OF CREATION. 31 



localities, is well adapted to illustrate the habits of 

 the group. 



The little animals Fi 9- 4 *V- 5 



in these cases secreted 

 and built up their 

 stone house, they ad- 

 ded compartment to 

 compartment, erect- 

 ing in succession one 



Story after another, CHAIN CORAL. (Catenipora.) 



and they continued at this work month after month, 

 year after year, century after century, until at length 

 they were replaced by others like them, when the 

 depth had changed in which they could most con- 

 veniently live, or when, owing to some cause, their 

 labours were brought to a close, and they disap- 

 peared from amongst existing forms. 



During every successive period from this their first 

 appearance in the infancy of the world to the present 

 day, animals of the polyp kind have been perpetually 

 adding to the solid matter of our globe, by these sin- 

 gular buildings of stone. These little creatures are 

 enabled to separate from the sea-water a proportion 

 of carbonate of lime, and they do this although the 

 quantity present is so minute as to be almost inappre- 

 ciable by the most careful chemical analysis. The 

 most common species are known to be unable to exist 

 at a greater depth than twenty or thirty fathoms ; 

 but there are many instances in the southern seas of 

 corals forming part of extensive reefs existing at a 

 much greater depth, and they are also sometimes ele- 

 vated high in the air. Great changes of level must, 

 therefore, have occurred ; and these are perhaps still 



