Sect. I. DISTRIBUTION OF CORAL-REEFS. 
81 
of the Sandwich Archipelago. In the Eed Sea there 
are coral-reefs in lat. 30°. In the Southern Hemisphere 
coral-reefs do not extend so far from the equatorial sea. 
In the Southern Pacific there are only a few reefs 
beyond the line of the tropic, but Houtmans Abrolhos, 
on the western shores of Australia, in lat. 29° S., are of 
coral-formation. 
The proximity of volcanic land, owing to the lime 
generally evolved from it, has been thought to be 
favourable to the increase of coral-reefs. There is, 
however, no foundation for this view ; for nowhere 
are coral-reefs more extensive than on the shores of 
New Caledonia and of north-eastern Australia, which 
consist of primary formations ; and the Maldiva, 
Chagos, Marshall, Gilbert, and Low Archipelagoes, 
the largest groups of atolls in the world, are formed 
exclusively of coral. 
The entire absence of coral-reefs in certain large 
areas within the tropical seas, is a remarkable fact. 
Thus no coral-reefs were observed during the survey- 
ing voyages of the Beagle on the west coast of South 
America south of the equator, or round the Galapagos 
Islands. It appears, also, that there are none 1 on this 
coast north of the equator ; Mr. Lloyd, who surveyed 
the isthmus of Panama, remarked to me, that although 
he had seen corals living in the Bay of Panama, yet he 
had never observed any reefs formed by them. I at first 
attributed this absence of reefs on the coasts of Peru and 
1 I have been informed that this is the case, by Lieut. Ryder, R.N., 
and others who have had ample opportunities for observation. 
