RIVER YARRA, VICTORIA 47 
found beneath the Newer Basalt at Burnley and Collingwood 
show that the pre-Newer Basalt river bed was well below sea-level 
at those points. This suggests that the basalt was extruded in a 
glacial low sea-level period. 
 Ponding of the Yarra River occurred at Fairfield, where the 
river was obstructed by the lava flows. Similar ponding occurred 
in some tributary streams with resultant deposition of alluvium. 
The shell-beds of the Williamstown area, a product of a post- 
Da eustatic sea-level, repose on the Newer Basalt. (Hills, 
a. 
MAIN CONCLUSIONS 
1. The Upper Yarra owes its westerly flow to a line of granitic 
intrusions, 1.е., to differential erosion. 
2. The Middle Yarra breached the Eastern Quartzites at 
Healesville because that was the edge of the Woori Yallock 
Basin lava field, and the site of a disrupting quartz porphyry 
intrusion. 
3. The Lower Yarra breached the Western Quartzites through 
post-Older Basalt drainage being diverted over a saddle in 
the Wurunjerri Range. This was possible because the lava 
was some 300 feet thick and lifted the thalweg of the stream 
above the level of the saddle. 
4. Two pre-Older Basalt peneplain surfaces are described—the 
Yarra Plateau (600-650 feet) and the Nillumbik Peneplain 
(400-450 feet). 
5. The pre-Older Basalt river system and divides are described 
in outline. 
6. The thalweg of the main stream (Melbourne River) was of 
the order of 500 feet below present sea-level on the site of the 
present Port Phillip Heads. The remainder of the depression 
shown by the Sorrento Bore is due to Selwyn’s Fault. 
7. After extrusion of the Older Basalt, marine transgression 
over a large part of the State betrunked the ancestral Yarra 
River system, and brought about physiographic senescence. 
The seaward basalts were covered with Tertiary strata, which 
were mostly limestones, because the depressed river system 
brought comparatively little material for deposition. 
8. Retreat of the sea brought rejuvenation and the deposition 
of the Red Beds sands and gravels which resulted therefrom. 
