Page:The Journal of geology (IA journalofgeology21894univ).pdf/24
expect, for after the foundation of the fauna of the bottom was laid it became, and has ever since remained, difficult for new forms to establish themselves.
Most of our knowledge of the sea bottom is from three sources: from dredgings and other explorations; from rocks which were formed beyond the immediate influence of continents, and from the patches of the bottom fauna which have gradually been brought near its surface by the growth of coral reefs, and from all these sources we have testimony to the density of the crowd of animals on favorable spots. Deep sea explorations give only the most scanty basis for a picture of the sea bottom, but they show that animal life may thrive with the dense luxuriance of tropical vegetation, and Sir Wyville Thomson says he once brought up at one time on a tangle which was fastened to a dredge over twenty thousand specimens of a single species of sea urchin. The number of remains of palæozoic crinoids and brachiopods and trilobites which are crowded into a single slab of fine grained limestone is most astounding, and it testifies most vividly and forcibly to the wealth of life on the old sea-floor.
No description can convey any adequate conception of the boundless luxuriance of a coral island, but nothing else gives such a vivid picture of the capacity of the sea-floor for supporting life. Marine plants are not abundant on coral islands and the animals depend either directly or indirectly upon the pelagic food-supply, so that their life is the same in this respect as that of animals in the deep sea far from land.
The abundant life is not restricted to the growing edge of the reef, and the inner lagoons are often like crowded aquaria. At Nassau my party of eight persons found so much to study on a little reef in a lagoon close to our laboratory that we discovered novelties every day for four months and our explorations seldom carried us beyond this little tract of bottom. Every inch of the bottom was carpeted with living animals, while others were darting about among the corals and gorgonias in all directions; but this was not all, for the solid rock was honeycombed every-