190 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAISTD 



Dr. Jensen^** has also advocated the assimilation of 

 carbonate rocks by the parent magma with the resultant 

 production of alkaline material. Daly*^ has elaborated 

 this view, and indicates that, in the localities with which 

 we are here concerned, highly calcareous Mesozoic sedi- 

 ments and possibly Palaeozoic limestones have been cut by 

 the alkaline eruptives. While small lenticular patches of 

 limestone a few feet in diameter, and sandstone beds con- 

 taining abundant calcareous material, are occasionally met 

 in the Mesozoic sediments of this area, the use of the term 

 " highly calcareous" does not seem at all justified for the 

 formation as a whole ; and, as far as the author can learn, 

 there is no justification at all for assuming that Palaeozoic 

 limestones have been cut through, for the Mesozoic sedi- 

 ments lie unconformably on the old Palaeozoic schists which 

 are not at all specially calcareous but rather the reverse 

 and which are older than any known deposit of limestone 

 in this portion of Queensland. An analysis of a typical 

 sample of these schists by the Agricultural Chemist, Bris- 

 bane, gave 1-59 per cent. CaO, 3-39 per cent. NagO, 3-07 

 per cent. KgO. 



As far as this area is concerned the evidence is rather 

 against any special limestone assimilation by the sub- 

 alkaline magma. 



Daly apparently holds that the sub-alkaline magma as 

 it traverses the formation absorbs the limestone or dolomite 

 with the resultant production of alkaline material. The 

 thickness of Mesozoic formations traversed by the alkaline 

 rocks in the Glass House Mountains and Mount Flinders 

 area is really small, especially at Mount Beerwah, and it 

 seems inconceivable to the author that the alkaline nature 

 of this material resulted subsequently to the passage of the 

 material into the Mesozoic material. If it did so, then one 

 is faced with explaining why one finds alkaline lavas and 

 sub-alkaline lavas resting one on top of the other and poured 

 out in all probability from the same opening. 



At the Main Range, we have alkaline trachyte occur- 

 ring between sub-alkaline, sub-basic, and basic lavas. 



'" Proc. Linn. Soc, N.S.W., 1908, vol. xxxiii. 

 " Op. cit. 



