212 Proceedings of the Royal Society of Victoria. 



A few yards above the road on the right bank the ferruginous 

 grits are in their lower part replaced by a band of cream coloured, 

 earthy, polyzoal limestone about live feet thick. It is full of 

 foraminifera, echini spines and polyzoa, though, as is usually the 

 case in such rocks, other fossils are scarce. In patches the lime- 

 stone is altered to a tine grained, hard, reddish rock with a 

 conchoidal fracture. The limestone is immediately succeeded in 

 depth by decomposed volcanic rock seamed with sheets of 

 secondary ironstone. The limestone is very quartzose in places 

 and passes up gradually into ferruginous grit, in which we have 

 not been able as yet to find any fossils. 



The alteration of the limestone overlying the volcanic rock 

 here is of interest when taken into consideration with similar 

 developments elsewhere. At Maude the alteration is so pro- 

 nounced in places that the officers of the survey were led to 

 ascribe it to the effect of an overlying thin sheet of volcanic- 

 rock. We have shown in a previous paper (17) that there is no 

 intercalated basalt, and that the appearances which suggest its 

 presence are really due to the deposition of the limestone in the 

 clefts and crannies of a denuded basalt surface. The alteration 

 cannot then have been produced as suggested. In fact the same 

 section shows similar polyzoal limestones overlain by 100 feet of 

 basalt, but no marked changes have been brought about by the 

 flow. We noticed that at Maude the alteration of the rock was 

 most pronounced where it lay on the denuded basalt surface, and 

 became less marked at higher levels, but were quite at a loss to 

 account for it. 



Since then we have examined similar altered polyzoal lime- 

 stones at Airey's Inlet where it lies on the denuded surface of 

 the great basaltic dykes which seam the ash beds and on the ash 

 beds themselves. Again at Point Addis we have the pink finely 

 crystallised limestone passing up into the usual loose-textured 

 polyzoal rock. The limestone rests on a great thickness of 

 remarkable black clays. In the Grange Burn, near Hamilton, 

 we find a similar limestone highly altered and plastered down 

 into the joints and irregularities of the porphyry where the latter 

 crosses the stream. Further removed from the junction of the 

 two formations the alteration is less pronounced. Similar altera- 

 tion is found in the polyzoal rock overlying ash beds at Curlewis 



