GEOGRAPHICAL DISTRIBUTION. 263 



extend to the south beyond the mainland 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 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 older metamorphic 

 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 compara- 

 tively small, and scarcely indicated on the charts ; while on 

 the dry or western side, they often extend thirty miles from the 

 shores. The theory of subsidence accounts fully for the great 

 prolongation of the New Caledonia reefs. The reefs indicate, 

 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, Lafu, has been described {Quart. 

 Jour. Geol. Soc, 1847, p. 61) by Rev. W. B. Clarke as an elevated 

 coral island, with fringing reefs ; 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 

 occasionally thrown on the beach, but no reefs. 



Between Australia and New Caledonia the islands are all 

 of coral. The Australian reef extending south to the east 

 cape, in latitude 24° S., has already been described. Such 

 long reefs on the shores of continents are not common. In 

 the case of Australia, the zoophytes are not exposed to the 

 destructive agents usual on continental shores, as the land has 

 a dry climate, the shores are mostly rocky, and there are 

 no streams of any extent emptying into the ocean. The 

 east cape is the southern limit, because here the tropical 

 current, owing to the direction of the coast above, trends off 

 to the eastward of south, away from the land, while a polar 

 current follows up the shores from the south as far as this 



