280 PKOFS. LLOYD MORGAN AND REYNOLDS ON THE [Aug. 1 9© I, 



rock, and the silica-percentage, which, if raised to a moisture-free 

 basis, would be 63*42. He remarks also upon the somewhat small 

 alkali-percentage, and suggests that it may be accounted for by 

 removal of alkali owing to hydrous decomposition. In section the 

 rock is seen to be fsLuly coarse-grained, and to be mainly composed 

 of altered felspar-laths, giving a maximum extinction-angle of 

 19°, which would indicate andesine of an acid type. Some of the 

 felspars are larger than the others, but there are none which clearly 

 belong to an earlier generation than the remainder. Minute 

 colourless needles, giving an oblique extiQction, and probably of 

 felspar, can also be detected with a high-power lens. Small bastite- 

 pseudomorphs after enstatite are plentiful, as are also grains of 

 magnetite. Small irregular patches of a green chloritic mineral 

 occur, and the whole section is stained with ferric oxide. The 

 silica- and alkali-percentages, specific gravity, and microscopic 

 characters, all show that this rock lies rather on the border-line 

 between andesites and basalts. It may be called a basaltic 

 enstatite-andesite. 



The rock exposed on the right bank of the stream east of the 

 cottage differs from that just described in several respects. In a 

 hand-specimen it is seen to be browner in colour (less stained with 

 ferric oxide), and to contain numerous dark amygdules, generally 

 between 2 and 4 mm. in length. In section the felspar-laths are 

 seen to be much smaller than in the rock just described, and minute 

 needles, probably of felspar, can be detected with a high power. 

 There are no phenocrysts of felspar. Small grains of magnetite 

 and patches of a green serpentinous mineral, some of the latter 

 being probably pseudomorphs after enstatite, are very plentiful and 

 evenly distributed. The am5-gdules are generally formed of a pale- 

 green, highly spherulitic chlorite, or sometimes partly of chlorite, 

 partly of calcite. Round the amj-gdules the rock is stained with 

 ferric oxide. 



(2) The westerly or upper band is best exposed in the 

 old quarry (Cullimore's) by the railway. It is a much-weathered 

 rock, with abundant calcite occurring not only in large amygdules, 

 but also in irregular patches uniformly disseminated. In section 

 it is seen to contain comparatively little magnetite. It differs 

 from many of the rocks of the district in containing a few large 

 phenocrysts of felspar, which are very greatly altered and show 

 corrosion. 



The exposure of this band on the Bibstone road, opposite Waroer's 

 Court, is noteworthy for the fact that the rock here contains rounded 

 grains of quartz. Similar grains are met with at several other 

 localities in the district, and will be dealt with later (p. 282). This 

 rock shows also well-marked phenocrysts of altered felspar, and 

 an exceptionally large amount of magnetite. It may be termed 

 a porphyritic basalt. 



