148 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAND 



As Wearne^' has pointed out, Jensen has called the 

 southern portion of the Main Range the Little Liverpool 

 Range. However, while trachytic rocks are found along 

 the Main Range as far north as Mount Castle, they do not 

 extend from there on to the Rosewood district, also the top 

 of the Main Range and the culminating peaks such as 

 Mount Roberts, Mount Huntley, Spicer's Peak, Mount 

 Mitchell, Mount Cordeaux and Mount Castle, consist of 

 basaltic rocks, for the most part olivine-basalt. 



At Spring Bluff, there seems to be no evidence of 

 trachytic rocks at all, but on the other hand, the basalt 

 is found resting on the Walloon shales and sandstones. 

 The map and sketch-section on page 74 of Jensen's paper 

 on the Geology of Mount Flinders and Fassifern Districts 

 are rather misleading in showing the extent of the trachytic 

 rocks on the Main Range, and also of the rhyolitic rocks in 

 the south-west portion of the area. The sketch-section also 

 seems to the author incorrect, in showing Cretaceous rocks 

 underlying the basalt of the Darling Downs. There is 

 no record of such being the case, but on the other hand, 

 where the basalt flows have been worn down by the streams 

 to the underlying rocks, these are seen to be, in all cases, 

 the so-called Trias-Jura sediments. Also in the section 

 through Mount Tamborine no indication is given of the 

 rhyolitic rocks which occur on the eastern side. 



The trachytic rocks in the Fassifern and Mount 

 Flinders districts have been dealt with by Jensen in several 

 papers, and also by Wearne and Woolnougli, but hitherto 

 the Esk, Woodhill and Cainbable Creek material has not 

 been really described. 



The Cainbable trachyte is apparently the base of a 

 worn-down plug, and the Woodhill trachyte has apparently 

 come up as a sill. The Esk trachytes occupy an inter- 

 mediate position between the alkaline and sub-alkaline 

 series; this is best illustrated by the variation diagrams. 

 {Sec Plates VI.-VIII.) The Cainbable Creek trachyte is 

 sub-alkaline, but the other trachytes are all of a definite 

 alkaline nature. 



^' Proc. Roy. Soc, N.S.W., xlv., p. 137. 



