170 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAND 



noted for the abundant and large phenocrysts of this 

 mineral. These are usually sub-idiomorphic and have an 

 average diameter of 1 mm. 



The plagioelase, which occurs only in the groundmass 

 is basic andesine, AbggAn^g. An analysis of this rock is 

 given. The specific gravity is 2-87. Name: Olivine Basalt. 



Specimen 221. — Locality: 3,000 feet level, south-east 

 side of Mount Lindsay. This represents the uppermost 

 flow of the lower division of basic rocks and lies directly 

 underneath the pitchstone and rhyolite dome of Mount 

 Lindsay. In the hand-specimen it is seen to be extremely 

 fine-grained. It has a hyalopilitic groundmass showing 

 a very good fluxion structure. {See Plate XIV., fig. 6.) 

 It has small porphyritic crystals of plagioelase and olivine 

 about 1 mm. long, but these phenocrysts are not plentiful. 

 The groundmass consists of felspar mierolites, very small 

 granules of augite, and a great abundance of very fine 

 granules of iron-ore. This is probably largely ilmenite 

 as the norm shows 5-93 per cent, of ilmenite and 2-55 per 

 cent, magnetite. Occasional rectangular patches of magne- 

 tite -05 mm. in diameter are seen. A very similar rock to 

 this is met among the lower basalts on Christmas Creek, 

 near Burge's Crossing, and on the western termination of 

 Buchanan's tramline. The specific gravity is 2-79. Name: 

 Basalt. 



Specimen 225. — Locality: 2,400 feet level, south-east 

 side of Mftunt Lindsay. This flow is one of the lower divi- 

 sion, and occurs somewhat below the rock just described. 

 It differs considerably, however, in being holocrystalline 

 and it does not exhibit the same fluxion structure. The 

 olivine is nearly all altered and the augite, which is 

 titaniferous, occurs in definite ophitic patches. Name: 

 Basalt. 



Specimen 112.— Locality : Coulson's Creek, portion 51 v, 

 parish of Clumber. This occurs as a dyke, 2 feet wide, 

 cutting through a coal-seam which it has coked on either 

 side. It is indistinguishable in the hand-specimen from 

 many of the surface flows. 



It is holocrystalline, and is made up of very abundant 



