1836.] THEIR RELATION TU 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 still distinguishable, not one of them is 
known to have ever been in eruption. Hence in these cases it 
would appear, that voleanos burst forth into action and become 
extinguished on the same spots, accordingly as elevatory or sub- 
siding movements prevail there. WNumberless 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 atoils, where not a single 
peak of high land has been left above the level of the 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 oeeans. The reef-constructing corals have indeed 
reared and preserved wonderful memorials of the subterranean 
