614 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



spare SiOo (quartz of the norm) would also be used up and 

 conditions for the production of leucite or analcite in the base 

 would be brought about. 



4. Name : Corundum (?) Basalt (with sphene, melilite and 

 laavenite), Magmatic name, Monzonose. 



Note : the occurrence of blue corundum in rare grains in this 

 rock is confirmative of the Rev. J. M. Curran's theory as to the 

 origin of our sapphires. 



The rock (W.40) has many points in common with W.58, but 

 contains no olivine. 



W.64. Loc: Tableland south of Belar Creek. 



1. Handspecimen dark grey rock with rough fracture; looks 

 like andesitic basalt. 



2. Texture : holocrystalline, uneven-grained, with ophitic 

 fabric. 



3. Composition : labradorite felspar in laths, but not as pheno- 

 crysts. Only one generation is developed. Brownish, titani- 

 ferous, somewhat pleochroic augite, occasionally pierced by felspar 

 laths. Colourless olivine in corroded phenocrysts. Magnetite 

 in idiomorphic grains; segirine in needles lying interstitial ly 

 between felspar laths: and orthoclase also interstitial. An 

 isotropic mineral of the noselite group, or perhaps leucite, also 

 occurs interstitiaily. 



4. The occurrence of segirine and orthoclase in this rock justifies 

 its classification as a trachy-dolerite. 



5. JSame : Ophitic Olivine Trachy-Dolerite. 



Other specimens from other parts of the same tableland were 

 similar macroscopically and microscojjically. This rock covers a 

 great area. , 



M.6. Loc: 34-mile peg, Gunnedah-Coonabarabran Road. 



This rock is a holocrystalline, fine-grained, ophitic dolerite 

 with porphyritic olivines. It is composed of labradorite, titan- 

 iferous augite, and olivine, with magnetite and apatite as 

 abundant minor constituents. 



