RIVER YARRA, VICTORIA 25 
across the Anti- Wurunjerri Range, and in so doing released the 
waters impounded behind it (see below). The first reason, then, 
for the position of this water-gap, is that the Older Basalt lava 
field extended to that point. 
A second reason for the breaching of the Eastern Quartzites at 
Healesville is that there is an intrusion of quartz porphyry there. 
The river finds its way over the southern extension of this small 
boss. The intrusion has been fairly recently uneovered, as is 
shown by the fact that parts of it are still capped by country rock. 
The eutting on the west side of the railway tunnel (which pierees 
the porphyry) shows that there was some disturbance of the sedi- 
ments by the intrusion. The broken bedrock would facilitate the 
breaching of the barrier at that point. 
The Middle Yarra receives the waters of the Don River at 
Launching Place and the Watts River at Healesville. This greater 
volume of water is restricted in its passage through what may be 
called the Healesville Gorge, and so the river at this point is 
characterized by rapids. The widespread Healesville flats are 
evidence of ponding, and indeed at the present time they are 
flooded after heavy rains. 
In Wurunjerri times, the ancestors of the Don and Watts 
Rivers must have carried their waters to the south of the 
Warramatte Hills and so eonnected with the Wurunjerri River. 
The infilling of the Wurunjerri Valley with basalt made this 
impossible, and the waters there must have ponded deeply to form 
a large lake until they were released by the breaching of the Anti- 
Wurunjerri Range. This ponding could. be ealled the Healesville 
Lake. It is analogous to the Yarra Lake further west (repre- 
sented now by the Yarra Flats), although the latter was probably 
never of the nature of a permanent deep lake like the former. 
The Healesville Lake probably stretched as far south as Woori 
Yallock, where residuals suggest this area to have been the margin 
of the Older Basalt lava field in this direction. 
The alluvial flats from the Healesville and Yarra Lakes and the 
gorges which confine them are the most charaeteristie features of 
the Middle Yarra. 
BREACHING OF WESTERN QUARTZITES 
How the Wurunjerri Range (the Western Quartzites) could be 
breached to allow the Yarra through has engaged the attention of 
physiographers, and the following theories have been adduced: 
1. Keble (1918, p. 148) : “The Wurunjerri Range was breached 
by a tributary of Watson's Creek, and the basin of the Middle 
Yarra was diverted through the breach." 
