BY H. C. RICHARDS. 121 



<>:xplosive element seems to have become more pronounced 

 towards the end, and the extrusions were apparently 

 carried out through vents of the central type, and accom- 

 panied by moderate explosive action except at Toowoomba, 

 where it seems to have been particularly violent. The 

 sequence from below upwards might then be stated as 

 follows: — Normal sub-alkaline basalts followed by olivine- 

 basalts, then the normal rhyolites, trachytes and the various 

 alkaline lavas; these in turn were succeeded by olivine- 

 basalt, andesite, andesitic basalt and olivine-basalt, 

 generally speaking in that order. 



Comparison with Cainozoic Volcanic Bocks of Neiv South 

 Wales and Victoria. 



When one compares the threefold development of 

 volcanic rocks in this area with the Cainozoic volcanic 

 rocks of New South Wales and Victoria, a most interesting 

 correlation is seen. In New South Wales there is a con- 

 siderable development of older sub-alkaline basalts which 

 rest upon leaf beds which are considered to be of early 

 Cainozoic age, and these older basalts are especially deve- 

 loped in the New England district. A series of alkaline 

 lavas and tuffs occurring in the Canoblas. Warrumbungle, 

 and Nandewar regions is, in part at least, ascribed to the 

 Upper Miocene,^- and the remarkable similarities between 

 many of these lavas and those of south-eastern Queensland 

 have been pointed out by Dr. Jensen. In addition to these 

 two developments, there is a series of newer sub-alkaline 

 basalts at Ben Lomond, Gulgong, Inverell &c., which are 

 regarded as probably Pliocene. 



In Victoria ^•' an older and a newer series of sub-alka- 

 line basalts, belonging to the Lower and Upper Cainozoic 

 respectively, occur, and also a development of alkaline 

 lavas which are mainly trachytic and in many respects 

 very similar to the alkaline types from this area. This 

 alkaline series is believed to be of Middle Cainozoic age. 

 and is certainly older than the newer series of sub-alkaline 

 basalts. 



'^T. W. E. David, N.S.W. Handbook. B.A.A.S., 19H. 

 "E. W. Skeats, A.A.A.8., vol, xii., 1909. 



