Haast.—On the Geological Structure of Banks Peninsula. 497 
Thus a sub-marine hill stood here in the young mesozcic sea, of which 
portions of the summits and the slopes were gradually covered by agglo- 
merates and brecciated beds. These beds were formed during and after the 
eruption of quartziferous porphyries, of which here and there portions of 
the coulées have been preserved. Some of these quartziferous porphyries 
resemble in every respect those from the Malvern Hills and Mount Somers. 
They are also accompanied by pitchstones, porphyritic from the presence of 
numerous well-formed crystals of sanidine or glassy felspar, and occasionally 
of garnets. Other portions of the quartziferous porphyries, as for instance, 
the whole coulée of which Manson's Peninsula is formed, have a rougher, 
more trachytic matrix. They are full of grains and small crystals of white 
greyish or smoky quartz. The brecciated beds have a hard felsitic matrix, 
and the angular fragments of rock enclosed in them belong to a variety of 
eruptive rocks of many colours, and of different texture, often forming a 
rock of striking character. They appear conspicuously on the summit of 
Gebbie’s Pass, having been washed into cliffs of picturesque forms, and 
covering the paleozoic sedimentary beds from one side of the pass to the 
other. After the formation of the brecciated agglomerates, new eruptions 
of acidic rocks took place, now in the form of rhyolites, the highly liquid 
matter reaching the surface through broad channels, of which one has been 
preserved as a large dyke, forming a beautiful section on the northern side 
of Gebbie’s Pass, not far from the summit. The dyke is here about 100 
feet thick, half of which is formed by the central portion, consisting of a 
whitish rhyolite with a fine laminated structure, breaking in prismatic 
blocks; the rest on both sides, where in contact with the agglomerates, has 
cooled more rapidly, and has assumed the character of an obsidian. This 
obsidian is greenish or brownish-black, very brittle, and imperfect crystals 
of sanidine are enclosed in it. This dyke can be traced for a considerable 
distance upwards. Where overflowing and covering the agglomerates it 
forms the highest peak on the western side of Gebbie’s Pass, well visible 
from Lyttelton Harbour. The rock here is divided into small pentagonal 
columns, with a vertical arrangement; lower down the pass, the same 
coulée has a tabular structure. 
The oldest crater, of which the principal boundaries can be traced at the 
present time, is the Lyttelton Harbour caldera, having a general diameter 
of about two miles, the centre of which is situated a little to the south of 
Quail Island. . The general structure of this crater, even before the Christ- 
church and Lyttelton Railway tunnel was entirely pierced through, could 
easily be made out by studying the numerous sections exposed in many 
directions, and by ascending the steep escarpments of the caldera wall, 
where a succession of streams of stony or scoriaceous lava, interstratified 
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