476 CHANGES IN CORAL-REEFS. [cHap. xx 
are subject to changes of some kind is certain; on some atolls 
che islets appear to have increased greatly within a late period ; 
on others they have been partially or wholly washed away. The 
inhabitants of parts of the Maldiva archipelago know the date 
of the first formation of some islets; in other parts, the corals 
are now flourishing on water-washed reefs, where holes made 
for graves attest the former existence of inhabited land. It is 
difficult to believe in frequent changes in the tidal currents of an 
open ocean; whereas, we have in the earthquakes recorded by 
the natives on some atolls, and in the great fissures observed on 
other atolls, plain evidence of changes and disturbances in pro- 
gress in the subterranean regions. 
It is evident, on our theory, that coasts merely fringed by 
reefs cannot have subsided to any perceptible amount; and 
therefore they must, since the growth of their corals, either have 
remained stationary or have been upheaved. Now it is remark- 
able how generally it can be shown, by the presence of upraised 
organic remains, that the fringed islands have been elevated: 
and so far, this is indirect evidence in favour of our theory. I 
was particularly struck with this fact, when I found to my sur- 
prise, that the descriptions given by MM. Quoy and Gaimard 
were applicable, not to reefs in general as implied by them, but 
only to those of the fringing-class; my surprise, however, ceased 
when I afterwards found that, by a strange chance, all the severai 
islands visited by these eminent naturalists, could be shown by 
their own statements to have been elevated within a recent geo- 
logical era. 
Not only the grand features in the structure of barrier-reefs 
and of atolls, and of their likeness to each other in form, 
size, and other characters, are explained on the theory of sub- 
sidence—which theory we are independently forced to adimit in 
the very areas in question, from the necessity of finding bases 
for the corals within the requisite depth—but many details in 
structure and exceptional cases can thus also be simply explained. 
I will give only a few instances. In barrier-reefs it has long 
been remarked with surprise, that the passages through the reef 
exactly face valleys in the included land, even in cases where the 
reef is separated from the land by a lagoon-channel so wide ana 
30 much deeper than the actual passage itself, that it seems hardly 
