BY H. I. JENSEN. . 149 



aad anorthoclase. The blue hornblende is essentially an almost 

 opaque riebeckite, and occurs in grains and rods of various sizes. 

 Some phenocrysts of a species closely resembling arfvedsonite are 

 also present. A small quantity of regirine in minute needles is 

 also present. A cryptographic intergrowth of quartz and felspar 

 is common in the base. Spherical pores infilled with chalcedony 

 are present. 



(3) The riebeckite and felspar separated out together, except 

 at the last, when there was left a eutectic mixture of felspar and 

 quartz. 



(4) Name : Orthophyric Riebeckite Comendite. The chemical 

 analysis showed that this rock is not a true trachyte. The 

 magmatic name derived from the norm is alaskose, closely allied 

 to liparose. 



Note.— Some varieties are not quite holocrystalline, containing 

 a little glass in the base. Others show flow-structure. Occasion- 

 ally patches of micrographic intergrowth of two felspars are met 

 with, apparently two very closely allied forms in different optic 

 orientation, for there is almost no difference of refractive index 

 between fiem. 



(iii.) Vesicular Trachyte. Loc: Bridge's Hill, near Caboolture. 

 Under the microscope this rock is hypocrystalline, of uneven 

 grain-size, and trachytic fabric. It consists of sanidine (or 

 anorthoclase) showing Carlsbad, and frequently Baveno, twinning; 

 magnetite, eegirine, a bluish or purplish glass, and some decompo- 

 sition products 



(iv.) Pilotaxitic iEgirme Trachyte. Loc: Mt. Miketeebumulgrai. 

 This is a pilotaxitic, vesicular, ?egirine trachyte, very like the 

 previous. 



(v.) Riebeckite Trachyte or Comendite. Loc: Trachyte Range. 

 This is a very tine-grained rock, containing both riebeckite and 

 cossyrite in characteristic dendritic aggregates. 



