dred miles of open sea now separate
Australia from Timor, which island is connected with Java by a chain of
broken land divided by straits which are nowhere more than about twenty
miles wide. Evidently there are now great facilities for the natural
productions of Java to spread over and occupy the whole of these
islands, while those of Australia would find very great difficulty in
getting across. To account for the present state of things, we should
naturally suppose that Australia was once much more closely connected
with Timor than it is at present; and that this was the case is rendered
highly probable by the fact of a submarine bank extending along all the
north and west coast of Australia, and at one place approaching within
twenty miles of the coast of Timor. This indicates a recent subsidence
of North Australia, which probably once extended as far as the edge
of this bank, between which and Timor there is an unfathomed depth of
ocean.

I do not think that Timor was ever actually connected with Australia,
because such a large number of very abundant and characteristic groups
of Australian birds are quite absent, and not a single Australian mammal
has entered Timor--which would certainly not have been the case had
the lands been actually united. Such groups as the bower birds
(Ptilonorhynchus), the black and red cockatoos (Calyptorhynchus),
the blue wrens (Malurus), the crowshrikes (Cracticus), the Australian
shrikes (Falcunculus and Colluricincla), and many others, which abound
all over Australia, would certainly have spread into Timor if it
had been united to that country, or even if for any long time it had
approached nearer to it than twenty miles. Neither do any of the most
characteristic groups of Australian insects occur in Timor; so that
everything combines to indicate that a strait of the sea has always
separated it from Australia, but that at one period this strait was
reduced to a width of about twenty miles.

But at the time when this narrowing of the sea took place in one
direction, there must have been a greater separation at the other end of
the chain, or we should find more equality in the numbers of identical
and representative species derived from each extremity. It is true that
the widening of the strait at the Australian end by subsidence, would,
by putting a stop to immigration and intercrossing of individuals from
the mother country, have allowed full scope to the causes which have
led to th