XX 
THEIR RELATION TO VOLCANOES 
5ii 
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-reef a proof that the land has 
