GEOGRAPHICAL DISTRIBUTION. 103 



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; hut 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 thiee times 

 the area of the present island. 



Between New Caledonia and the New Hebrides are several 

 high islands, one of which, Lnfu, has heen recently described by 

 Rev. W. 13. 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. Lain, 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 nautical 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 

 shores of continents are not common. In this case the zoo- 

 phytes are not exposed to the destructive agents usual on such 

 shores, as the laud is in 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 cur- 

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

 eastward of south, away from the land, while a polar current fol- 

 lows up the shores from the south as far as this cape. South of 

 this cape there are only a few scattered species of coral zoophytes. 

 The Louisiade Group is described as a region of extensive reefs. 



* Quarterly Journal of the Geological Society, No. 9, p. 61. 



