest steamship in the world; and is, indeed, the largest vessel of any kind in the world. You can see from the portion of the deck given in the picture that the whole ship must be of an enormous size. The scene on the deck is a busy one, for the vessel is being prepared for a voyage; the workmen are putting on the finishing touches in the way of carpenter-work and painting; and the sailors are busy with the sails and rigging. Hundreds of people are employed with steam engines, hoisting cranes, and various machines, and yet there is plenty of room for them to do their work without confusion. For the upper deck of this great steamer measures 680 feet from stem to stern, which is twice the length of the largest of other ocean steamers. The deck, in the widest part, is 82 feet wide. From this deck rise six great masts, and five smoke stacks.