304 PETROLOGICAL NOTES_, i., 



The rock is interesting in that it sliows the order of crystallisa- 

 tion, which is : — 

 Apatite'! 



Zircon / ^ 



Magnetite 



Hypersthene 



Biotite 



Plasrioclase 



The position of biotite is uncertain. 



The fragmentary evidence afforded by the other rocks agrees 

 with this order. 



(iQ'2) Felspathic andesite. — A fresh-looking, yellowish to red- 

 dish-brown rock, porphyritic with numerous, glassy yellow 

 felspars up to 2 mm. long; fracture fairly smooth, but splintery. 

 The specimen studied contains a small fragment of a foreign, 

 black, cherty rock. 



Plagioclase, magnetite, zircon, and apatite are developed. 

 Femic minerals are represented by occasional doubtful pseudo- 

 morphs. 



The plagioclase is an andesine, twinned on the Carlsbad, 

 albite, and pericline laws. It is well zoned, passing from a basic 

 kernel, through several oscillations, to an acid margin. It is 

 slightly spangled by resorbtion-cavities, and the centres of some 

 crystals are partly replaced by chlorite, epidote, and sericite. 

 Some of the crystals are broken and recemented. Magnetite, 

 zircon, apatite, and, in one place, vestigial hornblende(^) are in- 

 cluded. Corrosion by the groundmass is very slight. 



Scanty pseudomorphic aggregates of quartz, chlorite, and epi- 

 dote, are the sole representatives of pyroxene or amphibole. 



Biotite is completely altered and very rare. One piece is re- 

 presented by a mosaic of secondary quartz and chlorite, through 

 which run thin parallel strings of minute stony inclusions, in- 

 dicating the original biotite-cleavages. 



Magnetite includes zircon and apatite. Zircon is more abund- 

 ant than apatite. 



