1 58 THE BUILDING OF EASTERN AUSTRALIA 



Australian area, but even as far as Bo\\en in Queensland 

 The climate was so cooled that the rich flora of the coal 

 measures was driven north, and likewise the moUusca 

 and corals migrated to the north. Of corals only the hardjr 

 zaphrentis remained when the cooling of the climate set in, 

 I During the Pernio- Carboniferous cataclysms com- 

 menced the break up of the great Gondwana continent 

 4nd the separation of Australia from India and South Africa 

 was commenced. 



At the close of this period, the New England area of 

 N.S.W. became compressed between the adjoining segments 

 of the earth's crust, so that the Permo-Carboniferous strata 

 of this region were folded as intensely as the Silurian in 

 other parts of Australia. [6] 



To summarise the geological history of Palaeozoic 

 Australia, we may say : — 



(1) The Pre-Cambrian is a conglomeration of forma- 

 tions — both acid and basic igneous rocks were intruded. 



(2) The Cambrian was an era of uplift, Continental 

 extension, and mountain building. Whether the Cambrian 

 ice age was caused by earth movements having super- 

 elevated many mountains and produced glaciers, or whether 

 the cause of the ice age is due to any astronomical factors 

 is hard to say. Eruptions and intrusions were of an acid 

 nature. 



(3) The Ordovician was a period of quiet subsidence 

 over most of Eastern Australia : a great thickness of 

 sediments accumulated. Vulcanicity was at a minimum^ 

 and the igneous masses which have been proved of this age 

 were of an intermediate (andesitic) to basic character. 



(4) The Silurian was a period of slow elevation of the 

 sea floor over Eastern Australia, and of Continental exten- 

 sion by the piling up in the seas of the weathering products 

 of the Continents. Vulcanicity became more and more 

 marked towards the end of the period, and the intrusions 

 and lavas became more and more acid in character. 



(5) The Early Devonian was an era of rapid elevation 

 in some parts, downthrow in others. Great folds and 

 great faults were produced. The lavas, tuffs and intrusive 

 rocks of the period were very acid in character. 



The Devonian uplifts must have caused the isolation 

 of many seas, for the Devonian sandstones of some parts. 



