BY H. I. JENSEN, D.SC. 181 



physiographic considerations it seems likely that an early 

 Tertiary age must be assigned to them. 



{B). The Alkaline Rocks. [29] It is quite possible 

 that the lavas of this series were in part at least contem- 

 poraneous with the Older Volcanics. Although petro- 

 logical analogies have tempted the writer in the past to 

 consider all the Alkaline rocks of Eastern Australia to be 

 of identical age, their more detailed physiographic study 

 renders this view questionable. 



Alkaline rocks of Tertiary age exist in Victoria, at 

 Mount Macedon, and detailed investigations in this 

 important type district have led Skeats to the conclusion 

 that their age is Middle Tertiary. They are certainly 

 mountains of accumulation and not residules. 



In Queensland, the writer has investigated the Glass 

 House Mountains and the Yandina district volcanoes, 

 all of which have been satisfactorily shown to be true 

 mountains of accumulation. Their age, probably, ante- 

 dates the formation of the Middle Tertiary peneplain, 

 which is represented in this district by the Woodford 

 peneplain, for although dykes of alkaline rocks occur on 

 the peneplain surface, no true lavas and tuffs of an alkaline 

 nature have been detected on this level. A monoclinal 

 fold, along the D'Aguilar and Blackall Ranges, broken by 

 occasional faults, has depressed the coastal region so as to 

 preserve it in the volcanic representatives of the alkaline 

 rocks. This fold must have been forming at the time 

 when the alkaline rocks were erupted, and if some of these 

 eruptions were not actually submarine, as maintained 

 by J. Malcolm Newman, B.E., there can be little d,oubt 

 that the whole present broad coastal belt was submerged 

 in late Tertiary times, and has only recently been re-elevated. 

 The late uplift can date back only to the Pleistocene, as 

 far as can be judged by the evidence of the marine shells 

 of the raised beach deposits. 



The Mount Flinders and Fassifern Alkaline rocks, 

 studied by Mr. Wearne and myself, are probably also in 

 part of early Tertiary age, slightly antedating the for- 

 mation of the Middle Tertiary peneplain. There is, however, 

 strong evidence that in this region the eruptions lasted 

 long enough to leave some of their accumulations on the 

 peneplain surface. They were, therefore, partly of Middle 



