BY H. I. JENSEN, D.SC. 163 



From the nature of the Mesozoic sediments generally, 

 we may conclude that the Mesozoic period was not 

 <;haracterised by intense vulcanicity, but some eruptions 

 probably took place, such as the andesitic ejacamenta 

 of the Narrabeen period, the basic tuffs of Wianamatta 

 age, and others mentioned above. If any eruptions took 

 place in the Hawkesbury period, they must have been of 

 an acid nature. The Trias-Jura of the Clarence River 

 district of New South Wales contains basic tuffs probably 

 contemporaneous, and this is also the case with the 

 Mesozoic rocks between Nambour and Yandina, Queens- 

 land. [13] The latter also contain rhyolites and associated 

 tuffs, some of which show close resemblance to the felsitic 

 tuffs at the base of the Trias-Jura in Brisbane. ISone of 

 the rocks igneous definitely assignable to the Trias-Jura 

 have an alkaline facies. 



The points of major interest in connection with the 

 Mesozoic rocks of Eastern Australia are :• — 



(1) Our Mesozoic sediments show no folding of conse- 

 quence. Generally speaking, they show only slight dips, 

 and have never been under the influence of tangential 

 pressure like the Mesozoic sediments of the Alps, Himalayas, 

 Java, etc. 



(2) Even our Per mo- Carboniferous rocks are only 

 strongly contorted in the area of the New England district. 

 Since the Per mo- Carboniferous, Eastern Australia has been 

 a stable unit of the earth's crust, if not actually rising, 

 so that any sedimentation of late Permo-Carboniferous, 

 and later age, is due to marine transgressions and epi-con- 

 tinental seas invading the landmass. 



(3) Mountain building from the Permo-Carboniferous 

 on has been by plateau uplift, not by folding, except in the 

 New England, where tangential thrusts must have taken 

 place in the Mesozoic. Faulting has aided in the formation 

 of our mountains, but intense folding of this age has only 

 occurred in the Northern Tableland of New South Wales. 



(4) The most folded rocks of late Permo-Carboniferous 

 and Mesozoic age are in a few small subsidence areas, among 

 which the Gympie Goldfield [14], the New England, and 

 the Ipswich Coalfield are prominent. 



(5) The discovery by R. A. Wearne, of Fenestella 

 in horizontal sandstones resembling Ipswich coal-measures, 



■C 



