146 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND, 



the Finney 's Hill United Silver ]\Iines Ltd., near Indooroo- 

 pilly, and supports in a very decided manner his hypo- 

 thesis that the silver-lead and other ores of this area are 

 closely associated with rhyolitic ("felsitic") intrusions. 

 (See ^Microphotograph Plate III., No. 10.) 



Megascopic. — A fine-grained light-coloured rock 

 evidently made up for the most part of felspathic material 

 and quartz, and traversed by numerous veins of quartz. 

 Part of the surfac-e of the specimen is coated with galena, 

 accompanied by well-shaped quartz crystals. 



Microscopic. — In order to preserve the appearance of 

 this specimen a slice was cut not through the metalliferous 

 part, but from a chip of the rock within one centimetre of 

 it. Curioush^ enough this section shows no trace whatever 

 of any metals except a few very small crystals of pj^rites. 

 The rock is similar in all its essentials to that described 

 above (D. 12), but has numerous quartz veins through it and 

 clusters of crystals of secondary quartz. 



Xame. — Intrusive Rhyolite. 



(e) The Porphyritic Series. 

 The members of this series are usually easily separated 

 from those of the Ehyolitic Series, but as pointed out by 

 the author in Part I. of this paper, one occasionally meets 

 Viith dykes that appear to be intermediate between these. 

 This is. of course, only to be expected, as the two series are 

 almost certainly genetically related. The evidence as to 

 the relative time of intrusion of the Rhyolitic and Porphy- 

 ritic Series is, so far, not conclusive, but points to the latter 

 series as being later than the former. 



(D.7) 166. 



Dj^^e across West Ithaca Creek in eastern part of Por- 

 tion 678, parish of Enoggera. (See ]\licrophotograph Plato 

 III., No. 11.) 



Megascopic. — A white prophyryritic rock made up of 

 rounded colourless phenocrysts of (piartz (in which can be 

 seen numerous inclusions of a white mineral), with smaller 

 phenocrysts of a white felspar set in a fine-grained light- 

 coloured ground mass. 



