liv FLORA OF TASMANIA. [Extra-tropical Flora 
be created in the smaller and more isolated area of western Australia, different from what eastern 
Australia presents, seems at first sight favourable to the idea that these are' derivative genera and 
species, formed during the gradual migration of certain of the Orders and Genera of the east towards 
the west. But on the other hand, this massing of most of the peculiar features of the Australian 
Flora in the west, unmixed there with Polynesian, Antarctic, or New Zealand genera, is an argument 
for regarding western Australia as the centrum of Australian vegetation, whence a migration proceeded 
eastward ; and the eastern genera and species must in such a case be regarded as the derivative forms. 
Had we any idea of the comparative geological age of eastern and western Australia, this inquiry 
might be proceeded with a little further; though even then it would be soon brought to a stand- 
still, by the necessity of determining the antecedents of the whole Australia!] Flora. This Flora, 
though manifestly more allied to the Indian than to any other, differs from it so organically, that 
it is impossible to look upon one as derived from the other, though both may have had a common 
parentage. 
The local character of the south-western Australian plants is another singular feature that must 
not be overlooked in any inquiry as to the relative ages of countries and their vegetation. So 
singularly circumscribed are its species in area, that many are found in one spot alone, and, of 
some Natural Orders, the species of Swan River differ very much from those of King George's 
Sound. I am quite at a loss to offer any plausible reason for this rapid succession of forms in area, 
and the contrast in this respect between the south-western and eastern districts is all the more re- 
markable, because the latter also, as compared with other parts of the world, presents a very consi- 
derable assemblage of local species. But so it is, that there are far more King George's Sound 
species absent from the Swan River, though separated by only 200 miles of tolerably level land, than 
there are Tasmanian plants absent from Victoria, which are as many miles apart, and separated by 
an oceanic strait. It would indeed appear that the mixture of several Floras of different character 
in one area tends to keep down the total number of species in that area, and if so, we may connect 
the richness in species of the western Australian Flora with its singular uniformity of character, 
for it is purely Australian, without admixture of any other element. As this excessive multiplication 
must, under the theory of creation by variation, have occupied a great length of time, it seems 
to be more natural to assume, on purely botanical grounds, that the western Australian Flora is 
the earliest, and sent colonists to the eastern quarter, where they became mixed with Indian, Poly- 
nesian, etc., colonists, than that the western Flora was peopled by one section only of the inhabitants 
of the eastern quarter. 
So much for the botanical aspect of the question. The geological one suggests a different 
explanation. That part of the Australian continent which alone is clothed with any considerable 
amount of vegetation, may be likened to a horse-shoe of more or less elevated land, with its con- 
vexity to the north, and a vast enclosed central depressed area, that opens to the sea on the south, 
and advances north almost to the Gulf of Carpentaria. According to Mr. Jukes's clever ' Sketch 
of the Physical Structure of Australia,' this central and southern area was recently an oceanic bay, 
and existing species of Mollusca are found on its surface for many miles along the coast, and inland 
from it, in an almost unchanged condition* To the east of this depressed area, the mountains 
are far loftier and the rocks of a much greater age than to the west of it; and were the question of 
the age of the Floras comprised in that of the rocks they inhabit, little doubt would be cnter- 
* Great beds of shells, with the colours retained, are found at Jurien Bay, at forty to eighty feet above the 
sea-level. (Von Sommer, in Quart. Journ. Geol. Soc. v. p. 52.) 
