For as mountain after mountain, and island after
island, slowly sank beneath the water, fresh bases would be
successively afforded for the growth of the corals. It is
impossible here to enter into all the necessary details, but I
venture to defy any one to explain in any other manner how it is
possible that numerous islands should be distributed throughout
vast areas--all the islands being low--all being built of corals,
absolutely requiring a foundation within a limited depth from the
surface. (20/12. It is remarkable that Mr. Lyell, even in the first
edition of his "Principles of Geology," inferred that the amount of
subsidence in the Pacific must have exceeded that of elevation,
from the area of land being very small relatively to the agents
there tending to form it, namely, the growth of coral and volcanic
action.)
(PLATE 94. BARRIER-REEF, BOLABOLA.)
Before explaining how atoll-formed reefs acquire their peculiar
structure, we must turn to the second great class, namely,
Barrier-reefs. These either extend in straight lines in front of
the shores of a continent or of a large island, or they encircle
smaller islands; in both cases, being separated from the land by a
broad and rather deep channel of water, analogous to the lagoon
within an atoll.
Pages:
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905