nd such as were best adapted
to the tropical climate and arid soil, would intermingle with them. Even if
numerous islands had occupied the area of Northern Australia for long
periods anterior to the final elevation, very much the same state of things
would result.

The existence in North and North-east Australia of enormous areas covered
with Cretaceous and other Secondary deposits, as well as extensive Tertiary
formations, lends support to the view, that during very long epochs
temperate Australia was cut off from all close connection with the tropical
and northern lands by a wide extent of sea; and this isolation is exactly
what was required, in order to bring about the wonderful amount of
specialisation and the high development manifested by the typical
Australian flora. Before proceeding further, however, let us examine this
flora itself, so far as regards its component parts and probable past
history.

_The Floras of South-eastern and South-western Australia._--The
peculiarities presented by the south-eastern and south-western subdivisions
of the flora of temperate Australia are most interesting and suggestive,
and are, perhaps, unparalleled in any other part of the world. South-west
Australia is far less extensive than the south-eastern division--less
varied in soil and climate, with no lofty mountains, and much sandy desert;
yet, strange to say, it contains an equally rich flora and a far greater
proportion of peculiar species and genera of plants. As Sir {494} Joseph
Hooker remarks:--"What differences there are in conditions would, judging
from analogy with other countries, favour the idea that South-eastern
Australia, from its far greater area, many large rivers, extensive tracts
of mountainous country and humid forests, would present much the most
extensive flora, of which only the drier types could extend into
South-western Australia. But such is not the case; for though the far
greater area is much the best explored, presents more varied conditions,
and is tenanted by a larger number of Natural Orders and genera, these
contain fewer species by several hundreds."[130]

The fewer genera of South-western Australia are due almost wholly to the
absence of the numerous European, Antarctic, and South-American types found
in the south-eastern region, while in purely Australian types it is far the
richer, for while it contains most of those found in the east it has a
large number altogether peculiar to it; and Sir