When the sea is perfectly clear and transparent, it allows the eye to distinguish objects at a very great depth. Near Mindora, in the Indian Ocean, the spotted corals are plainly visible under twenty-five fathoms of water. The crystalline clearness of the Caribbean sea excited the admiration of Columbus, who in the pursuit of his great discoveries ever retained an open eye for the beauties of nature. "In passing over these splendidly adorned grounds," says Schöpf, "where marine life shows itself in an endless variety of forms, the boat, suspended over the purest crystal, seems to float in the air, so that a person unaccustomed to the scene easily becomes giddy. On the clear sandy bottom appear thousands of sea-stars, sea-urchins, molluscs, and fishes of a brilliancy of colour unknown in our temperate seas. Fiery red, intense blue, lively green, and golden yellow perpetually vary; the spectator floats over groves of sea-plants, gorgonias, corals, alcyoniums, flabellums, and sponges, that afford no less delight to the eye, and are no less gently agitated by the heaving waters, than the most beautiful garden on earth when a gentle breeze passes through the waving boughs." With equal enthusiasm De Quatrefages expatiates on the beauties of the submarine landscapes on the coast of Sicily. "The surface of the waters, smooth and even like a mirror, enabled the eye to penetrate to an incredible depth, and to recognise the smallest objects. Deceived by this wonderful transparency, it often occurred during my first excursions, that I wished to seize some annelide or medusa, which seemed to swim but a few inches from the surface. Then the boatman smiled, took a net fastened to a long pole, and, to my great astonishment, plunged it deep into the water before it could attain the object which I had supposed to be within my reach. The admirable clearness of the waters produced another deception of a most agreeable kind. Leaning over the boat, we glided over plains, dales, and hillocks, which, in some places naked and in others carpeted with green or with brownish shrubbery, reminded us of the prospects of the land. Our eye distinguished the smallest inequalities of the piled-up rocks, plunged more than a hundred feet deep into their cavernous hollows, and everywhere the undulations of the sand, the abrupt edges of the stone-blocks, and the tufts of algæ were so sharply defined, that the wonderful illusion made us forget the reality of the scene. Between us and those lovely pictures we saw no more the intervening waters that enveloped them as in an atmosphere and carried our boat upon their bosom. It was as if we were hanging in a vacant space, or looking down like birds hovering in the air upon a charming prospect. Strangely formed animals peopled these submarine regions, and lent them a peculiar character. Fishes, sometimes isolated like the sparrows of our groves, or uniting in flocks like our pigeons