Cn. V. 
OF CORAL-REEFS. 
133 
change in form, whether or not from subsidence, on 
some of these coral-islands ; and there is evidence of 
subterranean disturbances beneath them. Will then 
the theory, to which we have thus been led, solve the 
curious problem — what has given to each class of reef 
its peculiar form ? 
Let us in imagination place within a subsiding area, 
No. 5. 
A A — Outer edge of the reef at the level of the sea. 
B B — Shores of the island. 
A'A' — Outer edge of the reef, after its upward growth during a period 
of subsidence. 
C C — The lagoon-channel between the reef and the shores of the now 
encircled land. 
B' B' — The shores of the encircled island. 
N.B. — In this, and the following woodcut, the subsidence of the 
land could only be represented by an apparent rise in the level of 
the sea. 
an island surrounded by a ‘ fringing-reef ’ — that kind 
of which the origin alone offers no difficulty. Let the 
unbroken lines in the woodcut (No. 5) represent a 
vertical section through the land and w r ater ; and the 
horizontal shading a section through the reef. Now, as 
the island sinks down, either a few feet at a time or quite 
