T]TE PACIFIC OCEAN. 



2o/ 



thfi solid rock has been gradually, and perhaps very 

 slowly, subsiding to a lower level. Now, let us 

 assume this state of things for a moment, and look at 

 the results. We must, however, mention two well- 

 ascertained instincts of the Polype : the one is, that 

 it works up towards the light ; the other, that its 

 proceedings are most vigorous at the outer edge, 

 where it is washed by the beating waves. Let A in 

 the following diagram represent the section of a 

 rocky island ; B, B, the level of low-water ; and D. 

 the reef of coral fringing the coast. After the lapse 

 of time, during which it has been subsiding, the 

 water-level stands at b, h ; the coral at D has died 

 from the too great depth, but the animals have been 

 working upwards upon the dead matter, so that 

 living coral is still near the surface ; the superior 

 vigour of the species inhabiting the seaward edge, 

 however, has caused that edge to be more elevated 



SECTION OF CORAL ISLAND. 



thiLU the interior, as at d, d ; so that the appearance 

 is now that of a rocky isle, diminished in extent, 

 surrounded by a reef at some distance, separated by 

 the intervention of a shallow channel, e, e .• this is 

 exactly the appearance of Tahiti and the larger 

 islands generally, as I shall mention more fully when 



