313 



high-level occurrence of the Miocene System is still preserved on the Hindmarsh 

 Tiers, 900 feet above sea level (Howchin, W., 1911). What otherwise is left 

 of these fossiliferous rocks in this faulted block is found on the beach, where 

 they have come under the control of the great rift-valley subsidence and have 

 been pitched down to the west in a vertical position. 



Tate's Geological Map of the District. 



In a paper by Tate and Dennant (1896) the first-named author, in plate ii., 

 gives a geological sketch map of the coast extending from the mouth of the 

 Onkaparinga River to Sellick's Hill beach. It is difficult to understand Tate's 

 map. There was, in the first instance, an error in the geological occurrences 

 and definitions which was corrected by an "erratum" slip in the following 

 volume. Apart from the occurrence of blown sand, in a few places, Tate shows 

 an uninterrupted surface exposure of "Older Tertiary" from the mouth of the 

 Onkaparinga to Sellick's Hill beach. These fossiliferous rocks, however, rarely 

 show at the surface, other than at the base of the cliffs on the sea front, and are 

 in almost all cases covered by thick deposits of Pleistocene and Recent alluvia 

 that form the upper portions of the cliffs. He does not distinguish between 

 the Freshwater Series (which has a great development on the northern side of 

 both Blanche Point and Witton Bluff) and the overlying fossiliferous marine 

 beds. He places on the map an exaggerated extension of the so-called 

 "Archaean," on the southern side of Pedler's Creek, and has not distinguished 

 from these "Archaean" cliffs the very important outcrop of fossiliferous 

 Miocene, which forms the main cliff for 100 yards in length, where he places the 

 older rocks adjoining the southern side of Pedler's Creek. 



Sea Encroachment. 



That the sea is encroaching on the land is evident from most places on both 

 sides of Gulf St. Vincent. Wide sea-platforms of hard rock exist between tide 

 marks in many places, and at high water the waves very commonly wash the 

 base of the cliffs or the heavy material left from recent falls from the cliffis. 

 One of these cliff falls that occurred on the north side of the outlet of the 

 Aldinga Creek in 1913 (see Howchin's Geology of South Australia, fig. 102, 

 p. 116) has since been practically swept away by the waves, leaving only a few 

 large and hard blocks on the beach as its residue. If the last local earth 

 movement on the coast has been an upward one, as is generally supposed, 

 then the elevatory movement must have spent itself ; or, otherwise, the rate of 

 marine denudation keeps pace with the movement of elevation in correspondingly 

 reducing the beach level. 



Bibliographical References. 

 Chapman, F. 



1914 — "Federal Handbook," Brit. Assoc. Adv. Sc. ("Corrigenda" facing 

 p. 240). 

 Clark, E. V. 



1900 — "Geological Notes on the Cliffs separating Aldinga and Myponga 

 Bays," Trans. Roy. Soc. S. Austr., vol. xxiv., p. 1. 



Dennant, J., and A. E. Kitson. 



1903 — "Catalogue of the Described Species of Fossils in the Cainozoic Fauna 

 of Victoria, South Australia, and Tasmania," Rec. Geo. Surv. 

 of Vict., vol. i., pt. II. 



