GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 



491 



occurs frequently in idiomorphic crystals enclosed by 

 another member of the group, and the soda orthoclase and 

 augite both play an interstitial role. Hence we conclude 

 that the periods of the two latter minerals were largely 

 coincident, and that the calcic plagioclase, whilst over- 

 lapping somewhat, both began and ended before them. 



Olivine — 



Ilmenite — — _ 



Biotite 



Apatite ■ 



Calcic plagioclase — — — 



Augite ___ __ 



Soda orthoclase — 



Specimens N, O, and Q. 

 Five other specimens from the Emu Quarry have been 

 examined in detail, and three of these deserve notice. Their 

 localities horizontally are all close to those of specimens 

 L and P, and their vertical relations to these latter speci- 

 mens, as well as their general characters, are shown in the 

 following table: — 



Specimen. 



L 



N 







Depth, below Junction. 



Metres. 



05 

 030 



1-5 



4-85 

 5-15 



Inches. 



Feet. 

 1 



16 

 17 



20 



Characters. 



Described above. 



Similar to L, but biotite (about 



and olivine (roughly 23%) some- 

 what more abundant. The iron 

 ore is partly magnetite. 



Similar to L, but augite has no 

 tendency to idiomorphism, and 

 both olivine and biotite are much 

 more abundant, chiefly at the 

 expense of labradorite. The rock 

 is crowded with olivine pheno- 

 crysts, and the proportions are 

 probably roughly: total olivine 

 25%, biotite 7%. 



Described above. 



Similar to P, but grainsize less, and 

 biotite more abundant. 



Similar to J (Reservoir Quarry) but 

 grainsize coarser (5 to 10 mm). 

 Unfortunately much decomposed. 



