SOME GEOLOGICAL FEATURES OF NORTHERN AUSTRALLV. Ill 



and, further north, the Yeppoon Ranges and the Springsure 

 district volcanics. The alkaline eruptions were in some cases 

 followed by basaltic flows.* Trachyte tuff has been recorded 

 by Maitland as far north as Mackay. 



These eruptions belong typically to the western margin of 

 the Cordilleran belt, though some of the groups are cjuite 

 within the area of late folding, in which cases their existence 

 is supposed to be indicative of trough faulting. 



In South-eastern Queensland the Carboniferous and 

 Permo-Carboniferous have been intensely folded, plicated, and 

 altered. Strata assigned to those periods have been changed 

 in the Stanthorpe-Texas district to homfels, in Gympie to 

 highly nietamorphic slates and schists. This intense alteration, 

 which is not noticed in the higher Jurassic strata, is in part due 

 to the effect of the granitic intrusions in the early Mesozoic 

 period. In New Guinea, where folding in Tertiary time was 

 accompanied by Tertiary granitic intrusions, Kainozoic rocks 

 are transmuted to an equal extent. 



North Queensland. — North of the Tropic of Capricorn Ave 

 find that the folding of the rocks corresponds with a series oi 

 plications forming arches, or festoons, round the Archean massif 

 of the Northern Territory and North Queensland. The Gulf of 

 Carpentaria regions are, in the writer's opinion, a part of the 

 great north-central massif of the Territory and West Australia. 



From the Sellheim gold and mineral field on the Suttor 

 River, north and north-westwards to Mungana, the Tate and 

 Georgetown, we have a region in which approximately east- 

 west strikes predominate over those meridional or nearly so. 

 It is an area in which the direction of folding has been east- 

 west. Within this area occasional north-south folds are found 

 as far north as Cooktown, secondary plications to the principal 

 north-south axis now faulted beneath the sea. and possibly to 

 some extent coincident with the Barrier Reef. The principal 

 north-south axes within the area are the Caims-Mareeba 

 district (strike north-north-west) and the Kidston-Einasleigh 

 district (strike north-south). The great majority of the strikes 



* See "The Alkaline Rocks of Eastern Australia," by H. I. Jensen, 

 Proc. Linn. Soc, N.S.W., 1908, and " The Volcanic Rocks of South- 

 Eastein Queensland," by H. C. Richards, D.Sc, Proc. Roy. Soc. of 

 Queensland, vol. xxvii, Xo. 7 (1916). 



