210 



three distinct beds which are unconformable with each 

 other. 



The lowest bed is very strongly coloured with iron in 

 irregular patches, which, in contrast with the rest of the 

 material, which is white, forms a mottled pattern (pi. xxviii.). 

 The bed is a fine-grained argillaceous sand-rock, sufficiently 

 indurated to resist the mechanical effects of rain, and is 

 operated upon only slowly by the sea. Scattered sporadically 

 through the finer material in places are small angular stones, 

 of local derivation, including examples of the chalcedonized 

 Miocene and small pellets of lateritic ironstone. The base 

 is not seen, as it forms a hard floor on the beach and passes 

 from view under the sea, and has been dredged adjacent to 

 the end of the jetty. The lower portions of the bed are freest 

 from stones, while towards the upper limits a layer of small 

 stones, like small gravel, occasionally occurs. The cliffs are 

 nearly vertical, and as the tide when high washes the base 

 with a depth of 4 feet of water, a certain amount of under- 

 mining is going on, which causes lateral cracks at the sur- 

 face, and finally sheets of the cliff face slip down to the beach, 

 where they become divided up into large cuboidal masses on 

 which the waves make small impression. These blocks between 

 tides, as well as the cliff face as far up as the tides go, are pene- 

 trated by countless numbers of holes caused by a small boring 

 phyllopod crustacean. This mottled bed, which comprises 

 generally two-thirds or more of the cliff face, agrees in all 

 respects with a similar mottled arenaceous clay that forms 

 cliffs on the other side of the gulf, as well as inland. The 

 upper portion of these mottled clays, when seen in section, 

 usually exhibit an eroded surface. 



The clay cliffs gradually decrease in height on the 

 northern side of Ardrossan jetty, and at a distance of 1^ 

 miles in that direction retreat in the form of low banks faced 

 by sandhills. They also decrease in height on the southern 

 side of the jetty and disappear, as a cliff feature, at Parara ; 

 but they are seen again at intervals where the cliffs rise to 

 any considerable height, as, for example, south of Meninie 

 Hill (half-way between Rogues Point and Muloowurtie 

 Point), where by a shallow syncline in the fossiliferous 

 Miocene the mottled clays are brought into the section show- 

 ing a thickness of 20 feet. 



The mottled beds can be seen in outcroo at many points 

 inland, as, for example, on either side of the roid going 

 north from Ardrossan to Winulta. They also occur iii many 

 sinkings and bores in the neighbourhood, as in the following 

 instances : — 



