12 
IXAITCrT UAL ADDRESS. 
drift which has been the result of a single flood in the ancient 
period. On the ridges around the lakes there existed a forest growth, 
as many species of opossum have left their bones as evidence ; but the 
timber evidently differed from the present scanty growth of eucalypti. 
"Whether the same abundant rainfall extended far into the western 
interior is uncertain, but the rivers evidently maintained a luxuriant 
vegetation adapted to the sustenance of these gigantic animals, as the 
discovery of a nearly complete skeleton of Diprotodon on the shore of 
Lake Mulligan, in South Australia, shows that these animals lived 
in this locality, as it is not probable that their bodies could have 
floated down the great river which drained the interior of the continent 
through Lake Ejre. 
ANOTHER CHANGE. 
It is evident that the climate gradually became drier, that the 
rivers nearly ceased their flow, and the lakes and marshes became dry 
land, while the vegetation was reduced to short grasses that no longer 
sufficed for the subsistence of the huge Diprotodon and gigantic 
kangaroo, though some of the smaller may still survive to keep com- 
pany with the dingo, who, while he left the impressions of his teeth in 
the hones of the Diprotodon, has shown a greater facility for adapting 
himself to altered conditions. Is this the survival of the fittest? It 
was in these later days that some of the rivers flowing direct to the 
coast cut through the sandstones into the softer shales beneath, and 
by their erosion formed considerable valleys bounded by rocky cliffs, 
and when the land was subsequently depressed the sea flowed in and 
formed inlets, of which Sydney Harbour, and the entrance to the 
Hawkesbury River on the east coast, Port Darwin, and Cambridge 
Gulf on the north-west, and the Pallinup River on the south-west of 
the continent may be cited as examples. 
CONCLUSION. 
Thus Australia, after its first appearance in the form of a group 
of small islands on the east, and a larger island on the west, was raised 
at the close of the Palaeozoic period into a continent of at least 
double its present area, including Papua, and with a mountain range of 
great altitude. In the Mesozoic times, after a grand growth of vege- 
tation which formed its coal beds, it was destined to be almost entirely 
submerged in the cretaceous sea, but was again resuscitated in the 
Tertiary period with the geographical form it now presents. Thus its 
climate at the time of this last elevation maintained a magnificent 
system of rivers, which drained the interior into Spencer’s Gulf, but 
the gradual decease in rainfall has dried up these watercourses, and 
their channels have been nearly obliterated, and the country changed 
from one of great fertility to a comparatively desert interior, which 
can only be partially reclaimed by the deep boring of artesian wells. 
