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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 re-
gions, 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 New Guinea, a dis-
tance of about a hundred and fifty miles. An elevation of only three hundred feet would con-
vert the whole of this sea into moderately high land, and make the Aru Islands a portion of
New 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 re-
mained nearly stationary, a not very improbable supposition, when we consider the great ex-
tent of the shallow sea, and the very small amount of depression the land need have under-
gone to produce it.
But the fact of the Aru Islands having once been connected with New Guinea does not
rest on this evidence alone. There is such a striking resemblance between the productions of
the two countries as only exists between portions of a common territory. I collected one
hundred species of land-birds in the Aru Islands, and about eighty of them have been found
on the mainland of New Guinea. Among these are the great wingless cassowary, two species
of heavy brush turkeys, and two of short winged thrushes, which could certainly not have
passed over the 150 miles of open sea to the coast of New Guinea. This barrier is equally ef-
fectual in the case of many other birds which live only in the depths of the forest, as the
kinghunters (Dacelo gaudichaudi), the fly-catching wrens (Todopsis), the great crown pi-
geon (Goura coronata), and the small wood doves (Ptilonopus perlatus, P. aurantiifrons, and
P. coronulatus). Now, to show the real effect of such a barrier, let us take the island of
Ceram, which is exactly the same distance from New Guinea, but separated from it by a
deep sea. Out of about seventy land-birds inhabiting Ceram, only fifteen are found in New
Guinea, and none of these are terrestrial or forest-haunting species. The cassowary is dis-
tinct; the kingfishers, parrots, pigeons, flycatchers, honeysuckers, thrushes, and cuckoos, are
almost always quite distinct species. More than this, at least twenty genera, which are com-
mon to New Guinea and Aru, do not extend into Ceram, indicating with a force which every
naturalist will appreciate, that the two latter countries have received their faunas in a radic-
ally different manner. Again, a true kangaroo is found in Aru, and the same species occurs
