unique; for I have heen unable to find any other record
of an island of the size of Aru crossed by channels which
exactly resemble true rivers. How these channels originated
were a complete puzzle to me, till, after a long consideration
of the whole of the natural phenomena presented
by these islands, I arrived at a conclusion which I will now
endeavour to explain. There are three ways in which we
may conceive islands which are not volcanic to have been
formed, or to have been reduced to their present condition,
—by elevation, by subsidence, or by separation from a
continent or larger island. 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. How the Aru Islands
are all coral rock, and the adjacent sea is shallqw 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-chan-
nels 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.
How 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 a shallow sea,
nowhere exceeding fifty fathoms,’ extends quite across to
Hew Guinea, a distance of about a hundred and fifty miles.
An elevation Of only three hundred feet would convert the
whole of this sea into moderately high land, and make
the Aru Islands a portion of Hew Guinea; and the rivers
which have their mouths at Utanata and Wamuka, might
then have flowed on across Aru, in the channels which are
now occupied by salt water. When the intervening land
sunk down, we must suppose the land that now constitutes
Aru to have remained nearly stationary, a not very improbable
supposition, when we consider the great extent of
the shallow sea, and the very small amount of depression
the land need have undergone to produce it.
VOL. II. u