MINRRAI.ndlCAl, NolKS ANHEK'SON. 13 



Mr. lioo:eiiriecler a stratum of clay, for this may fairly be lep^ardfd as the 

 insoluble, more or less amorphous residue resulting' from tiie desti-uction 

 of the felspars, and the beryl crystals, quart/, diuses, and lumps of 

 wolfram thus set free are now found embedded in this clayey matrix, 

 tlie wolfram, as might be expected from its greater density, at a lowei- 

 level than the beryl and quartz. 



As to the agent or agents which have been responsible for this series 

 of events we ai'e more or less in the dark ; in spite of the presence of 

 topaz fluorine was probably not the etching medium, for beryl is but 

 slightl}' affected by hydi-oflnoric acid. It is possible that some alkaline 

 solution, such as carbonate of potash, whicli at a high temperature is a 

 solvent of most silicates, may be i-esponsible ; carbonic acid is now 

 regarded by some authorities as the active agent in the kaolinisation of 

 felspars^^, and, as McLintock and HalP'' have suggested, the alkaline 

 carbonates thus set free would attack the other silicates, such as quaitz, 

 beryl, or topaz. 



Calcite. 



Belubula Caves, near Mandurama, N.S.Wales. 



(PI. iii., figs. 1, 2; PI. iv.) 



The Belubula Caves are in Parish MalonguUi, County Bathuist, 

 about fifteen miles west from Mandurama, and two miles north of the 

 main road from Carcoar to Canowindra. They were discovered by a man 

 named Rittmeister, who, when kangaroo hunting, rested neai" the spot 

 one winter's morning and observed steam rising from a huge cleft in the 

 limestone. Later, with some companions, he explored the caves, 

 descending to a depth of nearly eight liundred feet at a distance of about 

 a mile from the entrance, finding corridors and chambers interminable. 

 It was discovered later that this was only one of a. series of caves, and no 

 fewer than six entrances were found at different parts of tlie same hill. 

 The caves were subsequently explored and described by the late C. S. 

 Wilkinson, Government Ge()logist-'\ and 0. Trickett-'. 



lu 1917, I was privileged to pay a short visit to the neighbourhood 

 and to explore part of the caves, particularlj'^ the chamber where the 

 crystals occur, under tlie expei-t guidance of Mr. W. F. Hosie, Mi.ss Judy 

 Hosie, and Mr. W. F. Hai'ris ; without the hel[) of these my visit would 

 liave been practically without result, and my best thanksa re due to them 

 for their cordial assistance. 



The cavern in which tlie calcite crystals described in tliis paper were 

 discovered is reached by an opening on the slope of a limestone ridge, 

 situated about half a mile to the north of the Belubula ilivei-, and rising 

 about three hundred feet above the river bed. The ciystal chamber is 



18 Butler— Min. Mag., xv., 1908, pp. 128-146. 



'» McLintock and Rull- IhuL, xvi., 1912, p. TOl. 



-» Wilkinson— Rec. (ieol. Surv. N.S.Wales, iii., 1892, pp. 1, "). 



•J' Trickett— Ann. Rept. Dept. Mmes N.S. Wales, 1908 (1909), p. 172. 



