428 Capt. F. W. Hutton on the Origin of the 
(2) that South-western Australia 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 charac- 
teristic Australian flora and mammalian fauna were developed*. 
He supposes that during the Cretaceous period Eastern 
Australia, separated from Western Australia by a wide arm 
of the sea, supported a flora that was principally 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 stragglers from 
Western Australia, and also a few south-temperate forms from 
antarctic lands, which had arrived from ‘lasmania. 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 Cretaceous 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 Aus- 
tralia then invaded the east, and exterminated 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 
details, is so far gatisfactory, the only obvious objections 
being (1) that the origin of the Australian flora is attributed 
to a period 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 Eastern Australia and New Zealand, many of 
which belong to tropical and subtropical genera. Mr. Wal- 
lace’s explanation of the presence of these forms is that a 
migration took place through New Zealand, South Victoria 
Land, South Shetland Islands, and Tierra del Fuego over a 
* This had been indicated by the Rey. J. Tenison- Woods in the Proc. 
Roy. Soc. Tasmania, 1875, p. 20, and previously by Prof. Jukes in his 
‘Physical Structure of Australia,’ quoted by Hooker, ‘Flora Tasmania,” 
Intr. p. ci. 
