vi PRE FA TOR Y NO TE. 



to determine their period of growth, with a result that he 

 considers that it would take 1,000 or 1,200 years for coral to 

 grow upwards from a depth of seven fathoms to the surface 

 of the sea; this estimate cannot, however, be universally 

 applicable, since their rate of growth differs in different seas, 

 and varies according to the species. Thus, for example, on 

 a ship, which was sunk for twenty months in the Persian 

 Gulf, there was an incrustation of coral to a depth of two feet 

 on her copper bottom; while in the case of the sunken ship 

 Shannon, which was found crusted with coral, it was reckoned 

 that, even supposing the coral to have commenced growing 

 as soon as the ship reached the bottom, the growth could not 

 have been more than three inches in a year. Again, some 

 corals have been planted on the Madagascar coast, and these 

 were observed to have grown to a height of nearly three feet 

 in no less than six months. 



The second class, or 'barrier-reef (Fig. 2), differs from the first 

 class in that it is situated at a greater distance from the shore, 

 and that, as a consequence of this, the depth of the water on 

 both its littoral and seaward sides is much greater. They 

 occur in the middle of the Red Sea; they are common in the 

 Pacific, where they form the great barrier-reef on the north-east 

 coast of Australia, and extend around the Society Islands, the 

 Fijis, and New Caledonia; and they surround islands like the 

 Pelew Islands, and the Comora Isles in the Mozambique 

 Channel. Some of them are very large; — that surrounding 

 New Caledonia is four hundred miles long, and about ten miles 

 distant from the shore; and the one off the north-east coast 

 of Australia is from ten to ninety miles broad, about 1,250 

 statute miles in length, and rises from the ocean bed on its 

 seaward side from a depth which often exceeds 1,800 feet, 



Fig. 2.— Barrier-Reef. 



