310 



8. Perhaps the phenomena can be best explained by assuming an extensive 

 talus, fed by screes (such as exist on Mount Remarkable), and the material 

 redistributed by local streams. The latter would probably unite and form a 

 junction Avith the older outlet of the Onkaparinga, further to the westward. 



9. The age of the beds cannot be very definitely defined. The great thick- 

 ness of the alluvium is suggestive of the beds having been laid down during 

 the period when the country was slowly sinking and the Onkaparinga was 

 aggrading its bed by which the valley was filled up to the crest on its northern 

 side. This movement of depression may have had some relation to the gradual 

 development of the great "rift" which gave the adjacent Tertiary rocks a 

 vertical pitch. As the gravels are covered by the mottled clays and sands (which 

 are regarded as of Pleistocene age) the whole section may possibly be Pleistocene, 

 or the gravels may be of greater age than the mottled beds but newer than the 

 fossiliferous (Miocene) beds. 



10. The section is not likely to retain its bold and vertical outlines for any 

 great length of time. The rain is causing a rapid waste on the cliff face, and, 

 as a result of such weathering action on their upper portions, a secondary cliff 

 is being formed between the retreating heights and the beach, and on the ledges 

 separating the two vegetation is beginning to find a footing. 



Miocene Beds in Section G. 



The Miocene beds, which pass below sea level near Snapper Point, reappear 

 on the coast nearly a mile to the northward of the small creek described above. 

 Some exposures on the beach have heights up to 15 feet, and when seen in 

 washouts along the base of the cliffs they reach a height of 20 feet. The rock, 

 as a whole, is a finely triturated organic limestone, consisting mostly of polyzoal 

 fragments. The stone is relatively soft and is easily undermined by the waves, 

 a succession of caves has been excavated by the sea in the limestone along the 

 whole length of its exposure. The limestone ceases to form a clifif section shortly 

 before reaching the washout creek, but continues in exposure along the 

 littoral, between tides, the rock forming a moderately flat floor along 

 the beach. This feature continues until about opposite the first Waterfall 

 Creek, at the northern end of Sec. 278, Hundred of Myponga. At a 

 short distance up this creek is an isolated fragment of the fossiliferous bed which 

 has a dip to the north-west at 40°. It then disappears for about a third of a 

 mile, but reappears in the cliffs and on the beach with a high angle of dip, which 

 reaches 90°, and in one instance is reversed. 



The disturbed condition of the Tertiary beds in this locality is quite unique 

 for Australia, and is one of the concomitants of the great throwdown in the rift 

 valley of South Australia. After passing the ancient mouth of the Onkaparinga 

 the beds begin to roll in curves of 15° to the south-east and north-west; they 

 show an increased dip to 40° in the small Waterfall Creek, and then at a short 

 distance, further to the south, become vertical. [For a more detailed description 

 of these beds see Howchin, W., 1911.] 



Cambrian Beds in Section G. 



The Cambrian System, including slates, limestones, and quartzites, can be 

 studied to advantage on the northern slopes of Sellick's Hill [Howchin, W., 

 1897.] Earthy slates (or shales) which occupy the lowest position in this 

 section are seen just above the Sellick's Hill Hotel and in exposure in the 

 adjacent creek, and reach the coast by a south-south-west strike. The slates 

 are often of a very dark colour by the presence of carbonaceous material (up 

 to 25 per cent.) which has led some persons to imagine that coal might be found 

 in them. In many places the carbon has been oxidized and thereby changed the 

 colour of the rock to white, grey, or pinkish. Evidences of such change in progress 



