very rocky country, penetrated by numerous small streams, in the high limestone
cliffs bordering which the edible birds' nests of Aru are chiefly obtained. All my
informants stated that the two southern rivers are larger than Watelai.
The whole of Aru is low, but by no means so flat as it has been represented, or
as it appears from the sea. Most of it is dry rocky ground, with a somewhat
undulating surface, rising here and there into abrupt hillocks, or cut into steep
and narrow ravines. Except the patches of swamp which are found at the mouths
of most of the small rivers, there is no absolutely level ground, although the
greatest elevation is probably not more than two hundred feet. The rock which
everywhere appears in the ravines and brooks is a coralline limestone, in some
places soft and pliable, in others so hard and crystalline as to resemble our
mountain limestone.
The small islands which surround the central mass are very numerous; but
most of them are on the east side, where they form a fringe, often extending ten
or fifteen miles from the main islands. On the west there are very few, Wamma
and Palo Pabi being the chief, with Ougia, and Wassia at the north-west
extremity. On the east side the sea is everywhere shallow, and full of coral; and
it is here that the pearl-shells are found which form one of the chief staples of
Aru trade. All the islands are covered with a dense and very lofty forest.
The physical features here described are of peculiar interest, and, as far as I
am aware, are to some extent unique; for I have been 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. 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