100 SUNKLANDS OF PORT PHILLIP BAY AND BASS STRAIT 
to the former presence of one large inland lake behind it is 
improbable. 
On the mature surface of the Sunkland, the valley in which the 
Yarra River system flowed — Dannevig’s channel extending to- 
wards Port Phillip — referred to here as the Middle Pleistocene 
Yarra, is well defined. This mature surface probably extended 
some distance beyond Cape Otway into the region now covered 
FIG. 13 
Sections of the Floor of Bass Strait. 
by the Southern Ocean: it was an extensive plain of fluviatile 
sediments, resting on the Lower Dune Series, and belonging to the 
same cycle of erosion as the fluviatile deposits under the Keilor 
Plains Basalt or the mature flood plain of the middle Dandenong 
Creek, of which it is the downstream extension. This cycle 
reached maturity in the Middle Pleistocene. 
The trunk stream of this downstream extension of the Middle 
Pleistocene Yarra, flows in what appears to be a shallow valley 
that first shows up at the 45-fathom bathymetrical contour 8 miles 
W.S.W. of Cape Schanck as a shallow depression, and similar 
