BY H. I. JENSEN. 137 



like a chert is this rock in places that it has frequently been taken 

 for cherty Gympie slate. A microscopic examination showed this 

 rock to consist of a hypocrystalline mass, chiefly microspherulitic 

 with small patches of glass; quartz and orthoclase felspar are the 

 constituent minerals with a little magnetite and chlorite as 

 accessories. It is accordingly a Microspherulitic Ehyolite. The 

 whole of Nindherry Mountain is jointed in such a way as to 

 consist of large irregular columns. Silica percentage 72 - 39. 



Sp.No.43. (Plate xv., fig. 28). Loc: Maroochy River near Duna- 

 than Rock. 



This stone has been removed from the river bed to clear the 

 passage for boats to ply between Coolum and Yandina. It is a 

 banded rock showing flow-structure in handspecimen; it is of a 

 yellowish-grey colour with reddish and other coloured bands. 

 Under the microscope it is seen to contain phenocrysts of quartz, 

 highly corroded and frequently twinned on (0001), lying in a 

 cryptocrystalline base consisting of microspherulites and axiolites 

 of granular quartz and lath-shaped microliths of felspar. 



Name : Axiolitic (and Microspherulitic) Rhyolite. 



Sp. No.145. Loc: Summit of the W. peak of Mt. Eerwah. 



Rock greyish-white to yellowish; very considerably decomposed, 

 highly vesicular and often banded, indicating flow-structure. 

 Under the microscope the rock is seen to consist of an aphanitic, 

 hypocrystalline base in which a few phenocrysts of felspar are 

 found. The latter consists of an intergrowth of orthoclase and 

 albite, due evidently to a secondary change which has gone on in 

 soda orthoclase. The base is cryptocrystalline, with occasional 

 microspherulites, and occasional glassy patches, and consists of 

 quartz and felspar. Ferromagnesian minerals are practically 

 absent, only a few grains of magnetite and biotite being 

 represented. 



Name : Felsitic Rhyolite. 



Sp. No. 46. (Plate xv., figs. 29, 30). A yellowish-grey rather 

 decomposed specimen which contains a considerable amount of 

 kaolin and limonite, and which was taken from " The Mountain," 



