BY H. 1. JENSEN. 95 



of zoning is less universal, and not of such constant character. 

 It is due to the interlamellation of two or more kinds of felspar 

 in the same crystal, the more acid zone being usually exterior, 

 extinguishing practically straight, and the more basic zone 

 interior, extinguishing at 5°. Occasionally the core and the 

 outermost zone are identical in composition, and more acid than 

 an intermediate zone. The more acid zones consist of orthoclase 

 or anorthoclase, and in rare cases of albite. The second type of 

 phenocryst behaves like orthoclase, but exhibits shadowy extinc- 

 tion and sometimes very feeble polysynthetic twinning. It, too, 

 possesses mechanical zoning. It is evidently anorthoclase. 



All the phenocrysts are crowded with inclusions of sagenitic, 

 greenish to colourless, rutile needles. Some of the smaller inter- 

 stitial needles behave like orthoclase but are probably a soda-rich 

 variety. Others consist of light green or greenish-yellow, faintly 

 pleochroic augite-acmite which is also full of rutile inclusions, 

 and is decomposing to chlorite. The augite-acmite is almost 

 idiomorphic; its extinction angle is fairly high, approaching that 

 of diopside ; and it frequently has developed a hornblendic 

 cleavage (uralitic decomposition). A development of secondary 

 arf vedsonite round the augite-acmite is frequently distinct, and 

 is another point of affinity with bowralite (Mawson). The 

 arfvedsonite is much more sparing. It occurs in allotrioraorphic 

 patches enveloping augite, and is also seen in irregular cavities 

 associated with quartz, when it is probably formed in the pneu- 

 matolytic period of consolidation. AUotriomorphic ilmenite also 

 occurs interstitially ; it is largely decomposed to leucoxene. 

 Strands and grains of chlorite and kaolin-like decomposition- 

 products are in evidence between the crystals of ferromagnesian 

 mineral. A little iron-ore is also present. 



iSTame : Arfvedsonite-bearing Syenite-Pegmatite allied to 

 Bowralite. 



Note : this rock occurs in large bodies, not small veins. The 

 exact field-relations have not been worked out. It decomposes, 

 producing red or brown rich soil which supports luxuriant scrub. 



