BY H. I. JENSEN. 133 



(2) Constituents (in order of decreasing abundance). — Essential: 

 {a) albite, (6) orthoclase; Diminutive : (c) chlorite (after horn- 

 blende); Minute : (d) magnetite, (e) quartz, (f) apatite, (g) pyrites. 



(3) Remarks on minerals. — The albite occurs both as pheno- 

 crysts and in the base. Most of the base, however, consists of 

 orthoclase. The hornblende originally present has completely 

 changed to chlorite. Quartz occurs only as interstitial grains. 



(4) Order of consolidation normal. 



(5) Nomenclature and affinities. — This rock is a highly alkaline 

 soda-bearing "hornblende porphyry,'' not far removed from the 

 keratophyres. Owing to decomposition it is impossible to identify 

 it more closely. Rocks of this kind are common, inteibedded 

 with true rhyolites, on Mt. Delaney and Mt. Archer. The lavas 

 erupted in this region were alternately of the nature of true 

 rhyolites, and sodic porphyries and keratophyres. 



Very typical quartz-porphyries have been obtained from 



(a) Portion 9, Parish of Wararba, and (b) the D'Aguilar Range 

 at Battersby's selection, west of Mt. Tunbubudla. 



Sp.No.55 Solvsbergite. Loc: Fife's Range, Delaney's Ck. Road 

 (Plate xiii., fig. 18). 



i. Handspecimen : colour bluish-grey to greenish-grey when 

 fresh, decomposing to yellowish-grey. Grain-size aphanitic and 

 very even. It is a compact heavy rock. Dykes of it cut the 

 phyllites, gneisses, and schistose beds of Fife's Range. 



ii. Microscopic investigation. — (1) Texture: (a) noncrystalline; 



(b) fine-grained, microcrystalline and even, except for a few 

 felspar phenocrysts; (c) almost panidiomorphic granular with a 

 tendency to trachytic arrangement. 



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

 felspar, (b) segirine, (c) quartz, (d) decomposition products, viz., 

 kaolin and iron ores; (e) magnetite. Only felspar and aegirine 

 occur in notable quantity. 



(3) Remarks. — The felspar occurs in stunted laths. It has a 

 lower refractive index than Canada balsam and is probably 

 mainly orthoclase, with a little anorthoclase and albite. The 

 laths show Carlsbad and Manebach twinning or both together. 



