On Coral Reefs and Islands. 343 
west of Kauai, are represented as coral reefs, excepting the rocks 
Necker and Bird Island; the line stretches on to 28° 30’ N.,* 
the northern limit of the coral seas. 
The Ladrones, like the Sandwich Group, constitute aline or 
linear series of islands, one end of which has been long free from 
volcanic action, while the other has still its smoking cones. 
While the appearances of recent igneous action increase there- 
fore as we go northward, the extent of the coral reefs increase as 
we go southward ; no reefs occur about the northernmost islands, 
while they are quite extensive on the shores of Guam. ‘This 
group consequently, like the Hawaiian and Samoa, illustrates the 
influence of volcanic action on the distribution of reefs. 
same line, lie extensive reefs. Mackenzie’s is an atoll of large 
size. Yap, Hunter, Los Matelotas. and the Pelews are hi 
islands, with large reefs. In the last mentioned, the reef-grounds 
cover at least six times the area occupied by the high land. Still 
farther south, towards New Zealand, lie the large atolls Aiou, 
Asie, and Los Guedes. 
reason for this peculiarity. Tanna is one of the largest volca- 
noes of the Pacific; and nearly all the islands of the New Heb- 
tides, as far as known, indicate comparatively recent igneous ac- _ 
tion, in which respect they differ decidedly from the Feejees. 
The Vanikoro Group, north of the New Hebrides, according 
to Quoy, has large barrier reefs about the southernmost island, 
Vanikoro; but at the northern extremity of the range there is an 
active voleano Tinakoro, and no coral. Tikopia, to the south- 
east of Vanikoro, is high and volcanic, according to Quoy, though 
not now with active fires; and it appears from the descriptions 
given to have no reefs. Mendana, northeast of Tinakoro, ac- 
Sissi Sida Us eee 
* For an account of some of these islands, see Le uen 1803-6, in 
the Neva, 4to.,, London, 1814, pp. 254, 257; also Hawaiian » vol. i. 
