64 RIVER TERRACES OF THE MARIBYRNONG RIVER, VICTORIA 
The raised beach is plastered on the eroded scarp left by the 
subsidence of the Port Phillip Snnkland which assumed its 
present configuration at the close of the Pleistocene: the age of 
the raised beach and the wave platform is Recent. 
The Altona shell beds (Pig. 7) rest on Newer Basalt — the 
southerly extension of the Keilor Plains lava field. Hills (1940) 
points out that they are well bedded, and there is no evidence of 
current bedding : the bivalves are thin-shelled and well preserved, 
the majority lying with their convex surfaces uppermost, indicat- 
ing that they were deposited below high water mark out of the 
reach of the turbulent swash of the waves breaking on the beach. 
The ridges are 8 feet high, are relatively low and broad, and there 
is a succession of them. He states : 
“that the underlying form of some at least of the ridges is that of submarine 
banks formed when the level of the sea was sufficiently high to cause it to 
flood over the basalt plains in the areas where the above-described ridges occur. 
It appears probable that, either at this time or as the sea retreated, these banks 
were added to in places by the growth of beach ridges, but the shell beds near 
the William,stown Racecourse, and the lobate ridges near Altona, are regarded 
simply as upraised submarine banks.” 
There is general agreement that the shells are Recent. Of the 
nature of the emergence he remarks: 
“Evidence of Recent emergence is so common along the Victorian coast, . . . 
that a eustatic fall of sea level may be suspected of having contributed to it. 
Such Recent emergence has been described by others, or has been observed 
by the author at Mario, the Ninety-Mile Beach, Waratah Bay, Cape Patterson, 
Port Phillip, Apollo Bay, Warrnambool and Portland.” 
If some of the ridges of the Altona area are submarine banks 
formed when the level of the sea was higher, there is no doubt that 
the Yarra Delta was similarly inundated. As most of the Delta 
has been modified by human agency, we are compelled to rely on 
old records and maps. The maps show many features like those 
of the Altona area — an orderly succession of spaced depressions 
and, inferentially, ridges, trending west-north-west behind the 
north shore of Port Phillip Bay. In the West Melbourne Swamp 
littoral and estuarine shells have been found similar to those in 
the shallow ephemeral lakes of Altona. 
The West Melbourne Swamp (Fig. 7) was an open sheet of 
water between the Maribyrnong River and Moonee Ponds Creek ; 
in latter years it has been drained and reclaimed. It was formed 
by the lower reaches of the Moonee Ponds Creek being dammed 
back by sands deposited before the 15 to 20 feet eustatic fall of 
sea level, and was therefore flooded when sea level rose. There are 
records of fossil mollusca in the Swamp — all littoral or estuarine 
forms at present living in Port Phillip Bay. There are also 
