376 THE INHABITANTS OF THE SEA. 



for the great depths from which the coral- walls suddenly rise, 

 and the annular form of lagoon islands. Yet this theory, in- 

 genious as it was, could not stand the test of a closer examination: 

 for no crater ever had such dimensions as, for instance, one of the 

 Eadack Islands, which is fifty-two miles long by twenty broad ; 

 and no chain of mountains has its summits so equally high, as 

 must have been the case with the numerous reef-bearing sub- 

 marine rocks, considering the small depth from which the 

 lithophytes build. Another seemingly inexplicable fact was, 

 that, although corals hardly exist above low-water mark, reefs 

 are found at Tongatabu or Eua, for instance, at elevations of 

 forty and even three hundred feet above the level of the ocean. 



Mr. Charles Darwin was the first to give a satisfactory ex- 

 planation of all the phenomena of coral formations, by ascribing 

 them to the oscillations of the sea bottom, to its partial upheaving 

 or subsidence. 



It is now perfectly well known that large portions of the 

 continent of South America, Scandinavia, North Greenland, 

 and many other coasts, are slowly rising, and that other ter- 

 restrial or maritime areas are gradually subsiding. Thus 

 on every side of the lagoon of the Keeling Islands, in which 

 the water is as tranquil as in the most sheltered lake, Mr. 

 Darwin saw old cocoa-nut trees undermined and falling. The 

 foundation-posts of a storehouse on the beach, which, the in- 

 habitants said, had stood seven years before just above high 

 water, were now daily washed by the tide. 



Supposing on one of these subsiding areas an island-mountain 

 fringed with corals, the lithophytes, keeping pace with the 

 gradual sinking of their basis, soon raise again their solid 

 masses to the level of the water ; but not so with the land, each 

 inch of which is irreclaimably gone. Thus the fringing reef 

 will gradually become an encircling one ; and, if we suppose the 

 sinking to continue, it must by the submergence of the central 

 land, but upward growth of the ring of coral, be ultimately 

 converted into a lagoon island. 



The numerous atolls of the Pacific and Indian Ocean give 

 us a far insight into the past, and exhibit these seas overspread 

 with lofty lands where there are now only humble monumental 

 reefs dotted with verdant islets. Had there been no growing 



