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 

 east 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. 



