Geological Notes on the Cliffs Separating 

 Aldinga and Myponga Bays. 



By Edward Vincent Clark, B.Sc. 



[Communicated by Prof. Tate.] 



[Read November 7, 1899.] 



Travelling southwards along the coast from the Port Willunga 

 Jetty, the Eocene and overlying Miocene both dip downwards, 

 and after a mile or so the . Eocene disappears beneath the sand 

 strand ; about half a mile further on the Miocene also reaches to 

 sea-level. Both sets of beds are last seen as reefs between low 

 and high water, but as the dip of the Miocene is the smaller, the 

 reef formed by it is much larger than that of the Eocene, extend- 

 ing a considerable distance both seawards and southwards on the 

 shore, and also a good deal further below sea-level. It is last 

 seen about two miles from Port Willunga Jetty, but is visible 

 somewhat further if the sand has been swept by a storm. 



The Post-miocene clays which cap the cliffs then.gradually give 

 way to sandhills, which are well overgrown and contain a good 

 percentage of calcic carbonate. The beach is broad, and above 

 ordinary high tide is a bank of shingle, increasing in size as we 

 go south, while the sandhills become smaller. Two miles (roughly) 

 from where the Miocene reef disappears these are no longer 

 covered with vegetation, and behind them is a lagoon in a basin 

 that was formerly an arm of the sea, but which has been re- 

 claimed by the shingle drifting up from the south and the 

 sediment washed down from the Sellick's Ranges. This lagoon is 

 now fresh water, or only slightly brackish when full, but dries up 

 nearly every summer. Dead shells of Coxiella confusa are in 

 profusion in the silt. 



From this point the sandhills give place to a clayey deposit, 

 still flanked by the bed of shingle (which is much coarser here), 

 and rising somewhat rapidly in height — about one foot per chain. 

 This clay bears a considerable likeness to the mottled clays over^ 

 lying the Miocene at Blanche Point and the jetty, with the 

 exception that it contains a vast amount of gravel, arranged in 

 more or less horizontal layers. This gravel is mainly of quartzite, 

 shale, and ironstone ; and the pebbles are only slightly worn — 

 most with the corners just taken off, but many quite angular, and 

 a few well-rounded. Owing to the amount of gravel in this clay 

 it will stand at a great inclination, and being by no means in 



