The depth within the lagoon-channel also
varies much; from 10 to 30 fathoms may be taken as an average; but
at Vanikoro there are spaces no less than 56 fathoms or 336 feet
deep. Internally the reef either slopes gently into the
lagoon-channel, or ends in a perpendicular wall sometimes between
two and three hundred feet under water in height: externally the
reef rises, like an atoll, with extreme abruptness out of the
profound depths of the ocean. What can be more singular than these
structures? We see an island, which may be compared to a castle
situated on the summit of a lofty submarine mountain, protected by
a great wall of coral-rock, always steep externally and sometimes
internally, with a broad level summit, here and there breached by
narrow gateways, through which the largest ships can enter the wide
and deep encircling moat.
As far as the actual reef of coral is concerned, there is not the
smallest difference in general size, outline, grouping, and even in
quite trifling details of structure, between a barrier and an
atoll. The geographer Balbi has well remarked that an encircled
island is an atoll with high land rising out of its lagoon; remove
the land from within, and a perfect atoll is left.
Pages:
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907