176 THE BUIfiDING OF EASTERN AUSTRALIA 



As there was a steady displacement of the shoreline 

 in an easterly direction, we should expect the more easterly 

 portions of Eastern Australia to have deep sea deposits, 

 characterising the early Palaeozoic and shallow sea deposits 

 typical of late Palaeozoic. The late Palaeozoic rocks of 

 the eastern part of X.S. Wales and Queensland should, 

 therefore, be lithologically similar to the Cambrian of 

 Central Australia ; thus, conglomerates formed a dominant 

 series in the Cambrian of South Australia and Western 

 X.S. Wales, and conglomerates are typical of Permo- 

 Carboniferous and Carboniferous in more eastlying parts. 

 Volcanic rocks because of their want of fossils are 

 more difficult to study, but their study also leads to 

 important deductions. 



It appears that intermediate igneous rocks, that is 

 to say, those which are allied to diorite and andesite in 

 mac^matic character, are characteristic of any era of 

 subsidence. We see such rocks at the present day extruded 

 from the active volcanoes of the New Hebrides, theTongan 

 Islands and the Kermadecs in, the great Pacific subsidence 

 area. Rhyolites and Granites are more typical of an 

 era of quiet uplift and of mountain building by rise of 

 isogeotherms. Alkaline rocks, both basic and acid, are 

 typical of a period of general uplift accompanied by 

 faulting and Senkungsfeldt formation over portions of the 

 area. Basic lavas belong chiefly to periods of plateau uplift. 

 To illustrate by modern examples — we have in the North 

 Island of New Zealand, an area of post-tertiary elevation, 

 where many volcanoes are even to-day disseminating 

 acid lavas. Alkaline rocks are poured out by the Antarctic 

 active volcanoes on the troughfaulted perimeter of a 

 plateau which has undergone very recent uplifts. [24] 

 We have them under similar conditions in Italy and East 

 Africa. 



Basalts of an alkaline facies are to-day emitted 

 from the volcanoes of Tonga and Samoa, in which there 

 is probably a present tendency to general uplift, but calcic 

 and magnesic basalts are often poured over subsidence areas 

 in the period preceding their re-elevation. 



Let us now consider igneous action in the history of 

 Australia, investigating period^ after period, commencing 

 with the Cambrian. 



