SOME GEOLOGICAL FEATURES OF NORTHERN AUSTRALLV. 107 



folding since the Triassic, from which period on, plateau 

 movement, combined Avith faulting and Senkungfeld formation, 

 has been the dominant force. 



The Cordillera. — The rest of Eastern New South Wales 

 and Eastern Queensland to the Tropic of Capricom form a 

 geological unit characterised by a protraction of fold movements 

 into later geological periods. Li the northern portion of this 

 unit even Tertiary beds are folded. The Triassic and Jurassic 

 rocks are strongly folded in the Ipswich and Bundamba Coal 

 Measures, and the Upper Cretaceous in the Styx basin. The 

 area was also intruded by mixed lavas, of which the alkaline 

 form an important portion, in the Tertiary period. 



North Queensland is a region which is composed of a 

 north-western massif (the Queensland portion of which might 

 be styled the Carpentaria massif) and festoons of later for- 

 mations folded upon that massif. In the Carpentaria massif 

 fold movements ceased in early Palaeozoic times, as was the 

 case in the Northern Territory and Central West Australia, 

 which are but an extension of the same massif. Even Cambrian 

 rocks in the Northern Territory are but slightly folded. The 

 eastern fringe of Carpentaria massif extends fi^om Cape York 

 and Princess Charlotte Bay south and south-west to George- 

 town, thence south-west to Cloncurry and Camooweal. The 

 massif is surrounded by a zone in which the Silurian and 

 Devonian rocks are folded, but wherein the Carboniferous 

 rocks are untouched by compressional forces. Outside this 

 zone we have a festoon in which folding movements Avcre 

 protracted into the Carboniferous periods. The folded Silurian 

 zone with sub-horizontal Carboniferous and Permo-Car- 

 boniferous outliers extends from the Cooktown mineral field 

 through the Chillagoe field to the Charters Towers field, and 

 thence under the Cretaceous (at Hughenden) to the district 

 south of Cloncurry (Kynuna-Selwyn), and thence to the 

 McDonnell Ranges in the Northern Territory. The folded 

 Devonian belt extends from Maytown south-south-east to 

 Mareeba ; and thence as the Burdekin Series, forming the 

 next festoon it extends west -south-west from Kangaroo Hills 

 towards Boulia, but is largely hidden by the Cretaceous. It 

 recurs in the Arltunga area of Central Australia. Thus the 

 north-central massif if surrounded by successive festoons in 

 which folding was protracted into later and later periods, 

 which extended the area of continental movement (plateau 



