75 
SUNKLANDS OF PORT PHILLIP BAY AND BASS STRAIT 
also been referred to. Likewise, due to tilting, the Werribee and 
Keilor Plains lava fields shelve under the waters of Port Phillip 
along its north-western shore ; this movement is believed by Keble 
and Macpherson (1946) to have occurred near the close of the 
Pleistocene on the Pootscray Warp, parallel to, and a few miles 
inland from the north-west shore. The north-west and south-east 
tilts are suggested by a slight inclination of the delta terraces 
(Mg. 4). 
vfin,c.iwu TRRACf TERRACE OELTA TERRACE TERRACE vtRTiCfli SCMf 
The line along which the tilting met is beneath the waters of the 
Bay, probably along the Bellarine Fault (vide p. 95). 
The bathymetrical chart (Fig. 2) of the Inner Basin shows 
clearly that it is a sunkland — the submerged portion of the Yarra 
River System. The lower reaches of the tributaries that joined 
the lower Yarra are also clearly shown, and some of these join it 
on its delta. The tributaries from the west were the Werribee 
and Little Rivers, Kororoit Creek and the Skeleton Water Holes; 
from the east Mordialloc (sic), Kannanook, and other water- 
ways — ^the outlets of Dandenong Creek, Balcombe Creek, Dunn’s 
Creek and others. There are also valleys of streams that have 
ceased to function, their headwaters having been covered by 
basalt or dunes. 
The trunk stream flowed on to an extensive delta, the submerged 
level floor at 78 feet, north of the Nepean Bay Bar. The mud on 
the delta, as elsewhere on the floor of the Bay, has, presumably, 
been brought down by the Yarra and its ti-ibutaries during the 
glacial stage, or equivalent pluvial stage, and resorted by the tidal 
streams during the interglacial or postglacial stages ; the thickness 
of the sediment on the delta must be considerable. 
The section (Fig. 3) across the floor of the Sunkland shows 
marine terraces 30 and 40 feet above the delta with a maximum 
width of 4| and 2 miles ; respectively these surround the submerged 
delta except on the Nepean Bay Bar side, and extend northwards 
on both the east and west sides of the trunk stream, but some 
