When a chain of Coral rocks approaches close to the shore, so as to leave no intervening channel of deep water, they are called Fringing Reefs; and these constitute the fourth and last class of the Coral formation. They prevail everywhere in tropical regions, and appear as banks of Coral encrusting the rocky shores of islands and continents. As regards the geographical distribution of Coral Reefs, the first circumstance that claims our notice, is that they are exclusively confined to the warmer regions of the globe. They exist in great profusion within the tropics, and are rarely to be found beyond the thirtieth parallels of latitude on each side of the Equator. The only remarkable exception is in the case of the Bermuda Islands in 32° north latitude; but here, it is to be observed, the ocean is warmed by the waters of the Gulf Stream. Another singular fact is the almost total absence of Coral Reefs from the Atlantic Ocean. In fact, the Bermudas, we believe, constitute here again the only exception. The Pacific, on the contrary, is wonderfully productive of coral; also the Indian Ocean, the Persian and Arabian Gulfs, and the Red Sea. It may gratify, perhaps, the curiosity of some readers, if we add a word on the Red Coral which is now so favorite an ornament in the fashionable world. Though it never attains to the magnitude of those reefs and islands we have been describing, it partakes nevertheless of the same peculiar structure; and no doubt is entertained that, like them, it derives its existence from animal life, in the manner we shall presently explain. It is produced chiefly in the Mediterranean, in the Red Sea, and in the Persian Gulf; and is brought up from the great depths by means of a grappling apparatus attached to boats. The largest pieces have a shrub-like branching form, and are supposed to grow to the height of one foot in about eight years.[52]