BY H. I. JENSEN. 157 



addition to felspar, variety orthoclase, which occurs in acicular 

 crystallites, there is a profusion of apatite needles; a great deal of 

 ferromagnesian mineral has been present, but is now represented 

 only by hematite. The rock is very considerably decomposed. 



Name : Devitrified Hypocrystalline Trachyte. 

 Sp. No.115. Loc: Emu Mountain (Peregian). 



This is a fine-grained holocrystalline, pilotaxitic trachy-rhyolite, 

 very decomposed, so that the amphibole is now replaced by 

 hematite. The amphibole evidently had a dendritic habit like 

 riebeckite and cossyrite, for the hematite replacing it is distributed 

 in this way. The main constituent of the rock is sanidine, of 

 which a few phenocrysts occur, but most of it occurs in the form 

 of minute laths and crystallites. In handspecimen the trachyte 

 of Peregian is exactly like that of Coolum Mountain, columnar, 

 bluish-grey, typical trachy-rhyolite. Brown flakes of biotite are, 

 however, also found in it, as in the Green Hills trachy-rhyolite 

 (Green Hills, Mt. Eurungunder, Pt.Arkwright). 



Name: Decomposed Trachy-rhyolite. 



(c) The Andesites, 



There are two kinds of andesites represented. One of these is 

 exemplified by the quartz-andesite or dacite occurring at Bankfoot 

 House in the Glass House Mountains; the other is typical 

 quartzless andesite. A type-specimen of the former kind was 

 described in my last paper. The andesitic rock obtained at Mt. 

 Wappa, and at the saddle of Nindherry, is macroscopically 

 identical with the Bankfoot House dacite. 



The following are brief descriptions of some of the rocks 

 obtained. 



Sp.No.163. Sodic Quartz- Andesite. Loc: Railway line near the 

 78 m. peg, between Eumundi and Cooroy. 



i. In handspecimen a bluish-grey rock with pink specks; fine- 

 grained, but not aphanitic; in appearance it resembles a fine- 

 grained syenite. 



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

 holocrystalline; (b) grain-size, fine; (c) fabric, intersertal, pilotax- 

 itic, almost panidiomorphic. 



