BY H. C. RICHARDS. 119 



volcanic vents from which the material \Yas showered forth 

 at the same time. One of the characteristic included frag- 

 ments in the agglomerate is a black pitchstone containing 

 abundant white felspar phenocrysts, and it is an exception 

 to find any occurrence of the agglomerate without frag- 

 ments of this material. The only source of this pitchstone 

 actually encountered was Mount Lindsay, yet it characterises 

 agglomerates at least 36 miles away. Associated with the 

 acid agglomerate, extensive flows of rhyolite are found 

 particularly in the south-eastern portion of the area. The 

 highly-fluxioned lithoidal rhyolite of the Springbrook 

 Plateau and Tamborine Plateau differs from the porphy- 

 ritic rhyolite met at Upper Chinghee Creek and the less 

 porphyritic but more glassy type near Blount Lindsay, so 

 that one does not find the same similarity of lavas as of 

 pyroclastic material. The Chinghee Creek and Mount Lind- 

 say material can each be reasonably ascribed to two closely 

 adjacent volcanic vents, while the fine-grained more 

 tiuxioned and more extensive acid flows in the south-east 

 of the area are most likely derived from a fissure or series 

 of fissures with a general north and south extension. 



Associated with the trachytes of the Main Range, as at 

 Mount Roberts and near Spicer's Gap, there is fragmental 

 material, and while there has been a quiet welling out 

 along a north and south set of fis^ares of the trachytic 

 material, as well as explosive outbursts, there is a series 

 of plugs characteristic of the central type of eruption in 

 a general north-east and south-west direction from the 

 Main Range to ]\Iount Flinders. It is probable that also 

 during this period the rhyolitic and trachytic rocks were 

 formed in the Esk and Glass House ^Mountains districts. 



The material of the lower division appears to have 

 resulted rather from fissure eruptions than from central 

 vents, for although there is at Christmas Creek a develop- 

 ment of agglomerate, the general uniformity of the lava 

 and its widespread distribution taken into conjunction 

 with its comparative thinness point towards a series of 

 fissures forming the channels for the effusion. 



It is a somewhat difficult matter to determine the 

 sequence of the various volcanic products over the whole 



