BY H. I. JENSEN, D.SC. 179 



Marks has demonstrated the existence of dolerites 

 of Triassic age in more or less isolated patches of the 

 Ipswich coalfield. [27] Further, we have the period of 

 Trias Jura sedimentation in Southern Queensland ushered 

 in by eruptions of felsite (Brisbane tuffs), dacite, quartz 

 porphyry and andesite (Eumundi series). 



Yet Mesozoic eruptions were extremely localised. 

 Volcanic debris or lava is seldom met with in boring in Trias 

 Jura or Hawkesbury formations. 



It was only in the late Cretaceous that vulcanicity 

 became more intense, as evidenced by tuffy material in 

 the Desert Sandstone, the trachytic tuffs in the Upper 

 Cretaceous of the Mackay district (Q.). [For references 

 see 9 and 12.] 



It has only been shown that in the areas distinguished 

 by Alkaline eruptives in Tertiary time, monchiquites, 

 essexites, picrites and teschenites were erupted during 

 late Mesozoic times [12] ; the Alkaline rock being frequently 

 preceded by ultrabasic eruptions which were separated 

 from the main period of Alkaline effusions by a short period 

 of erosion. 



In Tasmania the Mesozoic, or at ad events a portion 

 of it, probably the Jurassic, was characterised by extensive 

 volcanic extravasation. The great diabase sills of that 

 State are usually assigned to the Jurassic. 



Tertiary Vulcanicity. 



The absence, except in very few cases of fossiliferous 

 aqueous rocks in the regions of tertiary volcanic action, 

 makes it extremely difficult to assign exact ages to Tertiary 

 igneous rocks. 



The Kainozoic eruptions may be roughly divided into 

 the Older Basalts, the Alkaline Rocks and the Newer 

 Basalts. 



{A) The Older Basalts. In many cases the exact 

 ages of these rocks cannot be determined on stratigraphical 

 evidence. In some cases an age can be assigned to them 

 on physiographic evidence. 



E. C. Andrews [1] states that the Leads of the 

 *' Older Volcanics " are characterised by the presence of 

 abundant plant leaves, lauraceous types predominating. 

 Fruits and seeds, he says, are characteristicallj'' absent. 



Their geographic position is above the level of the 



