BY H. I. JENSKN. 163 



Sp. No.94. Basalt found capping the Woondum Tableland. This 

 is an ordinary olivine basalt resembling the previous, but con- 

 taining a greater proportion of magnetite. The olivine is changing 

 to serpentine and dolomite. Augite is very sparingly represented. 



Sp.No.l. Olivine Basalt. Loc: Nindherry, near Yandina. 



i. Very dark, compact, heavy rock of typical basaltic appear- 

 ance. 



ii. Microscopic examination. — (I) Texture: (a) ciystallinity, 

 hypocrystalline; (6) grain-size, uneven, fine; (o) fabric, hyalopilitic, 

 porphyritic in olivine and augite. 



(2) Constituents (in order of decreasing abundance). — (a) essen- 

 tial, olivine felspar and augite; (6) important, magnetite and 

 glass; (c) minor, serpentine chlorite, apatite, and dolomite, 

 decomposition products. 



(3) Remarks. — The olivine exists in idiomorphic cori'oded 

 ciystals decomposing to serpentine. The augite is of two genera- 

 tions, (a) phenocrysts, corroded, and occasionally with hour-glass 

 structure, consisting of a colourless diopside; the cleavage is not 

 well marked ; (b) minute grains of a yellowish-green augite in the 

 base The felspar is subporpliyritic in laths with ragged ends, 

 and belongs to the labradorites; it has the " microtine " habit. 

 The magnetite is abundant and titaniferous, yielding leucoxene 

 as a decomposition product. The glass is of a greenish colour, 

 and fills cavities and interstices. 



(■i) Order of consolidation — 



(a) Olivine 



(b) Augite (I) 



(c) Felspar 



(d) Magnetite 



(e) Augite (2) 

 (/) Glass 



(5) Name and Relationship. — Hyalopilitic Olivine-Basalt. 

 The chemical analysis shows this rock to belong to the 



■*' Auvnrgnoses " ia the American classification. 



(6) Note. — The order of consolidation in this rock is somewhat 

 abnormal, the magnetite being late in crystallising. This feature 



