286 



From Curlew Point, going south, the Cambrian quartzites and slates form a 

 nearly vertical cliff, about 50 feet in height, in nearly a straight line, but are set 

 somewhat further back than those to the northward. The close relation which 

 rock structure bears to coast features is well illustrated here. The cliffs are 

 composed of alternating beds of soft and hard rocks in a strike that is nearly 

 parallel with the coast, having a high pitch (65° to 90°), and a dip slope facing 

 the sea, a form of rock structure which makes it easy for the waves to undermine 

 each layer in turn, and when thus undermined, the whole face slips down by 

 gravity to the beach. This explains the straight line of cliffs, their steep and 

 inaccessible face, and supplies the reason why the cliffs, at this point, have been 

 worn back at a quicker rate than the adjoining sections. This rapid retreat of 

 the cliffs has led to the formation of an extensive sea platform which is un- 

 covered at low water. Standing at . Curlew Point and looking southwards, the 

 truncated edges of the Cambrian beds are seen in detail, giving evidence of 

 tectonic compression having acted opposed to the strike of the beds, contorting 

 the same in a transverse direction. As often occurs in the Purple Slate Series, 

 the beds very commonly show the phenomenon of ripple marks. Towards the 

 end of this straight face of cliff's, at a distance of about half a mile from Curlew 

 Point, a sea-stack forms a conspicuous feature (Howchin, W., 1918a, fig. 98, 



P- 114). 



At the end of this straight line of cliffs, an angle occurs in the direction of 

 the latter, causing a slight easterly trend that brings in new features. At a 

 short distance from the sea-stack the line of cliff's is broken by a curved 

 recession, forming a shallow valley that is grass-grown and protected from the 

 sea by low sand ridges. The Cambrian slates are here decomposed, dipping 

 easterly, at a lower angle. Similar beds are seen on the beach, with a westerly 

 dip, indicating an anticlinal fold. 



On the southern side of the small cove, just described, the cliffs rise to a 

 considerable height, with an easterly dip, capped by a layer of the fossiliferous 

 Pliocene, and is followed by another slight indentation in the cliffs enclosing a 

 grassed valley. The southerly side of this indentation shows a broken face of 

 very siliceous quartzite, lithologically similar to a prominent outcrop that forms 

 ridges on the beach. The falls from the cliffs, added to the outcrops on the 

 shore, make an excessively rough beach, ending in a prominent "stack" at what 

 may appropriately be called "Rocky Point" (opposite Sees. 616, 617). The 

 latter has a dip east, with a slight curve at its summit, directed towards the 

 west, forming a segment of an anticlinal arch. The stone is typical of the thicker 

 quartzites of the Cambrian in being light coloured, very fine in the grain, 

 and highly siliceous, examples of which can be seen near the summit of Sellick's 

 Hill and in many localities in the Flinders Ranges ; it is very distinct from the 

 quartzites of the Cambrian in being light-coloured, very fine in the grain, 

 occupies the beach in high serried lines and pinnacles with a dip east, 10° south, 

 at 53°, and a strike from north-east to south-west, which soon takes it below 

 sea level. Overlying these very siliceous quartzites are soft purple slates stand- 

 ing at a high angle and contorted. A little north of this point is a ferruginous 

 conglomerate that rests on truncated Cambrian slates. The origin of this con- 

 glomerate was not investigated, but is probably a metasomatized form of the 

 Lower Pliocene sandstones. 



Permo-Carboniferous (Glacial) Beds in Section B. 



Hallett's Cove, as a depression in the older rocks, owes its existence, 

 primarily, to an over-deepened portion of the ancient glacial valley. The two 

 headlands, forming the northern and southern boundaries of the Cove, are 

 about a mile apart, and consist of dark-coloured purple rocks of Cambrian age. 



