let 
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 i'.self 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 more in appear- 
ance* than a brown slime spread over the stony 
nucleus. As one generation of these animals pass- 
es away, the structure which they have reared 
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 
