590 ALKALINE PETROGRAPHICAL PROVINCE OP E. AUSTRALIA, 



Likewise Lacroix* has pointed out the relationship which exists 

 between the alkaline rocks of Eastern Africa, all the way from 

 Madagascar to the Highlands of Abyssinia. 



The tests which are applied to determine consanguinity com- 

 prise — (1) Similarity in texture; (2) similarity in mineral com- 

 position; and (3) similarity in chemical composition. 



Eastern Australia is a large area, and contains a great diversity 

 of igneous rocks of most varied ages of intrusion. It is therefore 

 impossible to apply the term petrographical province to it without 

 qualification. This term can, however, be applied within its 

 strictest sense to a number of areas within Eastern Australia. 

 Thus, the Warrumbungle Mountains described by myselff form 

 a well marked petrographical province; so do the Glass House 

 Mountains, Q., the Nandewar Mountains, and to a smaller extent 

 the Mittagong area, the Macedon area, the Yandina area (E. More- 

 ton and Wide Bay), and the Canoblas (under investigation); I say, 

 in thesecases to a smaller extent, because in addition to comagmatic 

 lavas of alkaline nature, we have basic and acid rocks of totally 

 different ages, and in no wise, as far as can be seen, related to 

 the alkaline rocks. 



However, as far as alkaline rocks are concerned, Eastern Aus- 

 tralia undoubtedly forms a comagmatic region, The foyaitic 

 rocks throughout the whole extent are related in a number of 

 ways, comprised under the following heads : — (1) They all date 

 from approximately the same period of geological history; (2) they 

 exhibit close textural affinities; (3) they contain the same, or 

 allied minerals; (4) they are very similar in chemical composition. 



In other petrologicai features the eastern side of the Continent 

 also presents a less marked, yet quite noticeable, homogeneity. 

 For example, most of our granites, especially those of Permo- 

 Carboniferous age, are very rich in titanic acid (Ti0 2 ); this 

 feature is not at all confined to our granites, but it characterises 



* " Roches alcalines de Prov. Petrograph. d'Ampaindava. Nouv. Arch, du 

 Museum " 4me. Ser. Vols. i. and v. 1902, 1903. 



t Proc. Linn. Soc. N. S. Wales, 1907. 



