BY H. I. JENSEN. 139 



contorted and faulted layers suggestive of older sedimentary 

 rocks. 



Under the microscope it is seen to be a crypt ocrystalline rock 

 with plagioclase phenocrysts. Microspherulitic and flow-structures 

 are present. The phenocrysts are highly corroded and consist of 

 quartz and plagioclase, the former having almost wholly disap- 

 peared. The base consists of quartz and felspar. Hornblende 

 of a very pale fibrous variety is present; it is commonly included 

 in the quartz and felspar phenocrysts. 



This rock is apparently a quartz keratophyre; the appearance 

 of folding is probably due to the flow of constituents on a large 

 scale as seen under the microscope on a small scale. 



Sp. No.168. A white rock obtained near the 76A m. between 

 Eumundi and Cooroy. 



Under the microscope we see an aphanitic, microspherulitic 

 base consisting of cryptocrystalline to microcrystalline felspar 

 laths and granular quartz. Phenocrysts, highly corroded, often 

 perfectly rounded, occur in this base. Pseudomorphs in chlorite 

 and dusty magnetite after idiomorphic hornblende are present. 



Name : Rhyolite. 



Sp. No.15 is typical of most of the d} T kes and other rhyolitic masses 

 between Yandina and Nambour. Sp. No.168 is typical of 

 those between Eumundi and Cooroy. 



Sp.No.24. Loc: Bottle and Glass. 



A compact porphyritic greenish rock with large idiomorphic 

 phenocrysts of quartz, orthoclase and microcline. The base is 

 green and aphanitic. The greenish colour is seen by means of 

 the microscope to be due to a greenish glass which fills the 

 interstices between the minute crystals of felspar constituting 

 the base. The silica percentage of this rock is 68*72. 



Name : Porph}'ritic Rhyolite. 



Mt. Tinbeerwah, near Tewantin, consists of a very tine-grained, 

 even, microspherulite rock. It is cryptocrystalline to micro- 

 crystalline (felsitic), not unlike the Nindherry Rhyolite in 

 general appearance, but no glass appears to be present. Plates 



