168 



CORAL ANIMALCULES. 



CHAPTER XVI. 



AGENTS WHICH FORM ROCKS (CONTINUED). 



Agents which form Rocks. — Coral Animalcules. — Coral Reefs ; 

 how formed. — General Form. — Submarine Volcanoes. — Basil 

 Hall's description of Loo Choo. — Montgomery's poetical De- 

 scription. 



Coral animalcules, — The nature of coral animal- 

 cules is not, generally, correctly understood ; many 

 persons supposing that the hard calcareous sub- 

 stance which goes under the name of coral is the 

 animal itself. But the stony substance may be cor- 

 rectly compared to an internal skeleton ; for it is 

 surrounded by a soft animal substance, capable of 

 expanding itself, and, when alarmed, of contracting 

 and drawing itself almost entirely into the hollows 

 of the hard coral. Though often beautifully col- 

 oured in their own element, the soft parts become, 

 when taken from the sea, nothing morie in appear- 

 ance* than a brown slime spread ov^r the stony 

 nucleus. As one generation of these animals pass- 

 es away, the structure which they have reazed 

 serves as the foundation on which a succeeding 

 race continues to build. 



It was a prevailing opinion among naturalists not 

 many years since, that coral animals had the power 

 of building up steep and almost perpendicular walls 

 from great depths in the sea ; but it is now pretty 

 well ascertained that they cannot live in water of 

 great depths, and that they only incrust the tops of 

 submarine mountains with a calcareous covering a 

 few fathoms thick.f 



* Ehrenberg Nat. und. Bild. der Coralleninseln, &c. 



t It has been lately proved that the branched corals, which do 



