But we shall
immediately see, that in this, as well as in the crater-theory, a
most important consideration has been overlooked, namely, on what
have the reef-building corals, which cannot live at a great depth,
based their massive structures?
Numerous soundings were carefully taken by Captain Fitz Roy on the
steep outside of Keeling atoll, and it was found that within ten
fathoms the prepared tallow at the bottom of the lead invariably
came up marked with the impressions of living corals, but as
perfectly clean as if it had been dropped on a carpet of turf; as
the depth increased, the impressions became less numerous, but the
adhering particles of sand more and more numerous, until at last it
was evident that the bottom consisted of a smooth sandy layer; to
carry on the analogy of the turf, the blades of grass grew thinner
and thinner, till at last the soil was so sterile that nothing
sprang from it. From these observations, confirmed by many others,
it may be safely inferred that the utmost depth at which corals can
construct reefs is between 20 and 30 fathoms. Now there are
enormous areas in the Pacific and Indian Oceans in which every
single island is of coral formation, and is raised only to that
height to which the waves can throw up fragments, and the winds
pile up sand.
Pages:
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903