298 PETROLOGICAL NOTES^ i., 



Pyroxene is represented by idiomorphic pseudomorphs of 

 clinochlore and carbonate, in which traces of original cleavage 

 and fracture are preserved. Magnetite and apatite are included. 

 The original pyroxene appears to have been rhombic, and was 

 considerably less in amount than felspar. Alteration proceeded 

 inwards from the sides of the fractures, and outwards from 

 scattered centres in the crystals. 



Magnetite is moderately abundant, and is passing into limonite. 

 Apatite is quite rare. 



The chlorite of the rock (clinochlore) is in ragged plates and 

 fibrous spherulitic aggregates, yellow-green in colour, weakly 

 pleochroic, with a birefringence equal to that of quartz. 



The groundmass is of normal appearance in ordinary light, 

 thickly dusted with magnetite, limonite, and chlorite, and here 

 and there replaced by chlorite; a few tiny patches are clear, and 

 free from inclusions. It is holocrystalline, being a mosaic of 

 interlocking, untwinned plagioclase-grains, more acid than the 

 phenocrysts. As in (108), it is a devitrified plagioclase-glass, 

 but here the grainsize is much coarser, averaging 0*3 mm. (Pl.xl., 

 figs. 1-2). The clear patches, in ordinary light, are nests of 

 quartz. 



The order of crystallisation was normal. 



(lOo) Pyroxe7ie-amphiboIe-mica andesife. — A dirty puce-coloured 

 rock, porphyritic with numerous white felspars up to 3 mm. long, 

 and subordinate hornblendes of similar size. The felspars often 

 invest a ferromagnesian kernel. The groundmass is replaced in 

 patches by chlorite. The rock is soft, and evidently much 

 weathered, and tends to split in definite directions ; fracture 

 smooth. 



Plagioclase, hornblende, biotite, pyroxene, magnetite, zircon, 

 apatite, and quartz are developed (cf.l08). 



The plagioclase is an oligoclase-andesine, with a maximum sym- 

 metrical extinction of 15°. It resembles that of (108) exactly, in 

 both primary and secondar}- characters, even to the replacement 

 of the kernels by chlorite (here clinochlore) [PI. xL, fig.5]. 



Common hornblende, subordinate in amount to felspar, is like 

 that of (108) in pleochroism and absorbtion. The reaction-rings 



