BY H. C. RICHARDS. 201 



occurs as an incrustation on the surface of a fine-grained 

 white sandstone which is horizontally bedded and which 

 outcrops all round a hill about 100 feet above the surround- 

 ing country. The sandstone is capped by a bed of con- 

 glomerate containing abundant quartz pebbles about the 

 size of a walnut. The conglomerate is quite free from any 

 alunogen incrustation while the sandstone immediately 

 below it is thickly coated {see text-figure 30). 



In the most recent geological map* the sandstones 

 are mapped as belonging to the Star Series (Carboniferous). 

 The sandstone bed is not exposed for any great depth but 

 the main incrustation occurs on a cliff face about 16 feet high 

 and in a cave in the sandstone. The cave, which is some 30 

 feet long and 10 feet wnde, has its walls and roof thickly 

 coated with the incrustation. In some cases this is four 

 inches thick and shows a crusted banding, while here and 

 there through the material there are small specks of limonite. 

 The incrustation is much thicker on the walls and roof of 

 the cave than anywhere else. The beds have a slight down- 

 ward warp in the neighbourhood of the cave and this may 

 result in an increased percolation of water through the sand- 

 stone here and consequently a thicker incrustation. 



The forms taken on by the incrustation are varied, and 

 where it is thin the usual one is distinctly crenulate. In the 

 cave, however, where the deposit is thick one gets blanket- 

 like forms as in limestone caves, also structures resemb- 

 ling giant rose blooms (see text-figure 31). 



All round the hill the sandstone which is rather soft has 

 been scalloped out and small amphitheatres formed by the 

 action of wind and solution. Wherever there is a protective 

 covering by means of a ledge over these small amphi- 

 theatres, a deposit of the alum incrustation is invariably 

 found. lu the cave, hornet nests built on the walls have 

 become coated with the incrustation. 



As the surface of the sandstone wherever slightly pro- 

 tected from the weather invariably shows traces of alunogen 

 and the conglomerate bed above is quite free from it, the 

 source of the material seems to be within the sandstone. 

 Some of the sandstone in the cliff face had been scraped 

 to remove the incrustation six weeks previous to my visit, 



♦Queensland Mineral Index, Plate 11. 



