.214 OS CORAL ISLANDS. 



coa-nut, or the drupe of a pandanus, is thrown on shore ; 

 land birds visit it, and deposit the seeds of shrubs and 

 trees ; every high tide, and still more every gale, adds 

 something to the bank ; the form of an island is gra- 

 dually assumed; and last of all comes man to take pos- 

 session. 



Half-way Island is well advanced in the above pro- 

 gressive state ; having been many years, probably some 

 ages, above the reach of the highest spring tides, or the 

 wash of the surf in the heaviest gales. I distinguished, 

 however, in the rock which forms its basis, the sand, 

 coral, and shells, formerly thrown up, in a more or less 

 perfect state of cohesion. Small pieces of wood, pumice 

 stone, and other extraneous bodies which chance had 

 mixed with the calcarious substances when the cohesion 

 began, were enclosed in the rock ; and in some cases 

 were still separable from it without much force. The 

 upper part of the island is a mixture of the same sub- 

 stances in a loose state, with a little vegetable soil ; and 

 is covered with the casuarina and a variety of other trees 

 and shrubs, which give food to parroquets, pigeons, and 

 some other birds ; to whose ancestors, it is probable, the 

 island was originally indebted for this vegetation. 



NOTE K. 16. p. 53. 



On the Diminution of the Waters of the Ocean. 

 That the water of the ocean has diminished, and is still 

 diminishing, can scarcely be doubted ; yet the rate of 

 decrease since the period of the deluge has been so gradu- 

 al, being now effected not by the conversion of the water 

 into the earthy materials of which the globe is composed, 

 but principally by the agency of animals, vegetables, and 

 volcanoes, that, on a general view, it may be said to be 

 nearly imperceptible. The facts mentioned by Celsius and 



