556 



CORAL FORMATIONS. 



Aprils 1836. 



in New Caledonia^ where the reefs extend no less than 140 

 miles beyond the island. 



The great Barrier which fronts the N.E. coast of Australia, 

 forms a third class of reef. It is described by Flinders as 

 having a length of nearly one thousand miles, and as running 

 parallel to the shore, at a distance of between twenty and 

 thrty miles from it, and, in some parts, even of fifty and 

 seventy. The great arm of the sea thus included, has a 

 usual depth of between ten and twenty fathoms, but this 

 increases towards one end to forty and even sixty. This 

 probably is both the grandest and most extraordinary reef 

 now existing in any part of the world. 



It must be observed, that the reef itself in the three 

 classes, namely, lagoon, encircling, and barrier, agrees in 

 structure, even in the most minute details : but these I have 

 not space here even to allude to. The dilference entirely 

 lies in the absence or presence of neighbouring land, and the 

 relative position which the reefs bear to it. In the two last- 

 mentioned classes, there is one difficulty in undertaking their 

 origin, which must be pointed out. Since the time of Dam- 

 pier it has been remarked, that high land and deep seas go 

 together. Now when we see a number of mountainous 

 islands coming abruj)tly down to the sea- shore, we must 

 suppose the strata of which they are composed, are con- 

 tinued with nearly the same inclination beneath the 

 water. But, in such cases, where the reef is distant several 

 miles from the coast, it will be evident upon a little consi- 

 deration, that a line drawn perpendicularly from its outer 

 edge down to the solid rock on which the reef must be 

 based, very far exceeds that small limit at which the efficient 

 lamelliform corals exist. 



In some parts of the sea, as we shall hereafter mention, 

 reefs do occur which fringe rather than encircle islands — the 

 distance from the shore being so small, where the inclination 

 of the land is great, that there is no difficulty in understand- 

 the growth of the coral. Even in these fringing" reefs, as I 

 shall call them in contradistinction to the encircling,^^ the 



