197 



Unconformity. 



(b) An ironstone layer on top of Cambrian limestone, 



probably metasomatic 1 



(c) Bluish, somewhat earthy, pteropod limestone, 



containing numerous small pteropods and frag- 

 ments of trilobites, which weather in relief ... 30 



(d) Rubbly impure limestone ; the included earthy 



material weathers in relief, fossils scarce ... 40 



(e) Hard siliceous limestone with impurities, fossils 



scarce 15 



(f) White and yellow crypto-crystalline, marble-like 



rock, has a clean and smooth fracture, no 

 fossils observed at this spot (lowest bed exposed) 50 



186 



In ascending the gully the siliceous and marble-like 

 limestones, shown in the lower portions of the above section, 

 continue to occupy the bottom of the valley and contain, 

 sparingly, small brachiopod and niolluscan remains. The 

 limestone is sometimes laminated and pseudo-breeciated. 

 The Archaeocyathinae make their appearance near the head 

 of the gully, where the valley opens out before reaching the 

 north and south district road that makes the western 

 boundary of Section 22, a little east of the phosphate mine. 

 The fossiliferous beds are in outcrop on the hillsides, and 

 also in patches on cultivated land, where the stones collected 

 from the ploughed land are gathered into heaps and make 

 good hunting ground for fossils. The stone carrying the 

 Archaeocyathinae is a whitish and pinkish marble which has 

 a freer fracture than the bluish pteropod limestone, and 

 weathers to a smooth surface. With the exception of scat- 

 tered sponge spicules, which sometimes appear in relief on 

 the weathered surfaces, no fossils other than the Archaeo- 

 cyathinae were found in the limestone. Lithologically, the 

 matrix bears a close resemblance to the marble-like rock that 

 forms the lowest member (f) of the series shown in the sec- 

 tion given above, and in which no fossils were observed. They 

 may possibly be on the same horizon. The western outcrop, 

 so far as could be judged, forms the axis of an anticline, as 

 is the case with the beds referred to in the detailed section. 

 The Archaeocyathinae have a very local development, and 

 in many cases the fossils merge into indistinctness, as though 

 in course of absorption into the structureless matrix. It is 

 possible that this process of absorption of fossiliferous 

 structures has been effectively carried out in the case of the 

 similar marble-like limestone lower down the gully, and 

 accounts for its non fossiliferous condition. Associated with 

 the Archaeocyathinae limestones are layers and nodules of 

 cherts of various colours — reddish, greenish, dark coloured, 

 etc. 



