JOURNAL OF SCIENCE, 
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Ll. TrRacuytves. 
The three rocks which are to be considered trachytes are labelled. 
Quail Island, Lyttelton caldera and Tunnel, and are derived from 
veins. ‘Their habitus is so different, that a separate description seems 
necessary. 
The trachyte from Quail Island with 63.53 of silica consists of 
a yellowish to a light-brownish porous ground-mass, with somewhat 
shimmering lustre and abundant sanidine plates as much as 1 cm. in 
size, which lie with their largest planes in all directions. 
Under a lens the ground-mass appears to be distinctly crystalline 
and in consequence of the rough fracture its whole habitus is trachytic 
throughout. Under the microscope the rock is not nearly so much 
altered as we would be led to expect from its macroscopic appearance. 
The interpositions are mostly Karlsbad twins of sanidine; simple 
crystals together with plagioclase occur very sparingly. They occa- 
sionally harbour densely crowded gas-pores arranged in lines, and 
they are mostly fresh. 
The ground-mass is composed of a confused matting of narrow 
staves of feldspar which however do not completely fill the space. 
The numerous and comparatively large gaps were certainly originally 
filled by a base which however is much altered throughout and 
appears to be a dim grey, yellowish or brownish substance. Some- 
times a finely granular aggregate polarization is observable, but as a 
rule it exerts no influence on polarized light. Itis probable that the 
base was formerly glassy. Recognizable basic components are quite 
absent. The numerous and symmetrically arranged brownish or 
reddish grains of oxide and hydroxide of iron seem mostly to have 
originated from opaque iron ores, remains of which still appear in 
isolated patches. 
The trachyte from the Tunnel with 62.03 % of silica shows 
imperfectly slaty structure, is of a light greenish-grey colour and 
shows a brightly shimmering and somewhat oily lustre. It reminds 
one closely of the compact varieties of the well known trachyte from 
the Kiihlsbrunnen in the Siebengebirge. The ground-mass appears 
scaly under the lens. Tubular sanidines in parallel arrangement 
prevail amongst the interpositions, while plates of biotite and 
columns of bisilicates and ore grains also occur but in smaller number 
and size. In a few small cavities a colourless mineral lines the walls; 
this could not be successfully determined but is probably a zeolite. 
Judeing by the rhomboidal forms presented under the microscope it 
might be chabasite. 
The ground-mass is composed of narrow staves of feldspar and 
prisms of light-green augite in nearly equal parts; in addition small 
magnetite crystals which are often intergrown with small augite 
prisms occur in large numbers and symmetrically distributed. A few 
brown, hardly translucent fragments probably belong to biotite 
originally present. The staves of feldspar mostly show fluidal 
arrangement; here and there they also form bundle-like aggregates. 
(To be continued ). 
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