344 On Coral Reefs and Islands. 
all a line of reef full 400 miles in length. ‘Towards the north 
extremity, however, it is interrupted 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 proba- 
bly some sedimentary rocks. The streams of so large a land 
might be expected to exclude reefs from certain parts: and in ac- 
cordance 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 in- 
dicate, moreover, 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, Lafw, has been recently described by 
. Clarke as an elevated coral island, with fringing 
reefs; and it appears also from the remarks of this writer, that 
the other islets of what is called the Loyalty Group, are of the 
same kind. Lafu, the largest of the number, is about ninety miles 
in circumference.* ; 
South of New Caledonia lies Norfolk Island, in latitude 29° 
S., about which there is said to be some coral, which.is occasion- 
ally thrown on the beach, but no reefs. : 
_ Between Australia and. New Caledonia the islands are all of 
coral. The New Holland reef extends from Torres Straits to 
the east cape in latitude 24° S., a distance of 1000 nantical miles, 
though much interrupted along its course. It has been shown 
how this broken character might result during a subsidence, owing 
to a change in the abruptness of the land successively becoming 
the coast line, and also to the variations in the currents, retarding 
the growth in some places and aiding it in others, These causes 
might make a broken reef of one that was originally continuous? 
yet we have no reason to believe that the reef. was ever continu- 
ous, It will be found, as we proceed, that long reefs on the 
* Quarterly Journal of the Geological Society, No, 9, p. 61. 
