THEIR RELATION TO VOLCANOES 



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 still distinguishable, not one of them is known to 

 have ever been in eruption. Hence in these cases it would 

 appear that volcanoes burst forth into action and become 

 extinguished on the same spots, accordingly as elevatory or 

 subsiding movements prevail there. Numberless facts could 

 be adduced to prove that upraised organic remains are common 

 wherever there are active volcanoes ; but until it could be 

 shown that in areas of subsidence volcanoes were either absent 

 or inactive, the inference, however probable in itself, that their 

 distribution 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 

 statements 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 the sea, the sinking must have been 

 immense in amount. The sinking, moreover, whether con- 

 tinuous, 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 oscillations 

 of level ; we see in each barrier-rccf a proof that the land has 



