110 
Geology and Physical Geography : 
fresh channel during later Upper Tertiary times to be eroded 
along a different course deeper into the Silurian rocks than the 
previous stream. This channel was in its turn partly filled in by 
the Newer Volcanic lava-flows along the edges of or through 
which the present Yarra in the vicinity of Melbourne now winds. 
This basaltic strip lies between the hills of Northcote on the one 
side and Kew Asylum on the other, and thence passes by Haw- 
thorn and Richmond, between Jolimont and the Treasury gardens, 
on the north-east, and the Government House domain on the 
south-west. It undoubtedly covers an ancient river bed con- 
forming to the Yarra, and holding precisely the same relation to 
that river as the main trunk lead of Ballarat and Sebastopol 
does to the present Yarrowee River. This lava-flow* though 
covered with alluvial deposits below Princo’s-bridge, is no doubt 
connected beneath those deposits with the widespread flows of 
Footscray and Williamstown. 
Thus we have brought into juxtaposition in the Yarra basin 
evidences as to the fluviatile and volcanic operations of the Mio- 
cene period, which are most extensively developed iu Gippsland, 
and the similar operations of the Pliocene era, of which the 
Ballarat leads are the typical representatives. 
Changes with regard to the position of the mouth of the Yarra 
have evidently taken place within comparatively recent times. It 
is very evident that at one period the course of the river trended 
from where Prince’s-bridge now stands, in a direction passing 
between the Barracks and Emerald Hill, and over where tho 
Albert Park lagoon now lies, and that the outlet of tho river Avas 
between Emerald Hill and St. Kilda. The erosion of a channel 
between Emerald Hill and Batman’s Hill and the junction by 
that means of the Yarra with the Saltwater River must have been 
effected long subsequent to the outpouring of the Older Volcanic 
lava-flows. 
It may be noticed that some of the species of fossil-fruit de- 
scribed by Baron von Mueller are common to both Miocene and 
Pliocene drifts, specimens having been found in the gravels beneath 
Older Basalt at Tanjil precisely identical in species with some 
obtained from the lead-gravels beneath newer basalt at Hnddon. 
This tends to show that some of the Miocene types of flora con- 
tinued to flourish duriug Pliocene times. 
In some of tho Upper Tertiary clays of Daylesford, however, 
eucalyptus leaves, akin to the present vegetation, are found in a 
fossil state, thus showing that at some period during Upper 
Tertiary times the pre-existing Miocene flora was superseded by 
one of a type similar to that which now flourishes. 
Post Tertiary and recent action has developed the existing 
physical configuration. The present streams cut their way along 
or across tho lava-sheets, sometimes adhering approximately to the 
