464 
ISLAND LIFE. 
[rART ir. 
that are represented there by a very few species only, and these 
180 genera include nearly 1,100 species.’' 
Geological explanation of the differences of these two Floras . — 
These facts again clearly point to the conclusion, that South- 
western Australia is the remnant of the more extensive and 
more isolated portion of the continent in which the peculiar 
Australian flora was principally developed. The existence there 
of a very large area of granite — 800 miles in length by nearly 
500 in maximum width, indicates such an extension; for this 
granitic mass was certainly once buried under piles of stratified 
rock, since denuded, and then formed the nucleus of the old 
Western Australian continent. If we take the 1000-fathom 
line around the southern part of Australia to represent the 
probable extension of this old land we shall see that it would 
give a wide additional area south of the Great Australian 
Bight, and form a continent which, even if the greater part of 
tropical Australia were submerged, would be sufficient for the 
development of a peculiar and abundant flora. We must also 
remember that an elevation of 6000 feet, added to the vast 
amount which has been taken away by denudation, would 
change the whole country, including what are now the deserts 
of the interior, into a mountainous and well-watered region. 
But while this rich and peculiar flora was in process of forma- 
tion, the eastern portion of the continent must either have been 
widely separated from the western or had perhaps not yet risen 
from the ocean. The whole of this part of the country consists 
of Palaeozoic and Secondary formations with granite and meta- 
morphic rocks, the Secondary deposits being largely developed 
on both sides of the central range, extending the whole length 
of the continent from Tasmania to Cape York, and constituting 
the greater part of the plateau of the Blue Mountains and other 
lofty ranges. During some portion of the Secondary period, 
therefore, this side of Australia must have been almost wholly 
submerged beneath the ocean; and if we suppose that during 
this time the western part of the continent was at nearly its 
maximum extent and elevation, we shall have a sufficient ex- 
planation of the great difference between the flora of Western 
and Eastern Australia, since the latter would only have been 
