472 THE JOURNAL OF GEOLOGY. 



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 conti- 

 nents, 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 den- 

 sity of the crowd of animals on favorable spots. Deep sea explo- 

 rations give only the most scanty basis for a picture of the sea bot- 

 tom, 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 palaeozoic 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 support- 

 ing 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 sel- 

 dom 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- 



