BY H. I. JENSEN. 615 



Name : Olivine-Dolerite. 



This rock is calcic and has no relation with the alkaline series. 



M.l. Loc: Hilltop, Black Jack Coal Mine, Gunnedah. 



This is a holocrystalline, medium-grained dolerite porphyritic 

 in olivine and titaniferous augite. It contains labradorite (lath- 

 shaped), idiomorphic phenocrysts of purplish augite, corroded 

 olivine phenocrysts, idiomorphic grains and phenocrysts of 

 magnetite, and interstitially analcite ' Apatite occurs as an 

 accessory. The isotropic mineral darkens on heating and 

 gelatinises with acid. It is therefore analcite, but appears to be 

 of secondary origin in part at least. 



Name : Olivine-Analcite-Dolerite. 



The microscopic investigation of the rocks of the Warrum- 

 bungle Mountains brings out the following points, namely : — 

 (1) the existence in the district of a complete series of alkaline 

 rocks ranging from acidic comendites to basic sodalite-analcite 

 basalts; (2) the gradation of these rocks into one another; and 

 (3) that in the volcanic period older basic rocks were remelted at 

 depths in various places, and, after being mixed with more acid 

 alkaline magma, rose to the surface. 



The alkaline rocks include — 



(1) Riebeckite Comendites ) . , 

 ^ ' ) cp. Anal. 



(2) Pantellarites J 



(3) Arfvedsonite Trachyte. 



(4) Nosean-Leucite Trachytes and Phonolites. 



(5) u^girine Anorthoclase Trachydolerites and Trachytes. 



(6) Albite Magnetite Basalt without olivine or augite. 



(7) Sodalite and Analcite Basalts, sometimes with melilite and 



meliphanite (?). 



(8) Garnet and Corundum-bearing Basalts, with laavenite and 



melilite. 

 A comparison of the chemical analyses with one another and 

 with the mineral ogical characters is very instructive. 

 48 



