1836.] THEIR RELATION TO VOLCANOS. 481 



the Friendly Archipelago, which consists of a group of atolls 

 upheaved and since partially worn down, two volcanos, and 

 perhaps more, are historically known to have been in action. On 

 the other hand, although most of the islands in the Pacific which 

 are encircled by barrier-reefs, are of volcanic origin, often with 

 the remnants of craters *.till distinguishable, not one of them is 

 known to have ever been in eruption. Hence in these cases it 

 would appear, that volcanos burst forth into action and become 

 extinguished on the same spots, accordingly as elevatory or sub- 

 siding movements prevail there. Numberless facts could be 

 adduced to prove that upraised organic remains are common 

 wherever there are active volcanos ; but until it could be shown 

 that in areas of subsidence, volcanos were either absent or inac- 

 tive, the inference, however probable in itself, that their distri- 

 bution depended on the rising or falling of the earth's surface, 

 would have been hazardous. But now, I think, we may freely 

 admit this important deduction.. 



Taking a final view of the map, and bearing in mind the state- 

 ments made with respect to the upraised organic remains, we 

 must feel astonished at the vastness of the areas, which have 

 suffered changes in level either downwards or upwards, within a 

 period not geologically remote. It would appear, also, that the 

 elevatory and subsiding movements follow nearly the same laws. 

 Throughout the spaces interspersed with atolls, where not a single 

 peak of high land has been left above the level of tlie sea, the sink- 

 ing must have been immense in amount. The sinking, moreover, 

 whether continuous, or recurrent with intervals sufficiently long 

 for the corals again to bring up their living edifices to the surface, 

 must necessarily have been extremely slow. This conclusion is 

 probably the most important one, which can be deduced from the 

 study of coral formations ; — and it is one which it is difficult to 

 imagine, how otherwise could ever have been arrived at. Nor can 

 I quite pass over the probability of the former existence of large 

 archipelagoes of lofty islands, where now only rings of coral -rock 

 scarcely break the open expanse of the sea, throwing some light 

 on the distribution of the inhabitants of the other high islands, now 

 left standing so immensely remote from each other in the midst 

 of the great oceans. The reef-constructing corals have indeed 

 reared and preserved wonderful memorials of the subterranean 



