BY H. I. JENSEN. 161 



ii. Microscopic structure. — (1) Texture : holocrystalline, even- 

 grained, but for a few olivine phenocrysts, and almost panidio- 

 morphic granular in fabric. 



(2) The constituents (in order of decreasing amount) are olivine, 

 magnetite, plagioclase, and augite, all of which occur in consider- 

 able quantity. 



(3) The olivine occurs both in phenocrysts and in smaller 

 crystals. The phenocrysts sometimes enclose magnetite and 

 felspar. It is partly decomposed to greenish serpentine. The 

 magnetite is intergrown with augite and felspar in the ground- 

 mass. The felspar occurs in laths with ragged ends, and some- 

 times includes magnetite. The augite occurs in small granules 

 interstitially between magnetite and felspar. 



(4) The order of consolidation is abnormal. The magma must 

 have been extremely rich in iron ore, which separated all the time 

 during consolidation. It began crystallising first and finished 

 after the felspar. Olivine, magnetite and felspar crystallised 

 together for some time. Augite separated out last. 



(5) Name : Olivine-Magnetite-Basalt. 



(6) Note. — The felspars are of the microtine habit, and consist 

 of basic labradorite, showing high extinction angles. 



Many of the Maleny (Blackall Range) basalts are similar to 

 this rock. The basalt from the Woondum Tableland near Cooran 

 is also similar. A specimen in my collection from the Coorombin 

 road, near Murwillumbah, is also very rich in iron, consisting of 

 magnetite, albite and titaniferous augite. 



Sp. No.166. Loc: Basalt dyke at Battersby's (in the D'Aguilar 

 Range), 4-m. west of Mt. Tunbubudla. 



Handspecimen black, basaltic-looking. 



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

 crystalline; (b) grain-size, porphyritic with aphanitic base; (c) 

 fabric, hyalopilitic and ophitic. 



(2) Constituents (in decreasing order of abundance). — (i) Labra- 

 dorite occurring both in corroded phenocrysts and in minute 

 laths in the base; (ii) olivine changing to green serpentine (this 

 mineral occurs in phenocrysts); (iii)(a) augite partly in the form 

 11 



