THE ANIMAL KINGDOM. 69 



the polyp structures reach the level of the low tides, and 

 after that the great surges raise the middle part, by casting 

 back upon it incessantly the fragments which they tear 

 away from the circumference. When in the lapse of years 

 the island rises above water, the detritus of marine plants 

 raises it still more, and the virgin soil is speedily fecun- 

 dated by seeds which the winds, birds, and currents carry 

 thither. Soon after man comes to crown the handiwork of 

 nature by raising dwellings on the ruins of those of myriads 

 of unseen beings. Then a king arrives, who sits proudly 

 upon his throne amidst this mass of skeletons of Polypi 

 abandoned by the sea. 



Two of the most celebrated travellers of our epoch, Fors- 

 ter and Peron, think that these coral or madrepore reefs 

 and islands are formed with extraordinary rapidity, and 

 that a few years suffice to materially change the depths of 

 the sea, and strew with dangerous rocks and impassable 

 barriers tracts of the ocean in which, but a little while pre- 

 viously, navigators sailed in safety. These new lands some- 

 times spring up with such celerity as to baffle all nautical 

 science. One of the straits in the approaches to Australia, 

 which a few years ago only possessed twenty-six madrepore 

 islands, at present displays one hundred and fifty. 



Geologists themselves have dwelt upon the power of 

 these builders of worlds, as the illustrious Michelet calls 

 them, which recast and changed the surface of the globe at 

 certain antediluvian periods. At that time they swarmed 

 in the immense seas which rolled their tumultuous waves 

 over almost all the lands now covered by cultivated fields 

 and peaceful abodes. Certain countries in Europe possess 



