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2. Pebbles on Beach at Ardrossan. One of the most 

 remarkable features of the district is the occurrence of sea- 

 worn pebbles of the fossiliferous Cambrian limestones that 

 are strewn along the beach over a length of several miles. 

 They occur mostly on the southern side of the jetty and 

 for a distance of half a mile from the latter; the pebbles 

 have been mainly derived from the grey and pinkish marbles 

 that contain the remains of the Archaeocyathinae. The 

 homogeneous nature of the rock causes it to wear with a 

 smooth surface that shows up the structure of the included 

 fossils to perfection. It was here that the occurrence of the 

 Archaeocyathinae in our older rocks first attracted attention 

 in South Australia. On a stony spit, exposed at low water, 

 about three-quarters of a mile to the southward of the 

 Ardrossan jetty, the stones are of a more earthy kind, 

 having been derived from the pteropod-trilobite limestones 

 that overlie the grey and yellow marbles. Unlike the 

 Archaeocyathinae pebbles the former are deeply etched by the 

 action of the sea water, and consequently present a very 

 rough surface with the impurities in the limestone, as well 

 as the fossils, standing out in strong relief. It is a curious 

 feature that while the upper surfaces of these pebbles are 

 deeply incised, the undersides, that have been sunken in the 

 sand, are relatively smooth. At Parara, 2 miles to the 

 southward of Ardrossan, there is a clay platform, uncovered 

 at low water, that extends ror a mile out to sea. Here again 

 there are stony spits of shingle, resting on the clay floor, 

 among which are numerous angular stones of Cambrian lime- 

 stone, including the crystalline varieties as well as the impure 

 bluish pteropod limestones, some examples of which measured 

 2 feet in diameter. 



The origin of these fossiliferous beach stones raises an 

 interesting question. To account for their presence on the 

 beach one or two explanations appear to be possible: — 

 (a) River transport, or (b) outcrops of Cambrian limestones 

 below sea level but within the limits of wave action. In sup- 

 port of the first of these suggestions, the parent rock is in the 

 neighbourhood, and, under ordinary circumstances, their 

 presence on the beach could be easily explained by stream 

 erosion carrying the land waste to the sea ; but such a trans- 

 porting force has no existence in the neighbourhood at the 

 present time. Horse Gully is the deepest and longest gully in 

 the locality, and has undoubtedly been^ excavated by running 

 water, and further, it is equally certain that the transported 

 material in the excavation of the gully must have found its 

 way into the valley of the gulf. If the stones on the beach 

 came from the head of this gully, where a similar rock is 



