PACIFIC EXPLORATION: C. SCHUCHERT 
411 
edly lifted above the embrace of the Tasman sea, and most markedly 
so in the Pliocene, when all of eastern AustraKa was vertically elevated 
and block-faulted between 1500 and 7300 feet above sea-level (during 
the 'Kosciusko epoch'). In compensation for this elevation the 
Tasman sea sank, as now there are great depths close to the continent, 
in one place going down to 18,500 feet. 
Australasia has been the most remarkable asylum among the con- 
tinents for the preservation to this day of living examples of the plants 
and animals of the medieval world. Among these in great variety are 
the marsupial or pouch mammals, and the far less diversified, more 
primitive, but more remarkable egg-laying monotremes. The marsupials 
were at their culmination in the Pliocene, when forms existed larger 
than any living rhinoceros {Diprotodon australis) . Yxom the chronogenesis 
of these stocks and their diverse evolution in Australia, we learn that 
they must have been on that continent long before, and that they had 
been free from all Asiatic invasions and therefore escaped destruction 
by the higher, more intelHgent carnivorous placental mammals. We 
must therefore conclude that Australia has been an island continent 
at least since late Eocene time, for it is since then that the placental 
mammals have elsewhere dominated all other land life. 
The question next arises. When was Australia severed from Asia? 
From the paleogeography as now deciphered, we learn that Asia and 
Australasia were in complete connection throughout the early Paleozoic 
to the close of the Devonian. In Lower Carboniferous time, however, 
southeastern Asia began to be invaded by the Indian and Pacific oceans 
in the region of what are now the East Indian Islands. A greater sub- 
sidence here and in New Guinea, New Caledonia, and elsewhere in 
Australasia began in the Jurassic and probably persisted well into 
Cretaceous time. However, from the fact that carnivorous dinosaurs — 
land reptiles that arose either late in the Permian or shortly afterward — 
are known in the Triassic of AustraKa (none at all occur in New Zealand), 
we must conclude that there were still at this time intermittent land- 
bridges connecting this continent with Asia. The time of complete 
severance apparently came in the Jurassic, and the trough of separation 
seems to be the present Molucca-Banda sea, which has depths varying 
between 4650 and 21,100 feet. 
Finally we must ask, When did the thousands of oceanic islands — 
the Oceanides — arise? They are probably in the main of volcanic 
origin and occur singly, in groups, and most abundantly in Hnear ar- 
rangement. The isolated and the grouped islands probably all repre- 
sent great volcanic cones that have built themselves up from the ocean 
