1899] ORIGIN OF AUSTRALIAN FLORA 281 
provided the climate was suitable to a mixed flora. Unfortunately 
this is precisely the question to which no answer is possible in the 
present state of our knowledge, and it is greatly to be wished that 
steps should be taken to examine the lignite beds of the Fitzgerald 
River,’ which would in all probability suffice to solve the problem. 
But whether the primitive flora in its entirety flourished there or not, 
it is submitted that the peculiar flora of the south-west can be ex- 
plained on the assumption of a great difference in climate between 
the south-west and other parts of Australia, a difference dating either 
from Eocene (possibly late Cretaceous) times or from some period shortly 
after the Eocene. We have to suppose that long before the great 
plains of the central and eastern interior became desiccated, a consider- 
able area in the south-west was already under the influence of drought. 
Westward of this dry district, which could have supported only a 
meagre flora, a somewhat more genial climate must have prevailed, 
but one favourable, except in isolated areas, to xerophilous vegetation. 
And if any difficulty is felt in adopting this view on account of 
the proximity of the ocean, it must not be forgotten that in the Shark 
Bay district desert conditions actually prevail up to the sea-coast, and 
moreover that, although southward of this district there is a fair annual 
rainfall near the ocean, the precipitation rapidly diminishes in amount 
at short distances from it. I saw many scenes of desolation in the 
interior, but they were almost equalled in the neighbourhood of York, 
barely sixty miles inland, in the early summer of 1894; even on the 
coast itself, periods of drought, during which non-xerophilous vegetation 
has but a slender chance of survival except in specially favoured 
localities, are frequent in the summer season. In such a country as 
this, then, I venture to believe the rich flora of the south-west to have 
been mainly evolved, and not, as Mr. Wallace supposes, in one 
diversified by lofty mountain systems, which, if they ever existed, have, 
except for the lowly Darling and Stirling Ranges, the upland districts 
of the far North-West, and the insignificant hills scattered over the 
vast intervening territory, vanished without leaving a trace of their 
former presence. 
I cannot agree with Professor Tate in thinking that, except very 
rarely, there has been no interchange between the floras of Eastern 
and Western Australia. The flora of the Western desert has a fair 
number of species common to the two areas; there are also a 
considerable number common to the desert and the south-west, and 
some eastern species which advance to a greater or less distance into 
the desert, but without reaching the western coast region, and all this 
seems to indicate a filtration, most probably very slow, across the 
desert plains. It may also be remarked that recent discoveries have 
diminished the number of large genera having no species common to 
} This and a thorough exploration of the North-Western territories are the two most 
interesting and important achievements now remaining to naturalists in Australia. 
