AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 41 



In the swales there is a small accumulation of sand from the 

 disintegration of the ridges since they were formed. Inland 

 behind the inner ridges are ephemeral lakes — Lake Seaholme, 

 Lake Altona, and Lake Truganina — the bottoms of which are 

 black mud resting on the lava-plain. In the banks of Lake Trug- 

 anina, 5 feet 9 inches above L.W.M., are marine shells in situ; 

 some of the pelecypods are paired. The lower reaches of the 

 Kororoit Creek flow over a similar mud in which marine shells 

 occur. Marine shells are also found in the tidal deposits slightly 

 above present high-tide level on the flats north of the Williams- 

 town Racecourse which is on the right bank of the Kororoit 

 Creek. 



The highest inner ridge shown by Hills (1940 Fig. 3) is 10 feet 

 2 inches above high-tide level, or, as the tidal range at Altona is 

 about 2 feet, 12 feet 2 inches above L.W.M. It is apparent, then, 

 unless there has been very recent subsidence, the inner ridges 

 were submerged to a depth of from 3 to 8 feet by the Recent or 

 Postglacial rise of sea-level of from 15 to 20 feet above present 

 L.W.M. This inundation also filled the lakes behind the ridges. 

 Recent subsidence cannot however be discounted, for the writer 

 (1946) believes that the coastal strip on the eastward side of a 

 line from Footseray to Werribee and beyond is a down-warped 

 area partly responsible for the recent configuration of Port Phillip 

 Bay. 



Submergence during interglacial periods has occurred on the 

 Nepean Peninsula, the south-eastern land arm of Port Phillip; 

 there dune-deposits have been levelled and sediments and shell- 

 beds deposited on their levelled surfaces. The succession at 

 Altona is taken to be : 



A. — Newer Volcanic Basalt (Middle Pleistocene). 



B. — Margaret glaciation period, 

 a. — Emergence (W2). 



b —Submergence (W2/W3). Deposition of shell-beds, 

 c. — Emergence (W3). Formation of dunes. 



C. — Postglacial. 



a- — Ri se of sea-level, progressive submergence and levelling 



of dunes. 

 b — Maximum rise of sea-level from 15 to 20 feet above pres- 

 ent L.W.M. at Postglacial Optimum. 



c, Progressive emergence. Dunes uncovered with levelled 



surface, commencement of formation of beach ridge. 

 The symbols W2, W3 and W2/W3 represent the Wurm glacial 

 and inter-glacial stages. 



