THE ORIGIN OF THE OLDEST FOSSILS. 371 



from the opeu water to force themselves in among the okl ones, and 

 colonization soon came to an end. 



The great antiquity of all the types of structure vrhich are repre- 

 sented among modern animals is therefore what we should expect, for 

 after the foundation of the fauna of the bottom was laid it became, and 

 has ever suice remained, difticult 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 intiuence 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. IJeep-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 luxuri- 

 ance of tropical vegetation, and Sir Wy villa Thomson says he once 

 brouglit up at one time on a tangle, which was fastened to a dredge, 

 over twenty thousand specimens of a single sjiecies of sea-urchin. The 

 number of remains of paleozoic 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 descrii^tiou can convey any adeciuate 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 Avere darting about among the corals and gorgoiiias in all 

 directions; but this was not all, for the solid rock was honeycombed 

 everywhere by tubes and burrows, and when broken to pieces with a 

 hammer each mass of coral gave us si)ecimens of nearly every great 

 grouj) in the animal kingdom. Fishes, Crustacea, annelids, mollusca, 

 echinoderms, hydroids and sponges could be picked out of the fragments 

 and the abundance of life inside the solid rock was most wonderful. 



The absence of pelagic life in the landlocked water of coral islands 

 is as impressive and noteworthy as the luxuriance of life upon and near 

 the bottom. 



On my first visit to the Bahama Islands I was sadly disappointed by 

 the absence of pelagic animals where nil the conditions seemed to bo 

 X)eculiarly favorable. 



