602 ALKALINE PETROGKAPHICAL PROVINCE OF E. AUSTRALIA. 



the decomposition of the Alferric minerals, decomposition having 

 penetrated more deeply than in the dry and arid west. 



The facts above summarised tend to show that the alkaline 

 areas of Eastern Australia have great resemblance to one another, 

 and probably the same origin. 



Rocks Associated with the Alkaline Rocks. 



(a) Dacites, dacitic tuffs and breccias occur in the following 

 areas— The Glass House Mountains, Yandina, Mt. Flinders, Mt. 

 Macedon. 



(b) Basalts occur universally near to or capping the trachytes, 

 and they are of later age. 



(c) Andesites occur at Yandina, The Canoblas, Mt. Macedon, 

 and the Nandewars. 



(d) Trachy-andesites are abundant in the Warrumbungle and 

 Fassifern alkaline areas, and rare in the Nandewars and East 

 Moreton-Wide Bay. This rock-type is purely a differentiation- 

 product of the same magma. 



(e) Earlier basic rocks occur as — i. Essexite at Mittagong and 

 in the Nandewars; ii. analcite-dolerite (or gabbro) in the Fassi- 

 fern; iii. monzonitic porphyrite in the Wide Bay district. 



The rocks mentioned in (a), (b), (c), and (e) are only sometimes 

 differentiation-products of the alkaline magma. 



The foregoing notes, I think, fairly conclusively prove that 

 Eastern Australia forms an alkaline petrological province, and in 

 addition a titanium-rich province. 



