BY M. AUROUSSEAU. 297 



and absorbtion are as follows : — H brownish-pink, \) brownisli- 

 yellow, C greenish-grey; H>b^C- Multiple twinning is com- 

 mon. Magnetite is often, but felspar seldom, included. Aggre- 

 gates of irregularly intergrown hypersthene and felspar occur, 

 and large felspars are sometimes moulded on to large hyper- 

 sthenes. Evidently, the crystallisation of hypersthene com- 

 menced slightly before felspar; the periods overlapped, but hyper- 

 sthene finished first. Alteration to bastite is taking place. 



Magnetite is fairly abundant in rounded grains passing into 

 limonite. Apatite and zircon are very rare. 



The ground mass consists of minute felspar and hypersthene 

 individuals set in a preponderant glass. It is partly replaced 

 by limonite and bastite. 



{103} Fyroxene-andesite. — A compact, dark green, serpentinous 

 rock, porphyritic with numerous indistinct, greenish felspars up 

 to 4 mm. long, which become white on exposure, and finally 

 weather out; exposed surfaces, thus, have a rough, pitted appear- 

 ance, and are dark brown in colour; fracture fairly smooth. 



Phenocrysts and groundmass are in about equal proportions. 

 The minerals developed are plagioclase, pyroxene, magnetite, 

 and apatite. 



The plagioclase is a basic labradorite, with a maximum sym- 

 metrical extinction of 31", tabular-prismatic in habit, with wide 

 albite lamella3, and an occasional pericline-set. Zoning is pre- 

 sent, with slight oscillatory changes in composition as in (113). 

 The general change is from a basic centre to a more acid margin, 

 but there are often one or two zones more acid than the outer 

 shell. The felspar is sometimes moulded on to pyroxene-pseudo- 

 morphs, and includes magnetite. Minute stony inclusions are 

 zonally distributed. The crystals are much fractured and, at 

 times, recemented. The fractures are filled with yellow-green 

 clinochlore, which also occurs sporadically in the crystals, but 

 shows a marked preference for pseudomorphic replacement of 

 the acid zones. The centres of small crystals are entirely re- 

 placed, whereas in larger ones there are one or two ragged zones 

 of chlorite, concentric with those of the felspar. Irregular 

 carbonate-replacements also occur. 



