140 CORAL FORMATIONS. 
South of the equator again :— 
The New Hebrides constitute a long group of high islands, remark- 
able for the absence of coral reefs of any extent, though situated 
between two of the most extensive coral regions in the world,—the 
Feejees and New Caledonia. But the volcanic nature of the group, 
and the still active fires of two vents in opposite extremities are a 
sufficient reason for this peculiarity. Tanna is one of the largest 
volcanoes of the Pacific; and nearly all the islands of the New 
Hebrides, as far as known, indicate comparatively recent igneous 
action, 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 volcano, 
Tinakoro, and no coral. ‘Tikopia, to the southeast 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, according to Kruesenstern, as stated 
by Darwin, is low with large reefs; Duff’s Islands have bold summits 
with wide reefs. 
New Caledonia and the northeast coast of New Holland, with the 
intermediate seas, constitute one of the grandest reef regions in the 
world. On the New Caledonia shores the reefs are of great width, 
and occur not only along the whole length of the western coast, a 
distance of 200 miles, but extend beyond the main land, to the south 
50 miles, and north 150 miles, making in all a line of reef full 400 
miles in length. ‘Towards the north extremity, however, it is inter- 
rupted or broken into detached reefs. This surprising extent is partly 
explained by the fact that New Caledonia is not a land of volcanoes; 
but on the contrary, consists of the older Plutonic or metamorphic 
rocks, with probably some sedimentary rocks. The streams of so 
large a land might be expected to exclude reefs from certain parts: 
and in accordance with this fact, we find the reefs of the windward 
or rainy side comparatively small, and scarcely indicated on our 
charts; while on the dry or western side, they often extend 30 miles 
from the shores. The theory of subsidence accounts fully for the 
great prolongation of the New Caledonia reefs; they indicate, more- 
over, the existence of a former land near three times the area of the 
present island. 
Between New Caledonia and the New Hebrides are several high 
islands, one of which, Lafu, has been recently described by Rev. W. 
