The Existence Of Coral Rock, Or Of Raised Beaches Far
Inland, Indicates Recent Elevation; Lagoon Coral-Islands, And
Such As Have Barrier Or Encircling Reefs, Have Suffered
Subsidence; While Our Own Islands, Whose Productions Are Entirely
Those Of The Adjacent Continent, Have Been Separated From It.
Now
the Aru Islands are all coral rock, and the adjacent sea is
shallow and full of coral, it
Is therefore evident that they have
been elevated from beneath the ocean at a not very distant epoch.
But if we suppose that elevation to be the first and only cause
of their present condition, we shall find ourselves quite unable
to explain the curious river-channels which divide them. Fissures
during upheaval would not produce the regular width, the regular
depth, or the winding curves which characterise them; and the
action of tides and currents during their elevation might form
straits of irregular width and depth, but not the river-like
channels which actually exist. If, again, we suppose the last
movement to have been one of subsidence, reducing the size of the
islands, these channels are quite as inexplicable; for subsidence
would necessarily lead to the flooding of all low tracts on the
banks of the old rivers, and thus obliterate their courses;
whereas these remain perfect, and of nearly uniform width from
end to end.
Now if these channels have ever been rivers they must have flowed
from some higher regions, and this must have been to the east,
because on the north and west the sea-bottom sinks down at a
short distance from the shore to an unfathomable depth; whereas
on the east.
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