ON POLYPS, 31 



of these apparently insignificant creatures, of perpendicular cliffs 

 rising from immense depths, which are altogether the produce of 

 their secretions, we have only to turn to the details in our posses- 

 sion, concerning their habits and mode of increase, to assure us of 

 the inaccuracy of such statements.* In the hot climates in which 

 the saxigenous corals abound, they are found to frequent shallow 

 bays and sheltered spots, where they can enjoy the full influences 

 of light and air, un exposed to the agitation of the ocean, which, 

 were it to beat continually upon them, would infallibly destroy 

 their delicate substance : in such situations, the sub-marine rocks 

 become gradually encrusted with the calcareous skeletons which 

 they produce ; and if undisturbed, in the lapse of years, successive 

 generations will of course deposit such large quantities of calcareous 

 matter as to form beds of considerable thickness. That there are 

 at the bottom of the ocean bold and precipitous cliffs, rising from a 

 depth of 1000 or 1200 feet, their broad tops approximating the 

 surface of the ocean, every one will admit, without having recourse 

 to the labours of madrepores to account for their formation, although 

 the sheltered portions of the summits of such mountain ridges 

 afford an eligible position for their increase. In such situations, 

 therefore, they accumulate, and slowly deposit continually increas- 

 ing masses of earth upon the brow of these sub-marine mountains, 

 until at last the pile approaches the surface of the sea, and even at 

 low water remains uncovered by the waves. The further elevation 

 of the rock, as far as the polyps are concerned in its construction, here 

 ceases ; but a variety of causes tends gradually to heap materials 

 upon the newly appearing island : storms, which tear up the bottom 

 of the sea, perpetually throw to the surface sand and mud ; which 

 becoming entangled among the madrepore, and matted together 

 with sea-weed, forms a solid bed over which the waves have no 

 longer any power. The circumference of the islet is perpetually 

 augmented by the same agency: sea-weeds and vegetable sub- 

 stances cast upon it, by their decay cover its top with vegetable 

 mould ; and if its proximity to other land permit the united action 

 of winds and currents to bring the germs of vegetation from neigh- 

 bouring coasts, they take root in the fresh soil, and soon clothe with 

 verdure a domain thus rescued from the ocean. 



(43.) The coasts described by Cook and Bougainville, whereon 

 strata of coral are found much elevated above the level of the sea, 

 are undoubtedly of volcanic origin. The bottom of the ocean, 



* Quoy etGaimard, Op. cit. 



