BY H. C. RICHARDS. 109 



in the south-western portion of the area, and determined 

 the volcanic seciiience as — i. Trachytes, ii. Andesites and 

 daeites, iii. Rhyolites, iv. Basalts; while they believed the 

 ages of the volcanic eruptions to belong (i.) to the Walloon 

 stage of the Trias-Jura Coal Measures &c., (ii.) to the 

 Tertiary Era. 



E. 0. Marks, in 1910 and 1911, in referring more 

 particularly to the basaltic types of south-east Moreton, 

 set down one series, composed particularly of the andesites 

 and basalts of iMacPherson 's Range and the Tamborine 

 Plateau, as Trias-Jura, and another series, exemplified by 

 the basalts near Brisbane, as late or post-Tertiary. The 

 same writer in 1912*^ strongly favoured a Trias-Jura age 

 for the trachytic rocks in the Esk district. 



In 1913,^ R. A. Wearne gave further evidence for the 

 Trias-Jura age of a portion of the volcanic rocks of the 

 area. 



Microscopic investigations have not been carried out 

 previously on the sub-alkaline rocks, except on a few rocks 

 by Dr. Woolnough from the locality of Cunningham's Gap, 

 and a few by Dr. Jensen : while chemical investigations have 

 been, hitherto, almost entirely restricted to the alkaline 

 rocks. 



With respect to the time at which these volcanic rocks 

 have been extruded, we find Rands, Jack, Wearne, and 

 Marks have advocated a Trias-Jura age for either all or 

 a part of the volcanic series, whereas A. C. Gregory, 

 Skertchly, Jensen, and also Andrews of recent years 

 have advocated a Tertiary age for the rocks they have 

 particularly described. 



No previous record has been made by any of the 

 writers on this area of the threefold development of upper, 

 middle, and lower divisions of volcanic rocks which the 

 author has found developed extensively over a great part 

 of the area. 



^Queensland Govt. Min. Jour., xiii. (1912). 

 • A.A.A.S., xiv., Melb. 1913. 



