142 I'ROCKEDINGS OF THE ROVAL SOCIETY OF QUEENSLAND. 



— "The occurreuce of crystals of pyrites throughout the 

 rock, and of cavities or 'vughs' containing calcite pyrites, 

 &c., is a great disadvantage to this stone. "^^. 



These "vughs" or "druses" are peculiar to this rock 

 and this particular outcrop, the writer never having 

 observed them anywhere else in the area. They are of 

 various size and occur in perfectly fresh rocks, having been 

 found in the heart of the building-stone quarries. The 

 minerals associated with these vughs are mostly calcite and 

 pyrites, though quartz and prehnite are also found. These 

 minerals are certainly not secondary in the sense that they 

 are Aveathering products, but they are probably primary in 

 origin and result from the action of mineralisers at a late 

 stage of consolidation. They would thus be secondary only 

 in the sense that many of the zeolites of the Tertiary basalts 

 of Queensland are secondary. To use Sederholm's term, 

 they are " deuteric. "^^"^ 



Professor Richards points out that "a notewv)rthy 

 feature of the stone is the comparative absence of 

 segregations."^^ The present writer discovered small 

 patches of fine-grained more-basic material which he at 

 first regarded as segregations, but which microsections 

 proved to be small zenoliths of the Grey Phase. A com- 

 parison of Plate II. No. 6 (a zenolith) with No. 5, which is 

 described in the writer's field notes as "typical of the Grey 

 Phase in the west and north-west of the Enoggera area," 

 gives some idea of the close resemblance which is seen 

 between these rocks when placed side by side on the stage 

 of a petrographical microscope. 



Of especial interest is the occurrence in both slides of 

 rounded crystals of quartz, free from inclusions and 

 surrounded by a rim of idiomorphic crystals of biotite 

 arranged parallel to the outline of the quartz. 



Towards the edges of the (?) Hybrid mass one finds 

 irregular and vaguely defined patches of pink material of 

 varying size. This zone forms in the field a connecting link 

 between the Enoggera (?) Hybrid and the Pink Phase. 



(d) The Rhyolitic Iktrusives. 

 The intrusive rocks surrounding and associated with 

 the granitic rocks fall naturally into two distinct types, 



" Op. eit. p. 102. 



"a Bull, de la Coram. Geol. de Finlande No. 48, 1916, p. 142. 



•= Op. cit. p. 102. 



