BY H. I. JENSEN. 153 



However, owing to the riebeckite occurring largely in minute 

 grains and partly intergrown with felspar, this method gives far 

 too high a proportion of amphibole. The chemical analyses also 

 render this estimation unnecessary. 



(b) From localities remote from the Glass House Mountain 

 region : — 

 Sp. No.122 Soda-Felsite. Loc: Mt. Byron. 



i. Handspecimen of a yellow colour, very fine-grained (aphanitic), 

 with a few phaneric phenocrysts. It resembles trachyte. 



ii. Microscopic examination. — (1) Texture: (a) crystallinity, 

 noncrystalline; (b) grain-size, uneven, with a very fine-grained 

 base; (c) fabric, porphyritic, with an allotriomorphic granular base. 



(2) Constituents (in decreasing amount) — (a) plagioclase and 

 other felspar, (b) chlorite, (c) kaolin and other decomposition 

 products. The only constituent in more than diminutive quantity 

 is felspar. 



(3) The felspar phenocrysts consist of albite. The felsitic base 

 consists largely of plagioclase. That orthoclase also occurs is 

 likely, from the presence of kaolin as a decomposition product, 

 but, owing to the decomposition, it is impossible to ascertain 

 whether orthoclase and interstitial quartz are present or not. A 

 little secondai-y magnetite occurs with the chlorite: they repre- 

 sent some original hornblende. 



(4) Nomenclature. — This rock belongs to the Soda-Felsites or 

 Keratophyres. It is an Albite Keratophyre, closely allied to the 

 alkaline rocks of the Glass House Mountains. 



(5) Additional remarks. — The Mt. Byron keratophyre has 

 undergone considerable alteration. It appears to have had 

 originally a glassy base which has subsequently devitrified during 

 earth movements. Hence it probably antedated the folding 

 movement which produced the D'Aguilar Range. It is Post- 

 Triassic intruding Trias-Jura sandstone, and older than the Mt. 

 Mee basalt. 



Sp. No.125. Felsitic Trachy-rhyolite. Loc: Lillingstone's Ck. 

 (branch of the Obi-Obi), Maleny Tableland, Blackall Range, 

 i. Handspecimen light yellowish-grey in colour, compact, 

 aphanitic and somewhat more vitreous in lustre than trachyte. 



