136 THE WORLD'S LUMBER Roan. 



it is only here and there that it rises into an islet crowned 

 with feathery cocoa-palms, the rest of its outline being 

 marked by the snow-white breakers. 



The Laccadives, or " lac of islands," and the Maldives, 

 or " thousand islands," are just a series of such atolls.* 



Few animals, indeed, have left such vast and enduring 

 monuments of themselves as these humble zoophytes ; but 

 there are others which must not be passed over. Outside 

 the harbour of Pernambuco there is a reef of sandstone, 

 several miles long, which is composed of grains of silicious 

 sand, cemented together by carbonate of lime. Though 

 exposed to all the violence of the great Atlantic waves, with 

 their load of sand and sediment, which are unceasingly 

 driven against it by the trade-wind, the bar has lasted 

 hundreds, perhaps thousands of years, thanks to a few inches 

 of calcareous matter, formed chiefly by the growth and decay 

 of many generations of serpulse, together with a few barnacles 

 and some paper-like layers of a sort of sea-lichen, called 

 nullipora. The inner surface of the sand-bar, which has no 

 such protecting coat, is visibly worn in spite of its sheltered 

 position. 



Off the Bermudas there are reefs which are mainly 

 composed of these serpulae, whose tubes one may often see 

 on oyster-shells, though this gives one no idea of their real 



* It has been suggested that, as the bed of the ocean is not a plain, but 

 diversified by hills and even mountains, and as enormous quantities of 

 shells are constantly falling to the bottom, some of these hills may be so 

 heightened as to reach the point at which deep-sea corals, annelids, 

 sponges, mollusks, &c., can live, after which they would increase more 

 rapidly until they reached the zone of the reef-corals, which would grow 

 upwards as long as they could, and then outwards. 



