CORAL ANIMALCULES. 
171 
portion of compact limestone, which has doubtless 
been produced by chemical precipitation. As the 
coral animals* perish and become decomposed, the 
lime is set free to a considerable extent, and under 
circumstances favourable to deposition, and so the 
mass becomes of a compound or mixed charac- 
ter. The Pacific Ocean abounds in coral to the 
30th degree of latitude on each side of the equator ; 
so also do the Arabian and Persian Gulfs. On the 
oast coast of New-Holland is a reef 350 miles in 
length; and between that country and New-Gui- 
nea there is a chain of coral 700 miles long. The 
Maldivas, in the Indian Ocean, are coral reefs ex- 
tending 480 geographical miles north and south. 
These are circular islets, the largest being 50 miles 
in diameter, the centre of each being a lagoon from 
15 to 20 fathoms deep, and on the outside of each 
island, at the distance of two or three miles, there is 
a coral reef, immediately outside of which the wa- 
ter is generally more than 150 fathoms deep. | 
The following cut will serve to illustrate the gen- 
eral shape and formation of these islands. 
Fig. 38. 
Coral reefs or islands. 
The following section will enable the reader to 
get a correct idea of the usual form of such islands. 
In proof that the circular forms of these coral 
* It is stated by Lieut. Nelson, that among the Bahama Isl- 
ands, zones of coral enclose tranquil basins, within which the 
decomposition of numerous zoophytes produces a soft, white 
calcareous mud, so much resembling chalk that specimens de- 
posited in the Museum of the Geological Society of London 
cannot be distinguished from some of the common soft chalk of 
England. 
