FAUNA AND FLORA OF NEW ZEALAND. 3 
many representatives in New Zealand and in South America. 
Western Australia has no European, Antarctic, nor South 
American types, but it is far richer than Eastern Australia 
in true Australian forms, many of which are only found there. 
He also points out that a submarine ridge, nowhere more than 
1000 fathoms below the present sea surface, runs from New Zea- 
land to Northern Queensland, and that the distribution of the 
cretaceous rocks in Australia proves that at that period the sea 
flowed over the centre portion of the continent, dividing the east 
from the west. From these facts Mr. Wallace infers : (1) That 
the submarine ridge between New Zealand and North-eastern 
Australia was elevated above theocean at the same time that Cen- 
tral Australia was submerged ; and (2) That South-western Aus- 
tralia is the remnant of an extensive isolated continent which 
received the ancestral forms of its fauna and flora at a very early, 
probably jurassic date, by a temporary union with the Asiatic 
continent over what is now the Java sea; and it was on this 
continent that the characteristic Australian flora and mamma- 
lian fauna were developed.* He supposes that during the cre- 
taceous period Eastern Australia, separated from Western Aus- 
tralia by a wide arm of the sea, supported a flora that was princi- 
pally tropical and of Polynesian type, derived from the north 
through New Guinea ; but, in addition, there were fragments of 
the typical Australian vegetation which had reached it as strag- 
glers from Western Australia, and also a few south temperate 
forms from Antarctic lands, which had arrived from Tasmania. 
New Zealand, which at this time is supposed to have been joined 
to North-eastern Australia, was open to the immigration of the 
Polynesian flora, and of such Australian types as had reached the 
tropical portions of Eastern Australia. At the close of the cre- 
taceous period the northern prolongation of land between New 
Zealand and Queensland sank: New Zealand was separated 
from Australia, and has ever since remained isolated with its 
flora. Eastern Australia remained separated from the West 
until late in the tertiary era, when Central Australia was elevated. 
The flora of Western Australia then invaded the east and ex- 
terminated, to a large extent, the older tropical vegetation, and _ 
completely changed the character of the flora. 
Such is Mr. Wallace’s hypothesis, which, except in some de- 
tails, is so far satisfactory; the only obvious objections being : 
(1) That the origin. of the Australian flora 1s attributec to a 
eriod when no dicotyledons are known to have existed ; and 
(2) That the majority of the characteristic Australian mammals 
belong to Eastern and not to Western Australia. These are 
difficulties, however, which further knowledge may dispel, but 
the hypothesis cannot be considered as a complete solution of 
the problem, because one large class of facts is not satisfactorily 
explained. I allude to the South American types found in 
* This had been indicated by the Rev. |]. Tenison-Woods in the Pro. Roy. Soc. 
Tasmania, 1875, p. 20; and previously by Prof. Jukes in his ‘‘ Physical Structure of 
Australia,” quoted by Hooker, ‘‘ Flora Tasmaniz,” Int. p. ci, 
