202 PROCEEDINGS OF THE ROYAL SOCIETY OP QUEENSLAND. 



rhyolites. It is then in the alkalies, alumina, and silica that 

 one sees departures from the normal. 



A perusal of the analyses in Professional Paper 99 of the 

 U.S. Geol. Survey, by Dr. H. S. Washington, fails to furnish 

 a lava flow which is so rich in silica as the rhyohte under 

 consideration. The nearest approach to it is a metarhyolite 

 described by J. S. Diller from Bully Hill IVIine, California, but 

 this latter rock is nearly 4 per cent, poorer in silica and 3.6 per 

 cent, richer in alumina, and by its relative richness in magnesia 

 and poverty in lime and alkalies indicates much more alteration 

 than the Montville rhyolite. 



A particularly interesting analysis for comparison is that 

 of a spheroid from a pyromeride^ from Wuenheim, in the 

 Vosges. The analysis is given by Delesse in the Bull. Geol. 

 Soc. France, and used by G. J. Cole in his valuable paper on 

 the "Alteration of Coarsely Spherulitic Rocks " in the Q.J.G.S. 

 in 1886, p. 189. The analysis is incomplete and the alkalies 

 have been obtained by difference, so not much reliability may 

 be placed on that value. The silica, however, is extremely 

 high and the alumina very low, and Cole states, on p. 189, 

 " The silica percentage has again, however, been probably 

 raised by the removal of bases in solution." 



In a recent publication on the " Rhyolites of Banks 

 Peninsula," New Zealand,^ Mr. R. Speight publishes an inter- 

 esting analysis of a selected spherulite from the rhyolite on 

 Quail Island, in Lyttleton Harbour. This analysis is given for 

 purposes of comparison, and one notes that it is poorer in 

 silica and much richer in alumina and magnesia than the 

 rhyolite under consideration. The alkalies, too, are very 

 much lower, especially the soda. 



Mr. Speight, in comparing the analysis of the selected 

 spherulite with that of the spheruhtic rhyolite itself, states on 

 page 82 " that of the spherulite shows traces of the effect of 

 some agent, which has increased substantially the quantity of 

 sihca and magnesia, has increased slightly the amount of 

 lime, and reduced materially the alkalies and the alumina. 

 This has, in all probability, been effected by hot water, probably 

 charged shghtly with magnesian salts, the source of which it 

 is tempting to assign to the basaltic lavas which subsequently 

 to the rhyolitic eruptions inundated the locality." 



' A quartz -felsite or devitrified rhyolite characterised by conspicuous 

 sphervilitic or Hthophysal structure, and thus having a nodular appearance. 

 Nomenclature of Petrology by Arthur Holmes, p. 192. 



8 R. Speight. Rec. Cant. Mus. Vol. ii., 1922, pp. 77-89. 



