468 Transactions. — Geoloyj. 



igneous rocks can be most readily settled by recording their 

 occurrence or absence as rolled fragments in fossiliferous sedi- 

 ments. In the present case it is evident that the parent masses 

 from which these conglomerate fragments were derived must 

 be older than the Triassic period. The collection was made 

 by Professor Park from the cont^lomerates occurring at the 

 base of the Triassic formation in Nelson. 



C 275. — Granite. Dark-grey on weathered surface. Mica 

 plates distinct ; feldspar opaque. Stained with iron- 

 oxide. 



Section : Quartz rather plentiful, with very irregular out- 

 lines. Water clear, with undulose extinction. Feldspar 

 partly orthoclase, twinned on the Carlsbad law ; also in rather 

 greater abundance an albite-oligoclase with extinction angle 

 of 8°. Albite twinning general. Carlsbad less common. 

 Zonal structure general, showing progressively lower extinc- 

 tion angles towards the margin. Decomposition producing 

 cloudy appearance in centre of crystals, due to development of 

 very minute epidote crystals and other substances too fine- 

 grained for recognition. Hornblende in idiomorphic crystals 

 rare, with pleochroism from dark-green to pale-yellow. Biotite 

 more frequent, dark-green or pale-yellow, rather decomposed 

 to a viridite substance. Sphene not abundant, granular. Very 

 pale-grey. Slightly pleocbroic. 



C 276. — Granite. Fine-grained, light-pink. Biotite plates 

 fairly large. 



Quartz plentiful, perfectly clear, without undulose extinc- 

 tion. Feldspar chiefly microperthite, in places forming a 

 graphitic intergrowth with quartz. Albite sometimes forming 

 cores for microperthite. All feldspar rather decomposed and 

 cloudy. Decomposition products very fine. Occasional small 

 flakes of brownish-green mica. Small idiomorphic sphene, 

 and magnetite in very small quantity. 



C 277. — Granite. Pink, coarse-grained, with fairly large 

 biotite plates. Quartz white. Feldspar pink. 



Quartz abmidant, perfectly clear, granular. Feldspar 

 porphyiitic, tlie larger crystals being orthoclase or albite. 

 Much decomposed into epidote and muscovite. On the 

 margins of larger grains of quartz and feldspar a granular 

 intergrowth, tlie nearer portions of mineral matter similar 

 optically to the crystals; has similar orientation witli them. 

 Otherwise the structure is microgranitic. A little brownish- 

 green biotite, magnetite, and two or three minute crystals of 

 zircon. No sphene visible in the section. 



