R. H. Rastall — Rocks of New Zealand. 405 



and lower side of the rapids. No. 63 was obtained near the middle 

 of the rapids and about a quarter of a mile above No. 62. No. 65 is 

 about a quarter of a mile higher up, and No. 66 is again about the 

 same distance above No. 65. No. 67 was taken from an exposure 

 on the roadside above the rapids and about a mile south of No. 62. 



No. 64. A very vesicular rock with a few porphyritic crystals set 

 in a groundinass of reddish and yellowish glass, showing remarkably 

 fine flow-structure. 



The phenocrysts are chiefly a slightly zoned plagioclase with, 

 a narrow extinction near to oligoclase ; but there are also one or 

 two crystals of a remarkable and interesting femic mineral. This 

 occurs in the eight-sided prisms characteristic of the pyroxenes, but 

 its cleavages are unfortunately very indistinct. In colour it is 

 a rather deep reddish-brown and distinctly pleochroic ; each crystal 

 has a border of a much deeper colour. The extinction angle is 

 high, up to 40°. More material is required before the mineral can 

 be identified with certainty, but it appears to be a monoclinio 

 pyroxene, very rich in iron, and may possiblj'^ be the dimorphous 

 form corresponding to the rhombic ferriferous pyroxene amblystegite. 

 The deep red border may be only a separation of ferric oxide, but its 

 appearance strongly recalls that of the peculiar soda-iron-amphibole, 

 cossyrite, in the Pantellarites. The border is narrow and too opaque 

 for its optical properties to be determinable. 



The bulk of the rock consists of a very vesicular glass, varying 

 from colourless to yellow or pale reddish-brown, and showing very 

 fine flow-structures. This encloses a good many minute prisms of 

 felspar. Occasional roundish patches of minute felspar prisms seem 

 to be due to devitrification. A good deal of the glass shows 

 a fragmentary appearance suggesting the inclusion of lumps of 

 glassy tufi" in a lava while in motion. 



No. 62 is a pink rock very similar to the last, but in addition 

 to the peculiar mineral described above it shows several well- 

 developed prisms of a brownish pyroxene, with a dark border, 

 strong pleochroism, and straight extinction, which may be identified 

 as amblystegite. These two rocks must be regarded as mixtures of 

 lava and tuff" of very similar composition, probably indicating a rain 

 of fragments into a lava-flow while still fluid. 



No. 63. A markedly spherulitic rock with a few phenocrysts of 

 a zoned plagioclase felspar ; coloured minerals are absent, except 

 for a few grains of magnetite. The spherulites may be as much as 

 3 mm. in diameter, and consist of long regular radiating prisms of 

 felspar, giving a good black cross. They seem to be due to 

 devitrification, since flow-structures, indicated by lines of crystallites, 

 pass through them. This rock also contains rounded lumps of glass 

 of slightly different structure. 



No. 65 is practically identical with the last, the only differences 

 being that flow-structure is more pronounced and the spherulites are 

 larger, up to 5 mm. in diameter. 



In No. 66 spherulitic and perlitic structures are both very strongly 

 marked, and perlitic cracks pass through the spherulites. 



