

BY H. I. JENSEN. 593 



Osann's name, paisanite, to them. These rocks have a wonderful 

 resemblance from all the localities mentioned. The felspar 

 phenocrysts may be prismatic, but are usually nephilinitoid; the 

 base is microcrystalline to cryptocrystalline, and consists of idio- 

 morphic felspar, mossy (dendritic) aggregates of soda-amphibole, 

 sometimes riebeckite, more often arfvedsonite, and rarely cossy- 

 rite, similar feathery aggregates of segirine and interstitial quartz 

 and chalcedony which frequently form pseudo-spherulitic or star- 

 shaped (strahlenkbrnig) aggregates. A micrographic intergrowth 

 of quartz and felspar is frequently seen in the base, and very 

 often little parallel quartz strands in optical continuity exist 

 within the felspar phenocrysts. This feature is very character- 

 istic, and phenocrysts of this type I have occasionally referred to 

 in my papers as micrographic phenocrysts. Intergrowths of 

 albite and orthoclase are also frequent in the phenocrysts, and 

 often the intergrowth becomes so pronounced that a microcline- 

 microperthite is formed, as in many rocks from the Warrum- 

 bungles, Nandewars, the Canoblas, and Mount Flinders. 



The mossy, dendritic, and feathery aggregates of amphibole 

 and pyroxene, forming what is termed poecilitic (poikilitic) 

 structure, the microperthitic phenocrysts of felspar, and the 

 micrographic and micropoecilitic phenocrysts of felspar are very 

 characteristic features. 



(b) Next we have the light grey, rather fine-grained trachytes 

 associated with the more acid types mentioned above. These 

 rocks exhibit trachytic fabric, more rarely pilotaxitic fabric. 

 Fluxion-structure is often well marked. The average grain-size 

 is usually coarser than in the more acid types. The phenocrysts 

 consist usually of felspar of the same kinds as mentioned above 

 in the acid types, but phenocrysts of soda-amphibole and other 

 minerals occasionally occur as well. .ZEgirine or segirine-augite 

 is usually an abundant constituent, and occurs as small idiomor- 

 phic phenocrysts in stunted rods, and as fine acicular microlites. 

 The base is trachytic and contains little or no quartz. Soda- 

 amphibole when present occurs as minute rods and grains, or 

 more rarely as poecilitic (feathery) aggregates. 



