610 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



penetrated with felspar as to appear broken up into grains yet 

 optically continuous over small areas. The base is microcrys- 

 talline and consists of titaniferons augite in prismatic grains; 

 acid plagioclase (oligoclase and albite); an isotropic mineral with 

 very low refractive index occurring in irregular patches, probably 

 sodalite; and idiomorphic magnetite grains. The felspar pheno- 

 crysts contain inclusions of an isotropic colourless mineral 

 (analcite from decomi)Osition). 



Name : Porphyritic Ophitic Olivine-Sodalite Basalt. 



W.207. Loc: summit of Terra-Terra. 



1. Handspecimen somewhat decomposed, highly porphyritic in 

 plagioclase (albite). 



2. Texture : the base is very tine, microcrystalline, with hyalo- 

 pilitic fabric. 



3. Constituents (in order of decreasing amount): (a) felspar, 

 (b) magnetite, (c) ferrite and haematite, (d) sodalite (or analcite), 

 (f) glass, (g) nepheline. The felspar is essentially albite, and 

 occurs in the base in minute laths. The red iron ore is derived 

 from the decomposition of magnetite, though some of the haema- 

 tite may be original. Olivine and augite are absent. The com- 

 position being essentially made up of albite and magnetite, this 

 rock is necessarily very alkaline. I have examined specimens of 

 a rock of the same composition collected by my brother, Mr. Thor 

 Jensen, L.S., at Coorombin Creek, Q., near the McPherson 

 Range. 



4. Name : Nepheline-Sodalite Tephrite. 



W.58. Loc: one mile east of Gowang Station. (Plate xxxii., 

 figs. 2-3). 



1. Handspecimen coarsely porphyritic with aphanitic base and 

 splintery fracture. 



2. Texture : holocrystalline with phenocrysts exceeding 5 mm. 

 ill diameter, and a very fine microcrystalline base with pilotaxitic 

 fabric. 



