BY W. N. BENSON. 663 



A. Igneous Rocks. 

 These are described in the order of their geological age, as far as 

 is known, and the following divisions are adopted: — 



1. Devonian spilite-lavas. 



2. Keratophyre of Hanging Rock. 



3. Dolerite-intrusions associated with the spilites. 



4. Lower Carboniferous lavas. 



5. Middle Carboniferous peridotites, etc. 



6. Gabbro-rocks associated with the peridotites. 



7. Certain post-peridotite dolerites, and some acid dykes in the 

 serpentine. 



8. The Blue Knob group of dolerite and dolerite-porphyrites. 



9. Granites, granodiorites, and porphyries, varying in age from 

 late Carboniferous (?) to early Mesozoic. 



10. Lamprophyres. 



11. Alkaline rocks of the Nandewar Mountains. 



12. Tertiary basalts, with the basanites, teschenites, and dolerites 

 of the Nundle district. 



{I) The Spilites. — The name spilite, according to Brongniart's 

 original definition and Continental usage, indicated somewhat 

 altered lavas of a gabbroid composition, characterised by an amyg- 

 daloidal structure, platy or spheroidal parting (pillow-structure), 

 a tendency to a variolitic texture, and an abundance of secondary 

 silicated minerals, the last feature being especially emphasised. 

 Messrs. Dewey and Flett, however, have confined the term to those 

 rocks which are characterised by the presence of a very sodic 

 plagioclase, primary or secondary. Such rocks are very wide- 

 spread, very uniform in mineral-features and chemical composi- 

 tion, and should certainly be classed under a specific name; but it 

 is very questionable whether the old term "spilite" should be 

 revived and redefined for this purpose. Many of the rocks, 

 formerly classed as spilites, do not fall into this narrowed division, 

 as e.g., the only spilite-analysis quoted by Rosenbusch (Elemente 

 der Gesteinslehre. Edition of 1910, p. 410). Moreover, the rocks 

 described below, while their mineralogical and chemical composi- 

 tion is clearly that of the spilites of Messrs. Dewey and Flett, their 



