122 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSIAND 



A tabulated comparison is given in the next chapter. 



It is interesting also to note that J. A. Douglas," in a 

 paper on "Geological Sections through the Andes of Peru 

 and Bolivia, ' ' points out that after the intense folding and 

 elevation which took place in Middle Tertiary times, result- 

 ing in the raising of the Andes, volcanic activity continued 

 and vast sheets of rhyolitic lavas and tuffs were poured out, 

 and these were succeeded by the trachytic lavas which build 

 up Mount Taapaca and the andesites and basalts of Mount 

 Tacora and Chupiquiiia. 



(ii.) Age op Effusive Rocks. 



The acid pyroclastic material near Brisbane known as 

 the Brisbane Tuff^'' is unquestionably at the base of the 

 Ipswich Series of Coal Measures, and there is no doubt as 

 to its early Trias-Jura age. Apart from this minor 

 occurrence, however, the most recent opinions expressed by 

 writers, namely E. 0. Marks and R. A. Wearne, on the 

 volcanic rocks of this area have been certainly in favour 

 of a late Trias-Jura age for at least a considerable portion 

 of the extruded material. The author, after a most careful 

 investigation into all the evidence adduced in favour of 

 these opinions, is unable to accept them, but, on the other 

 hand, is convinced of a post-Walloon age for the whole 

 development. If the Walloon measures represent the upper- 

 most Trias-Jura deposits, then the whole volcanic develop- 

 ment is post-Trias-Jura. All the direct and indirect 

 evidence appears undoubtedly to point in this direction, 

 and I\Iessrs. ]\Iarks and Wearne, who have been the most 

 ardent advocates of an Upper Trias-Jura age for a great 

 deal of the volcanic material, have accepted the author's 

 interpretations of the sections and occurrences which had 

 formerly chiefly led them to their conclusions. 



The volcanic rocks are found resting on top of the 

 Trias-Jura sediments in all parts of the area, except in the 

 south-east, where they rest on the Pala30zoic schists. In no 



'* Q.J.G.S., vol. Lxx. (1914), pp. 47, 48. 



^' W. H. Eands, Q 'land Geol. Surv., Pub. 34. 



