BY H. C. RICHARDS. 135 



This rock is very similar to the rhyolite at Glennie's 

 Pulpit. Mount Alford. 



Specwien 54c. — Locality: South-east of Tamborine 

 Plateau. This specimen is greyish white in colour, and is 

 seen to be hypocrystalline. It consists of small grains of 

 quartz and felspar set in a micro-spherulitic groundmass 

 of quartz and orthoclase. {See Plate XII., fig. 6.) 

 Fluxion structure is common and thin veins of secondary 

 quartz are numerous. Name: Rhijolife. 



Speci))ien 134. — Locality: Glass Cutting, 4 miles north 

 of Springbrook. This is a pale lavender in colour, and is 

 lithoidal in character. In the hand-.specimen it shows 

 magnificent banding. The rock is cryptocrystaUine, and 

 apart from a very characteristic micro-spherulitic structure 

 little else is seen. The slight variations in texture of the 

 different bands through the rock, together with different 

 degrees of pale staining, account for the rather pronounced 

 banding which this rock shows. The fluxion structure 

 shown by the rock mass is very fine, and at its base is deve- 

 loped an excellent perlite. This rock is characteristic of 

 all the rhyolite lava on the Springbrook Plateau. Specific 

 gravity 2-38. Name: Lithaiclal Rhyolite. 



Specimen 223. — This rock was obtained from the base 

 of the upper dome of Blount Lindsay, at an elevation of 

 3,600 feet. The dome is made up of pitchstone and rhyolite 

 agglomerate, and has a very rough columnar structure. 

 The specimen described occurred as a large boulder in the 

 agglomerate. In colour it is a deep brownish black passing 

 into red in patches. It has a dull lustre and a conchoidal 

 fracture, while the phenocrysts of quartz and felspar are 

 particularly glassy. Under the microcope the groundmass 

 is seen to be cryptocrystaUine, and to have a very definite 

 fluxion structure. ]\Iicro-spherulitic structure is well deve- 

 loped. The phenocrysts are quartz, sanidine and possibly 

 anorthoelase. It is dopatie and phenocrysts which are 

 frequently corroded and embayed are traversed by curved 

 cracks. The perlitic cracks in many cases run right through 

 the phenocryst and into the groundmass. These cracks 

 are .stained with limonite. {See Plate XII., fig. 4.) 



This rock represents an intermediate stage between the 



