262 PROCEEDINGS OF SECTION C. 



The Chinaman Creek " Gynipie" area is surrounded like the type 

 district by a zone of highly foliated phyllites and schists, and appears 

 also to be a basin in which. Gympie rocks have escaped erosion. 



From petrological considerations it would, therefore, appear that 

 the succession in each of these districts was — 



(1) Cai'boniferous or Permo-Carboniferous : — A basin in which 



submarine tuffs accumulated, interbedded with clays, 

 sands, and lavas, and a period of deeper water was inter- 

 polated in the type district during which limestones 

 formed. Uplift follows. 



(2) Later in the same or subsequent period — Intrusions of 



andesite and dionte porphyry. Erosion simultaneously 

 progresses. 



(3) Permo-Carboniferous or Mesozoic (according as we look 

 upon the Gympie as Carboniferous or Perino-Carboniferous) 

 — Granitic intrusions, folding, very severe faulting and 

 formation of qua it z reefs. 



Note. — This period was possibly as late as Cretaceous. 

 (i) Between Trias and Tertiary — Intiiision of Amphibolites. 



Whatever age the Gympie beds may be it is certain that the 

 andesitic and andesito poi-phyry intrusions followed very closely upon 

 their deposition. The granite intrusions were much later (homblende- 

 biotite-tonalites), and may all belong to the Post-Triassic, the same as 

 the quartz-diorite-poi-phyrites of Noosa Heads and Point Arkwright. 



The igneous succession is therefoi"e not unlike that observed by E. 

 C. Andrews in the New England district. 



The causes of the metamorphism of the true Gympie rocks were 

 circulating heated siliceous vapours which undoubtedly in the China- 

 man Creek area, and probably also in the type area arose fi'om 

 granitic (tonalitic) magmas. All the rocks except the amphibolites 

 and the granites have had their composition altered by this pneu- 

 matolytic action. The arapliibolites are, therefore, probably post- 

 granitic. 



5. Rocks Older than True Gympie. — Most ofthe country mapped 

 Gympie by the geological suiTey in the areas which I have examined 

 is composed of formations which are far more metamorphosed than 

 the true Gympie. The raetamoi-phic rocks present the appearance of 

 having undergone regional metamorphism by having at one time been 

 encompassed in the middle and deepest zones of schist fonnation 

 (according to Gnibenmann's classification of the crystalline schists), 

 whereas the Gympie rocks belong to the upper zone. 



No doubt many of the quartz — sericite — and talc phyllites of the 

 rtrea also belong to the upper zone, but they are more highly foliated 

 than the true Gympie rocks, and, therefore, belong to a lower zone. 

 Such is tlie case with the Kin-Kin schists, the Kenilworth (Upper Mary 

 River) white phyllites and similar rocks east of the slates of Wararba 

 and Mount Mee. No age can at present be assigned to these schists 

 and phyllites. 



The Brisbane schists also provisionally marked Gympie by our 

 Geological Department are so crushed, folded, foliated, and faulted 

 that they must be assigned to the middle zone, and consequently they 

 are likely to be older than the true G}mipie. What age we cannot say, 

 but possibly Pre-Devonian. 



