XXI 



lost in the regions of the clouds : such are the madre- 

 porous islands so numerous in the South-eastern 

 Ocean, which Polypi are every day augmenting by 

 their inconceivable labours. Some authors have 

 imagined that these isles were only the summits of 

 submarine mountains, that had been covered by Po- 

 lypidoms ; but these submarine mountains, the almost 

 perpetual source of subterranean fires, are found in 

 all latitudes, and greatly vary in their extent and in 

 their forms : the madreporic islands, on the contrary, 

 exist only within the tropics, and present forms con- 

 stantly analogous to each other, and are never over- 

 turned by earthquakes or volcanic eruptions. They 

 are described by most modem voyagers who have 

 traversed those seas. 



If we compare this polypean mass, that rises from 

 the immeasurable depths of the ocean to its surface, 

 and that shoots into air under the form of mountains, 

 to that Melobesia, to that Cellepora, which has only 

 the appearance of a white spot, a small deposite of 

 calcareous particles, how striking is the difference ! 

 what an infinity of intermediates must exist between 

 the two extremes ! Generally speaking, the Cellular 

 Polypidoms, as well as the Calciferous and Car- 

 noid, seldom exceed a metre in height ; usually 

 they are much smaller. The Corticiferous are some- 



