INAUGURAL ADDRESS. 
11 
and some parts of the wider valleys changed to salt marshes or lakes, 
such as Lakes Amadeus and Torrens, while the entrance to Spencer’s 
Gulf is choked with sand. It was during this period, when the great 
valleys of the river systems were being excavated, that a great pro- 
portion of the outbursts of volcanic rock in the form of basalt occurred. 
The age of these basalts is established by their superposition on 
cretaceous rocks. Thus, at Roma, the Grafton Range is a mass of 
basalt, resting on the cretaceous sandstones and shales. Mount 
Bindango is a similar instance. On the Upper Warrego there is a 
deep ravine through cretaceous rocks partly undermining a basaltic 
cone. On the Victoria River a large basin has been eroded in the 
cretaceous rocks, and then several huudred square miles flooded by an 
eruption of basalt, through which watercourses have cut instructive 
sections, showing the subordinate sandstones baked and fused by 
contact, and the cracks filled by the covering basalt. 
It does not appear that the eruption of basalt has materially 
affected the geographical outline of the coast, but there were consider- 
able variations of level, and important tracts of fertile country were 
formed by the basaltic detritus, such as Peak Downs and Darling Downs 
in Queensland, and to the west of Melbourne in the south. 
LARGE ANIMAL PERIOD. 
It was not till after the convulsions which attended this outflow 
of basalt, and lakes, marshes, and rivers had been formed, and pro- 
duced a luxuriant growth of vegetation, that the gigantic marsupials 
gave any decisive evidence of their advent, as their fossil remains are 
found in the drifts of watercourses mixed with basaltic pebbles and 
detritus. The physical conditions of the country during the period of 
the Diprotodon, Nototherium, and associated fauna, differed materially 
from that which now subsists, for the structure of the larger quadru- 
peds would render them incapable of obtaining a subsistence from the 
short herbage now existing in the same localities, and it is evident that 
their food was of a large succulent growth, such as is found only in 
moist climates and marshy lands or lake margins. This view is also 
supported by the fact that on the Darling Downs and Peak Downs 
the associated fossils include crocodile and turtle, so that what are now 
open grassy plains must have been lakes or swamps, into which the 
streams from the adjacent basaltic hills flowed, and gradually filling 
the hollows with detritus, formed level plains. 
ENORMOUS RAINFALLS. 
That this gradual filling up of lakes actually occurred is shown by 
the beds of drift which are found in sinking wells and in sections 
exposed by erosion of watercourses ; but in all these instances there 
is evidence that the ancient rainfall was excessive, as even our present 
wettest seasons are inadequate to the removal of the quantities of 
