Ch. VI. DISTKIBUTION OF COKAL-KEEFS. 169 



which he thinks could not have been carried into their 

 present positions and subsequently been water-worn, 

 whilst the land stood at its present level. Nevertheless 

 it might, I think, have been anticipated that many 

 atolls would have presented the above appearance, if 

 they had long remained at a stationary level. The sea, 

 after the land had at some former period subsided a few 

 feet, would have continued for a long time breaking 

 over the whole reef, even after the living corals had 

 grown up to their full height on the outer margin. The 

 waters of the lagoon would thus have been disturbed and 

 raised, so that shells and corals, from being bathed by 

 the troubled waters, could have existed at a greater 

 height than that at which they could exist after the 

 reef had been raised by the agglutination of fragments 

 and sand, and after islets had been formed on its sur- 

 face. Even the mere outward growth of a reef, and the 

 consequent increase of its breadth, by checking the 

 inward rush of the breakers, would tend to lower the 

 level in the lagoon at which corals and shells can live. 

 We have seen that at the Keeling Islands there are 

 fields of rotten coral with the tips of their branches pro- 

 jecting abGve the surface of the lagoon, — the result of 

 the tides not rising so high as formerly (as is said to be 

 the case by the inhabitants), from the closing of the 

 channels between the islets on the outer reef, and from 

 the lagoon being partially choked up by the growth 

 of the corals. Here, so far from there having been 

 any recent elevation of the land, we have reason to 

 believe that there has been subsidence. Messrs. Dana 



